Tuberculous lesions in free-ranging white-tailed deer in Michigan

Persistent Spillback of Bovine Tuberculosis From White-Tailed Deer to Cattle in Michigan, USA: Status, Strategies, and Needs

Free-ranging white-tailed deer (Odocoileus virginianus) are believed to be a self-sustaining reservoir for bovine tuberculosis (bTB) in northeastern Lower Michigan, USA. Although a comprehensive control program is in place and on-farm mitigation strategies to curtail bTB transmission between cattle and deer have been implemented for over a decade, cattle and deer continue to become infected with the disease. Thus, renewed motivation to eradicate bTB is needed if that is truly the goal. Recurrent detection of bTB in cattle in the region is of mounting concern for state and federal agricultural agencies, producers, and wildlife managers. Current on-farm mitigation efforts include fencing and refined cattle feeding and watering practices. Liberal removal of antlerless deer through hunter harvest and disease control permits (DCPs) issued to cattle producers and agency sharp shooters have also been ongoing. Although these strategies have merit and efforts to reduce prevalence in deer and occurrence of positive farms are elevated, additional actions are needed. Heightened management actions to combat bTB in deer could include deer vaccination programs, strategic habitat manipulations to redistribute deer from farms, and precision removal of deer in proximity to high-risk farms. Foundational research to address development and delivery of vaccine to free-ranging deer is complete. Strategic management and habitat manipulation could reduce and disperse local concentrations of deer while better meeting wildlife, forestry, and agricultural goals. The responses of local deer populations to targeted removal of individuals are generally understood and there is potential to reduce deer activity around agricultural operations while allowing them to persist nearby on natural foods. We summarize the history and progress to date, discuss the realized merit of novel management strategies, and suggest options to rid deer and cattle in Michigan of bTB.

Use of whole-genome sequencing and evaluation of the apparent sensitivity and specificity of antemortem tuberculosis tests in the investigation of an unusual outbreak of Mycobacterium bovis infection in a Michigan dairy herd

OBJECTIVE To describe use of whole-genome sequencing (WGS) and evaluate the apparent sensitivity and specificity of antemortem tuberculosis tests during investigation of an unusual outbreak of Mycobacterium bovis infection in a Michigan dairy herd. DESIGN Bovine tuberculosis (bTB) outbreak investigation. ANIMALS Cattle, cats, dog, and wildlife. PROCEDURES All cattle in the index dairy herd were screened for bTB with the caudal fold test (CFT), and cattle ≥ 6 months old were also screened with a γ-interferon (γIFN) assay. The index herd was depopulated along with all barn cats and a dog that were fed unpasteurized milk from the herd. Select isolates from M bovis-infected animals from the index herd and other bTB-affected herds underwent WGS. Wildlife around all affected premises was examined for bTB. RESULTS No evidence of bTB was found in any wildlife examined. Within the index herd, 53 of 451 (11.8%) cattle and 12 of 21 (57%) cats were confirmed to be infected with M bovis. Prevalence of M bovis-infected cattle was greatest among 4- to 7-month-old calves (16/49 [33%]) followed by adult cows (36/203 [18%]). The apparent sensitivity and specificity were 86.8% and 92.7% for the CFT and 80.4% and 96.5% for the γIFN assay when results for those tests were interpreted separately and 96.1% and 91.7% when results were interpreted in parallel. Results of WGS revealed that M bovis-infected barn cats and cattle from the index herd and 6 beef operations were infected with the same strain of M bovis. Of the 6 bTB-affected beef operations identified during the investigation, 3 were linked to the index herd only by WGS results; there was no record of movement of livestock or waste milk from the index herd to those operations. CONCLUSIONS AND CLINICAL RELEVANCE Whole-genome sequencing enhanced the epidemiological investigation and should be used in all disease investigations. Performing the CFT and γIFN assay in parallel improved the antemortem ability to detect M bovis-infected animals. Contact with M bovis-infected cattle and contaminated milk were major risk factors for transmission of bTB within and between herds of this outbreak.

Mesenteric lymph node granulomatous lesions in naturally infected wild boar (Sus scrofa) in Portugal--Histological, immunohistochemical and molecular aspects

Several studies have demonstrated that wildlife reservoirs of mycobacteria are responsible for the maintenance and spreading of the infection to livestock and wildlife counterparts. Recent data report the role of wild boar (Sus scrofa) as a reservoir for Mycobacterium bovis. This study was conducted to evaluate the chronic inflammatory response in the mesenteric lymph nodes (MLN) of wild boar with granulomatous lymphadenitis (n=30). Morphological parameters of the lesions were recorded. The expression of CD3 and CD79α molecules was evaluated by immunohistochemistry. Molecular genotyping and culture to identify mycobacteria were performed. The lesions consisted mainly of stage III and stage IV granulomas. CD3 and CD79α positive cells were observed in 15 (50%) and in 11 (36.6%) MLN, respectively. In these lesions, higher percentages of T lymphocytes were found and a limited number of animals exhibited a tendency for an increased percentage of B lymphocytes. Our results suggest that there are similar percentages and distribution patterns of CD3 and CD79α in the lesions, regardless of the presence of Mycobacterium avium subsp. paratuberculosis (Map), M. bovis or Map-M. bovis co-infection, and confirm that wild boar is both susceptible and could be an important Map and M. bovis wild reservoir in the study area.

