The Gay Germ

The genetics of male homosexuality came up on a mailing list recently, so I had the opportunity to push the plague perspective, or as it is more commonly known, the gay gene theory or pathogenic hypothesis. Nor is the gay germ alone among infectious causes of personality:

Cochran claims that theories of the cause of narcolepsy - that it is an auto-immune disease triggered by a virus - make the mechanism of selective brain modification plausible. He also claims that only humans and sheep exhibit homosexual behavior at population levels near 1% or greater. He says that given their physical proximity, it would be plausible to expect a pathogen that affected both species.
Proponents cite increasing evidence that some cases of Schizophrenia may be linked to exposure with Toxoplasma gondii. Other studies suggest that a variety of mood disorders may be linked to Borna Virus.

Toxoplasmosis and You

Today's featured parasite is the stealthy and adaptable protozoan, Toxoplasma gondii.

This is the cat-litter bug that causes miscarriages and birth defects. The cat-loving parasite that lures rats to their deaths and causes traffic accidents. The latest schizophrenia suspect and a possible cause of epilepsy, psychosis, and migraines.

T. gondii may be making society rigid and neurotic, men more masculine, stupider, or more surly, and women more promiscuous. And if you think things are bad in the northern hemisphere, you should see the Brazilian strains.

About 16% 11% 33% of Americans are infected; infection rates are much higher in tropical countries (and France). Wikipedia tells the sad tale of Louis Wain, English cat artist, late-onset schizophrenic, and poster-child for the toxoplasmosis-schizophrenia connection.

T. gondii has its own book, conference, mugs and a blog, The Anti-Toxo, where you can follow mankind's losing battle with our one-celled masters.

Image by kqedquest. Some rights reserved.

The Left Hand of Disease

Gene Expression reports on "a new study in Epidemiology on longevity and handedness in a large, representative sample of Dutch women (Ramadhani et al. 2007)."

Table 2 shows that, after adjustment for age, SES, BMI, and cigarette smoking status, left-handed women had a 1.36 times higher risk of dying from all causes than non-left-handed women. The adjusted HR for total mortality, after excluding the first 5 years of follow-up time, was 1.58 (95% CI = 1.03--2.42). With regard to cancer mortality, left-handed women had a 1.7 times greater risk of dying from any type of cancer (CI = 1.0--2.7), a 4.6 times higher risk of dying from colorectal cancer (1.5--14), and a 2.0-fold higher risk of dying from breast cancer (0.83--4.6). Handedness was weakly associated with overall mortality from diseases of the circulatory system (1.3, 0.54--3.3), although left-handed women had a 3.7 times greater risk of dying from cerebrovascular diseases than non-left-handed women.

See the link for more co-symptoms of left-handedness, and for the most likely explanation:

One thing seems pretty clear, though: common cases of deviance from Darwinian fitness are most likely caused by environmental insults, with pathogens being the most obvious culprit (see Cochran, Ewald, & Cochran 2000 for the rationale).

Johne's Disease in Western Australia

The Australian reports an outbreak of Johne's Disease in Western Australian cattle after a twelve year lull:

Bovine Johne's Disease was confirmed yesterday [July 10th] in a beef herd near Albany, about 400km south of Perth.
It is the first case of its kind in Western Australia since 1994, but Animal Health Australia said the disease was known to have infected about 1350 cattle herds in NSW, Victoria, South Australia and Tasmania.
The highly infectious disease, which is most common in dairy cows, wastes the animal's intestines, preventing the absorption of minerals and proteins.

Johne's Disease is caused by Mycobacterium avium paratuberculosis and is suspected of causing Crohn's Disease in humans. The University of Wisconsin School of Veterinary Medicine has a webpage devoted to the controversy:

The triggering event for Crohn's disease is thought to occur early in life and then be followed by a 15-30 year incubation or latency period. Johne's disease also has a long interval between infection with M. paratuberculosis and onset of clinical signs (2-10 years). Clinical signs in both diseases are seldom seen before sexual maturity. Interestingly, a strong inverse relationship was found between Crohn's disease and gastric cancer using data from 26 countries.

PARA, the Paratuberculosis Awareness & Research Association, has more information on the bacterial theory:

In the early 1900's, the disease we call today "Crohn's disease" was characterized as an infectious disease, specifically intestinal tuberculosis. However, by the early 1930's, definitive classification (proof) that this disease was infectious was not forthcoming. More specifically, when Dr. Burrill B. Crohn failed to prove an infectious cause in 1932, the disease became formally known as "Crohn's disease" (named after Dr. Crohn) and the search for an infectious cause was largely discontinued.

A Virus for Prostate Cancer

Via Gene Expression: An article in the March issue of PLoS Pathogens, "Identification of a Novel Gammaretrovirus in Prostate Tumors of Patients Homozygous for R462Q RNASEL Variant", connects yet another cancer to a viral agent.

Prostate cancer is the most frequent cancer and the second leading cause of cancer deaths in US men over the age of 50. Several genetic factors have been proposed as potential risk factors for the development of prostate cancer, including a viral defense gene called RNASEL. A common genetic variant in this gene, R462Q, was recently implicated in up to 13% of prostate cancer cases. Given the antiviral role of RNASEL, the authors sought to examine if a virus might be present in prostate cancers associated with the R462Q variant. Using a DNA microarray designed to detect all known viral families, the authors identified a novel virus, named XMRV, in a subset of prostate tumor samples. Polymerase chain reaction testing of 86 prostate tumors for the presence of XMRV revealed a strong association between the presence of the virus and being homozygous for the R462Q variant. Cloning and sequencing of the virus showed that XMRV is a close relative of several known xenotropic murine leukemia viruses. This report presents the first documented cases of human infection with a xenotropic retrovirus. Future work will address the potential connection between XMRV infection and the increased prostate cancer risk in patients with the R462Q RNASEL variant.

Gene Expression also links a second article about Borna disease virus and neurological disease.

Toxoplasma

Technovelgy speculates about Toxoplasma Parasite Mind Control in rats and people:

Oxford scientists discovered that the minds of the infected rats have been subtly altered. In a series of experiments, they demonstrated that healthy rats will prudently avoid areas that have been doused with cat urine. In fact, when scientists test anti-anxiety drugs on rats, they use a whiff of cat urine to induce neurochemical panic. However, it turns out that Toxoplasma-ridden rats show no such reaction. In fact, some of the infected rats actually seek out the cat urine-marked areas again and again. The parasite alters the mind (and thus the behavior) of the rat for its own benefit. [...]
Dr. Torrey got together with the Oxford scientists, to see if anything could be done about those parasite-controlled rats who were driven to hang around cat urine-soaked corners (waiting for cats). According to a recent press release, it turns out that haloperidol restores the rat's healthy fear of cat urine. In fact, antipsychotic drugs were as effective as pyrimethamine, a drug that specifically eliminates Toxoplasma.

From the press release from Imperial College London:

Research published today in Procedings of the Royal Society B, shows how the invasion or replication of the parasite Toxoplasma gondii in rats may be inhibited by using anti-psychotic or mood stabilising drugs.
The researchers tested anti-psychotic and mood stabilising medications used for the treatment of schizophrenia on rats infected with T. gondii and found they were as, or more, effective at preventing behaviourial alterations as anti-T. gondii drugs. This led them to believe that T. gondii may have a role in the development of some cases of schizophrenia.

HPV Vaccine

MedBroadcast reports on the new vaccine against human papilloma virus, the STD responsible for most cases of cervical cancer.