Hemolytic uremic syndrome (HUS) in history–part 2

As I mentioned yesterday, the epidemiology of hemolytic uremic syndrome (HUS) was murky for several decades after it was first defined in the literature in 1955. In the ensuing decades, HUS was associated with a number of infectious agents, leading to the general belief that it was a “multifactorial disease”–one that had components of genetics and environment, much like we think of multiple sclerosis today, for example.

Several HUS outbreaks made people think twice about that assumption, and look deeper into a potential infectious cause. A 1966 paper documented the first identified outbreak of HUS, which occurred in Wales. The researchers examined a number of possible environmental factors the patients may have had in common–including food, water, and various toxins–but came up empty. They sum up:

Since it is almost invariably preceded by a gastrointestinal or respiratory illness, it seems probable that it represents a response to an infection. Although Gianantonio et al. (1964) have identified one possible causative virus, it may be that various infective agents can initiate the syndrome.

This idea held throughout the next 20-odd years, as numerous studies looked at both environmental and genetic effects that may be leading to HUS. A 1975 paper examined HUS in families, suggesting that there may be two types of HUS (which we now know to be true–the genetic form is less often associated with diarrhea, and tends to have a worse prognosis as I mentioned yesterday). But still, no definitive cause for either.

There were also a number of studies testing individuals for many different types of pathogens. A 1974 paper enrolled patients in the Netherlands between 1965 and 1970, but one of the inclusion criteria was a “history of a prodromal illness in which gastrointestinal or respiratory tract symptoms were present.” The respiratory tract symptoms are mentioned in a number of papers, and were probably a red herring that sent people in search of the wrong pathogens for awhile. In this particular paper, they examined children for infection with a number of viral and bacterial pathogens, using either culture or serological methods (looking for antibodies which may suggest a recent infection). In that portion of the paper, they note a possible association with adenoviruses, but state that the data don’t support a bacterial infection–a viral etiology was deemed more likely. Regarding basic epidemiology, they did note a few small clusters of cases in families or villages, as well as a peak in cases in spring/summer–as well as an increasing number of cases from the first year of their study to the last. The epidemiology of HUS was starting to become clearer, and the syndrome appeared to be on the rise.

Even as additional case reports occasionally targeted foods as a precursor to HUS outbreaks, it wasn’t until the late 1970s and early 1980s that HUS really started to come into focus. In 1977, a paper was published identifying the “Vero toxin”–a product of E. coli that caused cytotoxicity in Vero cells (a line of African green monkey kidney cells, commonly used in research). Researchers were closing in.

Hemolytic uremic syndrome (HUS) in history–part 1

It appears that the E. coli O104 sproutbreak is starting to wind down, with more than 3,500 cases diagnosed to date and 39 deaths. Though sprouts remain the key source of the bacterium, a recent report also documents that human carriers helped to spread the organism (via H5N1 blog). In this case, it was a food service employee working at a catering company, who spread infection to at least 20 people before she even realized she was infected.

As with many infectious diseases, there are potential lingering sequelae of infection, which can occur weeks to years after the acute infection has cleared up. Like almost 800 others involved in this outbreak, the woman who unwittingly infected others via food developed hemolytic uremic syndrome, or HUS. We now know that the most common cause of HUS are bacteria such as STEC (“shiga toxin-producing E. coli“); the “shiga toxin” that they produce inhibits protein synthesis in the host and cause cell death. This can have systemic effects, and leads to clotting in affected organs–most commonly the kidneys, but other organs can also be affected. Dialysis may be necessary, and the infection can lead to kidney failure and the need for organ transplantation. There is already concern that, because of the huge numbers of HUS cases, many patients will have long-term kidney damage, including the potential need for additional organs (and possibly, re-vamping the way donations are made as well):

In previous E. coli outbreaks, up to half of patients who developed the kidney complication were still suffering from long-term side effects 10 to 20 years after first falling sick, including high blood pressure caused by dialysis.

In addition to possible kidney problems, people who have survived serious E. coli infections may also suffer from neurological damage, as the bacteria may have eaten away at blood vessels in the brain. That could mean suffering from seizures or epilepsy years after patients recover from their initial illness.

While it’s common knowledge in the medical community now that STEC can lead to HUS, which can lead to chronic kidney issues, for many years, the link between E. coli and HUS was obscured. HUS first appears in the literature in 1955, but the link to STEC wasn’t confirmed until the early 1980’s. In the interim, myriad viruses and bacteria were examined, as well as genetic causes. (There are cases of HUS caused by host mutations and other etiologies, but they are much less common than HUS caused by STEC and related organisms). In future posts this week, I’ll delve into the history of HUS and look at a few studies which examined alternative hypotheses of causation, until finally STEC was confirmed as the causative agent. I’ll also discuss what this means as far as discovering infectious causes of other “complex” and somewhat mysterious diseases whose causes are unknown, as HUS was a mere 30 years ago.

Is There a Viral Cause for Idiopathic Pulmonary Arterial Hypertension?

Student guest post Dayna Groskreutz

Pulmonary hypertension (PH) refers to a condition in which there is high blood pressure in the vessels carrying blood from the heart to the lungs. Pulmonary arterial hypertension (PAH) is a subset of PH referring specifically to an increase in the pressure within the pulmonary arteries (rather than the pulmonary veins or capillaries). The high blood pressure in the vessels causes thickening of these arteries, making it hard for the heart to pump blood to the lungs. Pressure builds up and backs up. Over time, stress on the heart causes it to enlarge, and it becomes more difficult for blood to get to the lungs so that it can get oxygen. Patients become tired, dizzy, and short of breath. Their quality of life is significantly reduced. Data from the National Institute of Health PAH registry in the 1980s concluded that the average survival of untreated PAH is 2.8 years from diagnosis, with 1-year, 3-year, and 5-year survival rates of 68%, 48%, and 34%, respectively. With the development of effective therapy over the last 30 years, survival has improved slightly.