Anatomical distribution of Mycobacterium bovis genotypes in experimentally infected white-tailed deer

Mycobacterium bovis (M. bovis) causes tuberculosis in white-tailed deer (WTD). Natural infection of WTD with M. bovis is most closely mimicked by instilling inoculum into palatine tonsillar crypts. One hundred fifty days after intratonsillar inoculation, M. bovis was cultured from 30 tissues originating from 14 deer. Whole-genome sequencing (WGS) was performed on the original inoculum, single colonies subcultured from the original inoculum, and M. bovis isolated from each culture positive tissue. Single nucleotide polymorphisms (SNP) were identified by comparing the derived sequences to the reference strain AF2122/97. Results indicate that the majority of the SNPs that were identified were homogeneous between the inoculum and the isolates from the tissues. The majority of individual tissues had different WGS genotypes from each other, suggesting that dissemination of M. bovis beyond the initial site of infection may require few mycobacteria representing a bottleneck.

The epidemiology of Mycobacterium bovis in wild deer and feral pigs and their roles in the establishment and spread of bovine tuberculosis in New Zealand wildlife

In New Zealand, wild deer and feral pigs are assumed to be spillover hosts for Mycobacterium bovis, and so are not targeted in efforts aimed at locally eradicating bovine tuberculosis (TB) from possums (Trichosurus vulpecula), the main wildlife host. Here we review the epidemiology of TB in deer and pigs, and assess whether New Zealand's TB management programme could be undermined if these species sometimes achieve maintenance host status. In New Zealand, TB prevalences of up to 47% have been recorded in wild deer sympatric with tuberculous possums. Patterns of lesion distribution, age-specific prevalences and behavioural observations suggest that deer become infected mainly through exposure to dead or moribund possums. TB can progress rapidly in some deer (<10%), but generalised disease is uncommon in wild deer; conversely some infected animals can survive for many years. Deer-to-deer transmission of M. bovis is rare, but transmission from tuberculous deer carcasses to scavengers, including possums, is likely. That creates a small spillback risk that could persist for a decade after transmission of new infection to wild deer has been halted. Tuberculosis prevalence in New Zealand feral pigs can reach 100%. Infections in lymph nodes of the head and alimentary tract predominate, indicating that TB is mostly acquired through scavenging tuberculous carrion, particularly possums. Infection is usually well contained, and transmission between pigs is rare. Large reductions in local possum density result in gradual declines (over 10 years) in TB prevalence among sympatric wild deer, and faster declines in feral pigs. Elimination of TB from possums (and livestock) therefore results in eventual disappearance of TB from feral pigs and wild deer. However, the risk of spillback infection from deer to possums substantially extends the time needed to locally eradicate TB from all wildlife (compared to that which would be required to eradicate disease from possums alone), while dispersal or translocation of pigs (e.g. by hunters) creates a risk of long-distance spread of disease. The high rate at which pigs acquire M. bovis infection from dead possums makes them useful as sentinels for detecting TB in wildlife. It is unlikely that wild deer and feral pigs act as maintenance hosts anywhere in New Zealand, because unrestricted year-round hunting keeps densities low, with far less aggregation than on New Zealand farms. We conclude that active management of wild deer or feral pigs is not required for local TB eradication in New Zealand.

Oral vaccination of white-tailed deer (Odocoileus virginianus) with Mycobacterium bovis Bacillus Calmette-Guerin (BCG)

Wildlife reservoirs of Mycobacterium bovis represent serious obstacles to the eradication of tuberculosis from livestock, particularly cattle. In Michigan, USA tuberculous white-tailed deer transmit M. bovis to other deer and cattle. One approach in dealing with this wildlife reservoir is to vaccinate deer, thus interfering with the intraspecies and interspecies transmission cycles. Thirty-three white-tailed deer were assigned to one of two groups; oral vaccination with 1 × 10(8) colony-forming units of M. bovis BCG Danish (n = 17); and non-vaccinated (n = 16). One hundred eleven days after vaccination deer were infected intratonsilarly with 300 colony-forming units of virulent M. bovis. At examination, 150 days after challenge, BCG vaccinated deer had fewer gross and microscopic lesions, fewer tissues from which M. bovis could be isolated, and fewer late stage granulomas with extensive liquefactive necrosis. Fewer lesions, especially those of a highly necrotic nature should decrease the potential for dissemination of M. bovis within the host and transmission to other susceptible hosts.

