Isolation of canine distemper viruses from domestic dogs in South Africa using Vero.DogSLAM cells and its application to diagnosis

Studies comparing canine distemper virus (CDV) strains from Africa with that of previously described lineages have been hampered due to a lack of field strains for in vitro experiments. Since the attenuation of the Onderstepoort strain in the 1940s, there have not been any reports of CDV isolations in southern Africa. Clinical specimens consisting of whole blood, spleen, lungs, brain and cerebrospinal fluid from dogs with clinical signs compatible with distemper diagnosis were obtained from private veterinary practices and diagnostic laboratories. The animals all displayed various catarrhal, systemic, or nervous signs of the disease. One hundred and sixty two specimens from 124 dogs were inoculated into Vero cells expressing canine signalling lymphocyte activation molecule (Vero.DogSLAM). Cytopathic effects (CPE) in the form of syncytia formation and cell necrosis were observed in 33 (20.4%) specimens within 24 h of inoculation and the presence of CDV was confirmed with the aid of the direct fluorescent antibody test and electron microscopy (EM). Four of the CDVpositive dogs had a history of canine distemper vaccinations. Seventy three percent of all positive dogs were less than 12 months old. Local isolates of wild-type CDV were generated and we conclude that isolation of CDV using Vero.DogSLAM is a specific and practical method for the antemortem diagnosis of distemper in dogs.