In some cases, PH is caused by an underlying disease, such as sleep apnea, lung disease, or heart disease. A familial form of PH has been described and characterized. PH caused by diet medications like Fen-Phen has been widely publicized. One infectious agent, human immunodeficiency virus (HIV), has been shown to be an independent risk factor for pulmonary hypertension, but neither the virus nor its proteins have been demonstrated in the pulmonary arteries. In many cases, the cause of PH is idiopathic, meaning we do not know why the patient has pulmonary hypertension. This lack of knowledge has led researchers to search for an infectious agent as a cause for idiopathic pulmonary arterial hypertension (IPAH).

Although a causal relationship between IPAH and a viral infection has not been established, a relationship is suspected. Human herpesvirus-8 (HHV-8) is the causative agent of Kaposi’s sarcoma, primary effusion lymphoma, and Castleman’s disease, a rare blood disorder. In 2003, Bull and colleagues reported HHV-8 infection in the lung tissue and in the cells of the pulmonary artery of a patient with PH and Castleman’s disease. They suggested that HHV-8 might be a causative agent for this patient’s PH. The same year this group published a case-control study in the New England Journal of Medicine. The cases consisted of 16 patients with IPAH, and the controls consisted of 14 patients with PH caused by an underlying disease (or secondary PH). They detected HHV-8 infection using both antibody and polymerase chain reaction (PCR)-based techniques. 10 of 16 patients (62%) with IPAH had HHV-8 detected with antibody and PCR techniques, while none of the control (secondary) PH group had HHV-8 detected with antibody, and one patient had PCR evidence of virus. This study provided evidence of HHV-8 infection in the lung and pulmonary arterial cells of patients with IPAH; however, the study did not provide evidence of causation as it was not prospective in design.

A subsequent study by Laney et al compared 19 patients with IPAH, 29 patients with secondary PH, and 150 controls, and looked for evidence of HHV-8 in their blood using serologic tests. The rate of HHV-8 in the blood of IPAH was 0%, controls 0.7%, and secondary PH 10.3%. Two of the three secondary PH patients with HHV-8 in their blood had HIV-associated PH, and the association of HIV and HHV-8 is well documented. The authors concluded that HHV-8 does not have a role in IPAH or non-HIV-associated PH.

Nicastri et al next retrospectively analyzed data from 75 patients referred to their institution for lung transplant. 16 had IPAH, 17 had secondary PH, 7 had PH due to repetitive blood clots in the lung, and the remaining 10 had PH associated with miscellaneous other diseases including autoimmune disease and HIV. The 42 patients without PH consisted of patients with cystic fibrosis and other lung diseases. They performed antibody tests to detect HHV-8 in the blood. Of the patients with PH, 3% had HHV-8 detected in their blood, while 19% of patients without PH had HHV-8 detected. The authors concluded there was no direct relationship between HHV-8 infection and PH.

Finally, a German study by Henke-Gendo et al examined lung tissue from 26 patients who underwent lung transplant for IPAH from 1993-2003. Using an antibody test, they detected HHV-8 protein in the diseased lungs removed at the time of transplant in 61.5% of the cases; however, they were unable to confirm HHV-8 infection by PCR in all cases. They concluded that HHV-8 is unlikely to play a role in the pathogenesis of IPAH.

In recent years, there has been a search for a causative infectious agent for idiopathic pulmonary arterial hypertension. Two papers published by the same group at the University of Colorado provided some evidence that an association might exist, but these findings have not been confirmed in three subsequent studies by other investigators. The original authors at the University of Colorado recently published a cell-based study showing that HHV-8 can infect pulmonary endothelial cells, or the cells that make up the pulmonary arteries, lending further plausibility to the association

However, in absence of further evidence at this time, HHV-8 and PH appears to be an inconclusively proven association.


1. D’Alonzo, G. E., Barst, R. J., Ayres, S. M., Bergofsky, E. H., Brundage, B. H., Detre, K. M., Fishman, A. P., Goldring, R. M., Groves, B. M., Kernis, J. T., and et al. (1991) Ann Intern Med 115, 343-349

2. Keogh, A., McNeil, K., Williams, T. J., Gabbay, E., Proudman, S., Weintraub, R. G., Wlodarczyk, J., and Dalton, B. (2009) Intern Med J

3. Bull, T. M., Cool, C. D., Serls, A. E., Rai, P. R., Parr, J., Neid, J. M., Geraci, M. W., Campbell, T. B., Voelkel, N. F., and Badesch, D. B. (2003) Eur Respir J 22, 403-407

4. Cool, C. D., Rai, P. R., Yeager, M. E., Hernandez-Saavedra, D., Serls, A. E., Bull, T. M., Geraci, M. W., Brown, K. K., Routes, J. M., Tuder, R. M., and Voelkel, N. F. (2003) N Engl J Med 349, 1113-1122

5. Laney, A. S., De Marco, T., Peters, J. S., Malloy, M., Teehankee, C., Moore, P. S., and Chang, Y. (2005) Chest 127, 762-767

6. Nicastri, E., Vizza, C. D., Carletti, F., Cicalini, S., Badagliacca, R., Poscia, R., Ippolito, G., Fedele, F., and Petrosillo, N. (2005) Emerg Infect Dis 11, 1480-1482

7. Henke-Gendo, C., Mengel, M., Hoeper, M. M., Alkharsah, K., and Schulz, T. F. (2005) Am J Respir Crit Care Med 172, 1581-1585

8. Bull, T. M., Meadows, C. A., Coldren, C. D., Moore, M., Sotto-Santiago, S. M., Nana-Sinkam, S. P., Campbell, T. B., and Geraci, M. W. (2008) Am J Respir Cell Mol Biol 39, 706-716

Can your pet dog make you sick? Multiple Sclerosis and Canine Distemper Virus

Student guest post by Raj Nair.