Mycobacterium bovis (bovine tuberculosis) infection in North American wildlife: current status and opportunities for mitigation of risks of further infection in wildlife populations

Mycobacterium bovis (M. bovis), the causative agent of bovine tuberculosis, has been identified in nine geographically distinct wildlife populations in North America and Hawaii and is endemic in at least three populations, including members of the Bovidae, Cervidae, and Suidae families. The emergence of M. bovis in North American wildlife poses a serious and growing risk for livestock and human health and for the recreational hunting industry. Experience in many countries, including the USA and Canada, has shown that while M. bovis can be controlled when restricted to livestock species, it is almost impossible to eradicate once it has spread into ecosystems with free-ranging maintenance hosts. Therefore, preventing transmission of M. bovis to wildlife may be the most effective way to mitigate economic and health costs of this bacterial pathogen. Here we review the status of M. bovis infection in wildlife of North America and identify risks for its establishment in uninfected North American wildlife populations where eradication or control would be difficult and costly. We identified four common risk factors associated with establishment of M. bovis in uninfected wildlife populations in North America, (1) commingling of infected cattle with susceptible wildlife, (2) supplemental feeding of wildlife, (3) inadequate surveillance of at-risk wildlife, and (4) unrecognized emergence of alternate wildlife species as successful maintenance hosts. We then propose the use of integrated and adaptive disease management to mitigate these risk factors to prevent establishment of M. bovis in susceptible North American wildlife species.

Surveillance for Mycobacterium bovis transmission from domestic cattle to wild ruminants in a Mexican wildlife-livestock interface area

OBJECTIVE

To assess the prevalence of Mycobacterium bovis infection in cattle and wild ruminants (WRs) in a wildlife-livestock interface area (WLIA) of the Mexican highland plateau.

ANIMALS

24,400 cattle from 793 herds (including 17,351 commercially slaughtered cattle) and 142 WRs (110 white-tailed deer [Odocoileus virginianus], 20 red deer [Cervus elaphus], and 12 North American elk [Cervus canadensis]) harvested via controlled hunting.

PROCEDURES

Cattle were serially tested for M bovis infection via caudal fold tuberculin and comparative cervical tuberculin tests during field surveillance. Carcasses of cattle and WRs were inspected for gross lesions; samples suggestive of tuberculosis were analyzed via histologic evaluation and mycobacterial culture (HMC). A PCR assay to detect Mycobacterium tuberculosis complex organisms was performed to confirm positive results of HMC.

RESULTS

WRs had inflammatory lesions in lungs and lymph nodes, although HMC results did not indicate M bovis infection. Eight cattle had positive results for both tuberculin tests, and 31 had positive results for HMC of grossly detected lesions; all were from 7 herds, and ≥ 1 cow in each herd had positive PCR assay results. These 7 herds were depopulated; adjacent herds and herds related via commerce were quarantined. Calculated true prevalence of M bovis infection was 0.86% (95% confidence interval, 0.24% to 1.49%) in cattle; M bovis was not detected in any WRs.

CONCLUSIONS AND CLINICAL RELEVANCE

M bovis infection was present in cattle. Although transmission to WRs in this WLIA was not detected, diagnosis and prevention activities should be implemented and consolidated to prevent potential M bovis transmission between cattle and WRs.

Persistence of Mycobacterium bovis bacillus Calmette-Guérin (BCG) Danish in white-tailed deer (Odocoileus virginianus) vaccinated with a lipid-formulated oral vaccine

Mycobacterium bovis, the causative agent of tuberculosis in animals, has a broad host range, including humans. Historically, public health concerns prompted programs to eradicate tuberculosis from cattle in many nations. Eradication efforts decreased the prevalence of bovine tuberculosis; nevertheless, some countries encountered significant obstacles, not least of which was a wildlife reservoir of M. bovis. Efforts to decrease the size of the affected wildlife populations have neither eliminated disease nor eliminated transmission to cattle. Consequently, the use of a vaccine for wildlife is being explored. The vaccine most studied is M. bovis BCG, an attenuated live vaccine, first developed 100 years ago. The most efficient and effective means of vaccinating wildlife will be an oral vaccine. White-tailed deer in Michigan, USA, constitute a reservoir of M. bovis. White-tailed deer are a popular game species, and as such, represent a food animal to many hunters. BCG persistence in deer tissues could result in human exposure to BCG. Although non-pathogenic, BCG exposure could induce false-positive skin test results, confounding the central component of public health surveillance for TB. The objective of the present study in white-tailed deer was to evaluate persistence of lipid-encapsulated BCG and a liquid suspension of BCG after oral administration at two different dosages. Vaccine was not recovered at any time after oral consumption of a bait containing a single dose (1 × 10(8) CFU) of lipid-encapsulated BCG. However, persistence was consistent in deer consuming 10 lipid-encapsulated baits (1 × 10(9) CFU), with BCG recovered from at least one deer at 1, 3, 6, 9 and 12 months after consumption. Persistence of up to 9 months was seen in deer vaccinated with orally with a liquid suspension. Persistence of BCG was limited to lymphoid tissue and never found in samples of muscle collected at each time point. Although the risk of exposure to hunters is low, BCG persistence should be considered prior to field use in white-tailed deer.

