Seroconversion in an industrial unit of rabbits infected with a non-pathogenic rabbit haemorrhagic disease-like virus

A serological survey of 238 rabbits for antirabbit haemorrhagic disease virus (RHDV) antibodies was made in an industrial rabbitry where no signs of the disease had been reported for four years. Seroconversion was repeatedly detected and was due to a calicivirus antigenically related to RHDV but without its pathogenicity. There was a seroprevalence of 33.3 per cent among young animals at weaning at 31 days old, 27.6 per cent at five to seven days after weaning, 56.1 per cent at 13 to 14 days after weaning, 90.3 per cent at 19 to 20 days and 100 per cent at 32 to 33 days after weaning, and all the breeding rabbits were seropositive. In the last group and in the young at weaning, the anti-RHDV antibodies were mainly class IgG, but they were IgM and IgA at 13 to 14 days after weaning. In older fattening rabbits, there was a decrease of IgM and IgA and an increase of IgG confirmed seroconversion without any specific signs of rabbit haemorrhagic disease. On the basis of these results, the probable time of infection of the meat rabbits with this non-pathogenic virus was immediately after weaning.