Description
In cats, Toxoplasma gondii infections are mostly subclinical, but disseminated toxoplasmosis can cause fever, lethargy, anorexia, weight loss, respiratory distress from interstitial pneumonia, icterus, uveitis/chorioretinitis, neurologic signs (seizures, ataxia, paresis), and myositis. In dogs, clinical disease is less common and usually seen in puppies or immunosuppressed adults, with non specific systemic signs (fever, dyspnoea, jaundice, diarrhoea, weight loss) or focal CNS, ocular, muscular, or pulmonary involvement.
Samples for confirmation include serum for IgM/IgG serology (high IgM or a fourfold rise in IgG indicates active/recent infection), plus CSF, aqueous humor, BAL fluid, or tissue biopsies (brain, lung, muscle, lymph node) for PCR or histopathology. qPCR on these fluids/tissues is very useful to detect and quantify T. gondii DNA at low burdens, and a positive result in a clinically relevant sample, together with compatible signs and serology, strongly supports a diagnosis of clinical toxoplasmosis.
Canine distemper virus (CDV) primarily affects dogs and some wild carnivores. In dogs, acute systemic infection causes biphasic fever, lethargy, anorexia, serous to mucopurulent oculonasal discharge, cough, dyspnoea, vomiting, diarrhoea, and often hyperkeratosis of nasal planum and footpads (“hard pad”). Neurological disease may follow or overlap, with seizures (often “chewing gum” fits), myoclonus, ataxia, paresis, or behaviour changes; enamel hypoplasia in juveniles and chorioretinitis can also occur.
Typical samples are conjunctival, nasal or oropharyngeal swabs, whole blood (EDTA), urine, and CSF in neurological cases. Antigen detection (immunofluorescence on conjunctival/urine smears) and serology (rising IgG titres in unvaccinated dogs) support infection, but qPCR targeting CDV RNA on swabs, blood, or CSF is now the preferred method to confirm active infection and distinguish field virus from vaccine where assays are strain specific.
Neospora caninum congenital infection in puppies classically causes progressive neuromuscular disease: hindlimb hyperextension and rigidity (genu recurvatum), “bunny hopping” gait, paraparesis progressing to tetraparesis, muscle atrophy, and hyporeflexia; adult dogs may show polymyositis, ataxia, seizures, or multifocal CNS signs, and some bitches have abortion or infertility.
Samples include serum for Neospora IgG/IgM serology and CSF for antibody detection or cytology in neurological cases, plus biopsies/aspirates of affected muscle, nerve, or CNS tissue for histopathology and immunohistochemistry to visualize tachyzoites/cysts. qPCR on blood, CSF, or tissue (especially muscle or CNS) is highly sensitive for detecting N. caninum DNA, helps distinguish it from T. gondii in neuromuscular cases, and supports a definitive diagnosis when combined with compatible clinical and imaging findings.