Single nucleotide polymorphisms in the Mycobacterium bovis genome resolve phylogenetic relationships

Mycobacterium bovis isolates carry restricted allelic variation yet exhibit a range of disease phenotypes and host preferences. Conventional genotyping methods target small hypervariable regions of the M. bovis genome and provide anonymous biallelic information that is insufficient to develop phylogeny. To resolve phylogeny and establish trait-allele associations, we interrogated 75 M. bovis and 61 M. tuberculosis genomes for single nucleotide polymorphisms (SNPs), using iPLEX MassArray (Sequenom Inc., CA) technology. We indexed nucleotide variations in 306 genic and 44 intergenic loci among isolates derived from outbreaks in the United States from 1991 to 2010 and isolated from a variety of mammalian hosts. Two hundred six variant SNPs classified the 136 isolates and 4 previously sequenced strains (AF2122/97, BCG Pasteur, H37Rv, and CDC1551) into 5 major "SNP cluster groups." M. bovis isolates clustered into three major lineages based on 118 variant SNPs, while 84 SNPs differentiated the M. bovis BCG lineage from the virulent isolates. Forty-nine of the 51 human M. tuberculosis isolates were identical at all 350 loci studied. Thus, SNP-based analyses resolved the genotypic differences within M. bovis strains and differentiated these strains from M. tuberculosis strains representing diversity in time and space, providing population genetic frameworks that may aid in identifying factors responsible for the wide host range and disease phenotypes of M. bovis.

Mycobacterium bovis: A Model Pathogen at the Interface of Livestock, Wildlife, and Humans

Complex and dynamic interactions involving domestic animals, wildlife, and humans create environments favorable to the emergence of new diseases, or reemergence of diseases in new host species. Today, reservoirs of Mycobacterium bovis, the causative agent of tuberculosis in animals, and sometimes humans, exist in a range of countries and wild animal populations. Free-ranging populations of white-tailed deer in the US, brushtail possum in New Zealand, badger in the Republic of Ireland and the United Kingdom, and wild boar in Spain exemplify established reservoirs of M. bovis. Establishment of these reservoirs is the result of factors such as spillover from livestock, translocation of wildlife, supplemental feeding of wildlife, and wildlife population densities beyond normal habitat carrying capacities. As many countries attempt to eradicate M. bovis from livestock, efforts are impeded by spillback from wildlife reservoirs. It will not be possible to eradicate this important zoonosis from livestock unless transmission between wildlife and domestic animals is halted. Such an endeavor will require a collaborative effort between agricultural, wildlife, environmental, and political interests.

Live-trapping and bovine tuberculosis testing of free-ranging white-tailed deer for targeted removal

Context Significant efforts have been made in Michigan, USA, to reduce the prevalence of bovine tuberculosis (TB) in free-ranging white-tailed deer (Odocoileus virginianus) over the past 15 years. Since 2002, however, prevalence has changed little, prompting the need for new control strategies. Aims In January–March of 2007 and 2008, a trap–test–cull project was conducted on an 11 000-ha property in the north-eastern Lower Peninsula of Michigan. The objectives were to assess the feasibility of live-trapping and testing white-tailed deer for TB as a means for targeted removal and estimate the cost of this effort. Methods Live-trapped deer were ear-tagged and a blood sample was drawn for use with the CervidTB STAT-PAK (commonly called Rapid Test) for TB diagnosis in the field. Deer testing negative were released, whereas deer testing positive were euthanised to confirm blood-test results via bacterial culture. Key results In all, 762 (741 with known sex and age) individual deer were captured and tested for TB. Adults comprised 59% (437 of 741) of the captures. Eight (1.8%) adults were positive on the blood test; six of eight (1.4% of adults) were confirmed TB positive via bacterial culture. Estimated TB prevalence in the present study was 2.5% (adjusted for Rapid Test sensitivity of 56%), being lower than what would be expected on the basis of routine hunter-harvest surveillance for this site which has yielded prevalence rates from 3.4% to 4.8%. Results demonstrated the ability to trap and test a substantial number of deer given high deer densities (16–20 deer per km2), availability of traps and abundant workers. The 2-year project cost a total of ~US$228 000, or US$38 000 per culture-positive animal. Conclusions Because of the cost and effort involved, a project such as the present one applied to Michigan’s larger TB-management area (148 018 ha) is not feasible. Implications If the efficiency and effectiveness of a trap–test–cull project could be improved by vaccinating test-negative animals, should a vaccine be approved for use in free-ranging white-tailed deer, a trap–test–cull project applied on a scale similar to the present study may prove beneficial by possibly reducing disease transmission, in addition to removing TB-positive animals.

