Evidence for continued transmission of parasitic nematodes in reindeer during the Arctic winter

Living in the high Arctic, the Svalbard reindeer (Rangifer tarandus platyrh ynchus) and its trichostrongyle nematodes experience a long cold winter fro m October to late May/early June. Over this period, transmission would be e xpected to be low. However, in culled reindeer the abundance of infection i ncreased from autumn to late winter, providing evidence for continued trans mission within this period. To our knowledge this is the first time this ha s been demonstrated in a climate with temperatures consistently below 0 deg rees C. In one winter (1996-1997), the average fraction of nematodes found as larvae in the abomasal mucosa increased from around 10% to 50% between O ctober and March. This suggests that arrested development took place throug hout the winter. We found no evidence for an efficient acquired immune resp onse towards the nematodes. The abundance of infection did not tend to decr ease with increasing host age after an earlier peak, but levelled off inste ad, as predicted by a simple immigration-death model. In the late winter wh en the nutritional plane is low, both adult reindeer and calves had high wo rm burdens at intensities that may affect their condition and fitness. (C) 1999 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.