Abstract
Bovine TB caused by Mycobacterium bovis is becoming a disease of major concern in free-ranging ungulate populations in North America. An adaptive management program to determine the prevalence and eventually eradicate bovine TB in elk, white-tailed deer and cattle has been instituted in the region of Riding Mountain National Park in south-western Manitoba, Canada. Measures to help reduce the prevalence of bovine TB have included barrier fencing for hay storage yards, legislation changes to make baiting cervids outside the park illegal, enhanced surveillance of cattle and farmed bison surrounding the park, increased harvest of elk through liberalized hunting seasons, and targeted herd reduction of elk within the park. The apparent prevalence of bovine TB in elk in the western half of RMNP based on preliminary blood sampling using net gun capture and parallel interpretation of a lymphocyte stimulation test (LST), fluorescence polarization assay (FPA) and polymerase chain reaction (PCR) is approximately 35%. Selective removal of 87 elk, including 37 elk with suspicious blood results, followed by necropsy and bacterial culture of tissues confirmed bovine TB in 15% of elk. Ongoing studies will attempt to determine the effectiveness of management actions, determine the prevalence of bovine TB in the RMNP regional elk and white-tailed deer populations, identify potential spillover hosts in and around the park, and improve methods for the diagnosis of bovine TB.
Introduction
A focus of bovine tuberculosis (Mycobacterium bovis) has recently been identified in free-ranging elk (Cervus elaphus manitobensis), white-tailed deer (Odocoileus virginianus) and domestic cattle in the area of Riding Mountain National Park (RMNP) in south-western Manitoba, Canada.1 Historically, cattle grazing was common in the park up until 1970 and tuberculosis was known to be common in the area in the early 1900s. Bovine tuberculosis was considered to be not uncommon in cattle in the 1950s and 1960s and there were four outbreaks in a total of eleven cattle herds around RMNP Since 1991.2 This resulted in the creation of the Riding Mountain TB Eradication Area (RMEA) to detect and control the spread of bovine TB in cattle herds in January of 2003. In 1992 an adult bull elk was found dead which tested positive for bovine TB after which time a passive surveillance program using samples provided by hunters identified an additional eight elk and one white-tailed deer with bovine TB.1 In response the Interagency TB Task Group was formed in 2000 consisting of personnel from the Canadian Food Inspection Agency, Parks Canada Agency, Manitoba Agriculture and Food, and Manitoba Conservation with input from local stakeholder groups. A Wildlife Health Action Plan was developed consisting of a 5-year TB management strategy and implementation plan. The vision is to eradicate bovine TB from the greater Riding Mountain ecosystem and the long-term goals are to achieve and maintain bovine TB-free status in domestic cattle; to eradicate bovine TB in wildlife that may pose a risk to agriculture; to minimize wildlife-livestock interactions in the Riding Mountain region; and to minimize unnatural cervid herding behavior which occurs where cervids feed on agricultural produce, thereby minimizing the potential for disease transmission. The following paper will describe management actions and research initiated since 2000 to reduce the spread of bovine TB and to understand the epidemiology of bovine tuberculosis in RMNP.
Methods
Three hundred-and-three elk were captured to determine disease prevalence and geographic clustering within the park by helicopter net gunning3 in 2002, 2003 and 2004. Forty elk were captured in 2002, 113 in 2003 and 150 in 2004. Elk captured in 2002 and 2003 were primarily from the west side of RMNP while in 2004, 50 elk were captured on the west side and 100 were captured on the east side of RMNP. GPS or VHF radio collars or ear tag transmitters were affixed to animals to determine habitat use and movement within and around the park.4 Blood was drawn by jugular venipuncture into sterile Vacutainer™ tubes with lithium heparin, sodium EDTA or nothing. Samples were kept at room temperature until analyzed within 48 hours or serum was separated by centrifugation and frozen. Parallel interpretation of three different blood tests was used to evaluate M. bovis status: a lymphocyte stimulation test (LST), a fluorescence polarization assay (FPA), and a polymerase chain reaction (PCR). Although blood was collected from all elk captured, only 229 samples were of sufficient quality or quantity to permit completion of all three tests. The remaining 74 samples were analyzed with one or two tests only. Forty of 153 elk captured from February 2002 to March 2003 tested positive on at least one of the three blood tests. Thirty-seven of these elk were re-captured in April 2003 and killed by anesthesia and intravenous potassium chloride administration. A sub-sample of fifty of 110 elk that tested negative on the blood tests were re-captured in December 2003 and killed by captive bolt gun and exsanguination. A complete necropsy was performed on all killed elk. All identifiable lymph nodes from the head, thorax, abdomen and peripheral limbs were harvested fresh and in 10% buffered formalin. Bacterial culture and acid-fast staining were completed on lymph nodes and any other tissues with visible lesions suggestive of bovine TB. Animals were considered positive if M. bovis was isolated in pure culture from at least one lymph node or suspicious tissue sample or a positive PCR result was obtained from tissue.