Diseases of red deer introduced to Patagonia and implications for native ungulates

The red deer (Cervus elaphus) invasion in Patagonia has been continuing for nearly a century, with occurrence in all habitats between 34°S and 55°S. Their distribution, movement patterns and locally high densities raise concerns over their potential epidemiological role in maintaining disease reservoirs or transmitting diseases such as foot-and-mouth disease or tuberculosis, with potential severe health and economical impacts at the interface of humans, livestock or native wildlife. Among adult females collected by rifle and radio-collared deer that died naturally, no ectoparasites were found (n = 73). Fasciola hepatica was encountered in three surveys at prevalences ranging from 9% to 50% (n = 108). Taenia ovis krabbei was identified, and Cysticerus tenuicollis was found at a prevalence of 8% (n = 12). Ostertagia sp., Bunostomum sp. and Dictyocaulus sp. had a prevalence of 75%, 25% and 13% (n = 9), respectively. Several gastrointestinal parasites reported at low prevalence in endangered Patagonian huemul (Hippocamelus bisulcus) are common in livestock and considered commensals in domestic ruminants. Sympatry of huemul with livestock is commonplace, whereas with red deer it occurs in <2% of known populations, in which case there were 1.2 red deer, but 25.2 livestock per huemul, making livestock the determining epidemiological factor regarding disease transmission or reservoir. As red deer have been coexisting with livestock for >100 years in Argentina, both red deer and livestock play epidemiological roles for shared diseases. Research, conservation and management efforts should be directed towards livestock herd health programs or restriction of free livestock movements, particularly if diseases are shown to have an impact on recruitment of endangered natives. Livestock are routinely researched and inspected at slaughter and thus provide a proxy for diseases afflicting co-existing ungulates. Testing for antibodies to foot-and-mouth disease viral antigen was negative (n = 41). A tentative diagnosis of mycobacterial infection was based on typical visceral lesions. Antler damage occurred on 73% of shed antlers, with 36% having major breaks of tines and main beams, possibly indicating mineral imbalances. One male had both antlers, including pedicles with portions of frontal, parietal and occipital bones, broken off the skull, causing his death. The prevalence of 0.9% of campylognathia (n = 776) indicates that the disease is unlikely to be inheritable, because the founding stock of 20 animals would have had a prevalence of at least 5%. Among deer, handedness of scoliosis related significantly to the hemisphere where specimens originated (P < 0.001, n = 131). Coriolis forces are known to affect early stages of development, such as the innervation pattern of the mammalian vestibular system, or the plane of bilateral symmetry. It is, therefore, conceivable that the networks processing these environmental cues, or the mechanisms responsible for compensation, are malfunctioning and thus result in a preponderance of facial scoliosis in accordance to the earth’s rotation.

Descriptive epidemiology of bovine tuberculosis in michigan (1975-2010): lessons learned

Despite ongoing eradication efforts, bovine tuberculosis (BTB) remains a challenge in Michigan livestock and wildlife. The objectives of this study were to (1) review the epidemiology of BTB in Michigan cattle, privately owned cervids, and wildlife between 1975 and 2010 and (2) identify important lessons learned from the review and eradication strategies. BTB information was accessed from the Michigan BTB Eradication Project agencies. Cattle herds (49), privately owned deer herds (4), and wild white-tailed deer (668) were found infected with BTB during the review period. BTB has occurred primarily in counties located at the northern portion of the state's Lower Peninsula. Currently used BTB eradication strategies have successfully controlled BTB spread. However additional changes in BTB surveillance, prevention, and eradication strategies could improve eradication efforts.

Persistence of Mycobacterium bovis Bacillus Calmette-Guérin in white-tailed deer (Odocoileus virginianus) after oral or parenteral vaccination

Mycobacterium bovis is the cause of tuberculosis in cattle and a serious zoonotic pathogen, most commonly contracted through consumption of unpasteurized dairy products. To control this zoonosis, many countries have developed bovine tuberculosis eradication programmes. Although relatively successful, efforts are hindered in many regions by spillover from wildlife reservoirs of M. bovis to cattle. Such is the case in the United States where spillover of M. bovis from free-ranging white-tailed deer to cattle occurs. One approach to control such inter-species transmission is vaccination of wildlife. The live, attenuated human vaccine M. bovis Bacillus Calmette-Guérin (BCG) has been shown to reduce disease severity in white-tailed deer; however, vaccine persistence within tissues has also been noted. Consumption of venison containing BCG by hunters may present a public health concern as BCG exposure, although unlikely to cause disease, could cause false positive tuberculin skin test results. To examine BCG persistence further, 42 white-tailed deer were vaccinated orally or subcutaneously (SC) with BCG Danish. Three deer from each group were killed and examined at periods ranging from 2 weeks to 11 months after vaccination. BCG was recovered from orally vaccinated deer as late as 3 months after vaccination, while BCG persisted in SC vaccinated deer for as long as 9 months. At no time was BCG isolated from meat; however, prolonged persistence was seen in lymphoid organs. Although vaccine persistence was noted, especially in SC vaccinated deer, the distribution of culture-positive tissues makes human exposure through consumption unlikely.

