Seroprevalence and risk factors related to small ruminant lentivirus infections in Belgian sheep and goats

Maedi-Visna virus (MVV) and caprine arthritis encephalitis virus (CAEV) are two prototype members of the group of small ruminant lentiviruses (SRLVs). Both result in progressive and persistent infections of sheep and goats that impact animal health and cause economic losses. In Belgium, the sheep and goat sector is small and consists mostly of hobbyist farmers keeping few animals. A voluntary control program however exists, but less than 2% of the farmers participate to the program. The current lack of SRLV seroprevalence data and knowledge on risk factors related to SRLV seropositivity in this hobbyist sector makes it difficult to evaluate the risk of SRLV transmission from non-certified to SRLV free certified farms. We performed a nationwide SRLV seroprevalence study based on a stratified sampling proportional to the number of sheep and goat holders per province. Randomly selected sheep and goat owners were invited to participate and subject to a short questionnaire to collect information about flock size, animal health condition, age, flock constitution and housing conditions. Samples were collected from maximum 7 animals per farm and tested in a commercial ELISA. In total, we received samples from 87 sheep and 76 goat farms. Sheep flocks showed an overall seroprevalence of 9% (CI (95%): 5-15) and a between-herd seroprevalence of 17% (CI (95%): 11-27). Seroprevalence at animal level in goat flocks was 6% (CI (95%): 3-12) and the between-herd seroprevalence was 13% (CI (95%): 7-23). Multiple sheep and goat breeds were found SRLV seropositive. Answers provided during the questionnaire confirmed the mostly hobbyist nature of the sector and showed that more than 65% of sheep and goat farmers had never heard of the disease. The only risk factor found to be related to SRLV seroprevalence was flock size. Herds of more than 10 goats had significantly higher chance to harbor seropositive animals (OR: 4.36; CI: 1.07; 17.73). In conclusion, it was shown that participants to the SRLV free certification program are at risk for reintroduction of the disease in their herds since SRLVs are present on about 15%-20% of non-certified farms. Except from flock size, no clear risk factors were found that are helpfull to identify flocks at risk. Greater effort should be made to inform sheep and goat fanners about the existence and consequences of this disease in order to promote the voluntary control program and further reduce the disease prevalence.