Abstract
BackgroundCanids are definitive hosts of the apicomplexan parasite Neospora caninum, the leading cause of abortion in cattle worldwide. For horizontal transmission from canids to occur, oocysts of N. caninum must be shed by the definitive host into the environment of susceptible intermediate hosts such as cattle. The purpose of this study was to determine the prevalence of N. caninum in canids in Victoria, Australia’s leading dairy producing state.ResultsNeospora-like oocysts were observed in 8% (18/234) of faecal samples from wild dogs, domestic dogs and red foxes from Victoria, Australia. However, none tested positive for N. caninum DNA using a quantitative PCR. In a separate sample population, blood sera from 483 domestic dogs were tested for anti-N. caninum antibodies using competitive ELISA. A subset of cELISA samples were re-tested using indirect fluorescence antibody test (IFAT). A seroprevalence of 29.8% (144/483; 95% CI: 11.7–47.8%) was calculated when using cELISA; whereas it was 32.9% (27/80; 95% CI: 15.8–51.8%) using IFAT. Potential risk factors were evaluated using univariable analyses and then assessed in separate multivariable models. Using ‘aged’ dogs as a reference, the seroprevalence of ‘adolescent’ and ‘adult’ dogs was 88% (P = 0.05) and 91% (P = 0.08), respectively, indicating seroprevalence increases with age. There was a 19% higher likelihood of infection in rural locations (P = 0.10) relative to urban areas. Jack Russell Terriers had a 22% higher risk of a cELISA-positive result (P = 0.05) regardless of geographical location, age or sex.ConclusionThese results demonstrate that exposure to N. caninum in domestic dogs is widespread in Victoria, although faecal oocyst shedding is infrequent. Our results indicate increased N. caninum seroprevalance status in dogs over the past two decades. The results imply that dogs get either exposed to the infected meat more frequently or that vertical dam to foetus transmission is more frequent than previously thought. Our study calls for re-evaluation of historical N. caninum seroprevalance studies, because the attitude to dog diet changes.
Highlights
Canids are definitive hosts of the apicomplexan parasite Neospora caninum, the leading cause of abortion in cattle worldwide
Presence of N. caninum-like oocysts in faecal samples Of the 234 canid faecal samples, 18 samples contained oocysts matching the morphological characteristics of N. caninum spp.-like oocysts (Table 1)
To determine the identity of the oocyst-like structures found in fox and dog faeces, we used a PCR reaction with primers that preferentially amplified DNA of cyst-forming coccidia [17, 18, 27]
Summary
Canids are definitive hosts of the apicomplexan parasite Neospora caninum, the leading cause of abortion in cattle worldwide. For horizontal transmission from canids to occur, oocysts of N. caninum must be shed by the definitive host into the environment of susceptible intermediate hosts such as cattle. The purpose of this study was to determine the prevalence of N. caninum in canids in Victoria, Australia’s leading dairy producing state. Neospora caninum is an obligate intracellular, tissue cyst-forming, coccidian parasite regarded as the leading cause of abortion in cattle worldwide [1, 2]. Horizontal transmission is facilitated by the shedding of oocysts in the faeces of the definitive host which sporulate and are infectious when ingested, the primary route of infection for canids [6,7,8,9]. A study of N. caninum infection in dogs from Melbourne, Victoria, found a seroprevalence of 5% [14], but nothing has been done since to determine the seroprevalence of Victorian dogs
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