©2018 WebMD, Inc. All rights reserved. eMedicineHealth does not provide medical advice, diagnosis or treatment. See Additional Information.

Symptoms and Signs of Toxoplasmosis

Doctor's Notes on Toxoplasmosis

Toxoplasmosis is a parasitic disease (Toxoplasma gondii), usually asymptomatic, but may become latent and produce symptoms when reactivated, especially in immunocompromised people. People that produce signs and symptoms usually have cervical lymph node swelling and flu-like symptoms that resolve in a few weeks without treatment. However, the parasites stay in the body and reactivate if the person’s immune system fails to keep them suppressed (HIV infection, chemotherapy). Then the parasites may cause vision and hearing damage or loss and brain damage (encephalitis, seizures). Congenital infections can follow a similar course.

Toxoplasma gondii is the protozoan parasite that causes Toxoplasmosis. It can infect most warm-blooded animals (humans, dogs, sheep, pigs, mice, birds) but cats are the only host that allow this parasite to complete its lifecycle; cats shed millions of oocysts in feces for weeks and the oocytes can survive for a year in the environment. Humans and other animals ingest them from contaminated food or water sources. .

Medical Author:
Medically Reviewed on 3/11/2019

Toxoplasmosis Symptoms

Most people infected with Toxoplasma are asymptomatic. Those who develop symptoms usually have cervical lymph node swelling and flu-like symptoms that resolve in a few weeks or months without treatment. The organism remains in the body in a latent state and may reactivate if the person becomes immunocompromised. For example, patients with AIDS can develop lesions in the brain due to Toxoplasma reactivation. Chemotherapy patients can develop eye, heart (myocarditis), lung or brain involvement when parasites become reactivated. Congenital Toxoplasma infections can cause serious eye, ear, and brain damage at birth. However, congenital infections may be asymptomatic until the first few years of life or even until the second or third decade when eye (decreased vision or blindness), ear (hearing loss), or brain damage symptoms (encephalitis, seizures, mental-status changes) develop. Toxoplasmosis is the leading cause of chorioretinitis (inflammation of the retina and choroid of the eye) in the United States.

Toxoplasmosis Causes

Toxoplasma gondii is a protozoan parasite that infects most species of warm-blooded animals (for example, cats, pigs, sheep, and humans) and causes the disease toxoplasmosis. The only known host animal that allows the parasite to complete its life cycle is the cat (domestic cats and other relatives in the family Felidae). After primary infection, cats shed millions of oocysts in their feces for about one to three weeks; the oocysts take one to five days to sporulate, which then can infect mice and birds (termed intermediate hosts) when these animals ingest water, plants, or soil containing the sporulated oocysts. The oocysts can remain viable in the environment for about a year. These sporulated oocysts become tachyzoites when ingested and migrate into muscle and neurological tissues where they further develop into bradyzoites. When a cat ingests an infected mouse or bird, the ingested bradyzoites develop into either tachyzoites or oocysts. The life cycle of Toxoplasma is completed when oocysts are shed in the cat's feces. Humans and other animals are not part of the complete life cycle (unless eaten by a cat) The majority of infections occur when humans, domesticated or wild animals ingest food, soil, or other animals that contain either sporulated oocysts or animal tissue containing Toxoplasma bradyzoites. Humans usually become infected by ingesting undercooked infected meat, food, or water. Infection may also be transmitted by contaminated blood transfusions, transplantation of infected organs, or from an infected mother to fetus. Finally, the disease may be acquired by directly ingesting cat feces, which may occur when cleaning out litter boxes.

Uncommon and Common Food-Poisoning Dangers in Pictures Slideshow

Uncommon and Common Food-Poisoning Dangers in Pictures Slideshow

Listeria bacteria can contaminate fresh produce, like cantaloupes, as well as some processed foods, like cheeses. Symptoms of infection include fever, muscle aches, upset stomach, or diarrhea -- occurring 2 days to 2 months after exposure.

Safety: Scrub raw produce and dry before cutting. Store in fridge below 40 F. Clean everything in contact with a whole melon.


Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.