Nugent G, Yockney I J, Whitford E J
Landcare Research, PO Box 40, Gerald St., Lincoln 8152, New Zealand.
J Wildl Dis. 2011 Apr;47(2):364-72. doi: 10.7589/0090-3558-47.2.364.
We investigated intraspecific transmission of Mycobacterium bovis (etiologic agent of bovine tuberculosis [Tb]) among penned pigs (Sus scrofa) in New Zealand. Between 2002 and 2006, we conducted two trials, each involving two 1-ha pens in natural habitat in which uninfected sentinel pigs were kept with wild-caught feral pigs, many of which were infected with M. bovis. The rate of M. bovis transmission to sentinels was used to assess whether intraspecies transmission between live pigs could explain the high levels of infection in the wild population. In trial 1, no new infection was detected in 18 penned sentinels after total exposure of 3.9 yr (2.6 mo/sentinel); three of 11 sentinels in the wild became infected. In trial 2, a more heavily infected source pig population (94% prevalence compared with 42% in the first trial) was used, and one (4%) of 25 penned sentinels became infected. However, 75% of the eight sentinels released to the wild became infected. Combining trials, the difference in apparent annual incidence was significant (mean ± 95% confidence interval = 0.03 ± 0.12 for penned sentinels vs. 1.06 ± 6.74 for released sentinels; t=-3.51, P=0.04). In the pens, infected pigs were kept in contact with susceptible sentinels for 7 yr in total, but only one transmission event was detected. Taking pig longevity into account, the R(0) value (the basic reproductive rate of disease) for intraspecies infection between live pigs seems unlikely to exceed 0.25, even under highly conducive conditions. We suggest that live pigs are unlikely to transmit M. bovis to wild conspecifics often enough to sustain Tb in pigs by this route of transmission alone. The high prevalences seen in some New Zealand feral pig populations are likely to result from transmission from another host or route.
我们调查了新西兰圈养野猪（Sus scrofa）中牛分枝杆菌（牛结核病 [Tb] 的病原体）的种内传播情况。在2002年至2006年期间，我们进行了两项试验，每项试验涉及自然栖息地中两个1公顷的围栏，未感染的哨兵猪与野生捕获的野猪饲养在一起，其中许多野猪感染了牛分枝杆菌。牛分枝杆菌传播给哨兵猪的速率用于评估生猪之间的种内传播是否可以解释野生种群中的高感染水平。在试验1中，18只圈养的哨兵猪在总共暴露3.9年（2.6个月/只哨兵）后未检测到新的感染；野生的11只哨兵猪中有3只被感染。在试验2中，使用了感染程度更高的源猪种群（患病率为94%，而第一次试验为42%），25只圈养的哨兵猪中有1只（4%）被感染。然而，放归野外的8只哨兵猪中有75%被感染。综合两项试验，明显的年发病率差异显著（圈养哨兵猪的平均值±95%置信区间 = 0.03 ± 0.12，放归哨兵猪的为1.06 ± 6.74；t = -3.51，P = 0.04）。在围栏中，感染猪与易感哨兵猪总共接触了7年，但仅检测到一次传播事件。考虑到猪的寿命，生猪之间种内感染的R(0)值（疾病的基本繁殖率）即使在高度有利的条件下似乎也不太可能超过0.25。我们认为，生猪不太可能经常将牛分枝杆菌传播给野生同种个体，仅靠这种传播途径不足以在猪中维持结核病。在新西兰一些野猪种群中看到的高患病率可能是由另一种宿主或传播途径引起的。
