Despite its reputation as a scourge of antiquity, Yersinia pestis–the bacterium that causes bubonic plague–still causes thousands of human illnesses every year. In modern times, most of these occur in Africa, and to a lesser extent in Asia, though we have a handful of cases each year in the U.S as well.
When Y. pestis was first confirmed as the cause of bubonic plague during an 1894 outbreak in Hong Kong, most people assumed that we also now knew the cause of the 14th-century Black Death, and the later plague outbreaks that resurfaced periodically. However, there has been lingering resistance to the idea that Y. pestis actually caused the Black Death. I covered the reasoning behind this resistance in a series of posts back in 2008, so I’ll just give the Cliff notes version here. Basically, many of those advocating “not Y. pestis” pointed to differences in the epidemiology of the Black Death compared to modern outbreaks of Y. pestis. Today, people are much less likely to die of plague; the outbreaks aren’t nearly as big; and the pneumonic form (which infects the lungs and is therefore able to spread directly person-to-person) seems too rare to account for the number of cases that occurred during the Black Death. Also, they argue that transmission across Europe was much too fast, given that rodents (typically rats) are the disease vector. Instead of Yersinia, some authors have suggested that the Black Death was instead caused by a hemorrhagic fever virus, or perhaps by an unknown microbe that went extinct sometime in the last 600 years.
More recently, we’ve been able to test these claims, using paleomicrobiology to look for molecular evidence of Y. pestis in skeletons that presumably died of plague. Many of these come from mass graves that have been dated to the time of the Black Death–some also have parish or other town records to attest to the timing of the grave. In most cases, investigators found Y. pestis DNA. In a few cases, they didn’t, which led to controversy and charges of contamination in the positive samples.
However, the tide has turned. In 2010 and 2011, three papers came out which, um, put the nail in the coffin for the Y. pestis naysayers. At the time, the papers got press not necessarily because of what they explained, but because the ancient Y. pestis strains looked fairly ordinary–there was nothing obvious to suggest why, from the bacterial point of view, the Black Death was so deadly. However, I hadn’t had a chance to read these closely until now, and one of the punches never made it into the mainstream media. From the discussion section of this paper, the authors note:
Two of the authors (SW and JM) have previously argued that the epidemiology, virulence, and population dynamics of the Black Death were too different from those factors of modern yersinial plague to have been caused by Y. pestis (13). Given the growing body of evidence implicating this bacterium as responsible for the pandemic, we believe scientific debates should now shift to addressing the genetic basis of the epidemic’s unique characteristics.
The reference cited within is this paper, where the authors cast doubt on another group’s finding of Y. pestis DNA in ancient corpses. So it took them 10 years and probably a dozen or more papers, but two “Black Death doubters” have now come around. Score one for the weight of scientific evidence changing minds.
Schuenemann VJ, Bos K, DeWitte S, Schmedes S, Jamieson J, Mittnik A, Forrest S, Coombes BK, Wood JW, Earn DJ, White W, Krause J, & Poinar HN (2011). Targeted enrichment of ancient pathogens yielding the pPCP1 plasmid of Yersinia pestis from victims of the Black Death. Proceedings of the National Academy of Sciences of the United States of America, 108 (38) PMID: 21876176
Bos KI et al. A draft genome of Yersinia pestis from victims of the Black Death. Nature, 2011.
Haensch, S et al. Distinct Clones of Yersinia pestis Caused the Black Death. PLoS Pathogens, 2010.
Previous posts in the series
Regular readers don’t need to be told that I’m a bit obsessed with zoonotic disease. It’s what I study, and it’s a big part of what I teach. I run a Center devoted to the investigation of emerging diseases, and the vast majority of all emerging diseases are zoonotic. I have an ongoing series of posts collecting my writings on emerging diseases, and far too many papers in electronic or paper format in my office to count. Why the fascination? Zoonotic diseases have been responsible for many of mankind’s great plagues–the Black Death, the 1918 “Spanish” flu pandemic, or more recently, HIV/AIDS. So you can imagine my delight when I read about Spillover, a new book by David Quammen on zoonotic diseases.
I’ve previously highlighted some of Quammen’s work on this site. That link goes to a 2007 story he wrote for National Geographic on “infectious animals,” which really serves as a preview to “Spillover,” introducing some of the concepts and stories that Quammen elaborates on in the book.
“Spillover” is wide-ranging, tackling a number of different infectious agents, including viruses like Nipah, Hendra, and Ebola; bacteria including Coxiella burnetii and Chlamydia psittaci; and parasites such as Plasmodium knowlesi, a zoonotic cause of malaria. HIV is a big part of the story; Quammen devotes the last quarter or so of the book to tracing the discovery and transmission of HIV from primates to humans, and from 1900 to present-day. He even takes the time to explain the basic reproductive number–something that’s not always a page-turner, but Quammen manages to do it well and without being too tangential to the rest of the story; much more of a Kate-Winslet-in-Contagion than Ben-Stein-in-Ferris Bueller delivery.
Indeed, “Spillover” is somewhat unique in that it doesn’t read quite like your typical pop science book. It’s really part basic infectious disease, part history, part travelogue. Quammen has spent a number of years as a correspondent for National Geographic, and it shows. The book is filled with not only well-documented research findings and interviews with scientists, but also with Quammen’s own experience in the field, which gives the book a bit of an Indiana Jones quality. In one chapter, he details his adventure tagging along with a research team to capture bats in China, entering a cave that “felt a little like being swallowed through the multiple stomachs of a cow.” This was after an earlier dinner in which he describes his encounters with the an appetizer of the “world’s stinkiest fruit” (I’ll keep the description of the smell to myself) with congealed pig’s blood for a main dish (bringing to mind the scooping out of monkey’s brains in “Temple of Doom”–and the various zoonotic diseases that could be associated with those, come to think of it).
Quammen’s book is an excellent, and entertaining, overview of the issues of zoonotic disease–why do they emerge? Where have they come from? How do they spread? The only thing that’s missing is more of a cohesive discussion about what to do about them. However, that’s rather understandable, as we certainly have less of a grasp of this question than we do about the others (and even with some of those, our knowledge is spotty at best). I hope “Spillover” will inspire another generation of future germ-chasers, as “The Coming Plague” did almost 20 years ago.
This is the last of 16 student posts, guest-authored by Jessica Waters.
Climatologists have been warning us about the ongoing and impending consequences of global warming for years. But the results of climate change affect more than just polar bears and penguins – if you live anywhere in the northeastern, north-central or west coast states of the U.S.., you could be at a greater risk for contracting Lyme Disease.
Lyme disease is an infection of the Borrelia burgdorferi bacterium that is spread through black legged ticks (otherwise known as deer ticks) who feed on the white footed mouse species, also known as the wood mouse, which carries the bacteria. The symptoms of the disease itself include fever, headache, fatigue, and a telltale “bulls eye” rash near the site of the tick-bite. Left untreated, Lyme disease can spread to affect the joints (causing arthritis), heart, and nervous system – often causing irritability and mood swings.
Lyme disease transmission occurs in a Reservoir à Vector à Host cycle. A Reservoir is the habitat in which an infectious agent normally lives, grows and multiplies – in this case, it is the white-footed mouse. A disease vector is a carrier animal (usually an arthropod) that transfers an infective agent from one host to another- i.e. the blacklegged tick. And the host in this scenario is an organism that harbors an infective agent – us, our pets, and other animals.
