Description
In dogs and cats,Toxoplasma gondii? infection is often subclinical, but when disease (toxoplasmosis) occurs, it typically presents with nonspecific signs such as fever, lethargy, anorexia, and weight loss, or with more specific involvement of the central nervous system, eyes, lungs, liver, or muscles.
In cats, disseminated toxoplasmosis can cause severe respiratory distress (due to interstitial pneumonia), icterus and liver failure, uveitis or chorioretinitis, seizures, ataxia, and sometimes, cutaneous nodules or ulceration, especially in kittens or immunocompromised adults (e.g., those with FeLV, FIV, or on immunosuppressive drugs).
In dogs, clinical toxoplasmosis is less common than in cats and can mimic other diseases; reported signs include neurological deficits (seizures, tremors, ataxia, paralysis), myositis with stiffness and muscle wasting, anterior uveitis or chorioretinitis, and occasionally pneumonia or gastrointestinal signs like vomiting and diarrhoea.
To confirm toxoplasmosis, a combination of clinical signs, serology, and direct detection methods is used, with samples depending on the affected organ system. Serum is collected for serology (IgG and IgM antibodies) to demonstrate exposure and recent/active infection; a high IgM titre or a fourfold rise in IgG titre supports active disease, but serology alone is not diagnostic.
For direct detection, samples such as aqueous humor (for ocular disease), cerebrospinal fluid (for neurological signs), bronchoalveolar lavage fluid (for pneumonia), or tissue biopsies (liver, lung, brain, lymph node) can be submitted for PCR or histopathology.
Quantitative PCR (qPCR) is increasingly used because it can detect and quantify T. gondii DNA in these samples, helping to confirm active infection and distinguish it from latent infection; a positive qPCR in a relevant clinical sample (e.g., CSF, aqueous humor, or affected tissue) strongly supports a diagnosis of clinical toxoplasmosis, especially when combined with compatible signs and serology.
