Onchocercosis: a newly recognized disease in dogs.

In the past 15 years, onchocercosis has been reported with increasing frequency in dogs in Europe and the United States, and 64 cases have been described so far. According to some authors, the Onchocerca sp. responsible for canine cases spills over from domestic or wild ungulates into dogs. However, canine Onchocerca does not match any of the descriptions for species of Onchocerca reported from domesticated and wild animals in Europe or North America. The nucleotide sequences of canine Onchocerca are also unique within the genus. Moreover, patent Onchocerca infections can be seen only in accidental hosts closely related to the natural hosts. In canine onchocercosis cases, high microfilarial load could be observed indicating that canids might be the definitive hosts of the parasite. Therefore, others suggested that Onchocerca lupi Rodonaja, 1967 originally described from a wolf (Canis lupus) can be responsible for these infections, which is a typical example for host switch and site shift, the dominant modes of speciation of the genus Onchocerca. The morphology, molecular characteristics, phylogeny, life cycle, host specificity, geographical distribution of Onchocerca sp. infecting dogs, as well as the clinical signs, pathology, laboratory diagnosis, therapy and possible zoonotic significance of canine onchocercosis are reviewed. Research into human onchocercosis has been hampered by the lack of analogous models. As infections in dogs may provide a practical experimental system, further studies should be encouraged to try to establish experimental Onchocerca infections in dogs.