A litter of puppies from a breeding operation in New York developed the clinical manifestations of Neospora caninum shortly after their adoption at 8 weeks old. The attending veterinarian submitted serum samples from the five breeding bitches to the Animal Health Diagnostic Center for the Neospora caninum (N. caninum) indirect fluorescent antibody test to detect antibodies. Testing revealed that two of the five dogs had high N. caninum antibody titers (1:1600). The veterinarian suspected that the breeding bitches became infected after ingesting locally sourced raw deer meat, an intermediate host and reservoir of N. caninum.

N. caninum is an obligate intracellular protozoan parasite. In the N. caninum life cycle, the definitive hosts include dogs, coyotes and wolves. The predominant intermediate hosts in domestic environments are cattle. Sheep, goats, horses, donkeys, dogs and chicken are potential intermediate hosts. Economic consequences in the livestock sector are through reproductive loss. White-tailed deer are a major wildlife reservoir for N. caninum in the United States, with a high seroprevalence. Deer act as a reservoir for N. caninum, which is transmitted to wild canids upon ingestion of infected muscle tissue. In dogs, transmission occurs both horizontally, through ingestion of tissues from intermediate hosts, and vertically, via transplacental (resulting in fetal infection) or transmammary routes.

The most severe clinical disease is observed in puppies as young as 3-9 weeks old. Clinical signs may be attributed to polymyositis-polyradiculoneuritis and encephalomyelitis. When dogs older than 6 months develop clinical signs, it is likely due to recrudescence of a latent chronic infection, which can lead to severe multisystemic and neurological presentations. Dogs with chronic infection are often asymptomatic. However, periods of immunosuppression, such as during gestation, can reactivate latent infection and lead to vertical transmission to offspring. This explains the breeding bitches serving as inconspicuous reservoirs in this breeding operation.

A diagnosis of N. caninum can be made through the detection of antibodies via immunofluorescence assay (IFA). In the case of a puppy testing serologically positive for N. caninum, it is important to test the rest of the litter to treat all positive cases. Testing the dam is also important to determine the source of infection. Future breeding of seropositive individuals is not recommended, as the organism cannot be eradicated and will likely recur during gestation, leading to vertical transmission to the puppies.

Treatment for N. caninum consists of Clindamycin or Clindamycin and Sulfonamide, which target the actively replicating tachyzoites. This treatment is most effective when started before muscle contracture occurs in young dogs. The bradyzoite cystic stage is not affected by these drugs and therefore persists, even after prolonged courses of treatment.

Further prevention of N. caninum in dogs includes avoiding consumption of fetal membranes and raw meats from intermediate hosts.

References

• Jokar M, Shams F, Rahmanian V, Farhoodi M, Nadali B, Raziee Y. The global seroprevalence of Neospora caninuminfection in deer: a systematic review and meta-analysis study. Small Ruminant Research. 2022;214:106745.
• Silva RC, Machado GP. Canine neosporosis: perspectives on pathogenesis and management. Vet Med (Auckl). 2016;7:59-70.