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease that affects the central nervous system (CNS) consisting of the brain and the spinal cord [1]. It is thought to be an autoimmune disease since individual’s immune system attacks their own healthy tissues [1]. However, studies to ascertain triggering factors such as genetic, environmental, and infectious causes are still in progress [2]. So one wonders “Who is more susceptible to develop MS” Literature reveals that typically people between 20 and 50 years of age are commonly diagnosed with MS, affects more women than men, and Caucasians of Northern European ancestry are more prone to develop this disease [1, 2]. Knowledge on the pathophysiology of this disease is that immune system attacks myelin, which forms a protective coat surrounding the nerve fibers of the brain and the spinal cord [2]. The myelin sheath can be compared to insulation around an electrical wire. Loss of this protective layer impedes transmission of nerve signals [1]. Consequences of this damaged connection are the spectrum of symptoms seen in MS. Some of these symptoms are blurred vision, loss of balance, poor coordination, extreme fatigue, tremors, loss of sensation or odd sensations (pin and needle sensations), slurred speech, blindness, difficulty concentrating, poor memory and judgment, and in severe cases paralysis [1]. However, every person is wired differently and so these symptoms are not consistently seen in all patients with MS [1]. Considering all of the above facts my guess is symptoms may vary depending on a person’s immune system and the external or other internal factors governing their immune system. The disease is rarely fatal and most of the people are only mildly affected. Moreover, most of the affected people remit spontaneously [3].

Why should anyone care…. Because MS is unpredictable [1,3], there is no universal cure for the disease [3], can be a chronic condition [1], possibility of disease recurrence [4], and the most important being ‘a single cause’ for the disease has not been identified. As in all diseases with multiple interacting causes, in MS too there is no single pathogen or environment to complete its disease triad. Evidence has it that the disease is more common in Northern America and Canada demonstrating a north-south gradient [5]. Migration studies have established that risk for acquiring MS remains unchanged for those who move from a high prevalence area after age 15, while risk decreased for those who moved at an earlier age [5]. In addition, the genetic angle has been studied by conducting twin studies and studies on specific types of genes. Results yielded prove that genetics can lead to an increase in MS susceptibility but probably not cause MS [5]. In order to make more sense of all the above susceptibility factors and with my interest in infectious causes of diseases, I decided to probe into existing infectious perspectives on MS.

History has it that in 1868, Jean Marie Charcot described the first human demyelinating disease, Multiple Sclerosis. It was postulated then that the disease was a result of exposure to dampness or injuries or emotional stress. However, in the era of microbiological advances, one of Charcot’s students postulated an infectious etiology for MS [7]. Moreover, the CNS pathology and presence of IgG antibodies and oligoclonal bands are known to be consistent with an infectious or immune mediated neurological disorder [6]. Several infectious agents such as Epstein Barr virus, Canine Distemper virus (CDV), measles virus, Chlamydia pneumoniae, Varicella, Human Herpesvirus-6 (HHV-6), and mumps virus have been associated with MS. Viruses win hands down against bacteria in having a strong association with MS. Studies have a tilt towards a viral cause of MS due to the following reasons: low concordance of MS in monozygotic twins similar to what was seen in paralytic poliomyelitis (also a viral infection), spontaneous viral models of CNS demyelination, and increased titers of viral antibodies in MS patients (particularly measles virus). However, these associations can only be strengthened using criteria such as consistency of association across studies, biological plausibility, temporal association, specificity and dose -response relation (epidemiologists know these are the Bradford-Hills criteria!) I will briefly attempt to establish the causal role of CDV in development of MS. Reason I chose this virus? I lost my pet dog to Old Dog Encephalitis (ODE) due to chronic CDV infection. Now I am left thinking ‘Am I or any of my family member’s ideal candidates for developing MS later in life?”

CDV is an RNA virus belonging to the family of Paramyxoviridiae, is closely related to the measles virus in humans and is the most neurotropic form of morbillivirus. As observed in the measles virus, CDV can jump species [5] and causes fatal CNS demyelination in animals including primates [9]. However, the catch-22 is that there has not been one virus (measles or CDV) consistently detected in samples from MS patients to prove its causal role. To make things worse, there is a possibility of cross-reaction in testing for CDV and measles virus using molecular techniques in samples obtained from MS patients [10, 13]. Neutralization assay used to identify viral antibodies in patients have shown considerable variation in the CDV/measles antibodies ratio [10, 11]. This implies that there is a potential for CDV to produce undiagnosed or subclinical human infections [10]. To explain MS on the basis of owning dogs per se, several studies have observed that significantly higher proportion of dogs were kept indoors in the colder northern United States as compared to the southern and western region [12]. This may explain the north-south gradient noted in the prevalence of MS. So logically, greater exposure to dogs before onset of neurological symptoms was expected. However, this phenomenon could not be studied well using case-control studies owing to the higher exposure of humans to dogs in Western countries particularly the United States [6].

An interesting aspect studied was exposure to CDV infected dogs. Most of these studies yielded significant exposure to dogs with distemper-like illness at least 5-10 years before development of MS [12, 14]. Historically other studies have shown significant increase in MS incidence rates preceded by a CDV epidemic in locations such as Newfoundland [16], Key West [15], Sitka [17], and the Faroe Islands. One of the most interesting readings was a study conducted to determine environmental changes implemented that may have lead to a reduction in MS incidence in Key West [15]. An animal shelter on the island which was used to dump euthanized dogs was shut down. This change was said to have attributed to reduction in the MS incidence on the island.

With all of the above evidence and in context with the Hills criteria, I will conclude that there is biological plausibility of CDV playing a causal role in development of MS owing to the demyelinating nature of illness caused by this virus. In addition, this virus still causes disease in dogs despite the widespread use of vaccines [18]. This reinforces the possibility of contracting the virus via exposure to infected dogs (zoonotic disease). However, temporal association could not be established between the virus and occurrence of MS. This may be due to the fact that there are other viruses too causing demyelinating diseases such as measles and HIV, which have a well established role in human diseases. Similar symptoms of demyelinating diseases caused due to viruses other than CDV may have resulted in incorrect estimation of MS prevalence or incidence. There is some consistency among case-control studies which demonstrate exposure to CDV or dogs before the development of MS. However, owing to chronic nature of the CDV these studies do not really make a concrete argument for the role of this virus in MS causation. There does not seem to be any study conducted to examine a dose-response relation of the virus with respect to development of MS. In lieu of the above evidence, a criterion of specificity has been wasted and is best overlooked.

So one real conclusion from observations made so far is that CDV may be responsible for the causation of MS. However, it is definitely not the only factor in the causal pathway. This implies that CDV may be a necessary factor in the development of MS as could be other infectious agents (bacterial or viral). However, an individual’s environment, genetics and immune system are other sufficient factors crucial in disease causation. Also I take this opportunity to highlight the cause ‘Take good care of your pet dog and yourself’. It is the rule of nature, “What goes around, comes around”.


