Raghavan Bindu, Bavananthasivam Jegarubee, Kugadas Abirami, Haldorson Gary J, Srikumaran Subramaniam
Department of Veterinary Microbiology & Pathology, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-7040, USA.
Department of Veterinary Microbiology & Pathology, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-7040, USA.
Vet Microbiol. 2017 May;203:56-61. doi: 10.1016/j.vetmic.2017.02.013. Epub 2017 Feb 27.
Leukotoxin producing (lkt+) members of Pasteurellaceae, particularly Mannheimia haemolytica and Bibersteinia trehalosi are important pathogens of pneumonia in bighorn sheep (BHS; Ovis canadensis), causing fatal disease. Predisposing or concurrent infection with Mycoplasma ovipneumoniae enhances the severity of the disease, resulting in increased morbidity and mortality. Several studies have investigated the effectiveness of vaccines against lkt+ members of Pasteurellaceae in preventing fatal pneumonia in BHS. In all of these studies, however, vaccinated animals were challenged experimentally, by direct inoculation of the pathogens, rather than by natural challenge. Moreover, none has investigated the efficacy of the vaccines under conditions of concurrent infection with M. ovipneumoniae. We immunized three bighorn rams and one pregnant ewe with an experimental multivalent vaccine along with a commercial vaccine. The immunized animals were then commingled with two bighorn ewes known to be carriers of lkt+ members of Pasteurellaceae, to simulate natural infection or disease transmission. All vaccinated animals remained healthy. We then inoculated the two carrier ewes with nasal washings from domestic sheep containing M. ovipneumoniae. Within a week, all animals developed mild to moderate signs of pneumonia. While the rams died within two-three months post-inoculation (p.i.), the vaccinated ewe and her lamb died five and eight months p.i., respectively. Taken together, these results suggest that vaccination of BHS against lkt+ members of Pasteurellaceae alone can protect them from natural challenge by these pathogens. However, it may not be adequate to protect them against pneumonia compounded by concurrent infection with M. ovipneumoniae.
巴氏杆菌科中产生白细胞毒素（lkt+）的成员，特别是溶血曼氏杆菌和海藻比伯斯坦氏菌，是大角羊（BHS；加拿大盘羊）肺炎的重要病原体，可导致致命疾病。感染绵羊肺炎支原体的诱发或并发感染会加重疾病的严重程度，导致发病率和死亡率增加。多项研究调查了针对巴氏杆菌科lkt+成员的疫苗在预防大角羊致命性肺炎方面的有效性。然而，在所有这些研究中，接种疫苗的动物是通过直接接种病原体进行实验性攻毒，而非自然感染。此外，尚无研究调查过在并发感染绵羊肺炎支原体的情况下疫苗的效力。我们用一种实验性多价疫苗和一种商业疫苗对三只大角羊公羊和一只怀孕母羊进行了免疫接种。然后将免疫接种的动物与两只已知为巴氏杆菌科lkt+成员携带者的大角羊母羊混养在一起，以模拟自然感染或疾病传播。所有接种疫苗的动物均保持健康。随后，我们用含有绵羊肺炎支原体的家养绵羊鼻腔冲洗液对两只携带病原体的母羊进行接种。在一周内，所有动物都出现了轻度至中度的肺炎症状。公羊在接种后两到三个月内死亡，而接种疫苗的母羊及其羔羊分别在接种后五个月和八个月死亡。综合来看，这些结果表明，单独对大角羊接种针对巴氏杆菌科lkt+成员的疫苗可以保护它们免受这些病原体的自然感染。然而，这可能不足以保护它们免受并发感染绵羊肺炎支原体而加重的肺炎。
