Intestinal infection following aerosol challenge of calves with Mycobacterium avium subspecies paratuberculosis

A challenge experiment was performed to investigate whether administration of Mycobacterium avium subsp. paratuberculosis (MAP) via the respiratory route leads to MAP infection in calves. Eighteen calves from test negative dams were randomly allocated to four groups. Six calves were challenged with MAP nasally and six calves were challenged by transtracheal injection; three orally challenged calves served as positive controls, and three non challenged calves as negative controls. The challenge was performed as a nine-fold trickle dose, 107 CFU in total. Blood and faecal samples were collected frequently. Calves were euthanized three months post-challenge and extensively sampled. Blood samples were tested for the presence of antibodies and interferon gamma producing cells by ELISA. Faecal and tissue samples were cultured in a liquid culture system and the presence of MAP was confirmed by IS900 realtime PCR. Fourteen out of fifteen calves had no MAP antibody response. The negative controls remained negative; all positive controls became infected. Two nasally challenged calves showed a Purified Protein Derivative Avian (PPDA) specific interferon gamma response. In all nasally challenged calves, MAP positive intestinal samples were detected. In three calves of the nasal group MAP positive retropharyngeal lymph nodes or tonsils were detected. In all calves of the transtracheal group MAP positive intestinal tissues were detected as well and three had a MAP positive tracheobronchial lymph node. These findings indicate that inhalation of MAP aerosols can result in infection. These experimental results may be relevant for transmission under field conditions since viable MAP has been detected in dust on commercial dairy farms

Age and Dose Dependent Susceptibility to Mycobacterium avium subspecies paratuberculosis Infection in Dairy Calves

Mycobacterium avium subspecies paratuberculosis (MAP) causes Johne’s disease (JD), a chronic enteritis in ruminants. Control programs focus on prevention of infection of susceptible individuals: calves < 6 months of age. However, this age-cut-off for susceptibility is not well supported scientifically. Additionally, control programs struggle with low sensitivity of diagnostic tests in the early stages of JD. The main objective of this thesis was to determine age-dependent susceptibility in dairy calves. Additionally, the course of immune responses as well as fecal shedding was assessed. Furthermore, gross lesions, histology and MAP-culture from tissues were used to confirm infection status of each calf, and to investigate age-dependent susceptibility. Fifty calves were inoculated per os on 2 consecutive days at 2 weeks and 3, 6, 9, or 12 months. Within each age group calves received either a high (5 x 109 CFU) or low dose (5 x 107 CFU) of MAP. Six calves served as a negative control group. Serum, whole blood and fecal samples were collected regularly until necropsy at 17 months of age. Macroscopic and histological lesions were assessed and bacterial culture was performed on tissue samples. Calves were successfully infected with MAP up to 1 year of age even with a low dose of MAP. Calves inoculated at 2 weeks, 3, or 6 months of age with a high dose of MAP had more severe necropsy lesions, were shedding MAP in feces more frequently, and had a stronger humoral and cellular immune response, than calves inoculated with a low dose. Shedding and humoral immune responses differed between individual calves and were detected in about half of the calves, which was more than anticipated. A dose-dependent cellular immune response was detected in each inoculated calf soon after inoculation using an interferon-gamma release assay and is therefore a good candidate test for early diagnosis. To conclude, calves are susceptible to MAP infection up to 1 year of age and could be infectious to other calves. Keeping the infection pressure low on-farm could reduce the severity of JD. Early diagnosis of MAP-infection is possible and this could improve the potential to control JD on-farm

Shedding patterns of dairy calves experimentally infected with Mycobacterium avium subspecies paratuberculosis

International audienceAlthough substantial fecal shedding is expected to start years after initial infection with Mycobacterium avium subspecies paratuberculosis (MAP), the potential for shedding by calves and therefore calf-to-calf transmission is underestimated in current Johne’s disease (JD) control programs. Shedding patterns were determined in this study in experimentally infected calves. Fifty calves were challenged at 2 weeks or at 3, 6, 9 or 12 months of age (6 calves served as a control group). In each age group, 5 calves were inoculated with a low and 5 with a high dose of MAP. Fecal culture was performed monthly until necropsy at 17 months of age. Overall, 61% of inoculated calves, representing all age and dose groups, shed MAP in their feces at least once during the follow-up period. Although most calves shed sporadically, 4 calves in the 2-week and 3-month high dose groups shed at every sampling. In general, shedding peaked 2 months after inoculation. Calves inoculated at 2 weeks or 3 months with a high dose of MAP shed more frequently than those inoculated with a low dose. Calves shedding frequently had more culture-positive tissue locations and more severe gross and histological lesions at necropsy. In conclusion, calves inoculated up to 1 year of age shed MAP in their feces shortly after inoculation. Consequently, there is potential for MAP transfer between calves (especially if they are group housed) and therefore, JD control programs should consider young calves as a source of infection

Evaluation of age-dependent susceptibility in calves infected with two doses of Mycobacterium avium subspecies paratuberculosis using pathology and tissue culture

Article deposited according to agreement with BMC, December 2, 2010 and according to publisher policies: http://www.biomedcentral.com/about/copyright March 7, 2014Funding provided by the Open Access Authors Fund.Ye