Coprophagy in dogs interferes in the diagnosis of parasitic infections by faecal examination

Many dogs display coprophagic behaviour. Helminth eggs can passively pass the dog's digestive tract and this may result in a false positive diagnosis of infection with gastrointestinal helminth parasites. For a period of one year, faecal samples of dogs were examined monthly using the Centrifugal Sedimentation Flotation (CSF) technique with a sugar flotation solution (s.g. 1.27-1.30 g/cm3). If a sample tested positive for canine helminth eggs, the owner was asked to submit another sample after preventing the dog from eating faeces for 3 days. If the second sample again tested positive for the same type of helminth egg, the dog was considered to have a patent infection. If the second sample tested negative, the first sample was considered a false positive due to coprophagy. The focus of this study was on dogs shedding Toxocara eggs. At the first examination, 246 samples (out of 308 samples testing positive for canine-specific helminth eggs) tested positive for Toxocara spp. Of these, 120 (49%) tested negative at the second examination.Coprophagic behaviour was recognized by 261 of the 564 owners that answered the accompanying questionnaire. This concerned 391 dogs. Coproscopical examination also provided proof of coprophagy (e.g. oocysts of Eimeria spp. or non-dog typical helminth eggs) in dogs belonging to owners that did not report coprophagic behaviour in their dogs. Results indicate that coprophagy in dogs may result in an overestimation of the prevalence of patent helminth infections and that dogs may serve as a transport host for helminth eggs.