Coprophagy interferes with coproscopical diagnosis of helminth infections in dogs.

Coprophagial behaviour is common amongst dogs. Parasite eggs shed by other animals can pass the digestive tract of dogs what may result into a false positive diagnosis of infection with gastro-intestinal parasites.
As part of an ongoing longitudinal study in which dog owners submit fecal samples monthly for 2 years to detect the presence of enteropathogens in dogs, we were able to observe how often coprophagy occurs in dogs resulting in false positive samples.
Feces was collected between January and June 2013 and examined using the CSF-technique with a sugar flotation solution (density 1.3 g.cm-3). If a sample tested positive for helminth eggs, the owner was asked to collect another sample 3 days after keeping the dog from eating anything from the environment. If the samples were tested positive again it was considered a patent infection, if negative the first was considered to be false positive due to coprophagy.
So far, 102 of 1576 (6,4 %) samples tested positive. Of these, 44 (43%) tested negative in the repeated sample and consequently were considered false positive. Several of the samples considered to be false positive, were found to contain eggs in varying stages of development, including moving larvae in strongyle-type eggs. There were no differences in percentages of observed false positives between months.
286 of 567 (50%) dog owners mention that their dogs eat feces. 36% of 925 dogs actually have been observed to eat feces by their owners. Nonetheless, the percentage of dogs eating feces is likely an underestimation. 27.5% of Eimeria oocyst positive samples originated from dogs that do not eat feces according to their owner.
Results indicate that coprophagy may result in a serious overestimation of the prevalence of patent helminth infections in dogs. Further, dogs might act as transport hosts due to their coprophagic behaviour.