Results and Discussion
Several management actions were initially undertaken to attempt to reduce the prevalence and further spread of bovine TB within the RMNP ecosystem. A barrier fencing program was initiated in 2002 to fence winter haystacks around the park and prevent contact between cattle and elk. A total of 72 8-foot-high page wire barrier fences were erected with funding provided by the province of Manitoba and Parks Canada which has now fenced approximately 90% of hay storage yards within 1.6 km of the park boundary. An ongoing education program has also been actively encouraging landowners bordering the park to remove hay bales from fields prior to the onset of winter and clean up hay storage yards. Hunting seasons in the two game hunting areas (GHA 23 and 23A) surrounding the park were lengthened and additional permits given out to help in herd reduction efforts.
Legislation was also changed within the Manitoba Wildlife Act in 2002 to make the baiting of elk with either intentionally placed bait or the use of natural forage as bait outside the park illegal. Baiting and supplemental feeding of white-tailed deer has been implicated as a major risk factor in increasing the prevalence of bovine TB in white-tailed deer in Michigan.5 Provisions were made to allow wildlife officers to determine what was reasonably considered “bait” and to take measures to either fence or remove the bait. Hunting is not allowed within 800 metres of a cervid bait site within Manitoba Game Hunting Areas (GHA) 23 and 23A which surround the park on the north and south. Provisions were also made to provide additional protection for wolves (Canis lupus), which are the main predators of elk in RMNP to allow natural predator-prey mechanisms to remove diseased animals. Ongoing studies are in progress to further understand the predator-prey dynamics and dispersal of wolves within the RMNP ecosystem. Prescribed fire was also used as a management tool to improve elk forage habitat within the park and keep animals within the park boundaries during the winter months when forage availability is limited.
Special regulations were enacted to restrict the movement of cattle in and out of the RMEA in January 2003 in which a special TB management zone was created. Within the RMEA there are 55,000 breeding cattle on approximately 650 premises representing approximately 10% of Manitoba’s cattle herds and approximately 1% of Canadian cattle herds.6 In Manitoba, the RMEA is classified as TB-Accredited-Advanced according to current Canadian standards while the rest of Manitoba and Canada have been classified as TB-Free since 1997. A movement permit, based on a negative herd test and/or individual animal testing, has been required since January 1, 2003 to remove farmed bovids and cervids from the RMEA into other areas. From 1997 to 2002, cattle surveillance had involved the testing of all cattle herds in a 10-kilometer zone around positive cervid cases, and the testing of previously untested herds in a 6-kilometer zone around the western boundary of the park. In the fall of 2002, surveillance testing was expanded to encompass the regular testing of all cattle and farmed bison herds located within the RMEA every 12 to 36 months, resulting in the detection of three infected herds.2
An elk movement study was undertaken in 2002 to determine seasonal elk movements in and out of the park. Two broad groups of elk have been defined so far with Type I elk having been primarily located inside RMNP (<5% of locations outside of RMNP) and Type II elk having been primarily located both inside and outside the park (>5% of locations outside park).7 Based on the first 2 years of telemetry data, 61% of the collared elk have been located outside RMNP at least once with females using areas outside the park more than males. Elk have been documented using areas outside of RMNP more during the spring and summer months than in the winter months.4
Targeted herd reduction has been instituted within the park boundaries resulting in the removal of 87 elk in 2003 and another 27 elk in March 2004. Among animals that were removed in 2003, bovine TB was confirmed through culture or PCR on tissues in 13/87 (14.9%) animals, 8 (61.5%) which were adult females and 5 (38.5%) which adult males. These animals were primarily from the west end of the park where a geographic focus of bovine TB in elk had been previously identified.1 The apparent prevalence (AP) of bovine TB in elk captured on the west side of RMNP based on parallel interpretation of the three blood tests was 30/86 (34.9%), while in sampling throughout the entire park in 2004 it was 23/143 (16.1%). Test results from the 2004 removals are pending.
Passive surveillance of hunter-killed and road and predator-killed elk, white-tailed deer and moose (Alces alces) was also carried out in the areas surrounding the park since 1992. Samples from 10 of 1463 (0.7%) elk, 1 of 1079 (0.09%) white-tailed deer and none of 557 (0%) moose were culture positive for M. bovis between 1992 and 2002.1 Prevalence of bovine TB in the two rural municipalities on the west end of the park was estimated to be 2.5% and 2.9% respectively based on this type of sampling.1 As previously identified, this type of surveillance seems to underestimate the true prevalence of disease especially when animals are not collected directly from within geographic foci within in the park. In contrast, passive surveillance for bovine TB has been successfully used to determine trends in prevalence in Michigan in free-ranging white-tailed deer and elk with very little bias due to the ability to directly sample all areas uniformly.8
Continuing research will focus on the role of wolves in the spread and control of bovine TB, improving bovine TB diagnostic methods in wolves and elk, further clarification of the geographic extent of the infection as well as the identification and role of other species as reservoir and spillover hosts for bovine TB in the region.
Literature Cited
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