While many cats are exposed to Toxoplasma gondii at some point in their lives clinical disease is infrequent with most developing asymptomatic immunity. Very occasionally immunocompetent adult cats develop signs, however, the animals most at risk of clinical disease are immunologically naïve kittens and immunocompromised adults. Common clinical signs include fever, anorexia, lethargy, CNS dysfunction (tremors or seizures), ocular inflammation and hyperventilation/dyspnoea.
Antibody test interpretation and limitations
Following infection, organisms often remain in tissues for the life of the cat and provide a continual antigenic stimulus for antibody production. Consequently, a high antibody titre does not necessarily indicate an active infection.
In acutely infected cats and kittens, disease can sometimes be confirmed based on finding a four-fold or greater rise in serum antibody titre over 2 to 3 weeks. However, some cats with clinical disease will have reached their maximal antibody titre by the time that they are first tested. Additionally, rising antibody titres have been seen in healthy infected cats, so taken alone rising titres do not prove clinical toxoplasmosis.
In cats with recrudescence of toxoplasmosis, maximal or near maximal antibody titres (1/2048) may already be present and increasing antibody levels may not be detected.
In some cases, a definitive diagnosis can only be made based on observing the tachyzoites on histology or cytology of affected tissues.