Vaccination with Mycobacterium bovis BCG strains Danish and Pasteur in white-tailed deer (Odocoileus virginianus) experimentally challenged with Mycobacterium bovis

Wildlife reservoirs of Mycobacterium bovis represent serious obstacles to the eradication of tuberculosis in domestic livestock and the cause for many faltering bovine tuberculosis eradication programmes. One approach in dealing with wildlife reservoirs of disease is to interrupt inter-species and intraspecies transmission through vaccination of deer or cattle. To evaluate the efficacy of BCG vaccination in white-tailed deer, 35 deer were assigned to one of three groups; one s.c. dose of 10(7) CFU of M. bovis BCG Pasteur (n = 12); 1 s.c. dose of 10(7) CFU of M. bovis BCG Danish (n = 11); or unvaccinated deer (n = 12). After vaccination, deer were inoculated intratonsilarly with virulent M. bovis. Lesion severity scores of the medial retropharyngeal lymph node, as well as all lymph nodes combined, were reduced in vaccinated deer compared to unvaccinated deer. BCG Danish vaccinated deer had no late stage granulomas characterized by coalescent caseonecrotic granulomas containing numerous acid-fast bacilli compared to BCG Pasteur vaccinated or unvaccinated deer where such lesions were present. Both BCG strains were isolated as late as 250 days after vaccination from deer that were vaccinated but not challenged. In white-tailed deer, BCG provides protection against challenge with virulent M. bovis. Issues related to vaccine persistence, safety and shedding remain to be further investigated.

Tuberculosis: a reemerging disease at the interface of domestic animals and wildlife

Complex interactions involving humans, domestic animals, and wildlife create environments favorable to the emergence of new diseases. Today, reservoirs of Mycobacterium bovis, the causative agent of tuberculosis in animals and a serious zoonosis, exist in wildlife. The presence of these wildlife reservoirs is the direct result of spillover from domestic livestock in combination with anthropogenic factors such as translocation of wildlife, supplemental feeding of wildlife and wildlife populations reaching densities beyond normal habitat carrying capacities. As many countries attempt to eradicate M. bovis from domestic livestock, efforts are impeded by spillback from wildlife reservoirs. It will not be possible to eradicate M. bovis from livestock until transmission between wildlife and domestic animals is halted. Such an endeavor will require a collaborative effort between agricultural, wildlife, environmental and political interests.

Vaccination of white-tailed deer (Odocoileus virginianus) with Mycobacterium bovis bacillus Calmette Guerín

Wildlife reservoirs of Mycobacterium bovis represent serious obstacles to the eradication of tuberculosis in domestic livestock. In Michigan, USA tuberculous white-tailed deer transmit M. bovis to cattle. One approach in dealing with this wildlife reservoir is to vaccinate deer in order to interrupt the cycle of deer to deer and deer to cattle transmission. Thirty-one white-tailed deer were assigned to one of three groups; 2 SC doses of 10(7)CFU of M. bovis BCG (n=11); 1 SC dose of 10(7)CFU of M. bovis BCG (n=10); or unvaccinated deer (n=10). After vaccination, deer were inoculated intratonsilarly with 300 CFU of virulent M. bovis. Gross lesion severity scores of the medial retropharyngeal lymph node were significantly reduced in deer receiving 2 doses of BCG compared to unvaccinated deer. Vaccinated deer had fewer lymph node granulomas than unvaccinated deer, and most notably, fewer late stage granulomas characterized by coalescent caseonecrotic granulomas containing numerous acid-fast bacilli. BCG was isolated from 7/21 vaccinated deer as long as 249 days after vaccination. In one case BCG was transmitted from a vaccinated deer to an unvaccinated deer. In white-tailed deer BCG provides measurable protection against challenge with virulent M. bovis. However, persistence of vaccine within tissues as well as shedding of BCG from vaccinates remain areas for further investigation.

