Antibodies against rabbit hemorrhagic disease virus (RHDV) from 352 red fox (Vulpes vulpes) sera collected in Germany (Mecklenburg-Vorpommern) in 1993 were tested by a blocking enzyme-linked immunosorbent assay (ELISA) test kit. Ninety samples with positive or suspected results also were analyzed by the hemagglutination inhibition test (HIT). Eighteen serum samples (5%) were positive with the blocking ELISA and eight of these also were positive with HIT. The 18 positive sera also were tested by blocking ELISA for antibodies against European brown hare syndrome virus (EBHSV) and by sandwich ELISA to detect fox antibodies against RHDV and EBHSV antigen. Antibodies were not found against EBHSV using the blocking ELISA. With the sandwich ELISA, six samples were positive against RHDV and also against EBHSV, indicating cross-reactivity between determinants of both viruses. However, antibody titers against RHDV were higher than against EBHSV in five samples, and in one animal titers were similar. In addition, two positive samples were investigated by Western blot immunoassay which showed clear positive reactions with the two main peptide bands of EBHSV and RHDV. Comparison of the areas below the peaks of the bands after immunoblotting indicated that there was a stronger reaction with the two main polypeptides of RHDV than with the two main peptides of EBHSV. This is the first report of calicivirus antibodies in free-ranging red foxes. Based on the specificity of the tests, the antibodies detected against caliciviruses may be induced by RHDV. There is a potential link for RHDV between free-ranging rabbits and foxes.

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