Toxoplasma gondii infection is common in cats and people throughout the world. The seroprevalence in cats and people varies with the region and country, but is commonly 30–40%. Once infected with T. gondii, the organism probably remains in tissues for life. Fatal and serious clinical syndromes can occur in cats infected by T. gondii.

Intestinal toxoplasmosis. Cats are commonly infected by ingestion of T. gondii bradyzoites in tissues of prey species. The intestinal cycle is completed in about 10 days or less, and then oocyst shedding almost never reoccurs. Some experimentally inoculated cats develop self-limiting, small bowel diarrhea; this is presumed to be from enteroepithelial replication of the organism. However, detection of T. gondii oocysts in feces is rarely reported in naturally exposed cats with or without clinical disease. Thus, the intestinal phase of feline toxoplasmosis appear relatively unimportant clinically. By the time most cats seroconvert and become antibody positive, the oocyst shedding period has ceased. A seropositive cat is therefore a minimal zoonotic risk.

Other forms of toxoplasmosis. Toxoplasmosis induced transplacentally or by suckling in kittens is often clinically severe as a result of overwhelming tachyzoite replication. Anorexia, vocalization, signs of depression, lethargy, hypothermia, dyspnea, and sudden death are common clinical presentations in kittens born alive. Clinical signs develop within 2 days and as late as 25 days after birth. Necrosis with infiltrates of macrophages in lung, liver, cardiac, muscle, central nervous system, ocular, adrenal and renal tissues are characteristic findings. Clinical findings for 100 cats with histologically confirmed toxoplasmosis, diagnosed between 1952 and 1990, were as follows: 36 cats had generalized toxoplasmosis; principal lesions for the rest were pulmonary (26), abdominal (16), hepatic (12), cardiac (12), neonatal (9), neurologic (7), and pancreatic (1). Fever (73%); dyspnea, polypnea, anorexia, lethargy, icterus (24%); abdominal discomfort; and signs of central nervous system disorder and ocular inflammation were common.

Clinical toxoplasmosis of a more chronic course has been suspected in a number of cats. The primary clinical findings include anterior or posterior uveitis, fever, muscle hyperesthesia, weight loss, anorexia, seizures, and ataxia. Fever and muscle hyperesthesia usually resolve quickly following treatment and rarely reoccur. Uveitis can be unilateral or bilateral; severe anterior segment inflammation can occur with hypopyon, flare, and keratic precipitates which make visualization of the posterior segment difficult. Chorioretinitis can be unifocal or multifocal, and punctate or diffuse. Lens luxation and secondary glaucoma are common sequelae. Cats with uveitis are commonly seropositive for T. gondii and other potential ocular pathogens like FeLV, FIV, and FIP, which may complicate serologic and clinical diagnoses. Ocular and central nervous system disease may occur alone or concurrently and can be detected in cats without polysystemic signs of disease.