1. National Multiple Sclerosis Society. (n.d.). What is multiple sclerosis? Retrieved April 12, 2010.

2. The Journal of the American Medical Association. (2006). Multiple Sclerosis. Retrieved April 12, 2010.

3. National Institute of Neurological Disorders and Stroke. (2010). NINDS Multiple Sclerosis Information page. Retrieved April 12, 2010.

4. The Multiple Sclerosis Information Trust. (2008). All about multiple sclerosis. Retrieved April 12, 2010.

5. Cook, S.D. (1996). Epidemiology of multiple sclerosis: Clues to the etiology of a mysterious disease. Neuroscientist, 2, 172-80. Retrieved April 12, 2010.

6. Cook, S D, Rohowsky-Kochan, C, Bansil, S, et al. (1995). Evidence for multiple sclerosis as an infectious disease. Acta neurologica Scandinavica. Supplementum, 161, 34-42. Retrieved April 12, 2010

7. Johnson, R T. (1994). The virology of demyelinating diseases. Annals of neurology, 36 Suppl, S54-S60. Retrieved April 12, 2010.

8. Giovannoni, G, Cutter, G R, Lunemann, Jan, et al. (2006). Infectious causes of multiple sclerosis. Lancet Neurology, The, 5(10), 887-894.

9. Yoshikawa, Y, Ochikubo, F, Matsubara, Y, et al. (1989). Natural infection with canine distemper virus in a japanese monkey (macaca fuscata). Veterinary microbiology, 20(3), 193-205.

10. Hughes, R A, Russell, W C, Froude, J R, et al. (1980). Pet ownership, distemper antibodies and multiple sclerosis. Journal of the Neurological Sciences, 47(3), 429-432.

11. Rohowsky-Kochan, C, Dowling, P C, & Cook, S D. (1995). Canine distemper virus-specific antibodies in multiple sclerosis. Neurology, 45(8), 1554-1560.

12. Norman, J E, Cook, S D, & Dowling, P C. (1983). Household pets among veterans with multiple sclerosis and age-matched controls. pilot survey. Archives of neurology, 40(4), 213-214.

13. Haile, R, Smith, P, Read, D, et al. (1982). A study of measles virus and canine distemper virus antibodies, and of childhood infections in multiple sclerosis patients and controls. Journal of the Neurological Sciences, 56(1), 1-10.

14. Cook, S D, Natelson, B H, Levin, B E, et al. (1978). Further evidence of a possible association between house dogs and multiple sclerosis. Annals of neurology, 3(2), 141-143.

15. Macgregor, H S, & Latiwonk, Q I. (1992). Search for the origin of multiple sclerosis by first identifying the vector. Medical hypotheses, 37(2), 67-73.

16. Pryse-Phillips, W E. (1986). The incidence and prevalence of multiple sclerosis in newfoundland and labrador, 1960-1984. Annals of neurology, 20(3), 323-328.

17. Cook, S D, & Dowling, P C. (1982). Distemper and multiple sclerosis in sitka, alaska. Annals of neurology, 11(2), 192-194.

18. Cook, S D. (1987). Man, dogs, and hydatid disease. The Lancet, 1(8523), 21-22.

Worms: Are they good or bad for us?

Student guest post by Shylo Wardyn

“Of all the parasites I’ve had over the years, these worms are among the… hell, they are the best”.

Was Fry from the animated show ‘Futurama’ right in his assessment of worms being good for him? Did he know something about parasitic worm infections that I was unaware of? Well, in the show, his parasites were doing remarkable things for his body, but does this translate to real life at all? Some people think so. Altman reviews the idea that over evolutionary time, our ancestors were infected with all sorts of parasites and this led to an interaction between the worm gene products and the immune system. These interactions led to modulation of dendritic cells and establishment of T-cell networks. It has been hypothesized that in an environment without these interactions, as is the case for most people living in “Westernized” countries, there is a loss of the ‘fine tuning’ of the adaptive immune system.

In another review, Jackson et al. discuss how this mechanism could have co-evolved. It is generally believed that the T helper cell type 2 (Th2) evolved to counter infections with parasitic worms. These cells are activated in response to parasitic worm infection, which leads to a large regulatory T cell response. Our response to worms seems to involve an immune response that is less inflammatory than our response to microbes, and it also takes much longer to reach the peak of effectiveness. This is due in large part to an initial systemic suppression of innate and adaptive immunity in the host. This is likely caused by regulatory CD4+ and CD25+ T cells producing suppressive cytokines or other suppressor T cell subsets. Anti-inflammatory responses are also caused by alternatively activated macrophages. These macrophages secrete anti-inflammatory cytokines and express genes whose functions relate to wound healing and repair. Therefore, being infected with parasitic worms leads to a down-regulation of proinflammatory responses, while allowing mechanisms for wound repair and a controlled development of the Th2 response. This Th2 and T regulatory response is beneficial for both the worm and the host. For us, the regulated Th2 response is less costly than the generation of a strong immune response, which often can be detrimental to our own cells. For the parasites, they are able to survive the initial immune response and therefore reproduce, while later parasites would not be able to survive the developed immune response.

The overall thought is that since parasitic worm infections are ubiquitous in mammals and have been since mammals first evolved, there would be a positive selective pressure for those individuals whose immune systems respond well to worm infections. Our immune systems may have been selected to anticipate a chronic exposure to Th2 and T regulator inducing pathogens. Since our ancestors were chronically infected by worms, their immune systems would have developed to work well in this context, while not necessarily working as well in the absence of worms. This scenario may explain why in some cases the immune system goes haywire in populations that are free from parasitic worms.

