T. gondii Symptoms Continue at Various Stages of Infection
The level of T. gondii in the brain varied between the two types, with Type III showing high levels of both parasites and white blood cells in contrast to Type I cases, which had low levels of both parasites and immune response. In looking at behavior, however, higher parasite loads and higher levels of response did not correspond with lower levels of predator avoidance when tested at three weeks, two months, and four months post-infection.
Scientists previously thought that the presence of the parasite or cysts, or inflammation of the brain during active infection, might be the cause of these symptoms. According to Ms Ingram, however, these results suggest that ‘curing’ toxoplasmosis with treatment to eliminate parasite loads will not necessarily result in alleviation of symptoms such as loss of avoidance behavior.
This has implications for other intermediate hosts, such as humans who may become infected when exposed to infected cat feces, soil or undercooked meat.
Human infection with T. gondii has also been associated with behavioral changes, personality traits and cognition problems.
Next Steps for Toxoplasma gondii Research
Ingram told Decoded Science that work has already begun studies on ways to “understand the underlying mechanism of how T. gondii causes these behavioral changes. We are starting by looking at what aspects of the mouse immune response to T. gondii are necessary for the behavior manipulation.”
Preventing Toxoplasmosis in Cats and Humans
Infected cats can also show behavioral symptoms, although most symptomatic cases are associated with suppressed or immature immune systems. Cats positive for feline leukemia virus (FELV) or feline immunodeficiency virus (FIV) and kittens whose immune system is developing are at highest risk.
Taking precautions to prevent T. gondii infection remains the best strategy for humans and their feline friends.
Raw or undercooked meat, and unwashed fruits or vegetables are the primary sources of infection. Wear gloves when gardening, wash your hands and food preparation surfaces after handling raw meat, and use care when cleaning up your cat’s litterbox to reduce chances of infection.
Ingram WM, Goodrich LM, Robey EA, Eisen MB. Mice Infected with Low-Virulence Strains of Toxoplasma gondii Lose Their Innate Aversion to Cat Urine, Even after Extensive Parasite Clearance. (2013). PLoS ONE 8(9): e75246. doi:10.1371/journal.pone.0075246. Accessed September 18,2013.
Gulinello M, Acquarone M, Kim JH, et al. Acquired infection with Toxoplasma gondii in adult mice results in sensorimotor deficits but normal cognitive behavior despite widespread brain pathology. (2010). Microbes and Infection. 12:528-537. Accessed September 18,2013.
Toxoplasmosis-Schizophrenia Research. IV. Effects of T. gondii on Behavior and Psychiatric Symptoms. Accessed September 18,2013.
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