Lyme disease is transmitted when a nymphal (young) tick feeds on a B. burgdorferi carrying white-footed mouse. The contaminated bloodmeal that it ingests allows the bacterium to live on in the tick (the vector), and the infected tick can then transmit the bacteria to its next host – a dog, your child, you, or any other animal roaming around in a wooded area.
Nearly a quarter of all Lyme disease cases are in children, as they play near to the ground, where host-seeking ticks are often waiting. The CDC reports that pet owners and outdoorsy types are also at higher risk, as dogs and people traipsing through thick brush can easily pick up a tick or two without realizing it.
So how does climate change factor into this? According to ecologist Rick Osfeldt, a small mammal expert in Millbrook , New York, it all comes down to acorns.
“ Acorn abundance gives rodents a jump start on breeding. By the next summer, mice numbers are through the roof”.
This phenomenon gave rise to a “mouse-boom” in 2010, a low-acorn year in 2011, and what promises to be a busy summer for public health officials in 2012. As the theory goes, as nymphal ticks wake up to a low mouse count (from 2011), they will feed on the existing mice and then turn to the next best thing – humans.
While the exact science behind what causes oak trees to produce more acorns is not yet identified, studies suggest that plants in warmer climates produce more seeds.
More acorns means a bumper crop for hungry mice, and milder winters mean higher breeding rates and higher survival rates for the B. burdorferi carrying rodents.
Maria Diuk-Wasser, an assistant professor of epidemiology at the Yale school of public health also attributes an increase in Lyme disease to higher average temperatures, but for a different reason.
“One possible way in which temperature may limit tick populations is by increasing the length of their life cycle from two to three years in the north, where it is colder.” As average temperatures increase, climate change could be reverting the normal temperature pattern and increasing the production Lyme disease carrying ticks.
If both hypothesis prove to be true (and so far, CDC reported cases of Lyme disease have increased from 15,000 in the mid 1990s to over 40,000 today), an increase in both mouse and tick populations could indicate an increased prevalence of Lyme disease in years to come.
It may also be that the number of (geographically) susceptible people will increase as well. Nick Ogden, a zoonoses researcher with the Public Health agency of Canada recently published a paper suggesting that the tick-inhabitable regions of North America may be increasing – in Eastern Canada, the tick inhabitable region will expend from 18% to over 80% by 2020, while the average temperatures in Canada have simultaneously increased by 2.5 degrees Fahrenheit over the past 60 years.
While some measures can be taken to prevent infection of Lyme disease once a tick has made a meal of you, cautionary measures are the best way to prevent you and your loved ones from becoming hosts.
The CDC recommends using insect repellant, applying pesticides, reducing tick habitat (i.e. cutting down heavy brush areas in your yard), and wearing long sleeves and pants when in wooded areas. Prompt removal of ticks is also necessary, so continually check exposed skin areas when you are outdoors -the backs of your legs, the back of your neck, the ears of your dog, etc.
One creepy-but-saving grace in tick removal may be that once a tick has landed on you, it will not immediately attach, instead crawling around for up to three hours to find an ideal location to feed. While not pleasant to imagine, it may give you enough time to jump in a hot shower after time outdoors and wash off any unattached ticks. Even attached ticks still require 24 to 36 hours to spread the B. burgorferi bacteria into your blood – if you remove a tick within 24 hours, you are greatly reducing your chances of getting Lyme disease. Attached ticks should be removed gently with tweezers.
If diagnosed early, Lyme disease can be cured with antibiotics. If you find an attached tick, see a general practitioner. You may be offered a single dose of antibiotics if you were bitten by a Lyme disease carrying tick species and the tick has probably been attached for at least 36 hours.
So, perhaps most importantly, if you suspect that you may have been bitten by a tick or have symptoms of Lyme disease – get thee to a doctor, and consider saving the planet from further warming by riding your bike there.
Patrick A. Leighton, Jules K. Koffi, Yann Pelcat, L. Robbin Lindsay, Nicholas H. Ogden. Predicting the speed of tick invasion: an empirical model of range expansion for the Lyme disease vector Ixodes scapularis in Canada.Journal of Applied Ecology, 2012; DOI: 10.1111/j.1365-2664.2012.02112.x
This is the thirteenth of 16 student posts, guest-authored by Jessica Ludvik.
One Disease, Many Species
Brucellosis, more commonly known as undulant fever in humans or bangs disease in cattle, is one of the oldest bacterial scourges of livestock-producing nations, especially those in which the animals live in close proximity with the human population. The disease is caused by bacteria of the genus Brucella. Within this category are many species of bacteria, each almost exclusive to a particular animal species. A few of the most common seen in veterinary and human medicine today are listed in Table 1. Of these, all but B. ovis has been shown to be transmissible to humans .
Why Should I care about Brucellosis?
The presence of Brucellosis in a region is catastrophic to the economy and animal and human health. In many livestock species, the bacteria elicits its major effects on the reproductive system, leading to late term abortions and stillbirths in females, weak newborns leading to death soon after birth, and inflammation of the testicles and testicular abscesses in males . Abortion storms of 30-80% have been documented in cattle herds infected by B. abortus . B. abortus and B. melitensis are the most common of the strains associated with human infection, and the World Health Organization (WHO) estimates that 500,000 new cases of human cases of human Brucellosis occur annually, making it the most common zoonotic disease in the world . Its importance has earned it a spot on the Center for Disease Control’s (CDC) 2012 list of Nationally Notifiable Conditions. To view this list visit the CDC’s website at http://www.cdc.gov/osels/ph_surveillance/nndss/phs/infdis.htm.
Symptoms include fever, profuse sweating, headache, fatigue, depression, loss of appetite, irritability, cough, chest pain, and upset stomach . It can also affect bones and joints causing arthritis . If untreated, symptoms may recur after a latent period of many years . For the official case definition, click http://www.cdc.gov/osels/ph_surveillance/nndss/casedef/brucellosis_current.htm.
What’s the Risk?
Most human cases of Brucellosis are a result of occupational exposure to the bacteria . It can penetrate mucus membranes of the digestive or respiratory tract, or can enter through skin wounds or abrasion after contact with reproductive fluids, aborted fetus or placenta, or aerosolized particles from the aforementioned . Brucellosis can also be contracted by people via accidental injection with the cattle vaccine or by ingestion of unpasteurized dairy products of infected animals .
Most people diagnosed with Brucellosis recover fully with treatment, which usually consists of a six to eight week antibiotic regimen . Less than 2% of untreated individuals die, however chronic complications such as endocarditis and meningitis may occur .
On the Global Scale….
Figure 1: Worldwide incidence of human Brucellosis  Click to enlarge.