So is there any strong evidence linking parasites with populations free from allergies and autoimmune diseases? There have been many ecological studies which show an inverse correlation between the parasite load and allergy level for a particular region. Does this prove anything? Not really, the data is simply correlative. There have been other studies showing that treatment of worm infections is accompanied by an increase in skin test reactivity to allergens and IgE antibody levels. It appears that in the absence of worms, the immune system overreacts to allergens to which it normally wouldn’t mount a response in the presence of worms. This gives us a better idea about the link between parasitic worms and immune responses. While the evidence is still shaky, it is biologically plausible that the lack of worms in our environment has led to the massive increase in the amount of immune related diseases, such as asthma, multiple sclerosis, type 1 diabetes, and general allergies. However, the immune system is incredibly complex, as are those diseases, and I’ve barely scratched the surface of it for this topic. So while it seems being infected with worms may prevent immune system diseases, I doubt anyone would trade their asthma for a tapeworm. It does make for an interesting hypothesis (and Futurama episode) though and should be researched more thoroughly.


Altmann D. M. (2008). Review series on helminths, immune modulation and the hygiene hypothesis: Nematode coevolution with adaptive immunity, regulatory networks and the growth of inflammatory diseases. Immunology, 126(1); 1-2.

Jackson J. J., Friberg I.M., Little S. and Bradley J. E. (2008). Review series on helminths, immune modulation and the hygienehypothesis: Immunity against helminths and immunological phenomena in modern human populations: coevolutionary legacies? Immunology, 126(1); 18-27.

Weiss S.T. (2000). Parasites and asthma/allergy: What is the relationship? Journal of Allergy and Clinical Immunology, 105(2); 205-210.

Potential for common bacteria to cause colorectal cancer

Student guest post by Desiré Christensen

Colorectal cancer (aka colon cancer) includes cancers of the colon, rectum, and appendix. Colorectal cancer is more common in developed countries (e.g. United States and Japan) compared to developing countries in Africa and Asia. Each year in the United States, there are around 150,000 cases of colorectal cancer diagnosed and about 50,000 people die from this cancer. Risk factors for colorectal cancer include lifestyle factors (e.g. habitual alcohol use; high-fat, low-fiber diet; obesity; sedentary lifestyle; smoking), family history of intestinal polyps or colorectal cancer, and medical conditions (e.g. diabetes, familial polyposis syndromes, hereditary non-polyposis colon cancer syndrome, inflammatory bowel disease, intestinal polyps). [1]

Lifestyle factors are considered important risk factors for colorectal cancer, and they are modifiable unlike family history. Among the most important determinants of colorectal cancer are dietary habits. High-fat, low-fiber diets are associated with an increased risk for colorectal cancer. Diets with a protective effect include those high in vegetables, fruits, fiber, folate, and calcium. [2]

In addition to the risk factors listed above, an infectious cause of colorectal cancer has been suggested. Many bacterial species inhabit the human colon. Some may be friends, and others foes. Friendly colonic bacteria help with digestion, and in return, the colon provides the bacteria a place to live. The presence of friendly bacteria generally goes unnoticed by the host. Other bacteria in the colon may be harmful and are being investigated as potential causes for irritable bowel disease [3] and colorectal cancer. Enteroccocus faecalis (or E. faecalis) is one such bacterium under study for its role in colorectal cancer.

E. faecalis is common and present in most colons. It lives in disease-free individuals as well as people with colorectal cancer. For most, E. faecalis appears to be harmless. But recent studies have shown evidence that E. faecalis is not an innocent bystander in susceptible hosts.[4] The question arises: How could E. faecalis cause cancer in some and be harmless in others?

A characteristic feature of colorectal cancer is genomic instability. Genomic instability refers to chromosomal rearrangement, duplications, and other types of DNA damage. Theories have developed to explain how E. faecalis could contribute to genomic instability. One theory is that E. faecalis produces free radicals such as extracellular superoxide and hydrogen peroxide. Free radicals are highly reactive with other molecules. The free radicals could directly cause mutations in colonic DNA; it is also possible for free radicals to form carcinogens indirectly from dietary procarcinogens (a substance that becomes a carcinogen after being altered). [4]

Results from a study by Huycke et al [3] supports this theory. The investigators found that E. faecalis produces extracellular superoxide and reactive oxygen species capable of causing genomic instability. Free radical production by E. faecalis has the potential to damage DNA in the colon. If production of these free radicals becomes chronic, DNA damage would be ongoing leading to increased genomic instability and mutations. [4]

Dietary risk factors could be combined with the theory about DNA damage induced by E. faecalis to explain some cases of colorectal cancer. An interaction between diet and E. faecalis could also explain why some people develop cancer and others remain disease free. High-risk diets include diets rich in meat and iron. High concentrations of iron in the colon could accelerate formation of free radicals and mutagenic products. Low-risk diets such as those rich in fruits, vegetables and fiber, contain antioxidants that can “round-up” free radicals and reactive oxygen species to limit the potential for DNA damage. Dietary intake could influence the amount and types of carcinogens E. faecalis and other bacteria produce in the colon. Studies are needed to investigate the interaction between infectious causes such as E. faecalis and dietary intake. [5]

The link between colorectal cancer and an infectious agent has been investigated for other bacteria. Streptococcus bovis (S. bovis) has also been linked to colorectal cancer. A case-control study was done to determine the presence of S. bovis in 16 patients with colonic cancer and 16 age matched controls. The presence of E. faecalis was determined by looking for antibodies against E. faecalis. More antibodies often indicate a larger response by the host to bacteria in the body. An increase in antibodies against S. bovis was detected in patients with colonic cancer, but an increase in antibodies against E. faecalis was also seen. In fact, there was a greater increase in antibodies against E. faecalis compared to S. bovis. [5]

There are few epidemiological studies on E. faecalis in colorectal cancer. One study collected stools from patients undergoing colonoscopy who had no prior history of colonoscopy or colorectal cancer. Enterococci were later isolated from the stool samples. Free radical producing enterococci were found in 40 percent of the stool samples. No association was found between colonization with enterococci and colorectal cancer. The study had limitations. The patients were not tracked long enough to study chronic infection and genomic instability that occurs over decades instead of years. In addition, the presence of any enterococci was evaluated instead of focusing on E. faecalis. It is possible that E. faecalis differs significantly from other enterococci in the ability to cause colorectal cancer. [6]

Much remains unknown about the cause of colorectal cancer. Research linking lifestyle factors and infectious causes is lacking. There is a need for more epidemiological studies and studies describing potential pathways leading to the development of cancer. E. faecalis, or any other infectious cause, has not yet been definitively associated with colorectal cancer. Lifestyle factors and family history will remain important risk factors regardless of an infectious cause, but these factors may interact with bacteria found in the colon and help explain why some individuals are at an increased risk for colorectal cancer.

