Parasites: Tales of Humanity's Most Unwelcome Guests: toxoplasma

Showing posts with label toxoplasma. Show all posts

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.

Friday, 26 June 2015

Crazy – Cats, Toxoplasma, and Your Mental Health

Is your cat making you crazy? If you’ve been reading the many recent articles about a theoretical link between Toxoplasma gondii infection and schizophrenia (and other mental health issues) you may think that your cat is a significant threat to your mental health.

Infected rodents pass Toxoplasma gondii
to wild and domestic cats. Yintan, CC BY-SA 3.0

But to say that your cat could literally make you mentally ill is a bit disingenuous. It’s not the cat itself, it’s the parasite Toxoplasma gondii that’s linked to mental illness. And while it’s true that T. gondii is a parasite of cats, it’s equally true that it infects more than 300 other species of animals, and there are a number of ways to catch it without a cat being anywhere in sight. Don’t be too hard on your pampered kitty which, in all likelihood, is not capable of infecting you with T. gondii.

Cats and Toxoplasma gondii

Cats typically catch T. gondii by eating infected rodents. In the cat, T. gondii multiplies in the intestine and millions of microscopic oocysts (you might think of them as eggs, or germs) are released into the outside world in the cat’s feces. But an infected cat will usually only shed these oocysts for one to two weeks of its entire life - about 0.2 percent of its life if it lives to be sixteen. Cats that don’t hunt, don’t eat raw meat, and particularly cats that don’t go outside, are unlikely to be infected, and extremely unlikely to infect you with T. gondii.

Toxoplasma gondii in the Environment

There’s a bigger picture of course. Domestic cats have been instrumental in spreading T. gondii around the world and contaminating the environment everywhere with oocysts. But this parasite can survive without cats for a very long time, if not indefinitely. This is because the parasite multiplies asexually (clonally) in the tissues of any warm blooded vertebrate (and even fish can be infected). It can multiply in human tissues, in chickens, sheep, dogs, rats, mice, horses, and 300+ other animals. If a pig eats an infected rat, the pig will catch toxoplasmosis. If a wild or feral dog eats the pig, the dog will catch toxoplasmosis. So blaming it all on the cats at this point is like closing the barn door after the horses have left.

How Do Humans Get Toxoplasma

gondii?

The cat is the only animal in which Toxoplasma gondii

can reproduce sexually, but it is widespread in the

tissues of other species. CDC image.

Humans become infected with Toxoplasma gondii in various ways:
•    Eating undercooked meat
•    Consuming food or water contaminated with oocysts
•    Exposure to oocysts in soil (gardening etc.)
•    Congenitally, from mother to fetus
•    Through blood transfusion or organ donation
•    Direct contact with an acutely affected cat
•    Sexual transmission (theoretical)

In the end, it’s clear that while it is possible to catch T. gondii from contact with your beloved domestic cat, if the cat has an acute case of toxoplasmosis, this is an unlikely source of infection. And while cats certainly bear responsibility for spreading this parasite far and wide, it’s the parasite that’s linked to mental illness, not the cat.

Further reading

Centers for Disease Control and Prevention. “Toxoplasmosis (Toxoplasma infection).”

Flegr, Jaroslav (2015). “Schizophrenia and Toxoplasma gondii: an undervalued association?”
Expert Review of Anti-infective Therapy 13:7 , 817-820

Flegr, J., Klapilová, K., & Kaňková, Š. (2014). “Toxoplasmosis can be a sexually transmitted infection with serious clinical consequences. Not all routes of infection are created equal.” Medical Hypotheses, 83(3), 286-289.

McAuliffa, Kathleen. (2012). “How Your Cat is Making You Crazy.” The Atlantic

Zhang, M., Yang, Z., Wang, S., Tao, L., Xu, L., Yan, R., ... & Li, X. (2014). “Detection of Toxoplasma gondii in shellfish and fish in parts of China.” Veterinary Parasitology, 200(1), 85-89.

Thursday, 30 January 2014

Toxoplasma gondii - Andrew Alexander’s Terrifying Parasite

“I felt like Frankenstein,” Alice Smellie quotes Andrew Alexander in the MailOnline. The Downton Abbey star apparently picked up a “terrifying” parasite more than a year ago and waited months for a diagnosis. When that diagnosis came, it was disturbing, no doubt, but “terrifying” is a bit over the top. (Admittedly, the prevailing dramatic and negative response to anything parasitic could account for the terror.)

The series Downton Abbey is set in the early 1900s.
No one was worried about toxoplasmosis then, but
other parasites were much more common in England
than they are today.
Image by JB + UK_Planet; CC BY 2.0

Toxoplasma gondii, a Terrifying Parasite

Alexander had Toxoplasma gondii – often simply called toxoplasma. Smellie writes that the not-so-terrifying toxoplasmosis is actually “an incredibly common bacterial infection.” She’s right that it’s common; in fact, as many as a third of people living in the UK are infected with the parasite. But T. gondii is not a bacterium, it’s a protozoan.

What qualifies T gondii as a disturbing, and concerning, parasite? A handful of things:

It lives in your tissues, including the brain, and once you have it, you have it forever.
A first exposure during pregnancy can have truly terrifying implications for the fetus.
If you have it and your immune system falters (with AIDS for instance), reactivation of the infection can be fatal.
There is evidence that T. gondii can change behavior, and it is implicated in some forms of mental illness.
Acute infection can make you look like Frankenstein. (Well, it can cause swollen lymph nodes but it usually doesn’t).

Andrew Alexander’s Forever Parasite

Most people who walk around with T. gondii in their tissues never know they have it. The acute infection is typically mild and goes undiagnosed. Perhaps one or two in ten infected people have more severe symptoms like Alexander: flu-like symptoms with fever, headache, sore throat, achy muscles, swollen lymph nodes. Within a few weeks, even these people usually feel better, though it can take much longer.

When good health returns, it means that the immune system has won the battle – at least for now. The parasite is no longer multiplying rapidly and spreading; it has formed tiny cysts and basically gone dormant. In the parasite’s perfect world, a carnivore eventually eats the host and the parasite gets to infect that carnivore next. I suspect, however, that Andrew Alexander’s bradyzoites have reached a dead end.

How Did Andrew Alexander Catch Toxoplasma gondii?

Most people catch T. gondii in one of two ways:

By eating meat that is not fully cooked. Lots of people eat rare, or raw, meat; domestic and wild animals are often infected with T. gondii. The meat you buy from the butcher might well contain bradyzoites.
By swallowing infective oocysts that have been passed in cat feces. Cats are the only host in which T. gondii multiplies sexually, and during acute infection, a cat passes millions of oocysts.

Smellie’s article relates that Alexander became ill after returning from Africa. Did he catch T. gondii there? Possibly. But he could have picked it up just about anywhere. This parasite is ubiquitous. Where was he one to three weeks before becoming ill? That’s where he got it.