While cats have been adored as pets for many years, these popular pets can be hosts to an interesting parasite. A Danish study published in July’s Archives of General Psychiatry examined the relationship between Toxoplasma gondii infection in mothers and self-directed violence, specifically, suicide attempts. The study found that the T gondii parasite influences a mother’s behavior by increasing the risk of self-directed violence.
Toxoplasma gondii is an intracellular protozoan parasite affecting a third of the world population although there is large variations in prevalence among countries. The parasite multiplies in the gut of its host, which is in this case, domestic cats and other members of the felid family (carnivorous cats). Subsequently, the parasite is shed in cat feces. It can be taken up by other animals it comes into contact with, settling in various tissues including the brain.
Humans acquire T. gondii infection by ingestion of the parasite that is stable in the environment. Ingestion of contaminated and undercooked meat, using contaminated utensils, and drinking contaminated water are also pathways for acquiring infection. Often, T. gondii is cleared by the immune system. But in particularly acute infections, residual parasites hide in dormant cysts in eye, muscle and brain. Studies in rodents demonstrate localization of these parasites in various brain structures, including amygdala and prefrontal cortex, which regulate emotion and behavior.
T. gondii infection (Toxoplasmosis) is harmful especially in immunocompromised individuals and pregnant women. A woman infected during pregnancy rarely has any symptoms of infection herself; but results in congenital infection of the fetus. Presentations of this disease span the range of ocular and neurological impairments in congenitally infected children [1]. In severe cases, miscarriage or early death may occur. Post natal toxoplasmosis infection is often asymptomatic, or hard to detect in healthy individuals. They may remain healthy and be lifelong carriers [2]. Only a minority develops symptoms such as fever and malaise. Now, however, studies are showing that other symptoms, such as behavior change and self-directed violence, could appear.
The results from the Danish study show that mothers with T. gondii infection are 1.53 times more likely to commit self-directed violence and 1.81 times more likely to attempt violent suicide compared to mothers without infection. The rate of committing suicide was twice as much for infected mothers, although not statistically significant (statistically significant means unlikely to have occurred by chance). The immune response to T. gondii is suspected to mediate behavior change but the exact mechanism is not well understood yet. However, the authors of the study caution that other explanations including reverse causation were not ruled out and may explain the results.
Previous findings from the same cohort have also implicated higher level of IgG antibodies with risk of developing schizophrenia spectrum disorders. This strong affinity of the parasite for the developing fetal brain resulting in various congenital abnormalities is similar to other prenatal infections such as rubella or herpes simplex virus type 2 that have been similarly implicated in schizophrenia.
Good hygiene practices can prevent infection when handling uncooked meat. The phase of T. gondii in meat is effectively killed by washing hands thoroughly with soap and water, not forgetting any cutlery that has come in contact with the uncooked meat. The CDC recommends that meat be cooked to 74˚C/165˚F throughout so as to kill any T. gondii parasite. Other recommendations include feeding cats only dry, canned or cooked food and remove the litter box daily. The latter should not be carried out by pregnant women, who are also advised to avoid altogether contact with cats, soil and raw meat. If unavoidable, wear gloves during when clearing the litter box or during gardening. Currently, there is no vaccine to prevent infection. Full recommendations can be obtained from CDC website. With these prevention practices in mind, perhaps it is not yet time to bid your favorite cat goodbye.
References: [1] Desmonts, G., Jacques, C. (1974), Congenital Toxoplasmosis– A Prospective Study of 378 Pregnancies. New England Journal of Medicine, 290: 1110–1116. doi: 10.1056/NEJM197405162902003
[2] Munoz, M., Liesenfeld, O. and Heimesaat, M. M. (2011), Immunology of Toxoplasma gondii. Immunological Reviews, 240: 269–285. doi: 10.1111/j.1600-065X.2010.00992.x
