Seroprevalence of Neospora caninum in dogs from greater Sydney, Australia unchanged from 1997 to 2019 and worldwide review of adult-onset of canine neosporosis

Neospora caninum causes disease of the muscle and nervous systems in canine pups and is known for producing disease in older dogs. We aimed to determine anti-N. caninum seroprevalence in healthy adult dogs from greater Sydney, New South Wales, Australia and summarise published reports of adult-onset of canine neosporosis. Indirect fluorescent antibody tests (IFAT) were used to detect anti-N. caninum IgG and compared to the value from an equivalent 1997 study. The N. caninum seroprevalence (anti-IgG, 1:50 serum dilution) was 14.1% (27/192; 95% CI: 9.1–19.0%) demonstrating no significant change compared to 1997 (12%; 18/150; 95% CI: 7.7–18.2%) (P = 0.58). A literature search identified 56 published cases of adult-onset canine neosporosis, most associated with neurological or myopathic signs (66.1%, 37/56) or cutaneous lesions (25.0%, 14/56). We confirm that a single IFAT N. caninum IgG titre has limited diagnostic value regardless of the cut-off because healthy adult dogs exhibit a range of titres.