Location: Infectious Bacterial Diseases ResearchTitle: Virulence of two strains of Mycobacterium bovis in cattle following aerosol infection Author
Submitted to: Journal of Comparative Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/2014
Publication Date: 11/1/2014
Publication URL: http://handle.nal.usda.gov/10113/60604
Citation: Waters, W.R., Thacker, T.C., Nelson, J.T., DiCarlo, D.M., Maggioli, M.F., Greenwald, R., Esfandiari, J., Lyashchenko, K.P., Palmer, M.V. 2014. Virulence of two strains of Mycobacterium bovis in cattle following aerosol infection. Journal of Comparative Pathology. 151(4):410-419. Interpretive Summary: Despite highly successful eradication efforts in several countries, tuberculosis of cattle remains a serious health concern worldwide. In addition, recent outbreaks of tuberculosis in Michigan, Minnesota, California, Washington, Texas, Nebraska, Indiana, Colorado, and New Mexico demonstrate that the disease is far from eliminated from the United States. Improved methods of control are needed for this serious disease of cattle that also infects man. In this study, two strains of Mycobacterium bovis, the causative agent of tuberculosis in cattle, were compared for their ability to cause disease in cattle. A highly contagious strain was compared to a well-characterized strain that affects cattle and white-tailed deer in Michigan. Findings demonstrated that both strains had equivalent capacity to cause disease in cattle. Knowledge obtained from this study will be useful for determining which strain to use to test control measures, such as diagnostic tests and vaccines, in experimental infection trials. Additionally, it informs you on the nature of the disease causing agent.
Technical Abstract: Background Over the past two decades, highly virulent strains of Mycobacterium tuberculosis have emerged and spread rapidly in humans, suggesting a selective advantage based upon virulence. A similar scenario has not been described for Mycobacterium bovis infection in cattle (i.e., Bovine Tuberculosis). An epidemiologic investigation of a recent outbreak of bovine tuberculosis in a US dairy indicated that the causative strain of M. bovis (strain 10-7428) was particularly virulent with rapid spread within the herd. In the present study, the virulence of this strain (10-7428) was directly compared in the target host to a well-characterized and epidemiologically relevant strain of M. bovis (strain 95-1315). Results Aerosol inoculation of ~104 colony forming units of M. bovis strain 95-1315 (n = 8) or strain 10-7428 (n = 8) resulted in a similar distribution and severity of gross and microscopic tuberculous lesions as well as mycobacterial colonization, primarily affecting the lungs and lung-associated lymph nodes. Specific cell-mediated and antibody responses were also similar between the two treatment groups. Tuberculous lesions and M. bovis-specific immune responses were not detected in non-infected control cattle (n = 7). Conclusions Present findings demonstrate that the virulence of M. bovis strain 95-1315 and strain 10-7428 are similar when administered to cattle via aerosol inoculation. Other factors such as livestock management practices or transmission potential of the strain likely affected the severity of the outbreak in the dairy. Keywords: Bovine Tuberculosis, pathogenesis, strain virulence, cattle