Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA, USA.
Prev Vet Med. 2013 Feb 1;108(2-3):85-93. doi: 10.1016/j.prevetmed.2012.11.018. Epub 2012 Dec 17.
Pneumonia of bighorn sheep (Ovis canadensis) is a dramatic disease of high morbidity and mortality first described more than 80 years ago. The etiology of the disease has been debated since its initial discovery, and at various times lungworms, Mannheimia haemolytica and other Pasteurellaceae, and Mycoplasma ovipneumoniae have been proposed as primary causal agents. A multi-factorial "respiratory disease complex" has also been proposed as confirmation of causation has eluded investigators. In this paper we review the evidence for each of the candidate primary agents with regard to causal criteria including strength of association, temporality, plausibility, experimental evidence, and analogy. While we find some degree of biological plausibility for all agents and strong experimental evidence for M. haemolytica, we demonstrate that of the alternatives considered, M. ovipneumoniae is the best supported by all criteria and is therefore the most parsimonious explanation for the disease. The strong but somewhat controversial experimental evidence implicating disease transmission from domestic sheep is consistent with this finding. Based on epidemiologic and microbiologic data, we propose that healthy bighorn sheep populations are naïve to M. ovipneumoniae, and that its introduction to susceptible bighorn sheep populations results in epizootic polymicrobial bacterial pneumonia often followed by chronic infection in recovered adults. If this hypothesized model is correct, efforts to control this disease by development or application of vectored vaccines to Pasteurellaceae are unlikely to provide significant benefits, whereas efforts to ensure segregation of healthy bighorn sheep populations from M. ovipneumoniae-infected reservoir hosts are crucial to prevention of new disease epizootics. It may also be possible to develop M. ovipneumoniae vaccines or other management strategies that could reduce the impact of this devastating disease in bighorn sheep.
绵羊肺炎（Ovis canadensis）是一种高发病率和死亡率的严重疾病，最早于 80 多年前被描述。自首次发现以来，该疾病的病因一直存在争议，不同时期曾提出肺蠕虫、溶血曼海姆菌和其他巴斯德氏菌以及绵羊肺炎支原体是主要病原体。还提出了一种多因素“呼吸道疾病综合征”，以确认病因的方法一直困扰着研究人员。在本文中，我们根据因果关系标准（包括关联强度、时间性、合理性、实验证据和类推），审查了每种候选主要病原体的证据。虽然我们发现所有病原体都具有一定程度的生物学合理性，并且对溶血曼海姆菌有很强的实验证据，但我们证明，在所考虑的替代方案中，绵羊肺炎支原体最符合所有标准，因此是该疾病最合理的解释。强烈但有些争议的实验证据表明，疾病可以从绵羊传播给绵羊，这与这一发现一致。基于流行病学和微生物学数据，我们提出健康的大角羊种群对绵羊肺炎支原体没有免疫力，而将其引入易感大角羊种群会导致爆发性多微生物细菌性肺炎，通常在康复的成年羊中会继发慢性感染。如果假设的模型是正确的，那么通过开发或应用针对巴斯德氏菌的载体疫苗来控制这种疾病的努力不太可能带来显著的益处，而确保健康的大角羊种群与绵羊肺炎支原体感染的宿主隔离是预防新疾病爆发的关键。也有可能开发绵羊肺炎支原体疫苗或其他管理策略，以减轻这种毁灭性疾病对大角羊的影响。
