Diagnosis:

• CBC/serum chemistry/radiographic findings vary depending on the organ(s) involved.
• Tachyzoites are rarely found in CSF fluids or FNAs of tissues. However, they may be identifiable in thoracic or peritoneal effusion fluids.
• PCR assays for use on serum, aqueous humor or CSF and an ELISA for detection of Toxoplasma antigens are under development.
  • Caution: it is possible to detect T. gondii by PCR in the aqueous humor without active disease.
• Clinically affected cats are rarely shedding the organism, so fecal analysis for the presence of organisms is not useful. (Remember, cats only shed oocysts for 10-14 days immediately after infection, which is prior to the onset of clinical signs.)
  • Oocysts of Toxoplasma are much smaller than the more commonly seen Isospora organisms.
    • (Click here for a photo of Toxoplasma oocysts from cat feces)

Serologic diagnosis:

• ELISA
  • IgM ELISA titers rise within 2-4 weeks of infection; titers typically revert to (-) by 12 weeks, but can occasionally persist for many months.
  • IgG ELISA titers rise within 3 weeks of infection; titers persist for years.
  • Maternal antibodies decrease by 12 weeks of age.
  • To serologically support a diagnosis of toxoplasmosis, one should have either a (+) IgM titer or a 4-fold increase (or decrease) in IgG titer, along with compatible clinical signs (and response to therapy, if applicable).
  • One can also look for evidence of active antibody production in the local aqueous humor or CSF compartments via calculation of an antibody coefficient as the product of the following two fractions:

Toxoplasma titer in local site Serum titer to unrelated Ag
Toxoplasma titer in serum Local compartment titer to unrelated Ag

• Coefficients >1 (ideally >8) are suggestive of active Ab production in the local compartment.
• There are also IFA and latex agglutination (LAT) assays for anti-Toxoplasma antibody detection. The modified LAT is a very sensitive method of measuring anti-Toxoplasma IgG

Treatment of Toxoplasma gondii infection in cats and dogs:

• Clindamycin is currently the drug of choice in both dogs and cats.
  • 10-12.5 mg/kg BID in cats
  • 10-20 mg/kg BID in dogs
• Previously, combination therapy with pyrimethamine and sulfonamides was used, but this required folic acid supplementation to alleviate side effects.

Previous Toxoplasmosis topic

Next Toxoplasmosis topic

Return to Toxoplasmosis introductory page