Toxoplasmosis Causes Mice to Remain Easy Prey for a Long Time


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Toxoplasma gondii causes behavioral changes in mice

Mice lose fear of cats when infected with T. gondii. Photo by Live Auctioneers, painting by John Henry Dolph (1835–1903)

Does Toxoplasmosis make zombie mice?

Toxoplasmosis gondii is a very clever parasite. Mice infected with this protozoan lose their fear of cat odors, putting them at higher risk of being caught.

This increases the chance that T. gondii will get into its next level host, the cat, to complete its life cycle.

How does this happen? Science is still working on answers; Decoded Science interviewed Wendy Ingram, lead author of a new study on mice and toxoplasmosis, to learn more about the findings.

The Life Cycle of Toxoplasma gondii

Cats are the only known definitive host for T. gondii, i.e. the host wherein the parasites reproduce sexually. The oocysts produced are shed in cat feces.

Oocysts in the environment develop in about 1-5 days and are then infective. Intermediate hosts, such as mice, birds and domestic livestock, become infected when they consume soil, water or plants with oocysts present.

The oocysts develop into tachyzoites in these intermediate hosts. The tachyzoites then lodge in neural or muscle tissue, becoming  tissue cyst bradyzoites. These tissue cysts have been the suspected source of some of the longer term effects of T. gondii infection.

Study Compares Infected and Un-infected Mouse Behavior

Earlier studies focused on Type II T. gondii but this form is highly pathogenic (disease causing), making the level of aversion to cat smells, urine in this case, harder to measure, as the mouse’s overall activity level is often significantly decreased.

This study’s authors concentrated on the less-studied Type I and Type III Toxoplasma gondii infection, looking at various stages of infection.

The first part of the study compared infected and un-infected mouse behavior by placing a dish with urine, either bobcat (predator) or rabbit (non-predator) in their cages. Un-infected mice avoided the area with the bobcat urine, but not the rabbit urine. Infected mice didn’t avoid either. Those findings corroborated that of previous researchers’ work with Type II. This meant that a similar behavioral change occurred with all 3 types of T. gondii.

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