As the major mode of human infection is through direct contact with infected animals otr through the consumption of products from those animals, the most logical means of disease prevention in the human population has been through the prevention of the disease in animals. Many developed regions such as North America, Australia, and Northern Europe have dramatically reduced the prevalence of brucellosis in livestock through widespread vaccination efforts . The United States Department of Agriculture (USDA) implemented an eradication program in 1934, which involved the testing and identification of diseased animals, slaughter of infected animals, and trace back and investigation of their herds of origin . In 1951, Animal Plant Health Inspection Services (APHIS) made compliance of all states mandatory . Currently, RB51 vaccine is the standard in cattle and Rev-1 vaccine in goats. Both of these are attenuated live vaccines, which are strains of bacteria that cause a similar but less severe infection in the vaccinated individual, so the animal’s immune system will respond to and eliminate the agent. Immune cells then remember the bacteria, so that if the animal is exposed to the wild type strain of bacteria, it will destroy it before it becoming infected. One of the advantages of the RB51 vaccine that has helped to make testing for the disease effective is that the vaccine strain lacks a specific surface molecule that the wild type strain of bacteria possesses, so tests can distinguish between diseased cattle and those vaccinated with RB51 . The Program has decreased the number of infected herds in the US from 124,000 in 1957, to 2 as of December 2003 . These vaccines are not approved for human use, and as mentioned before may actually cause clinical illness if accidently injected into the handler .
In February of 2008, all States in the US were classified as disease-free . In September of that year however, the states of the Greater Yellowstone Area (GYA), Montana, Wyoming, and Idaho lost their disease-free status . For more information on this, see APHIS’s website at http://www.aphis.usda.gov/newsroom/content/2009/10/printable/brucellosis_concept_paper.pdf. What was the source of the infections that triggered this revocation? Brucellosis is endemic in the herds of elk and bison in the area. 8-60% of elk herds and 11-75% of bison herds were positive for B. abortus by serologic tests . Studies of mapping the molecular profiles of the isolates from this area show that cattle are more likely to be infected by elk than bison, and indicate that there may be a possibility of transmission between cattle and feral pigs, though it is unclear of the direction . These wild reservoirs pose another significant barrier to the complete eradication of the disease in the US.
In the Future
The issue of wildlife reservoirs for Brucellosis will need to be addressed to prevent transmission of the disease to people, especially those at particularly high risk of infection by this route, such as hunters, hikers, and campers. Some proposed strategies include the daunting tasks of selectively culling bison herds and vaccinating elk and bison .
Control of human Brucellosis through vaccination of livestock has been successful thus far because it virtually eliminates our exposure to the infectious agent, so it is a sort of indirect prevention. But how will we prevent disease outbreak should we be exposed by a different means? There is no human vaccine for Brucellosis, it can be aerosolized, and it only takes 10-100 organisms to cause disease in humans . All these characteristics make it a possible agent of bioterrorism . Although the mortality rate is low, the morbidity rate is high, so an outbreak would cause a tremendous consumption of money and resources to treat the affected, and a dramatic decrease in workforce and morale. Control of human Brucellosis is another area in which we must not allow ourselves to fall victims to our own success. We must continue to support the vigilant monitoring and livestock vaccination efforts and encourage efforts in the development of a vaccine that is safe and effective for use in humans.
 Ficht, TA, and LG Adams. Brucellosis. Vaccines for Biodefense and Emerging and Neglected Disease. Elsevier Inc. 2009. Ch 42.
 http://www.cfsph.iastate.edu/DiseaseInfo/disease.php?name=brucella-abortus&lang=en. Accessed 9 June, 2012.
 Atluri, VL, MN Xavier, MF de Jong, AB den Hartigh, RM Tsolis. Interactions of the Human Pathogenic Brucella Species in Their Hosts. Annual Review of Microbiology. 2011. 65:523-41.
 Solis Garcia del Pozo, J, J Solera. Systematic Review and Meta-Analysis of Randomized Clinical Trials in the Treatment of Human Brucellosis. PloS One. 2012. 7(2):e32090.
 Pappas, G, P Papadimitriou, N Akritidis, L Christou, EV Tsianos. The New Global Map of Human Brucellosis. Lancet Infectious Disease. 2006. 6:91-99.
 http://www.aphis.usda.gov/newsroom/content/2009/10/printable/brucellosis_concept_paper.pdf. Accessed 9 June, 2012.
 Higgins, J, T Stuber, C Quance, WH Edwards, RV Tiller, T Linfield, J Rhyan, A Berte, B Harris. Molecular Epidemiology of Brucella abortus Isolates from Cattle, Elk, and Bison in the United States, 1998 to 2011. Applied Environmental Microbiology. 2012. 78(10):3674-84.
This is the twelfth of 16 student posts, guest-authored by Stanley Corbin.
Disease in wildlife is an important concern to the health and safety of humans and domestic animals. The expanding growth of our nation and resultant land use changes with urbanization has resulted in a shrinking habitat and fragmentation for all animals, including humans. The effects of ecological disruption are universally recognized and adversely effects wildlife through multiple mechanisms.
Hand it to the coyote (Canis latrans) for its ability to exist with humans. The resilience of this animal can be attributed to its natural instincts, remarkable intelligence and survivability. Opportunistic is another word that can be used to define them. Once an animal roaming the mid-west prairies, their territory has expanded throughout the North American continent and beyond. Coyotes demonstrate their wily nature by meeting the challenges of the American landscape.
Progression of coyote range expansion throughout North America and Mexico. (7) Click to enlarge.
Precise population estimates of coyotes in the United States are not available and unclear at best. However, to put it in perspective, the California Department of Fish and Game estimates a population range of 250,000 to 750,000 animals.(1) The greater metropolitan area of Chicago estimates home to between 200-2000 coyotes. (3) The coyote population in New York during the summer is approximately 20,000-30,000. (2) In March 2010, a lone coyote led a police chase through lower Manhattan, deep in New York City.
Coyotes can thrive in suburban settings and even some urban ones creating a concern for public health. A study by wildlife ecologists at Ohio State University yielded some surprising findings in this regard. Researchers studied coyote populations in Chicago over a seven-year period (2000–2007), proposing that coyotes have adapted well to living in densely populated urban environments while avoiding contact with humans. They found, among other things, that urban coyotes tend to live longer than their rural counterparts. (3)
As with most all wild animals, the coyote population represents a reservoir for diseases. Zoonotic (animal to human) diseases in particular are on the rise, comprising 75% of emerging infectious diseases. Viruses, bacteria, fungi, internal and external parasites, and other pestilence are only the headings for what’s out there.
Fortunately, the rabies virus is rather uncommon in coyotes as reported. The only exception was the 1974-1998 rabies epizootic (epidemic in animals) in south Texas. The world’s largest wildlife oral rabies vaccine (ORV) drop, 11.6 million doses covering over 189.6 square miles, was performed beginning in 1995 and led to the total elimination of the domestic dog-coyote (DDC) variant by 2006. (4) A study performed by the USDA, APHIS, Wildlife Services, National Wildlife Research Center concluded; “In Texas, the use of the ORV stopped the northward spread and led to the progressive elimination of the DDC variant of rabies in coyotes”. (5) This campaign was a win for our tax dollars as well. The economic evaluation study yielded “total estimated benefits of the program approximately ranged from $89 million to $346 million, with total program costs of $26,358,221 for the study period”. This represents benefit-cost ratios that ranged from 3.38 to 13.12. (5)
Coyote rabies surveillance reported by the Center for Disease Control (CDC) for 2010 declared 10 confirmed cases. None of these cases were DDC variant, which remains non-detected from the populations. The raccoon variant and skunk variant represented 8 (AL, GA, NC, NJ, NY, NYC) and 2 (CA, CO) cases respectively. (6)These coyote rabies cases were diagnosed from New York City (1) on the east coast to California (1) in the west, confirming the widespread distribution of this terrestrial carnivore. An interesting fact that comes from this data is that the coyote is not a player in the zoonotic rabies front. From a public health concern, a human has a significantly greater chance of contracting the disease from the backyard domestic cat.
