Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: November 14, 2007
Publication Date: December 30, 2007
Citation: Stabel, J.R., Palmer, M.V., Robbe-Austerman, S., Harris, B. 2008. Pathogenesis of Mycobacterium avium subsp. paratuberculosis in Neonatal Calves after Oral or Intraperitoneal Experimental Infection. In: Proceedings of the 9th International Colloquium on Paratuberculosis, October 28th-November 2, 2007, Tsukuba, Japan. p.50-53. Interpretive Summary: Johne's disease is a chronic, debilitating intestinal disorder in cattle,sheep and wild ruminants, characterized by diarrhea, reduced feed intake, weight loss and death. Animals usually become infected when they are young by ingesting feces containing the causative bacteria. However, symptoms of disease do not usually present themselves until the animals reach 3 to 5 years of age or even older. During this time the animal is infected and may be shedding the organism in its feces without showing any clinical signs of disease. In addition to reduced production by these animals through reduced milk production, they also present a potential infective threat to the rest of the herd. Johne’s disease is difficult to diagnose and therefore to control. Animal infection models are necessary for the study of host responses to infection under controlled conditions. In this paper, we present results from a study designed to evaluate different methods of experimental infection in a calf model. Further, we discuss the results of infection on the presence of the bacteria in tissues along with the associated damage to the tissue. Results of this study suggest that experimental infection of calves by the oral method resulted in an increased number of bacteria in the tissues. This type of study will aid in the evaluation of new vaccines to prevent infection and disease.
Technical Abstract: There is a critical need for a ruminant infection model that can reproduce the progression from subclinical to clinical disease, thereby following a pattern of infection commonly recognized in the field. The objective of this study was to evaluate different methods of infection (oral, oral with dexamethasone pre-treatment, and intraperitoneal) of neonatal calves with either a laboratory-adapted K-10 strain or a clinical isolate of Mycobacterium avium subsp. paratuberculosis (MAP) on the pathogenesis of infection. Calves given the clinical isolate of MAP shed higher numbers of bacteria in their feces for up to 4 months post-inoculation with only sporadic shedding noted for calves given the K-10 strain. Fecal PCR results mirrored the culture results with infrequent positive reactions after the first 4 weeks of infection, regardless of infection group. Colonization was present in a number of intestinal tissues and lymph nodes with the lowest number of affected tissues in the IP calves and the highest for calves orally dosed with the clinical isolate. Similarly, histopathologic lesions were predominantly found in the ileal and jejunal sections and their associated lymph nodes. Strain typing of the 2 isolates before and after calf infection showed that neither strain of MAP changed genotype in the host but that the genotypes were different for the laboratory-adapted and clinical strains. These data suggest that oral inoculation remains the most effective method of experimental infection for MAP and that inoculation with a recent clinical isolate of MAP may induce more clinical signs.