SRLV monitoring in the post-eradication phase in Switzerland

In Switzerland, SRLV seroprevalence in goats is below 1% and as a result of an eradication campaign, clinical manifestations completely disappeared. Seroconversions, however, still occur and are caused by highly attenuated SRLV genotypes. We isolated several field strains of these lentiviruses and confirmed their phylogenetic association with the prominent A4 subtype. The pathological and histopathological analysis of infected, clinically healthy adult goats supported the hypothesis that these A4 viruses are of low pathogenicity for goats with, however, a caveat about the potentially detrimental effects on the mammary gland, where we found severe histopathological lesions compatible with a viral etiology. In fact and in contrast to all known SRLV target organs, such as carpal joints, plexus choroideus and lungs, showing a very low proviral load, the proviral load in the mammary gland was high and associated with clear histopathological lesions. This indicate that the immune system of the animals cannot control the infection with these attenuated viruses that also show a surprisingly phenotypic plasticity in vitro, showing a distinct cell tropism preference for goat or sheep cells and different cytopathic effects. This strongly argues in favor of a continuous and precise monitoring of these SRLV to avoid the risk of jeopardizing a long eradication campaign.

To this purpose we developed a novel ELISA based on synthetic peptides encompassing a variable and immunodominant region of the envelope glycoprotein. This ELISA permits us obtain serological evidence of the phylogenetic characteristics of the infecting viruses.
(Collaboration with the Swiss SRLV reference center).