An article by the Independent this week shines a light on the already known, but still tentative, link between the cat parasite Toxoplasma gondii and a potential for psychological disturbances in those humans it infects. Furthermore, the article draws readers’ attention to the fact that a report will be issued this week that shows British infection rates may be much higher than previously understood.
Due to recent research that has suggested a link between Toxoplasma infection and increases in psychological health problems in human hosts, and also an established risk to pregnant women, there is a renewed push to understand and highlight the dangers this parasite may pose. Unfortunately, with that comes a fresh chance at alarmist headlines. Here we take a look at Toxoplasma and attempt to give you the facts without the freak-out.
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.
However, 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 more research is needed before a causal link can be established.
Abandoning Pet Cats Not The Answer to Toxoplasma
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 taken seriously, both in terms of public guidance and personal hygiene practices.