Correlation of cytokine gene expression with pathology in white-tailed deer (Odocoileus virginianus) infected with Mycobacterium bovis

Mycobacterium bovis-infected white-tailed deer (WTD) in northeast Michigan are a reservoir of mycobacteria that pose a threat to both domestic animals and humans. Relatively little work has been done to characterize the immune response of WTD to M. bovis infection; however, an understanding of the immune response to infection and pathogenesis may be critical to the development of an effective vaccine. Immunological responses to infection were characterized by monitoring cytokine gene expression in M. bovis-infected and uninfected deer. Peripheral blood leukocytes (PBL) from infected WTD expressed more gamma interferon (IFN-gamma), interleukin-12p40 (IL-12p40), granulocyte-monocyte colony-stimulating factor, and IL-4 mRNA than did PBL from uninfected deer; however, differences were not detected in expression of IL-10 and transforming growth factor-beta mRNA. Infected animals could be divided into two groups based on pathology. Lesions were confined primarily to the lymph nodes of the head in animals with less severe pathology. Animals with more severe pathology had lesions in the lung and associated lymph nodes as well as the lymph nodes of the head. More robust IFN-gamma mRNA expression correlated with pathology early in infection. These findings indicate that IFN-gamma expression likely plays a role in both protection and pathogenesis.

Advances in bovine tuberculosis diagnosis and pathogenesis: What policy makers need to know

The mainstay of tuberculosis diagnosis in cattle and deer has been the tuberculin skin test. Recent advances have allowed the incorporation of blood based assays to the diagnostic arsenal for both cattle and deer. Use of defined and specific antigens has allowed for improved specificity of cell mediated assays in both cattle and deer and advances in antibody tests for tuberculosis have potential for use in free-ranging and captive cervid populations. Combined use of blood-based assays with skin testing will require further understanding of the effect of skin testing on the accuracy of blood based assays. Models of experimental infection of cattle have allowed for increased understanding of natural disease pathogenesis. Differences likely exist; however, between cattle and deer in both disease distribution and primary route of inoculation in naturally infected animals.

Managing the wildlife reservoir of Mycobacterium bovis: The Michigan, USA, experience

Historical, social and economic factors combined to provide a focus where bovine tuberculosis has become established in free-ranging wildlife in northeastern lower Michigan. White-tailed deer, the primary reservoir and maintenance host of tuberculosis, are highly valued by the public, and particularly hunters, for cultural and economic reasons. Since 1995, significant progress has been made in defining and reducing the reservoir of tuberculosis in deer. As yet, no other wildlife species has been shown to play an epidemiologically important role in the disease cycle. The importance of deer and deer hunting to Michigan has uniquely shaped tuberculosis control policies, and poses ongoing challenges as wildlife managers strive to maintain momentum for broad control strategies, and develop focused strategies that are publicly acceptable. Even if momentum and funding can be maintained, tuberculosis will likely continue to be present for a decade or longer. Thus, cattle producers waiting for tuberculosis to be eradicated from wildlife to eliminate risks to their herds and markets face disappointment for the foreseeable future. Such unrealistic expectations also place Michigan's federal tuberculosis accreditation status at perpetual risk. Accredited free status is unlikely to be regained without accompanying changes in cattle management. In Michigan, management of tuberculosis has clearly demonstrated that social issues and public approval are likely to be the critical limiting factors in control.

The role of wild animal populations in the epidemiology of tuberculosis in domestic animals: How to assess the risk

Tuberculosis is present in wild animal populations in North America, Europe, Africa and New Zealand. Some wild animal populations are a source of infection for domestic livestock and humans. An understanding of the potential of each wild animal population as a reservoir of infection for domestic animals is reached by determining the nature of the disease in each wild animal species, the routes of infection for domestic species and the risk of domestic animals encountering an infectious dose. The mere presence of infection in a wild animal population does not of itself provide evidence of a significant wildlife reservoir. Although at times counterintuitive, wildlife populations with high disease prevalence may not necessarily have a role in the epidemiology of disease in domestic livestock. The key concepts used in deciding whether an infected wild animal population is involved in the epidemiology of tuberculosis in domestic livestock is illustrated by reference to six well-researched cases: the feral pig (Suis scrofa) and feral Asian water buffalo (Bubalus bubalis) in Australia, white tailed deer (Odocoileus virginianus) in Michigan, and the brushtail possum (Trichosurus vulpecula) and other species, such as the ferret (Mustela furo), in New Zealand. A detailed analysis of Mycobacterium bovis infection in the Eurasian badger (Meles meles) in Ireland and their role as a reservoir of infection for cattle is also presented.

Advances in understanding disease epidemiology and implications for control and eradication of tuberculosis in livestock: the experience from New Zealand

A deteriorating tuberculosis problem in cattle and deer in New Zealand has been halted and then reversed over the last decade. Mycobacterium bovis infection in both wild and domestic animal populations has been controlled. This has been achieved by applying a multi-faceted science-based programme. Key features of this have been a comprehensive understanding of the epidemiology of tuberculosis in animals, confidence in sampling wild animal populations, effective application of diagnostic tests in cattle and deer, and the ability to map M. bovis genotypes.

Investigation of the transmission of Mycobacterium bovis from deer to cattle through indirect contact

OBJECTIVE

To investigate the infection of calves with Mycobacterium bovis through oral exposure and transmission of M. bovis from experimentally infected white-tailed deer to uninfected cattle through indirect contact.

