Troell K, Waller P, Höglund J
Department of Parasitology (SWEPAR), National Veterinary Institute and Swedish University of Agricultural Sciences, 751 89 Uppsala, Sweden.
J Helminthol. 2005 Dec;79(4):373-9. doi: 10.1079/joh2005286.
Five complimentary studies were undertaken with the overall aim to examine the ability of free-living stages of Haemonchus contortus to over-winter and tolerate cold stress. Two studies deal with the development and long-term survival of eggs and infective larvae of two geographically different isolates (Kenya and Sweden). Eggs and larvae were monitored in climatic chambers at temperatures that fluctuated daily between -1 degrees C and 15 degrees C, or at constant temperatures of 5 degrees C and 15 degrees C. The development from egg to larvae was dependent on temperatures over 5 degrees C. The long time survival was favoured at lower temperatures. Furthermore, the overwintering capacity of the free-living stages of these isolates was estimated under Swedish field conditions. Two groups of lambs were experimentally infected with different isolates, and kept separated on previously ungrazed plots. In early May the following year, two parasite-naive tracer lambs were turned out on each of the plots to estimate the pick up of overwintered larvae. This experiment was replicated in central and southern Sweden. In addition, two experiments were performed in 2003 on pasture previously grazed by naturally infected sheep. One trial was on a pasture in southern Sweden grazed by a commercial flock, where extreme numbers of H. contortus were found towards the end of the grazing season 2002. The other study was on a pasture plot in central Sweden grazed by a hobby flock in 2002, where three of six lambs died due to haemonchiasis. Overwintered H. contortus was recorded on three of four experimental sites. Worm burdens were in all instances extremely low. No differences in development and survival were found between the isolates. Consequently, overwintering on pasture is of no practical significance in the transmission of H. contortus between grazing-seasons in Sweden.
开展了五项补充研究，总体目的是检验捻转血矛线虫自由生活阶段越冬及耐受冷应激的能力。两项研究涉及两个地理上不同的分离株（肯尼亚和瑞典）的虫卵和感染性幼虫的发育及长期存活情况。在气候箱中，将虫卵和幼虫置于每日温度在-1℃至15℃之间波动的环境中，或置于5℃和15℃的恒温环境中进行监测。从虫卵到幼虫的发育取决于5℃以上的温度。较低温度有利于长期存活。此外，还在瑞典田间条件下估计了这些分离株自由生活阶段的越冬能力。两组羔羊分别感染不同的分离株，并分开饲养在以前未放牧的地块上。次年5月初，在每个地块上放入两只未感染寄生虫的示踪羔羊，以估计越冬幼虫的感染情况。该实验在瑞典中部和南部重复进行。此外，2003年在以前被自然感染绵羊放牧过的牧场上进行了两项实验。一项试验在瑞典南部一个商业羊群放牧的牧场上进行，在2002年放牧季节结束时发现了大量的捻转血矛线虫。另一项研究在瑞典中部一个2002年由一个业余羊群放牧的牧场地块上进行，六只羔羊中有三只死于血矛线虫病。在四个实验地点中的三个记录到了越冬的捻转血矛线虫。在所有情况下虫负荷都极低。未发现分离株之间在发育和存活方面存在差异。因此，在瑞典，牧场越冬在放牧季节之间捻转血矛线虫的传播中没有实际意义。
