Toxoplasmosis (toxo) is a parasitic infection that is caused by a single-celled parasite called Toxoplasma gondii.
Toxoplasma gondii is one of the most common parasites, and it is found all over the world. Individuals may be exposed to the parasite in soil, cat feces, or in raw or undercooked meat (especially lamb, pork, or venison). There have been rare reports of toxoplasmosis infection as a result of organ transplantation or blood transfusion. While the parasite can be found around the world, the disease occurs less frequently in areas where the environment is unfavorable for the oocysts, such as at the extremes of temperatures and at higher altitudes.
Toxoplasmosis is considered an opportunistic infection because it occurs in individuals who have weakened immune systems. It is estimated that more than 60 million Americans carry the parasite. However, 80-90% of infected patients experience no symptoms because their immune systems prevent the parasite from causing the illness.
Patients who have the human immunodeficiency virus (HIV) have a high risk of developing the infection because HIV primarily targets immune cells called CD4 T-cells. Patients progress to AIDS (acquired immune deficiency syndrome) when their CD4 cell counts drop to lower than 200 cells per microliter of blood. Healthy individuals have a CD4 cell count between 600 and 1,200 per microliter of blood. As the virus continues to weaken the immune system, patients become increasingly vulnerable to opportunistic infections.
According to the U.S. Centers for Disease Control and Prevention (CDC), toxoplasmosis is an AIDS-defining illness. This means that when HIV-infected patients develop the toxoplasmosis, their condition has progressed to AIDS.
Although the parasites are present in about 40% of the general population, few people actually develop an infection, unless they are severely immunocompromised. Researchers estimate that about 10-40% of HIV patients have antibodies against toxoplasmosis.
Pregnant women who are carriers of T. gondii may transmit the infection to their babies, even if the mothers experience no symptoms. During the first month after birth, infected babies may experience severe complications, such as mental retardation, convulsions, spasticity (muscle stiffness), cerebral palsy, deafness, and severely impaired vision. The baby's immune system is still developing during infancy and fetal infection with T. gondii may result in stillbirth or abortion.
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Cat feces: Infected cats excrete oocysts in their feces. Oocysts are extremely small. In fact, one million may be present in a single stool. Individuals should wash their hands thoroughly after gardening, working with soil, cleaning a cat's litter box, or touching anything that may have come into contact with cat feces.
Contaminated water: While uncommon in the United States, the drinking water in many areas of the world may be contaminated with Toxoplasma gondii. The world's largest outbreak occurred in the western Canadian province of British Columbia. Individuals who are traveling overseas should be aware of the possibility of contaminated drinking water.
Contaminated soil: Contaminated soil contains highly infectious cells that can survive longer than one year. Individuals who are exposed to soil during gardening or other outdoor activities should wear gloves and thoroughly wash their hands with soap and water.
Fruits and vegetables: Produce items may contain traces of the parasite because they grow in areas where the organism lives. Therefore, all fruits and vegetables should be thoroughly washed, especially when they are eaten raw, to avoid infection.
Infected organ transplant or transfused blood: There have been rare reports of toxoplasmosis infection as a result of organ transplantation or blood transfusion.
Knives, cutting boards or other utensils: Kitchen utensils should be washed thoroughly with antibacterial soap because they often come into contact with raw meat.
Undercooked, infected meat: Undercooked meat, especially venison, lamb, and pork, may be contaminated with Toxoplasma gondii. Thoroughly cooking meat may help prevent infection because the parasites are killed in high heat. Occasionally, unpasteurized goat's milk may also contain the cysts.