Barron M C, Pech R P, Whitford J, Yockney I J, de Lisle G W, Nugent G
Landcare Research, PO Box 40, Lincoln 7640, New Zealand.
N Z Vet J. 2011 Sep;59(5):209-17. doi: 10.1080/00480169.2011.595905.
To determine, for a variety of environmental conditions, how long Mycobacterium bovis might remain viable inside the carcass of a brushtail possum (Trichosurus vulpecula) that died of bovine tuberculosis (Tb), and to measure the rate of contact between free-ranging possums and possum carcasses.
Lesions of M. bovis were simulated by inoculating excised spleens weighing 0.5-1 g with 0.2 mL liquid culture containing approximately 5 x 10(7) cfu M. bovis/mL. Simulated lesions were inserted into possum carcasses (n=48) at the peripheral lymph nodes. Carcasses were placed in the field at two sites (a tussock grassland and a podocarp-broadleaved forest site) and in two seasons (summer and winter) for up to 62 days. Survival rates of M. bovis were estimated by sampling the simulated lesions over time, and culturing the recovered lesion to determine if any viable M. bovis bacteria were present. The time taken for a free-ranging possum to first encounter a dead possum in its home range was estimated by live-trapping possums and fitting them with proximity loggers (n=13). A 'contact' was recorded if these possums came within 40-50 cm of proximity loggers fitted to possum carcasses.
There were strong seasonal and site effects in the survival rate of M. bovis in possum carcasses. In the grassland habitat, no viable bacilli were cultured from any carcass after 3 days in summer, whereas in winter all samples were culture-positive for the first 20 days, and some were still positive after 27 days. The survival rates for forest habitat were intermediate between the results for grassland, and there were no culture-positive carcasses after 9 days in summer or 27 days in winter. In summer, infected carcasses (n=6) were first encountered by possums a mean 1.9 (range 0.4-6.7) days after placement.
Possum carcasses were contacted by free-ranging possums within the period that viable M. bovis were shown to survive in a carcass. The risk of such infection is likely to be most significant in winter or in areas with microhabitats where the survival of M. bovis is high. However, the generally low survival rate of M. bovis in possum carcasses and the low frequency of possum-to-carcass contacts indicate this route of transmission alone could not maintain Tb in a possum population.
确定在各种环境条件下，死于牛结核病（Tb）的帚尾袋貂（Trichosurus vulpecula）尸体内部牛分枝杆菌可能存活多长时间，并测量自由放养袋貂与袋貂尸体之间的接触率。
通过向重0.5 - 1克的切除脾脏接种0.2毫升含有约5×10⁷cfu/毫升牛分枝杆菌的液体培养物来模拟牛分枝杆菌病变。将模拟病变插入袋貂尸体（n = 48）的外周淋巴结。尸体被放置在两个地点（一个草丛草原和一个罗汉松 - 阔叶林地点）的野外以及两个季节（夏季和冬季）中长达62天。通过随时间对模拟病变进行采样并培养回收的病变以确定是否存在任何存活的牛分枝杆菌细菌，来估计牛分枝杆菌的存活率。通过活捉袋貂并为其安装近距离记录器（n = 13）来估计自由放养袋貂在其活动范围内首次遇到死袋貂所需的时间。如果这些袋貂靠近安装在袋貂尸体上的近距离记录器达40 - 50厘米以内，则记录一次“接触”。
袋貂尸体中牛分枝杆菌的存活率存在强烈的季节和地点效应。在草原栖息地，夏季3天后从任何尸体中均未培养出存活的杆菌，而在冬季，所有样本在前20天培养均为阳性，一些在27天后仍为阳性。森林栖息地的存活率介于草原的结果之间，夏季9天后或冬季27天后没有培养阳性的尸体。在夏季，感染的尸体（n = 6）在放置后平均1.9天（范围0.4 - 6.7天）首次被袋貂遇到。
在显示牛分枝杆菌在尸体中存活的时间段内，自由放养袋貂与袋貂尸体发生了接触。这种感染风险在冬季或牛分枝杆菌存活率高的微生境区域可能最为显著。然而，牛分枝杆菌在袋貂尸体中的总体存活率较低以及袋貂与尸体接触的频率较低表明，仅这种传播途径无法在袋貂种群中维持结核病。
