THE EFFECT OF COWPOX VIRUS-INFECTION ON FECUNDITY IN BANK VOLES AND WOOD MICE

Although epidemic infectious diseases are a recognized cause of change s in host population dynamics, there is little direct evidence for the effect of endemic infections on populations. Cowpox virus is an ortho poxvirus which is endemic in bank voles (Clethrionomys glareolus), woo d mice (Apodemus sylvaticus) and field voles (Microtus agrestis) in Gr eat Britain. It does not cause obvious signs of disease nor does it af fect survival, but in this study we demonstrate experimentally chat it can reduce tile fecundity of bank voles and wood mice by increasing t he time to first litter by 20-30 days. The pathogenic mechanisms causi ng this effect are at present not known, but this finding suggests tha t natural subclinical infection could have a considerable effect on th e dynamics of wild populations.