Canine Distemper Virus is an enzootic disease (prevalent in an animal population) in the coyote. The neurological form is rightfully confused with a rabies infection as the two appear similar clinically. Humans are not susceptible to the disease, however it is highly contagious to dogs. Greater Yellowstone Park has a dynamic management study to assist with the surveillance of the disease enzootic in the parks coyote population.
The parasitic disease Sarcoptic mange is what gives the animal the “mangy” look. Caused by the mite Sarcoptes scabei, the disease in humans is called Scabies. Severely affected coyotes are unsightly and are perceived as threatening by their appearance. The compromised condition may explain the increased frequency of nesting and scavenging in suburban areas, especially in daylight hours. Coyotes with extensive mange infections are not considered aggressive as concluded by The Cook County, Illinois, Coyote Project.(7) Human infections from animal sources are short-lived and self-limiting due the highly host species-specific nature of the bug.
A recent hot epidemiological study conducted in Santa Clara County, California, identified coyotes as a wildlife reservoir for a disease caused by Bartonella vinsonii subsp. Berkhoffii .(8) The disease in humans is characterized by endocarditis, an inflammation of the interior lining of the heart. The study was prompted by the coyote bite of a child who developed symptoms compatible with Bartonella infection. Among 109 coyotes sampled, 31 animals (28%) were found to be bacteremic and 83 animals (76%) had Bartonella vinsonii seropositve antibodies. The disease is thought to be transmitted by insect vectors (ticks, biting flies, fleas), however further studies are necessary to elucidate additional modes of transmission to humans.(8) Bartonellosis in domestic cats is commonly called “cat scratch fever”, caused by a different species variant of Bartonella. The role coyotes play in this emerging infectious zoonose and public health concern are yet to be resolved.
Additional diseases exist in the coyote populations warranting public health attention. Anyone concerned with coyote interaction and communicable diseases will need to seek information relative to their geographical location. The ubiquitous nature of this animal and the corresponding diseases posing risks to humans and domestic animals respectively are regionally specific.
Coyotes are here to stay. Most every state (excluding Hawaii) has a control program in effect to manage the public health risks and deprivation to human welfare. The Humane Society of the US has issued techniques to resolve coyote conflict and how to discourage coyotes. Project Coyote champions innovative solutions to live in peace with the coyote despite differences, especially in terms of human policy. (9) A collaborated and integrated management approach is required to maintain a balance of needs for this specie of animal and humans. Wildlife specialist Jeffery Green summarizes; “regardless of the means used to stop damage, the focus should be on damage prevention and control rather than elimination of coyotes”. (10)
Pet owners need to adapt to coyote presence and take precautionary measures in securing their animal’s health and safety. Routine core vaccinations and other preventative health care are effective in stopping the transmission of nearly all the important diseases from the coyote to a pet animal.
Coyote attacks on humans are rare; the coyote human avoidance factor is responsible for the low incidence. In the cases of human attacks, approximately 30% were reported as humans feeding coyotes. (8) Additionally, greater than 50% of the human attack cases were in California, (8) where coyotes have a longer history of habituation with humans.
A person who sees a coyote should feel lucky since they avoid humans and are mostly invisible.
The most important advice to prevent human exposure is: do NOT feed coyotes and ensure your environment is NOT coyote friendly. Any attempt to domesticate or habituate the coyote will surely be a kiss of death for its existence. Survival of coyotes is dependent on living side by side but not together with humans.
The “tricksters still run wild and provoke all sorts of all-too-human difficulties, pitting the spirit of the wild against the sturdy values of our American farmers and their need to protect livestock. Somehow we need both”. (11)
Our Canadian neighbors at The Royal Canadian Geographical Society conclude; “the more we cut down habitat and build, the happier the scavenging and opportunistic coyote”. (12)
- L.A. County Department of Animal Care and Control website. Accessed June 15, 2012. Available at: http://animalcare.lacounty.gov/coyote.asp
- New York State Department of Environmental Conservation website. Accesses June 15, 2012. Available at: http://www.dec.ny.gov/animals/9359.html
- World Science website: Thriving under our noses, stealthily: coyotes. Accessed June 13, 2012. Available at: http://www.world-science.net/othernews/060105_coyotefrm.htm
- Texas Department of State Health Service website. Accessed June 12, 2012. Available at: http://www.dshs.state.tx.us/idcu/disease/rabies/orvp/statistics/
- Stephanie A. Shwiff, PhD; Katy N. Kirkpatrick, BS; Ray T. Sterner, PhD. Economic evaluation of an oral rabies vaccination program for the control of a domestic dog-coyote rabies epizootic: 1995-2006. JAVMA, Vol.233, No.11, Dec.1, 2008. Available at http://www.avma.org/avmacollections/rabies/javma_233_11_1736.pdf
- Jesse D. Blanton, MPH; Dustyn Palmer, BA; Jessie Dyer, MSPH; Charles E. Rupprecht, VMD,PhD. Rabies surveillance in the United States during 2010. Vet Med Today: Public Veterinary Medicine. JAVMA, Vol. 239, No. 6, September 15, 2011. Available at: http://avmajournals.avma.org/doi/pdf/10.2460/javma.239.6.773
- The Cook County, Illinois, Coyote Project website. Accessed June 13, 2012. Available at: http://urbancoyoteresearch.com/Coyote_Project.htm
- Chang CC, Kasten RW, Chomel BB, Simpson DC, Hew CM, Kordick DL, Heller R, Piedmont Y, Breitschwerdt EB. Coyotes (Canis latrans) as the reservoir for a human pathogenic Bartonella sp.: molecular epidemiology of Bartonella vinsonii subsp. Berkhoffii infection in coyotes from central coastal California. J Clin Microbiol. 2000 Nov; 38 (11): 4193-200. Available at: http://www.ncbi.nlm.nih.gov/pubmed/11060089
- Project Coyote website. Accessed June 15. 2012. Available at: http://www.projectcoyote.org/programs.html
- Jefferey S. Green, Urban Coyotes: Some Summary Thoughts. Proceedings of the 12th Wildlife Damage Management Conference (D.L. Nolte, W.M. Arjo, D.H. Stalman, Eds. 2007
- Shake-Spear’s Bible.com website; Coyote: An Instant Classic. Post by Roger Strirtmatter, October 25, 2011. Accessed June 13, 2012. Available at: http://shake-speares-bible.com/2011/10/25/coyote-an-instant-classic/
- The Royal Canadian Geographical Society website. Accessed June 13, 2012. Available at: http://www.canadiangeographic.ca/wildlife-nature/?path=english/species/coyote/2
- Personal correspondence; James Wright; Tyler Texas. Retired Texas Department of State Health Service official.
This is the eleventh of 16 student posts, guest-authored by Ilze Berzins.
