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Understanding the dynamics of host-pathogen interaction is key to the management of epidemics. A pestivirus belonging to the border disease virus group 4 emerged around 2001 in Pyrenean chamois ( Rupicapra pyrenaica) in Spain and France. The virus had significant demographic impact in some populations, but it was less harmful and more endemic in other places. The determinants of these local variations are still unclear. Here, we documented empirical evidence of self-clearance of the virus in a chamois population in France. This population has regularly been counted, and chamois were trapped and harvested each year, providing unique demographic and epidemiologic surveys of the population since 1984 and 1994, respectively. The virus was detected using direct (PCR) and indirect (antibody) testing. We showed that virus transmission declined in 2011-12 and likely ceased in 2013, leading to a decline in antibody prevalence since 2014. Self-clearance may be due to limited exchanges with other populations, decrease in population size after an epizootic, and herd immunity. The age structure of captured animals shifted to younger age classes after virus self-clearance, suggesting a return to a colonizing population structure. The possible consequences of virus re-entry are discussed. This observation suggests that pestivirus dynamics occurs at the scale of the metapopulation of Pyrenean chamois. Local self-clearance and re-emergence may help explain the variation of virus dynamics at the local scale.

Outbreaks of a previously unrecorded disease have recently affected Pyrenean chamois (Rupicapra pyrenaica pyrenaica) populations across the mountain range. A pestivirus was hypothesized to be the cause of this emerging disease and this type of virus can cross the species barrier and be transmitted to or from wildlife. Using an epidemiological survey conducted from 1995 to 2004 at Orlu, France, we characterized the virus and analyzed its transmission. A phylogenetic analysis of viral sequences and virus neutralization tests showed that the virus belonged to the newly described border disease virus-4 group. The increase of seroprevalence with age indicated that infection can occur at any age and resulted in lifelong immunity. Overall, 70.3% of 323 samples were positive for anti-p80 antibodies and 10.2% of 167 samples showed viremia, as demonstrated by either positive ELISA antigen test or RT-PCR. Infection has thus been widespread in this population since 1995, whereas no mass mortality or clinical signs have been observed. Incidence and seroprevalence varied seasonally and according to number of individuals aged less than 2 years old in the population, so viral transmission was dependent on host population age structure. We propose that the virus is now endemic in this population and is likely detrimental for reproduction and juveniles. Further investigation is needed to estimate the impact of pestivirus on host population dynamics and the risk of cross-transmission to farm animals.

A pestivirus was detected and characterized in chamois (Rupicapra pyrenaica pyrenaica) originating from the French part of the Pyrenees. Phylogenetic analysis of the pestivirus was done on the basis of a fragment from the 5' noncoding region including 22 published nucleotide sequences of different pestivirus strains. Our strain was grouped within the clade of border disease viruses (BDV). However, it had an intermediate position between clade BDV and classical swine fever viruses representing a basal position to BDV strains of domestic sheep. Our strain was grouped as a sister unit to a novel pestivirus (Chamois-1) recently described from chamois in Spain. Therefore, we postulate that this virus occurs in the entire population of Pyrenean chamois. On the basis of the phylogenetic grouping of this isolate, a postulated cross-species transmission of pestivirus from domestic sheep to chamois via shared pastures seems to be unlikely.