Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2008
Publication Date: 5/12/2009
Citation: Stabel, J.R., Palmer, M.V., Harris, B.N., Plattner, B., Hostetter, J., Robbe-Austerman, S. 2009. Pathogenesis of Mycobacterium avium subsp. paratuberculosis in Neonatal Calves after Oral or Intraperitoneal Experimental Infection. Veterinary Microbiology. 136(3-4):306-313. 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: Understanding the infection process to Mycobacterium avium subsp. paratuberculosis is tantamount to the development of effective vaccines and therapeutics for the control of this disease in the field. The current study compared the effectiveness of oral and intraperitoneal methods of experimental inoculation and two strains of M. avium subsp. paratuberculosis (strain K-10 and clinical isolate 509) on level of infection and pathogenic lesions. Fecal culture and PCR data demonstrated that calves in the oral inoculation groups experienced shedding on d 7, 14, 21, and 28, indicative of “pass-through” shedding that is typically observed after large oral boluses of bacteria are administered. Fecal shedding of M. avium subsp. paratuberculosis was minimal and infrequent over the course of the study for calves in the oral and intraperitoneal infection groups that received strain K-10. However, calves orally inoculated with the clinical isolate shed high numbers of bacteria in their feces up to 4 months post-inoculation. Colonization was present in a number of intestinal tissues and lymph nodes with the lowest number of affected tissues in the intraperitoneally infected calves and the highest for calves receiving the clinical isolate via oral inoculation. Histopathologic lesions were predominantly found in the ileal and jejunal sections and their associated lymph nodes, as well as the ileocecal valve and node. These data suggest that oral inoculation remains the most effective method of experimental infection for M. avium subsp. paratuberculosis and that inoculation with a clinical isolate may increase infection of tissues compared to a laboratory-adapted strain.