When one hears the words “food-borne illness”, what comes to mind? For me, I think of a medium rare, pink, juicy hamburger, or something like potato salad that may be made with mayonnaise containing raw eggs, or maybe a fresh green garden salad sprinkled with sprouts. I am sure we have all heard about outbreaks or recalls surrounding these familiar dishes. And the usual suspects contaminating these food stuffs are often bacteria with familiar names such as E.coli or Salmonella. The fear of getting “food poisoning” from these products may encourage us to buy fresh seafood from the grocery store, or order the shrimp or salmon when out at a restaurant instead of steak, thinking seafood might be a safer bet. And of course, aren’t health benefits from seafood supposed to be an added bonus? But not so fast! Believe it or not, one can also become ill when eating, or even just handling, seafood. Gives the phrase “fresh catch of the day” a whole new meaning!
Seafood is a broad term…and no…it is not the game you played as a child that while eating you asked people if they wanted seafood and you opened your mouth (get it? SEE food?). Seafood refers to all species of fish and shellfish, coming from both fresh and saltwater sources. Salmon, snapper, trout, tuna, perch, tilapia are just a few of the fish that come to mind. But what is shellfish? Shellfish consists of a mixed group of mollusks and crustaceans that have a shell or shell-like body covering known as an exoskeleton. For the mollusks, this would include oysters, clams, mussels, abalone, and scallops. And although they don’t have an obvious shell (it is very small or absent), squid and octopus are also in this group. Crustaceans that are edible shellfish include lobsters, shrimp, crabs, and crayfish. Yum.
What can make you sick from eating seafood? There are several main categories including infectious pathogens (parasites, viruses, and bacteria – oh, my!), contaminants (heavy metals such as mercury in the form of methymercury), and drug and chemical residues. These can be synthetic compounds but can also come from natural bio-toxins. One such compound is found in the tissues of small aquatic organisms in overgrowth situations or “blooms” such as in red tide events.
Eating raw or undercooked seafood definitely increases the risk of a food-borne illness, but even just handling or processing seafood can cause problems for humans (7, 10). Topically acquired or contact zoonoses can be acquired through stings, bites, or spine/pincer puncture wounds. Zoonoses are illnesses transmitted from animals to humans. Some groups at risk include commercial fishermen, fish farmers (aquaculture), hobbyists, aquarists working in public display facilities, fish food processors, chefs, and even you when you are preparing dinner! Bacteria are the primary causative agents for zoonotic infections through a contact route. Viruses, fungi, and parasites contact infections have rarely been reported (7, 8). However, I am not quite sure how to classify a recent case report on a “parasite-like” infection by the squid Todarodes pacificus (5). A 63-yr-old Korean woman was reported to have experienced severe pain in her oral cavity immediately after eating a portion of parboiled squid along with its internal organs. She did not swallow the portion, but spat it out immediately. She complained of a pricking and foreign-body sensation in the oral cavity. Twelve small, white spindle-shaped, bug-like organisms stuck in the mucous membrane of the tongue, cheek, and gingival were completely removed. On the basis of their morphology and the presence of sperm, the foreign bodies were identified as squid spermatophores!! Not sure if I would call that “parasite-like”?! I digress! Let’s focus!
There are lots of species of seafood and many reports of associated food-borne illnesses (1,2). Where should we start? In this blog, I will focus on a group within the mollusks, the bivalves. Bivalves are mollusks with two shells including oysters, clams, and mussels. I want to focus on this group because given the propensity of humans to eat raw oysters, eating them raw elevates the risk of acquiring a viral or bacterial food-borne illness. In subsequent blogs, I will review other members of the mollusks, then on to crustaceans, and of course, fish, so stay tuned!
Safety issues for bivalves center around two categories; first, the quality of water in which these animals are grown in, and second, the conditions under which they are harvested, processed, and distributed (1,2,8). In 1925, the Bureau of Chemistry (now the United States Food and Drug Administration) met to establish guidelines for the oyster industry. Attendees resolved to control “the beds on which shellfish are grown” and “the plants in which the shellfish are shucked” (shucking refers to removing the animal from its shell)(11). In the late 1800s and early 1900s, most outbreaks of seafood food-borne illness resulted from sewage contamination in the areas where shellfish were grown (11). From the late 1970s through today, there has been an increased incidence of disease associated with naturally occurring shellfish pathogens (11). There are some that think this trend is suggestive of emerging environmental problems such as increasing water temperatures associated climate change. While the species of pathogen isolated in bivalves may vary with salinity of the water the oysters or clams grow in, it is noted that all of these pathogens increase in numbers with an increase in water temperature (11).
How often do we see illness? In a 10 year study on mollusk shellfish food-borne illness, a total of 2795 cases, with 96 deaths, were documented (11). Oysters accounted for the highest proportion of cases (49%) and death (97%). Shellfish from the East and Gulf costs were equally likely to cause disease. Most from the East Coast were viral contaminated clams, where as on the Gulf Coast, most cases were oysters infected with non-cholera bacteria in the family Vibronaceae.
The naturally occurring bacterial pathogens of concern include Vibrio vulnificus, V. parahaemolyticus, V. mimicus, V. hollisae, and V. furnissi. When eating raw oysters, one might become exposed to V. vulnificus. Incubation can take 1-5 days, though the median time is around 28 hours (3). Symptoms include high fever, chills, nausea, vomiting, diarrhea, and abdominal pain. The ill person can become rapidly dehydrated, and the infection can become systemic (body wide) if bacteria enter the blood. V. vulnificus in some cases can multiply so rapidly that blood vessels may become infected (known as vasculitis), and blood clots can develop which may lead to digit or limb amputation, or even death (3)!
How about from contaminated sources? Viral and bacterial enteric pathogens of public health concern are caused by fecal contamination of the waters from which molluscan shellfish are harvested and of the environment in which they are processed. Pathogens of concern that have been associated with disease include human enteric viruses; hepatitis A, non-A, non-B enteral hepatitis (hepatitis E), unclassified viruses; and such bacteria as Salmonella, Shigella, Campylobacter jejuni, and pathogenic Escherichia coli (11). The group of unclassified viruses includes the Norwalk and Norwalk-like viruses.
Do we stop eating seafood? NO!!! But measures to increase the safety of raw shellfish could be, and are being implemented (11). These measures might include policies on when and where to collect (season, time/temperature), requiring harvest areas near sewage treatment facility outflows to be more closely evaluated (9), and continuing to improvement the technology of sewage treatment. Some aquaculture techniques have included lowering temperatures and controlled purification which involves disinfecting (or purifying) the water in which the bivalves are grown. This may reduce gut bacterial levels but it does not entirely remove them. When processing shellfish, facilities can employ techniques such as rapid chilling and cold storage to reduce overgrowth and contamination. Irradiation of the harvested product has been suggested but has yet to be approved. Laboratory tests to detect contamination are moving beyond traditional culture techniques and include identifying pathogens based on their individual DNA using molecular methods (6). Focusing on identifying groups at risk such as those individuals who are immunocompromised (young, old, ill) and concentrating on the more common agents could help resources go further.
