Due to research that has suggested a link between Toxoplasma infection and increases in psychological health problems in human hosts, there is a renewed push in media to vilify Toxoplasma gondii and the people this little critter inhabits. Unfortunately, with that comes the usual batch of alarmist headlines such as "Liberal Thinking Linked to Deadly Disease," and even the claim that side effects include psychosis(!).
We take a look at Toxoplasma and attempt to give you the facts sans the hysteria.
What is Toxoplasma and how does it infect humans?
Toxoplasma gondii is a microscopic parasite whose primary host is the common house cat, though Toxoplasma is able to make a host out of mostly any warm-blooded mammal. Cats pick up the parasite through eating infected meat, such as by eating an infected rat or mouse.
Toxoplasma can only create eggs within the environment a cat host provides. To reproduce, the parasite exploits the cat’s biological processes and, as a result, for around 10-14 days the infected cat will shed millions of toxoplasma eggs or “oocysts” in its feces.
However, most human hosts will be infected through consuming undercooked meat, particularly rare lamb, or by coming into contact with water, soil or vegetables that have been contaminated by feline feces, or exposed to infected materials.
Toxoplasma infection: symptoms and possible psychosis?
Around a third of the world’s population may harbor the parasite and estimates suggest that in Britain alone, new infections may total as much as 350,000 a year. An indicator for Toxoplasma infection is the formation of cysts in the human brain and over other vital organs of the body.
Only a proportion of those infected will ever show what are known as clinical symptoms, and only a relatively small number of those people will ever be severely affected. That said, the problems infection has been linked to are of concern.
Acute symptoms may include flu-like episodes that, with medical intervention, gradually fade after a few days or months. There are cases in which toxoplasmosis has been fatal, but in the vast majority of such cases, this was when teamed with another underlying problem, such as HIV.
There is also a demonstrated risk to pregnant women. In particular, the parasite is able to cross the placenta and therein pose a risk to an unborn child, sometimes leading to miscarriage.
However, even in those people that do not display obvious clinical symptoms of infection, there is tentative evidence that infection may alter personality traits. Infected rats tend to be more prone to risk-taking, often with the fatal and highly useful consequence, at least for the parasite, of being eaten by cats.
Studies have also shown a link between infection in humans and psychological problems leading to self-harm and suicide attempts, with a 2011 study of 20 European countries showing the national suicide rate among women increasing in direct proportion to the prevalence of latent infection. There has even been a link made to an increased likelihood of schizophrenia. These results remain tentative, however, and much more research is needed before a causal link can be established.
Abandoning pet cats is NOT the answer to Toxoplasma
If you are scared of the 'Tox, it is important to stress that indoor cats pose little risk of Toxoplasma infection as their chances for exposure to infected materials is greatly reduced.
While some scientists have gone as far as to warn against keeping outdoor cats during pregnancy and around young children, others have pointed out that cats actually only shed oocytes for around two to three weeks of their life, after which they are unlikely to become reinfected. This period will usually occur when the cats are young and have just started to exhibit hunting behaviors. If infection is diagnosed, keeping cats away from at-risk groups while the cat is being treated is recommended, and practicing good home cleanliness, such as washing your hands after clearing out a cat’s litter tray, can help combat infection.
However, the risk from undercooked meat and unwashed vegetables remains a concern, and one that seems to have gone under emphasized until now. While the UK’s FSA prepares to publish a risk profile on Toxoplasma, Dr Richard Holliman of St George’s Hospital in London is quoted by the Independent as saying: “Toxoplasma is more important, or as important as salmonella and campylobacter, which affect a lot of people.”
He then clarifies the threat in stark terms: “Toxoplasma affects a few people but when it does affect them it can be devastating. A child born with congenital toxoplasma is damaged for life.”
The risk of Toxoplasma gondii impacting your life is relatively low. It is, however, something that should be considered seriously, both in terms of potential benefits and risks. Ultimately, living with Toxoplasma is a choice. Read, learn, listen, and make up your own mind. As for me, a young healthy CIS white male aware of the impact my privilege can have on the disadvantaged if not kept in check, I will continue to live in symbiosis with my little critters.