Heterobilharzia americana (HA) is a trematode parasite of dogs and is the causative agent of canine schistosomiasis. The life cycle of this parasite requires a definitive host (i.e.- dog), an intermediate freshwater snail host, and freshwater source. Dogs become infected when they stand, wade, or swim in cercariae (the infective form of the parasite) infested water. Dogs may remain asymptomatic, but those who experience symptoms most commonly experience vomiting, diarrhea, weight loss, blood in stool, reduction of appetite, or changes in thirst and urination.
Diagnosis of HA is typically achieved by specialized fecal testing such as fecal sedimentation, fecal HA PCR, or histopathology of affected tissues. Standardly employed fecal screening tests, such as fecal flotation, are rarely able to detect the eggs of HA as the eggs are too heavy to float. At present, there are no commercially available preventatives labeled for use to protect dogs against HA infection. Further, awareness of HA is limited amongst veterinarians and dog owners. Therefore, dogs may be chronically affected and have very advanced disease at the time of diagnosis. We have found significant prevalence of HA in the dogs that we have tested, surpassing that of other intestinal parasites. These findings support our concern that HA is endemic across a broad range of geographic regions within the United States and is an important parasite of dogs.
We are concerned that the dogs of the PWD breed have at least as much risk as the general population of dogs based on our other prevalence work across the country. However, there is reason to believe that there may be even more risk in the PWDs who participate in water trials as their practice and competitions are held in freshwater sources. In this cross-sectional study, we will perform fecal testing on 200 PWDs attending the 2025 PWDCA National Specialty to determine the prevalence of HA in this population of dogs. Further, we will determine if there are differences in prevalence of HA between dogs that participate in water trials and those that do not. The findings of this study will inform if intermittent screening or preventatives against HA in PWDs is indicated.
Heterobilharzia americana in Portuguese water dogs recruitment flyer