1. Colorectal Cancer Overview. (1999) Colon Cancer (Colorectal Cancer). Retrieved 4/10/2010, from Healthcommunities.com.

2. Sandler RS. (1996) Epidemiology and risk factors for colorectal cancer. Gastroenterol Clin North Am; 25(4):717-735.

3. Balish E and Warner T. (2002) Enterococcus faecalis induces inflammatory bowel disease in interleukin-10 knockout mice. Am J of Path; 160:2253-2257.

4. Huycke MM, Abrams V, and Moore DR. (2002) Enterococcus faecalis produces extracellular superoxide and hydrogen peroxide that damages colonic epithelial cell DNA. Carcinogenesis; 23(3):529-536.

5. Darjee R and Gibb AP. (1993) Serological investigation into the association between Streptococcus bovis and colonic cancer. J Clin Pathol; 46:1116-1119.

6. Winters MD, Schlinke TL, Joyce WA, Glore SR, Huycke MM. (1998) Prospective case-control study of intestinal colonization with enterococci that produce extracellular superoxide and the risk for colorectal adenomas or cancer. Am J Gastroenterol; 93(12):2491-2500.

Malignant Mesothelioma and Simian Virus 40 (SV40)

Student guest post by Andrew Behan

Malignant Mesothelioma (MM) is a rare type of cancer which manifests itself in the thin cells lining the human body’s internal organs. There are three types of MM; pleural mesothelioma, peritoneal mesothelioma, and pericardial mesothelioma, affecting the lining of the lungs, abdominal cavity, and lining of the heart, respectively (1). Pleural mesothelioma is most common, consisting of about 70% of all MM cases and has a poor prognosis; patients live a median time of 18 months after diagnosis. (Note: for the purposes of this article, MM will be used to represent pleural mesothelioma exclusively.) Despite its discovery in the mid-1800’s, MM was not linked to asbestos until the late 1900’s, when case reports of fast-growing lung cancers, different from previously described lung cancers, motivated investigators to uncover undisputed evidence linking asbestos to MM. Measures to reduce/eliminate asbestos from buildings reduced exposure to the cancer-causing agents found within the material, and public health officials remained confident by the year 2000 MM cases would decline in the U.S. and parts of Europe. Despite these predictions, MM cases have not declined. In fact, the incidence of MM is on the rise (1). Consequently, investigators have focused their attention on other factors to explain the steady incidence of MM in the U.S., eventually naming Simian Virus 40 (SV40) as a potential cause of MM.

You might be asking, “SV40? What’s that?” SV40 is a virus originally discovered in 1960 in kidney cells of rhesus monkeys. SV40 is dormant and asymptomatic in rhesus monkeys, but was later found to cause kidney disease, sarcoma, and other cancers in animal models. Later on, it was found SV40 attacks p53 gene (a tumor suppressor) and can interrupt the cell’s ability to perform apoptosis, or cell death. This makes the cells immortal, leading to tumor formation, or cancer (2). Controversy arose when the discovery of SV40 was found in the rhesus monkey kidney cells because these same cells were being utilized to form the polio vaccine. Consequently, many polio vaccines were contaminated with SV40 and when the vaccine was used to inoculate humans, SV40 was passed to humans along with the inactive form of the polio virus. It was estimated over 98 million Americans received the vaccine from 1955-1963, when a proportion of the vaccine was contaminated with SV40. Of the 98 million vaccinated during this time period, it was estimated 10-30 million of those individuals were exposed to SV40. Naturally, people who received contaminated forms of the vaccine were afraid they would develop cancer from exposure to SV40.

Since the controversy began in 1960, research has been devoted to confirming its role in cancer development in humans, as well as many animal models. As I mentioned above, presence of SV40 in animals has led to tumors and other cancers, and a few studies have found presence of SV40 in humans who have developed MM. For example, Carbone et al. found SV40 in mesothelial cells of humans who had developed MM, but not in the surrounding tissue (3). They did not find SV40 in patients who had other lung cancers, possibly reinforcing the specificity of their findings (3). Overall, 54% of MM cases were found to have SV40 infection within the mesothelial cells (3). The investigators determined more research needed to be done to see if SV40 infection alone could cause MM, or if other factors, such as immunosuppression or exposure to asbestos, were necessary for development of MM.

Other studies were not as convincing. For example, Lopez-Rios et al. reported that initially they detected SV40 in about 60% of MM specimens, and then they determined that most of the positive results were caused by plasmid PCR contamination, and that only 6% of the initially positive samples were confirmed to contain SV40 DNA (4). However, studies have shown the presence of SV40 in human specimens by using several other techniques besides PCR, including Southern blotting, immunostaining, RNA in situ hybridization, microdissection, and electron microscopy” (5).

Thus, the question remains: does SV40 cause MM, or does SV40 infection, in conjunction with asbestos exposure, generate a greater risk for the development of MM? This is a tough question to answer, because although asbestos is no longer mined in the U.S., it is still being imported; workers are still continually being exposed to asbestos. However, the use of asbestos has nearly ceased, decreasing from 813,000 metric tons in 1973, to 1700 metric tons in 2007 (6). The other problem in teasing out SV40 as a cause of MM from asbestos lies in the latency period between asbestos exposure and MM clinical diagnosis. According to the CDC, the latency period for someone who is first exposed to asbestos and clinical disease is 20-40 years. It may be, given asbestos still remains in many buildings, and exposure to it is inevitable when removal is completed, in addition to the long latency period between exposure and disease, that we have not yet come to the dramatic decrease in MM health officials have predicted. Or, is SV40 infection the culprit and the increase in incidence of MM will continue to rise? According to the SV40 Foundation, “SV40 is a problem that federal government authorities have not addressed responsibly because the government’s own vaccine programs are responsible for the spread of the virus throughout the western world”.(2) It is no question the public has not forgotten, even after almost 50 years, and much more research into this area is needed, to attempt to confirm SV40’s causal role, if any, in the development of MM.