Consumer education is also very important. Prevention strategies should focus on preparation and consumption. Cooking oysters to an internal temperature of 85-90°C will destroy both viruses and bacteria of public health concern. But what if you want to eat them raw? Maybe think about cooking oysters during periods of warm weather and go for raw during colder times of the year! An excellent, comprehensive web site about food safety issues is www.foodsafety.gov . It addresses a variety of audiences including consumers, food professionals and industry workers, and provides the latest news, safety alerts, recalls, and health warnings. The site also allows for individuals to report cases, and it has information for physicians on how to diagnose and manage food-borne illnesses. Other useful sites include www.foodsafetywatch.com and www.fda.gov.
With any food product, it is probably wise to stop and ask “To Eat or Not To Eat?”(4). Stay safe!
- Butt, A.A., Aldridge, K.E., and Sanders, C.V. 2004. Infections Related to the Ingestion of Seafood Part I: Viral and Bacterial Infections. Lancet Infect. Dis. 4: 201-212.
- Butt, A.A., Aldridge, K.E., and Sanders, C.V. 2004. Infections Related to the Ingestion of Seafood Part II: Parasitic Infections and Food Safety. Lancet 4: 294-300.
- Daniels, N.A. 2011. Vibrio vulnificus Oysters: Pearls and Perils. Clin. Infect. Dis. 52 (6):788-792.
- Galson, S.K. 2009. To Eat or Not to Eat: Food Safety in the United States: Practical Applications from the Surgeon General. J. Am. Dietetic Assc. 5(20): 1142.
- Park, G.M., Kim, J.Y., Kim, J.H., Huh, J.K. 2012. Penetration of the Oral Mucosa by Parasite-Like Sperm Bags of Squid: A Case Report in a Korean Woman. J. Parasit. 98 (1): 222-223.
- Huss, H. H., Reilly, A., and Ben-Embarek, P.K. 2000. Prevention and control of hazards in seafood. Food Control 11:149-156.
- Iwamoto, M., Ayers, T., Mahon, B.E., and Swerdlow, D.L. 2010. Epidemiology of Seafood-Associated Infections in the United States. Clin. Microbiol. Reviews 23 (2): 399-411.
- Rabinowitz, P.M., Gordon, Z., Holmes, R., Taylor, B., Wilcox, M., Chudnov, D., Nadkarni, P. and Dein, F.J. 2005. Animals as Sentinels of Human Environmental Health Hazards: An Evidence-Based Analysis. EcoHealth 2: 26-37.
- Vinh, D.C., Mubareka, S., Fatoye, B., Plourde, P., and Orr, P. 2006. Vibrio vulnificus Septicemia after Handling Tilapia sp. Fish: A Canadian Case Report and Review. Can. J. Infect. Dis. Med. Microbiol. 17(2): 129-132.
- Wittman, R.J. and Flick, G.J. 1995. Microbial Contamination of Shellfish: Prevalence, Risk to Human Health, and Control Strategies. Annu. Rev. Public Health 16: 123-40.
This is the tenth of 16 student posts, guest-authored by Jean DeNapoli.
I own a small back yard flock of sheep and lambing season is the most exciting and rewarding time of the year. Nothing is more enjoyable than watching a lamb who takes a few wobbly steps and nurses for the first time as her mother nickers encouragement. Within a day, the lamb will be playing, bucking, running, and exploring her world.
Despite the pastoral wonders of the season, lambing is also inherently stressful. I must constantly check the barn to monitor for birthing problems and help out when necessary. This help might include repositioning a lambs stuck in the birthing canal, pulling a lamb when the ewe is unable to push it out herself, and cleaning the face and airway of a newborn when its mother is too exhausted to follow through on her own. Shepherds all over the world share the same experiences that I do. But what many of them don’t know is that they are probably being exposed to Q fever.
When the disease was first recognized it was given the temporary name Query fever (since very little was understood about it). We now know it is caused by a bacteria called Coxiella burnetii. It is found word wide and it is estimated that 15-20% of all cattle, sheep and goats have been exposed to it. The livestock rarely show signs of illness, but it can contribute to reproductive problems such as abortions.
In an infected animal, the organism can be found in milk, urine, and feces. But the greatest concentration of bacteria is in the amniotic fluid and placenta. Ticks can spread the disease, but much more frequently, it is passed directly to other animals at the time of birth. It can develop into a long lasting spore-like form and can then contaminate dust and be carried by the wind. Q fever is very easily spread and it takes only one organism to cause disease!
Q fever is zoonotic; it can be passed from animals to people. When people become infected, they may have fevers, headache and weakness. Fortunately, the fatality rate is low (<2%). But some people, especially pregnant women and those with heart disease or who are immune deficient, end up with a more chronic and severe disease. Q fever may also cause pre-term delivery or miscarriage if women become infected while pregnant.
I am not only a shepherd, but I am a veterinarian and it surprises me that few shepherds (at least the hobby farmers I know) discuss Q fever or take the recommended precautions. In research facilities, Q fever is a biosafety 3 organism (on a scale of 1-4), requiring special laboratory containment precautions. To put this in perspective, other level 3 organisms include tuberculosis, anthrax, SARS, and yellow fever. Yet many farmers routinely assist in births without any thought to their own health.
Q fever is fairly common and can be difficult to detect in healthy animals, so experts recommend treating all sheep as if they are infected. Pregnant women or women who may become pregnant should avoid working with sheep at lambing time. Other people at increased risk (people with impaired immune systems and heart valve abnormalities) should also stay away from the barn at lambing time.
Shepherds should wear disposable gloves when assisting lambing or handling newborn lambs. Masks should also be worn, especially in dusty conditions. Farmers should not eat or drink in the barn and should clean their footwear and wash their hands when leaving the barn.
Clothes have also been shown to carry the organism and they are capable of causing infection in people handling the laundry. Therefore, high-risk people should not handle clothing that has been worn in the barn until it has been cleaned.
Farmers should use good sanitation when handling birthing materials and bury or compost the placentas. Birthing areas should be cleaned frequently and in a way that will not cause excessive dust. It is very important that farmers understand biosecurity precautions in general and specific Q fever prevention protocols to keep themselves, their families and their neighbors safe.
Shepherds should also work closely with their veterinarian to keep their flock as healthy as possible. In the event of an abortion, the fetal material (placenta) should be submitted to the veterinary diagnostic laboratory for testing.
But what if you are not a farmer, do you need to be concerned? Well, you should at least be aware of the disease.
Although usually associated with farm animals, dogs and cats may also transmit Q fever to people, most commonly at and around the time of birth. Again, people who are most susceptible should avoid association with pets at those times. Coxiella burnetii has been found in milk, so dairy products should be properly pasteurized before being consumed.
The organism is easily transmitted through the air (it is even considered a possible bioterrorism risk for this reason). The Netherlands had a recent outbreak of Q fever in people living close to goat farms due to unintentional airborne transmission. However, the people who generally are at the greatest risk are farmers, veterinary workers and researchers. They are the people most likely to be near animals giving birth or handling the organism during the course of their daily work.
With education and reasonable safety precautions, a visit to the barn does not have to be a risky event. Through the simple sharing of information, we can keep future generations of farmers safe, healthy, and productive.
