Tuesday, 31 January 2017

Is Your Cat Causing Your PMS? Actually, No

Late January 2017 brings a flurry of online articles about cats and premenstrual syndrome (PMS). Cats, it seems, cause PMS, or severe PMS, or a cat parasite causes PMS, or a cat parasite makes PMS worse, or women infected with the parasite are more likely to have PMS. Once again, cat owners are looking askance at their furry friends and wondering if it’s time to switch to a goldfish.
All this results from an article published in the Journal of Clinical Medical Research in October 2016 (online August 30, 2016): “Toxoplasma gondii Infection and Premenstrual Dysphoric Disorder: A Cross Sectional Study.” The authors of the study conclude that infection with the parasite might be associated with more severe symptoms of premenstrual dysphoric disorder, and that further research would help confirm or disprove the link. Do they think cats cause PMS? No.

PMS Is Not the Same Thing as Premenstrual Dysphoric Disorder

According to the Mayo Clinic, 75% of menstruating women experience PMS to some degree.  It brings both physical and emotional symptoms ranging from fatigue to depression. This is not premenstrual dysphoric disorder, and it isn’t the group that the researchers studied. They report that only 1.3% to 8% of women experience premenstrual dysphoric disorder, a severe form of PMS, which has serious psychological symptoms. Thus, the study had nothing to say about the PMS that the majority of women experience, and did not link PMS to Toxoplasma gondii (or cats!).

Are Women Infected with Toxoplasma gondii More Likely to Have PMS?

Toxoplasma gondii forms microscopic cysts
 in the tissues of cats, humans, and other hosts

The study didn't address this question; however, in this study group, the reverse appears to be true for premenstrual dysphoric disorder. The authors report that 10 out of the 151 women subjects tested positive for either antibodies to the parasite, or the parasite itself. That's 6.6%

​The prevalence of infection in humans varies widely from country to country, however in Mexico, where this study was done, 15% to 50% of the general population tests positive, depending on the region. There’s no evidence here that infection causes premenstrual dysphoric disorder.

Does Toxoplasmosis Make Premenstrual Dysphoric Disorder Worse?

The researchers looked at 59 distinct signs and symptoms experienced by women suffering from premenstrual dysphoric disorder. Their results suggested that the parasite might make two of them worse: feeling overwhelmed, and feeling out of control.
These results are preliminary at best. The sample size of 151 women was small, and there was low prevalence of T. gondii infection in the group. It’s inaccurate to draw conclusions about all women with both toxoplasmosis and premenstrual dysphoric disorder based on 10 women. It’s possible the parasite is unfairly maligned here, let alone the cat.

If You Are Infected With Toxoplasma gondii, Did You Get it From Your Cat?

Infective oocysts of Toxoplasma gondii
contaminate the environment via cat feces
Cats, and cat litter boxes, can be the direct source of T. gondii in humans, but there are quite a few other ways to catch toxoplasmosis. The most common source of infection varies from place to place, but most of us are more likely to catch it by eating undercooked meat or contaminated food or drinking contaminated water.
That’s not to say there isn’t a cat involved in the story somewhere because infected cats do cause contamination of food and water, but it’s not really fair to draw a straight line from a house cat to its owner. Feral cats and wild felines play a significant role.

Things to Remember About Cats and Toxoplasma gondii

A cat with toxoplasmosis will only pass oocysts in its feces for a couple of weeks when it’s first infected. For the rest of its life, the cat has the parasite but isn’t infectious (unless you eat your cat without cooking it first; I doubt this happens often).
Cats that don’t go out are less likely to become infected with T. gondii. Cats, too, catch it from eating raw or contaminated food (mice etc.).
Cats often become infected with
Toxoplasma gondii by eating infected prey
Is T. gondii a cat parasite? Cats are the only animals that host the sexually reproductive stage of the parasite (and pass oocysts). Hundreds of other species of animals host the parasite in tissues, and are infectious if eaten without thorough cooking.
If T. gondii does turn out to cause worse symptoms in premenstrual dysphoric disorder, should we blame the unfortunate cat, caught between a ubiquitous parasite and people who have spread millions upon millions of feral cats all around the globe? I think that’s misleading, to say the least.

Further reading

Alvarado-Esquivel, C., Sanchez-Anguiano, L. F., Hernandez-Tinoco, J., Perez-Alamos, A. R., Rico-Almochantaf, Y. del R., Estrada-Martinez, S., … Guido-Arreola, C. A. (2016). Toxoplasma gondii Infection and Premenstrual Dysphoric Disorder: A Cross-Sectional Study. Journal of Clinical Medicine Research, 8(10), 730–736. http://doi.org/10.14740/jocmr2699w
Hernandez-Cortazar, I., Acosta-Viana, K. Y., Ortega-Pacheco, A., Guzman-Marin, E. del S., Aguilar-Caballero, A. J., & Jimenez-Coello, M. (2015). Toxoplasmosis in Mexico: Epidemiological Situation in Humans and Animals. Revista Do Instituto de Medicina Tropical de São Paulo, 57(2), 93–103. 

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