A seroprevalence study of Toxoplasma gondii in ~14,000 sick cats in the USA ranged from16 to 40% based on climate (likely related to oocyst survival in the environment). In desert areas (AZ, NM), prevalence was 16%; in the Northeast was 45%, and TX, GA, and NC were ~ 35-45%.

Seroprevalence of T. gondii in cats with uveitis of undetermined etiology after physical examination by a board-certified ophthalmologist (n =116), was very high at 65%. Antibody-positive cats had IgM, IgG, or both antibodies directed against this organism.

As toxoplasmosis is recognized as a problem infection in renal transplant recipients, both donor and recipient are screened for toxoplasma antibodies. This risk seems to be greater for infection arising from the transplanted kidney, than from recrudescence of a previous infection in the recipient.

Reports of toxoplasmosis in cats being treated with immunosuppressive medications are scarce and the risk is considered to be slight.

Suspicion of toxoplasmosis would pertain in outdoor cats with hyperesthesia-like signs, fever, and uveitis. Some strains of T. gondii are oculotropic as ~ 2/3rds of experimentally inoculated cats develop uveitis.

Some cats with unexplained chronic lympho-cytosis (8-10,000 /µL) and occasional monocytosis (~2,000 /µL) have been diagnosed with toxoplasmosis.

The sensitivity and specificity of an IgG or IgM toxoplasma antibody titer at 1:64 is high, as 95-98% of cats with a 1:64 IgG or IgM titer will have antibodies confirmed by Western blot. For IgM titers, any titer greater than or equal to 1:64 is potentially significant, and IgM titers tend to be no higher than ~1:256 in healthy cats. However, in sick cats, IgM titers may increase beyond 1:256. Treatment with clindamycin does not blunt a rising toxoplasmosis titer.

Clindamycin (Antirobe®, Upjohn) is given at 10-12 mg/kg q12h for 4 weeks. Some cats do not tolerate the taste of clindamycin well, but the drops tend to be tolerated better if they are kept cold. As clindamycin does not penetrate the blood-brain barrier well, use a potentiated sulfonamide alone or in conjunction with clindamycin for cases with CNS disease. For ocular disease, clindamycin is preferred. Some cases are resistant to clindamycin, and so azithromycin or a potentiated sulfonamide would be used.

Azithromycin (Zithromax®, Pfizer) given at 10 mg/kg q24h for 4 weeks has produced some anecdotal successes. This drug is advocated for cats that do not tolerate clindamycin.

Some cats with uveitis and CNS disease may require pulse therapy long-term to control clinical signs of disease (generally 7d on, 7d off). Eventually, the cat may be stable enough clinically to be given the drug 7d on, 14d off.

Acute systemic toxoplasmosis was diagnosed in an adult male domestic shorthair cat, that had been on cyclosporine A (CsA) immunomodulatory therapy for feline atopy, over an 8 mo period. CsA has shown promising results as an immunosuppressive agent in the cat the treatment of eosinophilic plaque and granulomas, allergic cervico-facial pruritus, feline atopy and other immune-mediated dermatoses. However, as it is being used more frequently, activation of quiescent infections may also be seen as an adverse effect of this treatment, which inhibits T-lymphocyte function. The present case report describes a newly acquired, acute Toxoplasma gondii infection following treatment with CsA, as characterized by severe hepatic and pancreatic pathology and a heavy T. gondii parasitic load.