Is the gamma interferon assay in cattle influenced by multiple tuberculin injections?

Along with other developed countries, Canada is interested in adopting the gamma interferon (IFN-gamma) assay to test for bovine tuberculosis (TB). This study compared results of using the IFN-gamma assay in a large number of field-tested cattle in Manitoba, some previously tested with a caudal fold test (CFT) only, and others injected with tuberculins for both a CFT and a comparative cervical test (CCT). Parallel testing further compared the IFN-gamma assay and CCT results with the confirmed TB status of the animal (culture, histopathologic examination, polymerase chain reaction). Results from IFN-gamma assays did not differ following the CFT versus CFT and CCT injections. Parallel testing demonstrated an apparent higher prevalence of tuberculosis for the IFN-gamma assay versus CCT, which will assist in earlier removal of exposed animals and, ultimately, prevent populations from becoming infected.

Epidemiology of an outbreak of chronic wasting disease on elk farms in Saskatchewan.

An outbreak of chronic wasting disease (CWD) in farmed elk in Saskatchewan from 1996 to 2002 was reviewed to 1, determine the progression of CWD from infection to death in farmed elk; 2, assess animal risk factors for CWD infection in farmed elk; 3, assess farm management and exposure risk factors for within herd CWD transmission; and 4, assess the suitability of the Canadian Food Inspection Agency's (CFIA) current disease control policy for CWD in light of the findings. The results from animal movement tracing, animal testing, and a farm management questionnaire were used. The duration of CWD (time from exposure to death of a CWD test-positive animal) was between a mean minimum of 19 months and a mean maximum of 40 months. Age and sex were not associated with CWD infection, except that adult elk (> or = 2 y) were more likely to be infected than young elk (< 18 mo) (RR = 2.3, 95% CI 1.6-3.5). Elk calves born in the last 18 mo prior to the death or diagnosis of their dam were at higher risk if their dams died of CWD (RR = 4.1, 95% CI 1.5-11.4) or exhibited clinical signs of CWD (RR = 8.3, 95% CI 2.7-25.7). Significant risk factors for transmission of CWD on elk farms were the introduction from an infected farm of trace-in elk that died of CWD (RR = 13.5, 95% CI 2.0-91) or developed clinical signs of CWD (RR = 7.1, 95% CI 0.93-54) and the elapsed time in years since the incursion of CWD (OR = 5.6, 95% CI 1.8-17.4). The assumptions on which CFIA's disease control policies were based were validated, but based on this new information, quarantine in cases where exposure to preclinical elk has occurred could be considered as an alternative to whole herd eradication.

Learning from outbreaks of bovine tuberculosis near Riding Mountain National Park: applications to a foreign animal disease outbreak.

Riding Mountain National Park, Manitoba, is home to a population of free-roaming elk (Cervus elaphus manitobensis) that have been found to be infected with Mycobacterium bovis, the agent of bovine tuberculosis (TB). The disease has also been found in a number of cattle herds near the Park and, as a result, Manitoba has been assigned a split status for bovine TB. A number of government agencies, with input from representatives from the wildlife and agricultural sectors, have responded by devising a program to detect, investigate, control, eradicate, and prevent TB in both wild and domestic animals. Experience from these efforts can be applied to the control of other diseases, such a foreign animal disease, elsewhere in Canada.