(1) Mesothelioma. Retrieved April 2010.

(2) “Treating SV40 Cancers.” Retrieved April 2010.

(3) Carbone, M. “Simian virus 40 and human tumors: It is time to study mechanisms.” Retrieved from PubMed April 2010.

(4) López-Ríos F, Illei PB, Rusch V, et al. “Evidence against a role for SV40 infection in human mesotheliomas and high risk of false-positive PCR results owing to presence of SV40 sequences in common laboratory plasmids”. Lancet. 2004;364:1157-1166.

(5) Yang, Haining et al. “Mesothelioma Epidemiology, Carcinogenesis, and Pathogenesis.” http://www.ncbi.nlm.nih.gov.proxy.lib.uiowa.edu/pmc/articles/PMC2717086/. Retrieved from PubMed April 2010

(6) CDC. “Mesothelioma.” Retrieved from PubMed April 2010.

Chronic Fatigue Syndrome: a Legitimate Excuse for Missing Work

Student guest post by Jay Watson

Tired again? Perhaps it’s the crappy weather, because you’re sure that you’ve been getting enough sleep. After all, you can’t remember the last time you spent less than ten hours in bed per night. Hopefully it’s not mono; one of your friends had it a few months ago and it’s all but knocked her out. However, you soon realize that you’ve only talked to her on the phone since she got engaged, so there’s no way that’s it. It’s strange, even everyday activities like running errands has turned into something utterly exhausting. As you consider the reasons as to why you’ve felt so drained for… well for as long as you can remember, you whittle your way down through all the likely suspects. Worried, you finally make a trip into the doctor’s office. After seeing a couple doctors and explaining your medial history in depth each time, a specialist eventually mentions that you might be suffering from chronic fatigue syndrome.

According to the CDC, Chronic fatigue syndrome (or CFS) is a complex disorder that is characterized by severe chronic fatigue that lasts at least six months, as well as at least four of the following symptoms: impairment of short-term memory or concentration, sore throat, tenderness in lymph nodes, muscle or joint pain without swelling or redness, headaches, unrefreshing sleep, and post exertional malaise. In addition to the symptoms listed above, patients diagnosed with CFS have noted several other commonly observed symptoms. Because the laundry list of symptoms can be long, and due to the fact that ‘fatigue’ itself accompanies numerous other illnesses, diagnosis can only be made after eliminating other causes. Diagnosis includes more than one specialist, which typically involves detailed physical examinations and medical histories. Also, it is important to note that there is no laboratory technique currently available to test for chronic fatigue syndrome. Treatment for CSF focuses on the symptoms experienced by individual patients. Though there are plenty of gaps in the knowledge base for this disease, what is known is that CSF affects over one million Americans, and it occurs four times more frequently in women than men. Worldwide, CSF is estimated to affect 17 million, with a majority of people still undiagnosed. Also, CSF is a disease associated with adulthood, with people between forty and fifty most likely to have it. However, true to its name, the specific cause for this syndrome has not been established… yet!

Recently, actually very recently in fact, there has been much attention diverted to a potential factor involved with CSF: Xenotropic murine leukemia virus-related virus (or XMRV for short). Also according to the CDC, this virus is similar to a known mouse retrovirus. However, beyond knowledge of XMRV at the molecular level, little is known about the virus and its mode(s) of transmission. Even the CDC admits that the manner in which XMRV is transmitted is still uncertain and that more information is needed. Initially thought to be only associated with human prostate cancer, a study done by Vincent Lombardi and colleagues in October of 2009 found that approximately 67% of cases in the study diagnosed with CSF had detectible levels of XMRV versus about 4% of controls. Very quickly, additional studies to test this hypothesis have arisen. In contrast with Lombardi’s results, none of the subsequent studies have found an association between XMRV and chronic fatigue syndrome, including a both a case control study and a cohort study in the UK and a small cohort study done in the Netherlands. However, research is so incomplete regarding the association between these two factors that currently researches do not have the ability to say things are one way or the other.

Regardless of the complexity of CSF and the novelty of XMRV, research has undoubtedly unveiled some very important implications that I conclude with:

• Is/will there ever be a method developed so that we can prevent chronic fatigue syndrome rather than treat the symptoms of it alone?

• Why are women more likely than men to have it? What other epidemiologic factors play into CFS?

• Is there significant evidence to associate XMRV with CSF? How much is enough?

• What about XMRV and prostate cancer, as initially theorized?

• Is XMRV actually infectious? How is it transmitted? How virulent is it?

• If XMRV actually is a cause, or at least a within the causal pathway of CFS, what are some of the implications there? Would there be a cure? Can eventually eliminate chronic fatigue syndrome?

Obviously this is not an exhaustive list, but something worth pondering. Perhaps tomorrow’s research will lend insight into this intriguing disease and it’s mysterious cause(s).


Chronic Fatigue Syndrome. Center for Disease Control and Prevention. U.S. Department of Health and Human Services. Revised 5 May 2006.

Erlwein O, Kaye S, McClure MO, Weber J, Wills G, et al. 2010 Failure to Detect the Novel Retrovirus XMRV in Chronic Fatigue Syndrome. PLoS ONE. 5(1).

Groom HC, Boucherit VC, Makison K, Randal E, Baptista S, Hagan S, Gow JW, Mattes FM, Breurer J, Kerr JR, SToye JP, Bishop KN. 2010. Absence of xenotropic murine leukaemia virus-related virus in UK patients with chronic fatigue syndrome. Retrovirology. 7(10).

Infectious Mononucleosis. WebMD. Healthwise, Inc. Revised 8 September 2009.

van Kuppeveld FJM, de Jong AS, Lanke KH, Verhaegh GW, Melchers WJ, Swanink CMA, Bleijenberg G, Netea MG, Galama JMD, van der Meer JWM. 2010. Prevalence of xenotropic murine leukaemia virus-related virus in patients with chronic fatigue syndrome in the Netherlands: retrospective analysis of samples from an established cohort. British Medical Journal. 340(1018).

