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Encephalitozoon cuniculi, a microsporidian parasite of vertebrates, is considered a health risk to AIDS patients and other immunocompromised human beings. In most hosts, infection with the parasite runs a subclinical course. In some carnivore species, however, clinical disease affecting whole litters arises from intrauterine transmission of the parasite. In both blue foxes ( Alopex lagpus) and dogs ( Canis familiaris), outbreaks of encephalitozoonosis can be severe. Canine encephalitooonosis has been reported from various parts of the world, including South Africa and the United States. In Norway, there have been large outbreaks of the disease in blue fox farms, affecting also mink, but there have been no reports of encephalitozoonosis in dogs. Infection in dogs would represent a zoonotic problem, due to the close social relationship between dog and man. The purpose of the present study was to investigate the possible occurrence of E. cuniculi infection in Norwegian dogs by serological methods. In the study, 1,104 canine serum samples, originally submitted for biochemical analysis by veterinary practitioners throughout Norway, were screened by enzyme-linked immunosorbent assay for antibodies to E. cuniculi. Samples from 237 of the dogs were tested also by the indirect fluorescent antibody test. All samples were concluded as negative. The results indicate that the likelihood of occurrence of E. cuniculi infection in Norwegian dogs is small.

Encephalitozoon cuniculi has a wide host range among mammals, but whether it represents a homogeneous species is a subject of controversy. We have isolated, cultivated (in human MRC-5 cells) and, for the first time, characterized by immunological and molecular biological methods four isolates of E. cuniculi from Norwegian blue foxes with a history of encephalitozoonosis. The isolates were compared with nine isolates from domestic rabbits from Switzerland. Two E. cuniculi subtypes were identified according to their host species. A 5'-GTTT-3' tetranucleotide repeat was present twice in the rDNA intergenic spacer in all isolates from foxes as opposed to three times in all isolates from rabbits. Furthermore, random amplified polymorphic DNA analysis showed one polymorphic band among the subtypes, and Western-blot analysis using serum from an infected fox discriminated between the two subtypes on the basis of their banding patterns in the ranges of 31-33 and 38-40 kDa. The 5'-GTTT-3' tetranucleotide repeat is a valuable genetic marker for these two subtypes of E. cuniculi and will be of use in continued studies on the molecular epidemiology of this parasite.