Toxoplasmosis is a parasitic infection caused by the protozoan Toxoplasma gondii. The definitive hosts for the organism are domestic and feral cats, but birds, humans, and a variety of other animals can become infected by accidental ingestion of infectious oocysts.

Members of the family Felidae release the oocysts with their excrement and after a period of days or weeks, depending on environmental factors, the oocysts become infectious agents and may remain so for up to a year. If within this time an individual comes in contact with the oocysts when changing cat litter or from gardening, or other contact with infected soil, then they can become infected if contact with the mouth occurs before hands are washed. Infection can also occur from eating unwashed fruits or vegetables that have been contaminated with the oocysts or by consuming undercooked meat or untreated water that has been infected.

It is estimated that one-third to one-half of the inhabitants of the world have been infected with Toxoplasma gondii at some point in their lives. The primary evidence of such widespread exposure is the pervasiveness of toxoplasmosis antibodies since demonstrable symptoms of the infection are uncommon. Infection with Toxoplasma gondii may involve the spleen, liver, central nervous system, and other regions of the body, but symptoms, when they do occur, are usually very mild in otherwise healthy individuals and only entail a fever and some swelling of the glands. Occasionally muscle aches and pain, similar to those experienced with the flu, occur as well, and in very rare instances there may be damage to the eyes.

Ocular injury and other serious effects of toxoplasmosis are much more likely to occur in individuals with weakened immune systems. In AIDS patients, for instance, a form of encephalitis may develop following infection with Toxoplasma gondii. Symptoms of toxoplasmic encephalitis include headache, fever, psychosis, and impaired vision, speech, movement, and thought capacity. Similar grave effects are associated with congenital toxoplasmosis, which is passed on from expectant mothers that are exposed to Toxoplasma gondii to the developing fetus. In some cases, this transmission of the parasite can cause the child to be stillborn or born prematurely. In other severe cases of infection, the disease may affect many of the newborn’s organs, including the brain and eyes, and epilepsy, mental retardation, and blindness can ensue.

About half of the toxoplasmosis-related fatalities reported are thought to involve exposure to Toxoplasma gondii through the consumption of contaminated meat, making the disease one of the top causes of foodborne deaths in the United States (only foodborne infection with Salmonella and Listeria are more deadly). Ensuring that all meat consumed is cooked thoroughly can, therefore, significantly lessen one’s risk of developing toxoplasmosis, as can freezing meat for several days prior to its use. Other steps that can be taken to decrease the incidence of the disease are washing fruits and vegetables thoroughly or peeling them before eating, wearing gloves when gardening or changing cat litter, washing cutting boards, knives, and other items that come into contact with raw meat or unwashed plant matter with hot water and soap, and keeping domestic cats indoors and only feeding them commercial cat foods or well-cooked human foods.

Toxoplasmosis at 10x Magnification - Generally toxoplasmosis is not treated, but medicines, including sulfonamide drugs, folinic acid, pyrimethamine, clindamycin, and trimethoprim-sulfamethoxazole, can help eradicate the infection.

Toxoplasmosis at 10x Magnification - It is extremely important that women who are pregnant, or are attempting to become so, take precautionary measures to avoid toxoplasmosis.

Toxoplasmosis at 40x Magnification - Approximately 750 deaths are attributed to toxoplasmosis annually. Many of these deaths could be avoided by following relatively simple preventative recommendations.