Search

Disseminated infection (DI) of Mycobacterium avium subspecies paratuberculosis (MAP) in cattle may impair cow health, potentiate spread of disease, and is a potential food-safety risk. The objectives of this study were to determine the association between severity of histologic enteric lesions and the occurrence of DI, clinical signs, and positive fecal culture and serum ELISA results. Bacteriologic fecal culture and serum ELISA were performed on 40 dairy cows from MAP-infected herds. Cows were classified as having DI if MAP was isolated from any of 11 extra-intestinal tissues collected postmortem. A grade of 0-3, corresponding to the severity of histologically evident granulomatous inflammation was determined for sections of ileum, jejunum, mesenteric lymph node, and ileocolic lymph node. An overall intestinal inflammation (OII) grade of 0-3 was assigned to each cow. The proportion of cows with DI increased with tissue-specific lesion grade and OII grade. All cows with grade 3 inflammation in any single tissue had DI, however, some cows with DI had grade 1 inflammation or no lesions. In general, there was a positive association between OII grade and clinical signs, gross enteric lesions, and positive ELISA and fecal culture results. However, 12% of OII grade 0 cows had clinical signs (explained by other conditions recognized with necropsy), and the proportion of positive ELISA results was lower for OII grade 3 cows relative to grade 2 cows. Although MAP dissemination may occur early in the disease process, histopathology of intestinal tissues may be used to detect a substantial proportion of DI cows.

Mycobacterium avium subspecies paratuberculosis (MAP) disseminated infection in dairy cattle affects animal health and productivity and is also a potential public health concern. The study objectives were to characterize MAP disseminated infection in dairy cattle and to determine the role of antemortem tests in detecting cattle with disseminated infection. Forty culled dairy cows representing a variety of serum enzyme-linked immunosorbent assay (ELISA) results and body conditions were selected for the study. The physical condition of the cows was assessed via clinical examination prior to euthanasia and blood and feces were collected and tested by serum ELISA and fecal culture, respectively. Fifteen tissues were aseptically collected from each cow during necropsy and cultured for isolation of MAP. Disseminated infection was diagnosed when MAP was isolated in tissues other than the intestines or their associated lymph nodes (LNs) and was distinguished from infection found only in the gastrointestinal tissues and from absence of infection. Of the 40 cows in the study, 21 had MAP disseminated infection. Results showed that 57% (12/21) of cows with disseminated infection had average to heavy body condition and no diarrhea. Cows with disseminated infection had no to minimal gross pathologic evidence of infection in 37% (8/21) of cases. Only 76% (16/21) of cows with disseminated infection had positive historical ELISA results and only 62% (13/21) had a positive ELISA at slaughter. Thus, antemortem evidence of MAP infection was lacking in a high proportion of cows where MAP disseminated infection was confirmed.

The objectives of this study were to: (i) evaluate the results of an intradermal skin test, a modified IFN-gamma test, and a commercial ELISA in commercially raised dairy calves at 2, 4, 6 and 8 months of age relative to faecal shedding of Mycobacterium avium ssp. paratuberculosis (MAP); (ii) determine the proportion of 8-month-old calves shedding MAP in faeces as detected by culture and One Tube Nested Polymerase Chain Reaction (OTSN-PCR) and (iii) explore the association between results of tests described above in the calves and the Paratuberculosis (PTB) status of their dams as determined by faecal culture and/or serology. The study calves belonged to two dairy herds with different risk of exposure to MAP (high and low) and were enrolled based on their dam's ELISA results prior to calving. Approximately 3% of the calves were shedding MAP in faeces at 8 months of age. No agreement was observed among the evaluated immunity-based tests or between the immunity-based tests and the detection of MAP in faeces. Although no association was observed between the infection status of the dam and the results from the IFN-gamma and skin tests on the calves, there is an indication that calves born from dams that were faecal shedders might be at a higher risk of testing positive to the IFN-gamma test at 8 months of age. The disagreement among all tests evaluated in this calf cohort suggests that the detection of MAP infection in young stock requires the use of combined multiple tests. The early detection of PTB in calves is a challenge that requires further exploration of new methods to confirm infection status. These new testing methods should be both affordable and compatible with regular husbandry practices.

Objective: To estimate seroprevalence of Mycobacterium avium subsp paratuberculosis (MAP) infection among adult dairy cows in Colorado and determine herd-level factors associated with the risk that individual cows would be seropositive., Design: Cross-sectional observational study., Animals: 10,280 adult (> or = 2 years old) dairy cows in 15 herds in Colorado., Procedure: Serum samples were tested with a commercial ELISA. A herd was considered to be infected with MAP if results of mycobacterial culture of > or = 1 individual cow fecal sample were positive or if > or = 1 culled cow had histologic evidence of MAP infection., Results: 424 of the 10,280 (4.12%) cows were seropositive. Within-herd prevalence of seropositive cows ranged from 0% to 7.82% (mean, 2.6%). Infection was confirmed in 11 dairies. Cows in herds that had imported > or = 8% of their current herd size annually during the preceding 5 years were 3.28 times as likely to be seropositive as were cows in herds that imported < 8%. Cows in herds with > or = 600 lactating cows were 3.12 times as likely to be seropositive as were cows in herds with < 600 lactating cows. Cows in herds with a history of clinical signs of MAP infection were 2.27 times as likely to be seropositive as were cows in herds without clinical signs., Conclusions and Clinical Relevance: Annual importation rate, herd size, and whether cows in the herd had clinical signs typical of MAP infection were associated with the risk that individual cows would be seropositive for MAP infection.

Objective: To determine the proportion of adult cattle that change test status when an ELISA for antibodies against Mycobacterium avium subsp paratuberculosis (MAP) is used to assay samples collected twice at variable intervals and to determine whether cows with an initial strong positive result were more likely to maintain positive status, compared with all cows with an initial positive result., Design: Cross-sectional observational study., Animals: 3,757 adult dairy cattle., Procedure: Serum samples were obtained twice from cattle at intervals ranging from 77 to 600 days between collections. Samples were tested with an ELISA for detection of antibodies to MAP., Results: Of 157 cattle with initial positive results (value for the sample divided by the value for positive-control serum [S/P] > or = 0.25), 62 (39.5%) had negative results for the second sample. Of 71 cattle with an initial S/P value > or = 0.40, 13 (18.3%) had a negative result (S/P < 0.25) for the second sample. Of 33 cattle with an initial S/P > or = 0.70, 3 (9.1%) had a negative result (S/P value < 0.25) for the second sample. Interval between collection of samples did not affect results., Conclusions and Clinical Relevance: Many cows changed ELISA status between samples collected at variable intervals. Cows with an initial high S/P value (> or = 0.70) were more likely to maintain positive status than cows classified as positive on the basis of cutoff values of > or = 0.25 or > or = 0.40. Veterinarians should expect variability in ELISA results when repeated testing of cattle is used as part of an MAP control program.