Cleaveland S, Dye C
Institute of Zoology, Zoological Society of London, UK.
Parasitology. 1995;111 Suppl:S33-47. doi: 10.1017/s0031182000075806.
Whether and how microparasites such as rabies persist in their host populations are among the fundamental questions of infectious disease epidemiology. Rabies is fatal disease of all mammalian species, but not all mammalian species can maintain the infection as reservoirs. The approach to control depends on which of the affected species do act as reservoirs. Bringing together old and new data, we examine here the role of wild and domestic animals in maintaining rabies in the Serengeti region of Tanzania, presenting our findings in two parts. In Part I, we argue that domestic dogs are the likely reservoirs because: (1) rabies has been continuously present in the dog population since its (re)introduction in 1977, whilst (2) wildlife cases have been very rare over this period, despite intensive study of Serengeti carnivores; (3) outbreaks of rabies in wild canids (jackals) elsewhere in Africa (Zimbabwe) have followed, rather than preceded, outbreaks in the dog population; (4) all viruses isolated from wild carnivores in the Serengeti ecosystem (including the Kenyan Masai Mara) are antigenically and genetically indistinguishable from the typical domestic dog strain; (5) dog rabies control in the Serengeti between 1958-77 apparently eliminated the disease from both dogs and wildlife. Having identified dogs as reservoirs, Part II explores some possible mechanisms of maintenance in dog populations. In theory, infection is more likely to be maintained at higher dog densities, and we provide evidence that rabies is maintained in one district with a dog density > 5/km2, but not in two other districts with densities < 1/km2. Because 5 dogs/km2 is much lower than the expected density required for persistence, we go on to investigate the role of atypical infections, showing: (1) from serology, that a substantial proportion of healthy dogs in the Serengeti have detectable serum levels of rabies-specific antibody; (2) from mathematical models that, whilst we cannot be sure what seropositivity means, persistence in low-density dog populations is more likely if seropositives are infectious carriers, rather than slow-incubators or immunes.
狂犬病等微寄生物是否以及如何在其宿主种群中持续存在，是传染病流行病学的基本问题之一。狂犬病是所有哺乳动物的致命疾病，但并非所有哺乳动物物种都能作为宿主维持感染。控制狂犬病的方法取决于哪些受影响物种充当宿主。综合新旧数据，我们在此研究了坦桑尼亚塞伦盖蒂地区野生动物和家畜在维持狂犬病方面的作用，并分两部分呈现我们的研究结果。在第一部分中，我们认为家犬可能是宿主，原因如下：（1）自1977年狂犬病（重新）引入犬类种群以来，狂犬病一直持续存在，而（2）在此期间，尽管对塞伦盖蒂食肉动物进行了深入研究，但野生动物感染病例却非常罕见；（3）非洲其他地区（津巴布韦）野生犬科动物（豺）的狂犬病疫情是在犬类种群疫情之后而非之前爆发的；（4）从塞伦盖蒂生态系统（包括肯尼亚马赛马拉）的野生食肉动物中分离出的所有病毒，在抗原性和基因上与典型的家犬毒株没有区别；（5）1958 - 1977年间在塞伦盖蒂对犬类狂犬病的控制显然使犬类和野生动物中的这种疾病都得以消除。在确定犬类为宿主后，第二部分探讨了犬类种群中狂犬病维持的一些可能机制。理论上，在犬类密度较高时感染更有可能持续存在，我们提供的证据表明，在一个犬类密度>5只/平方公里的地区狂犬病得以持续存在，而在另外两个密度<1只/平方公里的地区则没有。由于5只/平方公里远低于维持狂犬病所需的预期密度，我们接着研究非典型感染的作用，结果表明：（1）从血清学来看，塞伦盖蒂地区相当比例的健康犬血清中可检测到狂犬病特异性抗体；（2）从数学模型来看，虽然我们不能确定血清阳性意味着什么，但如果血清阳性者是感染携带者而非潜伏期长的感染者或免疫者，那么在低密度犬类种群中狂犬病更有可能持续存在。
