More than two million Americans are living with schizophrenia. You may think people with schizophrenia are simply just born with the illness - even if it takes years to appear. However, an emerging line of thought suggests genetics may not be the only factor involved. Many experts believe infections play an important role in some cases of schizophrenia.Scientists are now beginning to recognize that many of these chronic illnesses are due to microbial infections. A recent report in the American Journal of Psychiatry suggests that schizophrenia, a mental illness leading to errors in perception, is associated with the pathogen, Toxoplasma gondii.

Toxoplasma gondii is an intracellular parasite in the phylum Apicomplexa. Its life cycle can be completed only in cats and other felids, which are the definitive hosts. However, T. gondii also infects a wide variety of intermediate hosts, including humans. In many mammals, T. gondii is known to be an important cause of abortions and stillbirths and to selectively infect muscle and brain tissue. A variety of neurologic symptoms, including incoordination, tremors, head-shaking, and seizures, have been described in sheep, pigs, cattle, rabbits, and monkeys infected with T. gondii

Other diseases are also showing microbial connections. The most famous example is Helicobacter pylori, the unequivocal cause of peptic ulcers and suspected agent of gastric cancer. Human papillomavirus is associated with 90% of cervical cancers. Hepatitis B is linked with 60% of liver cancers.

Some diseases look suspiciously like infections, such as Hodgkin’s disease, multiple sclerosis, juvenile onset diabetes and Crohn’s disease.

Humans may become infected by contact with cat feces or by eating undercooked meat. The importance of these modes of transmission may vary in different populations. Individual response to Toxoplasma infection is determined by immune status, timing of infection, and the genetic composition of the host and the organism.

Toxoplasma organisms have also been shown to impair learning and memory in mice and to produce behavioral changes in both mice and rats. Of special interest are studies showing that Toxoplasma-infected rats become less neophobic, leading to the diminution of their natural aversion to the odor of cats. These behavioral changes increase the chances that the rat will be eaten by a cat, thus enabling Toxoplasma to complete its life cycle, an example of evolutionarily driven manipulation of host behavior by the parasite.

In humans, Toxoplasma is an important cause of abortions and stillbirths after primary infection in pregnant women. The organism can also cross the placenta and infect the fetus. The symptoms of congenital toxoplasmosis include abnormal changes in head size (hydrocephaly or microcephaly), intracranial calcifications, deafness, seizures, cerebral palsy, damage to the retina, and mental retardation. Some sequelae of congenital toxoplasmosis are not apparent at birth and may not become apparent until the second or third decade of life. Hydrocephalus, increased ventricular size, and cognitive impairment have also been noted in some persons with schizophrenia and other forms of psychosis.

Some cases of acute toxoplasmosis in adults are associated with psychiatric symptoms such as delusions and hallucinations. A review of 114 cases of acquired toxoplasmosis noted that “psychiatric disturbances were very frequent” in 24 of the case-patients. Case reports describe a 22-year-old woman who exhibited paranoid and bizarre delusions (”she said she had no veins in her arms and legs”), disorganized speech, and flattened affect; a 32-year-old woman who had auditory and visual hallucinations; and a 34-year-old woman who experienced auditory hallucinations and a thought disorder. Schizophrenia was first diagnosed in all three patients, but later neurologic symptoms developed, which led to the correct diagnosis of Toxoplasma encephalitis.

Sources: CDC, Schizophrenia

Related Posts