Prevalence of Coxiella burnetii infection in domestic ruminants: A critical review. Raphael Guatteo, Henri Seegers, Ann-Freida Taurel, Alain Joly, Francois Beaudeau. Veterinary Microbiology 149 (2011) 1-16
Q Fever: Current State of Knowledge and Perspectives of Research of a Neglected Zoonosis. Sarah Rebecca Porter, Guy Czaplicki, Jacques Mainil, Raphael Guatteo, and Claude Saegerman. International Journal of Microbiology Volume 2011 (p 1-22)
Eurosurveillance, special issue on Q fever, vol. 17, 19 January 2012
New York Department of health Q fever facts sheet (2011) http://www.health.ny.gov/diseases/communicable/q_fever/fact_sheet.htm
World Organization for Animal Health (OIE) fact sheet on Q fever (2011) http://www.oie.int/fileadmin/Home/eng/Media_Center/docs/pdf/Disease_cards/Q-FEVER-EN.pdf
Center for Disease Control (CDC) Q fever information (2011) http://www.cdc.gov/qfever/index.html
Public Health Agency of Canada pathogen safety data sheet for Q fever (2010) http://www.phac-aspc.gc.ca/lab-bio/res/psds-ftss/coxiella-burnetii-eng.php
Health Protection Agency Q fever information for farmers (2010) http://www.hpa.org.uk/webc/HPAwebFile/HPAweb_C/1210834106356
University of Florida IFAS Extension, The Herd Health Handbook for Goat Producers: Biosecurity at the Farm Level, Ray Mobley and Carmen Lyttle-N’guessan. (2009) http://edis.ifas.ufl.edu/famu006
Wyoming State Veterinary Laboratory, Q fever fact sheet (2004) http://www.uwyo.edu/wyovet/disease-updates/2004/files/qfever.pdf
Institute for Biosecurity, Saint Louis University School of Public Health, Q fever fact sheet (2001) http://www.bioterrorism.slu.edu/bt/quick/qfever01.PDF
Eurosurveillance Q Fever in the Netherlands: an up date on the epidemiology and control measures, W van der Hoek, et al. (2010) http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19520
Photographs are courtesy of Laura Cowperthwaite and Triple J Farm.
This is the eighth of 16 student posts, guest-authored by Michelle Formanek.
For many of us in the scientific world, particularly budding infectious disease epidemiologists like myself, the Plague (or, more dramatically, the “Black Death”) is a prime example of the rapid and devastating spread of an infectious disease. So devastating, in fact, that it wiped out nearly one-third of the population in Europe in the mid-1300’s. That’s roughly equal to 25 million people. It then persisted and has caused various outbreaks throughout history, most notably the Great Plague of London in which 1 in 5 residents died.
So why should be care about the Plague today? Isn’t that old news?
While I will go into more detail about the history of the plague a little later, I first want to mention what prompted me to write about what many people consider to be a no-longer-relevant disease. In order to gauge modern perceptions of the plague, I took a very unofficial survey of friends and family from various backgrounds about what they knew about the Plague. While the knowledge base ranged quite a bit, most were very surprised to hear that we still have cases of the Plague here in the United States.
Yes, you heard me right. The Plague still exists in the United States.
Of course, due to increased knowledge and antibiotic therapy, we no longer see the sweeping epidemic that caused so much turmoil throughout history. Nevertheless, an Oregon man is currently suffering from a rare case of the “Black Death.”
According to reports, a stray cat bit the unidentified man while he was trying to pull a mouse away from the cat. (I won’t even begin to speculate as to why this man was attempting to steal a mouse away from what was likely a very hungry stray cat, but that’s another story.) Several days later the man began to feel ill and presented to the hospital with symptoms typical of the Plague. These included fever, swollen lymph nodes and stomach pain. It has since progressed to bleeding mouth, nose and anus, and dying tissue. Although the CDC has yet to confirm the diagnosis, all signs point to the Plague.
Only 10-15 people report becoming ill with the disease each year in the United States; this man is the fifth person in Oregon since 1995.
The Plague is caused by the bacterium Yersinia pestis., a rod-shaped bacillus that can live in various species of animals including rats, mice, squirrels, cats, prairie dogs, camels, and rabbits, among others. Yersinia pestis can then be transferred to humans through direct contact with infected animals, bites from fleas that have previously fed on infected animals (this is most common), or human-to-human through the air. Historically, the high population of small rodents and their flea friends in urban areas were attributed to the rapid spread of the disease.
While the Bubonic plague may be the most well known form of the disease, there are actually three different types of the Plague. The Bubonic plague is the most common form and is characterized by buboes – painful, swollen lymph nodes – in the groin, armpit or neck. Septicemic plague occurs when the bacteria begins to spread in the bloodstream. Lastly, the most infectious form of the disease is Pneumonic plague. This advanced stage strikes when the bacteria can be passed from person to person through airborne droplets coughed up from the lungs. Bubonic plague is fatal roughly half the time, while Septicemic and Pneumonic are almost uniformly fatal without antibiotic treatment.
The man in Oregon was first believed to be suffering from Bubonic plague, but is now beginning to show signs of Septicemic plague, meaning it has entered his bloodstream and is able to reach all different parts of the body. Luckily, antibiotics are effective in the treatment of the Plague if given early enough. Without antibiotics, 1 in 7 people infected end up dying.
So you may be asking yourself, as I did, where a deadly disease like this came from in the first place. The puzzling start of the epidemic went something like this:
“The Black Death arrived in Europe by sea in October 1347 when 12 Genoese trading ships docked at the Sicilian port of Messina after a long journey through the Black Sea. The people who gathered on the docks to greet the ships were met with a horrifying surprise: Most of the sailors aboard the ships were dead, and those who were still alive were gravely ill. They were overcome with fever, unable to keep food down and delirious from pain. Strangest of all, they were covered in mysterious black boils that oozed blood and pus and gave their illness its name: the “Black Death.” The Sicilian authorities hastily ordered the fleet of “death ships” out of the harbor, but it was too late: Over the next five years, the mysterious Black Death would kill more than 25 million people in Europe–almost one-third of the continent’s population.”
Unfortunately, the cause of the disease was not discovered until 1894, long after it swept through Europe with alarmingly high death rates. People had their ideas about what was causing the Black Death, but no one could actually figure it out. Some believed it was the spirit escaping the eyes of a sick man and infecting the nearest healthy person, others believed it was God’s way of punishing those who had sinned. Citizens were so panicked that they went to extreme lengths to avoid contracting the disease, even so far as to completely abandon loved ones who got sick. More details here.
As mentioned before, antibiotics can be extremely effective in fighting this bacteria. As of right now, the Oregon man is still fighting for this life, but thanks to modern medicine, his chances of living are fairly high. The man likely contracted the disease from the cat; however, the cat died shortly after and its remains have since been sent to the CDC for testing. Who knew that a stray cat in the Northwest U.S. could have possibly been harboring bacteria that once had the potential to wipe out entire cities. Fortunately, modern medicine is on our side.
So is the re-emergence of the Plague something that we should really be concerned about? Probably not. But it never hurts to be informed.
This is the sixth of 16 student posts, guest-authored by Anna Lyons-Nace.
