If a parasite infected the brains of 2 to 3 billion people, up to one-half of the world’s population, one would probably consider it a pretty serious public health emergency. But such a situation already exists, with the parasite Toxoplasma gondii, the cause of the disease toxoplasmosis. The parasite is the most common infectious cause of retinal damage, and can cause brain damage or death in its most severe forms.
Most people hear of toxoplasmosis from cases of mother-fetus transmission, the reason why pregnant women are advised to stay away from cats, who are known carriers and dispersers of the parasite. Toxoplasmosis can also flare up in people with compromised immune systems, due to diseases like HIV, cancer, and autoimmune disorders. But the Toxoplasma gondii parasite is also an apparently quiet, untreatable houseguest in the brains of billions more people, where its possible role in seizure disorders, schizophrenia, and memory loss is just starting to be investigated.
With a widespread infection where the proven effects are already scary and the unproven effects may be even worse, it would be great to have vaccine protection against toxoplasmosis. But while vaccines are typically designed for unwelcome visitors of bacterial or viral form, they are not normally used to prevent infection from protozoan parasites like Toxoplasma gondii. That did not discourage the laboratory of Rima McLeod, who has recently published three papers with collaborators on two separate potential vaccination strategies against toxoplasmosis.