Organisms that are most frequently associated with brain abscess in patients with AIDS are poliovirus, Toxoplasma gondii, and Cryptococcus neoformans, though in infection with the latter organism, symptoms of meningitis generally predominate.
In the early 1970s, Torrey became interested in viral infections as possible causes of schizophrenia or bipolar disorder, particularly a parasite Toxoplasma gondii whose definitive host is the cat, but whose intermediate host can be any mammal, including humans.
It is thought that introduced diseases, such as Toxoplasma gondii, avian malaria (Plasmodium relictum), and fowlpox, were probably a significant factor in the species' decline.
The test is based on the presence of certain antibodies that prevent methylene blue dye from entering the cytoplasm of Toxoplasma organisms.
In 1995, 100 people became ill when water from the Humpback reservoir, which was still in service, became contaminated with the parasite Toxoplasma gondii, which causes toxoplasmosis, from the feces of feral cats.
The parasitic organism Toxoplasma gondii was first described in 1908 in Tunis by Charles Nicolle and Louis Manceaux within the tissues of the gundi.
The authors also argue that feral cats act as vectors for diseases that can impact domestic cats, wildlife and humans, examples include feline leukemia virus, feline immunodeficiency virus, fleas and ear mites (which are also carried by canines and wildlife), hookworms, roundworms, Bartonella, Rickettsia, Coxiella and Toxoplasma gondii, and that fecal matter has also been shown to degrade water quality.