Natural…unprocessed…raw. These terms are often used by consumers, nutritionists and health experts to denote the most healthful, high-quality food options available for consumption. However, when pertaining to the recent increasing trend in raw milk consumption, can consumers be confident that they are choosing the safest and most healthful option? Statistical data and health studies would suggest otherwise.
Before we delve into the discussion any further, we should first establish what is considered raw milk and what is not raw. Raw milk is considered any animal milk, most often from cows, sheep and goats, which is not pasteurized, but still utilized for human consumption. Keep in mind that raw milk can also be used for producing other dairy products such as cheese and yogurt. Raw milk may also undergo a straining process, but it is otherwise unprocessed. Sources of raw milk are typically local farming operations. In fact, the interstate sale of raw milk for direct consumption has been prohibited in the U.S. by federal law since 1987, due to safety concerns regarding shelf life and disease risks. However, there are many states that allow the intrastate sale of raw milk, while a few states prohibit it completely. This means that the vast majority of what we see in our local grocery stores will have undergone the process of pasteurization, which will be clearly stated on the label. Pasteurization involves heating the milk to very specific temperatures for short time frames in order to kill potentially harmful germs. Pasteurization was introduced in the U.S. during the first part of the 20th century, at a time when millions of people were contracting life-threatening illnesses such as typhoid, diphtheria and tuberculosis, often through milk consumption. Applying the simple process of pasteurization, along with other health advances, led to a dramatic decline in such diseases, and is considered a major public health triumph. Decreasing or eliminating potentially harmful microbes through pasteurization, not only makes the product safer for consumers, it also increases shelf life.
So why is raw milk becoming a sought after commodity for many consumers? This can probably be attributed to such things as a general increase in societal demand for whole, natural and sustainable food products; as well as the perceived benefits of the milk itself. Raw milk drinkers claim that the unpasteurized product is higher in nutrients, protective enzymes and immune boosting probiotics, and can help treat a variety of ailments from asthma to gastrointestinal disorders. Supporters also claim that pasteurization is the cause of milk allergies and lactose intolerance. It is important to note that these claims remain largely unsubstantiated by published scientific studies. In many cases these claims have been categorically refuted by direct scientific evidence. The Food and Drug Administration (FDA) frankly states that “research shows no meaningful difference between the nutrient content of pasteurized and unpasteurized milk”. Science has also shown that most enzymes of concern by advocates are not altered by pasteurization. For those with allergy concerns, medical experts and research agrees that it is the proteins naturally present in milk (both raw and pasteurized) that are the cause of allergic reactions to milk and have no relationship to the pasteurization process. In regards to lactose intolerance, it needs to be understood that lactose intolerance is a genetic error of metabolism that some people are born with, and there is lactose present in both raw and pasteurized milk. So unfortunately for the lactose intolerant, raw milk is not the solution. As for probiotics, milk does not naturally contain probiotics; so if they are detected in the raw milk they are likely from another source such as air exposure or fecal contamination. But the good news is that we as consumers have many, safer options for experiencing the benefits of probiotics, including yogurt with active cultures and over the counter supplements.
Now that we have explored some of the common myths surrounding raw and pasteurized milk, it is most important to discuss the reality of the risks involved with raw milk consumption. Real world case studies, as well as research by such reputable organizations as the Centers for Disease Control and Prevention (CDC) and the FDA, consistently show that the risks of raw milk consumption far outweigh any real or perceived benefit. A 13 year study by the CDC showed raw milk and raw milk products are 150 times more likely to cause a disease outbreak than are pasteurized dairy products. These risks come in the form of a long list of disease causing germs that can contaminate dairy products, and are the reason that pasteurization was instituted in the first place. Some of the more significant contaminants that can be present in raw milk include such pathogens as Salmonella, E. coli, Listeria, and Campylobacter. These pathogens can cause a variety of symptoms, but most commonly produce gastrointestinal illness such as vomiting and diarrhea that can range from mild forms to fatal illnesses. The most vulnerable to becoming sick from drinking raw milk include babies, young children, those with weakened immune systems and pregnant women. But “healthy” people can become ill as well, and there are many documented cases. Data collected by the CDC from 1998-2009 documented 93 disease outbreaks due to raw milk and raw milk product consumption. These outbreaks caused 1,837 illnesses, 195 hospitalizations, and 2 deaths. It is important to note that for every case that is reported and diagnosed, there are many illnesses that go unreported, which means these case numbers in reality are certain to be much higher. The most recently reported outbreak occurred in Oregon this past April. The outbreak involved 19 people, 15 of which were children, with 4 of the children ending up in the hospital undergoing treatment for kidney failure. Eleven of the cases were confirmed to have been caused by a very dangerous strain of E. coli that was traced back to a dairy farm that supplied the families with raw milk. In reflecting on outbreaks such as these, it is important to remember that these illnesses are preventable. But hopefully, these sad cases will also serve to educate us as consumers, so that we can make informed and healthy choices for ourselves and our families.
- Langer AJ, Ayers T, Grass J, Lynch M, Angulo FJ, Mahon BE. Nonpasteurized dairy products, disease outbreaks, and state laws-United States, 1993-2006. Emerg Infect Dis. 2012 Mar;18(3):385-91.
- Oliver SP, Boor KJ, Murphy SC, Murinda SE. Food safety hazards associated with consumption of raw milk. Foodborne Pathog Dis. 2009 Sep;6(7):793-806. Review.
- Centers for Disease Control and Prevention, Trying to Decide about Raw Milk? Last Updated March 7, 2011, http://www.cdc.gov/foodsafety/rawmilk/decide-raw-milk.html (Accessed June 5, 2012)
- Centers for Disease Control and Prevention, Raw Milk Questions and Answers, Last Updated March 22, 2012, http://www.cdc.gov/foodsafety/rawmilk/raw-milk-questions-and-answers.html (Accessed June 5, 2012)
- Milk Facts, Heat Treatment and Pasteurization, http://milkfacts.info/Milk%20Processing/Heat%20Treatments%20and%20Pasteurization.htm (Accessed June 8, 2012)
- Food and Drug Administration, Raw Milk Misconceptions and the Danger of Raw Milk Consumption, Last Updated November 1, 2011, http://www.fda.gov/Food/FoodSafety/Product- SpecificInformation/MilkSafety/ConsumerInformationAboutMilkSafety/ucm247991.htm (Accessed June 5, 2012)
- Food and Drug Administration, Questions & Answers: Raw Milk, Last Updated November 1, 2011 http://www.fda.gov/food/foodsafety/product-specificinformation/milksafety/ucm122062.htm (Accessed June 5, 2012)
- Food Safety News, 19 Ill with E. Coli in Oregon Raw Milk Outbreak, Last Updated April 21, 2012, http://www.foodsafetynews.com/2012/04/post-5/ (Accessed June 5, 2012)
- International Association for Food Protection, Raw Milk Consumption: An Emerging Public Health Threat? Last updated 2012 http://www.foodprotection.org/events/other-meetings/3/iafp-timely-topics-symposium-raw-milk-consumption-an-emerging-public-health-threat/10/speaker-presentations/ (Accessed June 6, 2012)
- International Association for Food Protection, Nutritional Straight Talk on Raw and Pasteurized Milk, last updated 2012 http://www.foodprotection.org/files/timely-topics/TT_02.pdf (Accessed June 6, 2012)