Lombardi VC, Ruscetti FW, Gupta JD, Pfost, MA, Hagen KS, Peterson DL, Ruscetti SK, Bagni RK, Petro-Sadowski R, Gold B, Dean M, Silverman RH, and Mikovits JA. 2009. Detection of an Infectious Retrovirus, XMRV, in Blood Cells of Patients with Chronic Fatigue Syndrome. Science. 326(5952): 585-589

Malaise. 2010. Merriam-Webster Dictonary Online.

Retrovirus. 2010. Merriam-Webster Dictonary Online.

Xenotropic Murine Leukemia Virus-related Virus (XMRV). Center for Disease Control and Prevention. U.S. Department of Health and Human Services. Revised 18 February 2010.

The Uncertain Etiology of PMS and a Link to Infectious Disease

Student guest post by Anne Dressler

Ninety percent of menstruating women experience some kind of premenstrual symptoms during the luteal phase of the menstrual cycle, with 20-30% experiencing moderate to severe symptoms. With an even more severe collection of symptoms, is premenstrual dysphoric disorder (PMDD). 3-8% of menstruating women report symptoms severe enough to be considered suffering from PMDD. Yet another designation, premenstrual magnification (PMM), is used to describe women who are symptomatic the entire cycle but have a premenstrual exacerbation of a diagnosed psychiatric, medical, or gynecological condition.

With a large number of wide-ranging symptoms and the difficulty involved in making a diagnosis, it is not surprising that the various theories advanced to explain premenstrual syndrome (PMS) have yet to been proven. One problem is that PMS is a diagnosis of exclusion, meaning there could be a variety of poorly understood conditions responsible for these symptoms. Several theories attribute PMS to fluctuations in sex hormones and neurotransmitters. The observation that symptoms disappear when a women has a menstrual cycle during which she does not ovulate and a corpus luteum is not formed, led to the theory that sex steroids, estrogen and progesterone, produced by the corpus luteum are responsible. In addition, the neurotransmitters serotonin and gamma amino butyric acid (GABA) have been implicated in various pathways. The list of other hormones and their modes of action that are suspected to be involved is long and confusing, making it no wonder that there is still no known etiology.

One distinctly different hypothesis is that PMS is due to a broad set of persistent infectious illnesses that are exacerbated by cyclic changes in immunosuppression due to the fluctuating levels of progesterone and estrogen. In general, there have been studies looking at two major categories of causation- genetic and environmental and have found moderate correlations at the best. Infectious causation has been overlooked for the most part, with almost no empirical support in published literature. I don’t think this means there is no value to the theory, simply that it is a very hard one to test. One very convincing article by Doyle et. al explains how this possibility of infectious causation is integrated with the cyclic changes in hormone levels that have been observed and are generally thought to be involved in PMS.

As the article explains, immune function varies across the menstrual cycle. During the luteal phase, cell-mediated immunity is suppressed and humoral immunity is amplified. This appears to be related to higher levels of progesterone that enhances humoral immunity by promoting the development of type 2 helper T cells. In addition, progesterone is involved in suppressing type 1 helper T cells, which is associated with inhibition of natural killer cells and phagocytosis. This leads to less effective control of various fungi, viruses, and intracellular bacteria. Estrogen also seems to suppress cell-mediated immunity. These hormone driven changes to the immune system provide the possibility that persistent infections may be less well controlled during the luteal phase, leading to the symptoms that make up PMS.

Supporting evidence for this theory is a long list of infections, compiled by Doyle et. al, that are normally controlled by cell-mediated immunity but are exacerbated premenstrually. These include, increased proliferation of Candida albicans, increased proliferation of cytomegalovirus in the cervix, increased number of lesions from human herpes simplex virus-1, and exacerbated peptic ulcers from Helicobacter pylori among others. There are also chronic diseases that have infectious causes or are suspected to have infectious causes that are exacerbated premenstrually. A few examples are, Crohn’s disease, lupus, multiple sclerosis, rheumatoid arthritis, asthma, and chronic fatigue syndrome. The pathogens that are suspected causes for these diseases are also controlled by cellular immunity.

Finally, one group performed a double blind, randomized clinical trial to determine the effects of the antibiotic doxycycline on PMS. Compared to the placebo group, individuals taking the antibiotic had significantly decreased symptoms. Subsequently, the placebo group was also given the antibiotic and experienced similar symptom reduction. This reduction in symptoms was steady during a six-month follow-up period. The investigators also found a high percentage of endometrial biopsy cultures positive for Mycoplasma species, Chlamydia trachomatis, and anaerobic bacteria.

This theory seems to be strongly biologically plausible, but lacks any of the other criteria for causality due to the lack of published studies on the topic. It is not in disagreement with the currently accepted idea that sex hormones fluctuate during the menstrual cycle and are involved in symptom manifestation. However, Doyle et. al advance this idea by explaining how it is may not be the direct effects of the hormones, rather a hormone-driven suppression of cellular immunity that could lead to poor control of persistent infections causing symptoms. This is certainly an interesting theory, yet one that would be difficult to study. Practical applications of findings from studies on this subject could be to consider control of PMS symptoms with antibiotics.


Backstrom, T., et al. The Role of Hormones and Hormonal Treatments in Premenstrual Syndrome.” CNS drugs 17.5 (2003): 325-42.

Doyle, C., H. A. Ewald, and P. W. Ewald. “Premenstrual Syndrome: An Evolutionary Perspective on its Causes and Treatment.” Perspectives in biology and medicine 50.2 (2007): 181-202.

Korzekwa, M. I., and M. Steiner. “Premenstrual Syndromes.” Clinical obstetrics and gynecology 40.3 (1997): 564-76.

Pinkerton, J. V., C. J. Guico-Pabia, and H. S. Taylor. “Menstrual Cycle-Related Exacerbation of Disease.” American Journal of Obstetrics and Gynecology 202.3 (2010): 221-31.

Silberstein, S. D., and G. R. Merriam. “Physiology of the Menstrual Cycle.” Cephalalgia : an international journal of headache 20.3 (2000): 148-54.

Toth, A., et al. “Effect of Doxycycline on Pre-Menstrual Syndrome: A Double-Blind Randomized Clinical Trial.” The Journal of international medical research 16.4 (1988): 270-9.