ANIMALS

24 11-month-old, white-tailed deer and 28 6-month-old, crossbred calves.

PROCEDURE

In the oral exposure experiment, doses of 4.3 x 10(6) CFUs (high dose) or 5 x 10(3) CFUs (low dose) of M. bovis were each administered orally to 4 calves; as positive controls, 2 calves received M. bovis (1.7 x 10(5) CFUs) via tonsillar instillation. Calves were euthanatized and examined 133 days after exposure. Deer-to-cattle transmission was assessed in 2 phases (involving 9 uninfected calves and 12 deer each); deer were inoculated with 4 x 10(5) CFUs (phase I) or 7 x 10(5) CFUs (phase II) of M. Bovis. Calves and deer exchanged pens (phase I; 90 days' duration) or calves received uneaten feed from deer pens (phase II; 140 days' duration) daily. At completion, animals were euthanatized and tissues were collected for bacteriologic culture and histologic examination.

RESULTS

In the low- and high-dose groups, 3 of 4 calves and 1 of 4 calves developed tuberculosis, respectively. In phases I and II, 9 of 9 calves and 4 of 9 calves developed tuberculosis, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that experimentally infected deer can transmit M. bovis to cattle through sharing of feed. In areas where tuberculosis is endemic in free-ranging white-tailed deer, management practices to prevent access of wildlife to feed intended for livestock should be implemented.

Milk containing Mycobacterium bovis as a source of infection for white-tailed deer fawns (Odocoileus virginianus)

SETTING

White-tailed deer represent the first wildlife reservoir of Mycobacterium bovis in the United States. The behavior of does with nursing fawns provides several potential mechanisms for disease transmission. Little information exists concerning transmission between doe and fawn, specifically transmammary transmission.

OBJECTIVE

Determine if fawns can become infected by ingestion of milk replacer containing M. bovis, thus simulating transmission from doe to fawn through contaminated milk.

DESIGN

Seventeen, 21-day-old white-tailed deer fawns were inoculated orally with 2 x 10(8) CFU (high dose, n=5), 2.5 x 10(5) to 2.5 x 10(6) CFU (medium dose, n=5), and 1 x 10(4) CFU (low dose, n=5) of M. bovis in milk replacer. Dosages were divided equally and fed daily over a 5-day period. Positive control fawns (n=2) received 1 x 10(5) CFU of M. bovis instilled in the tonsillar crypts. Fawns were euthanized and examined 35-115 days after inoculation and various tissues collected for bacteriologic and microscopic analysis.

RESULTS

All fawns in the tonsillar, high oral and medium oral dose groups developed generalized tuberculosis involving numerous organs and tissues by 35-84 days after inoculation. Three of five fawns in the low-dose oral group had tuberculous lesions in the mandibular lymph node, and one of five had lesions in the medial retropharyngeal lymph node when examined 115 days after inoculation.

CONCLUSION

White-tailed deer fawns can become infected through oral exposure to M. bovis. Therefore, the potential exists for fawns to acquire M. bovis while nursing tuberculous does.

Epidemiology of Mycobacterium bovis in free-ranging white-tailed deer, Michigan, USA, 1995-2000

An endemic area of bovine tuberculosis (TB) (Mycobacterium bovis) currently affecting wild white-tailed deer (Odocoileus virginianus) in northern lower Michigan, USA, constitutes the first self-sustaining outbreak of the infection in free-ranging North American cervids. Given this precedent, epidemiologic insights gained from the outbreak afford the opportunity to guide not only current surveillance and intervention but also control efforts for future outbreaks involving wildlife reservoirs. Our specific objectives were to evaluate retrospective data from field surveillance conducted from 1995 to 2000 to determine apparent prevalence, trends in apparent prevalence, and the effects of various factors on the odds of being M. bovis positive. Data were gathered from post-mortem examinations of 62,560 wild deer collected from all 83 Michigan counties. Records of survey method, sex, age, geographic area and infection status as determined by mycobacterial culture were subjected to trend analysis and multivariable logistic regression. Apparent prevalence for the period was 0.54% (336/62,560) statewide. Prevalence varied widely with geographic area, but significantly decreased since 1995 in the core area of the outbreak-which coincided with implementation of control strategies. Significant risk factors were geographic area, sex, age, and the sex-by-age interaction. The survey method by which deer were obtained for testing was not a predictor of infection. Our results to date suggest an outbreak characterized by broad areas of very low prevalence surrounding focal areas where prevalence is sometimes orders-of-magnitude higher (e.g., deer originating from the core area were up to 147 times more likely to be TB positive than deer from other areas). Our results also identify older male deer as most likely to be M. bovis positive (OR=11.3, 95% CI 3.2, 40.3 for bucks > or =5 years vs. does < or =1.5 years)-an observation consistent with the biology and behavior of the species. Synthesizing these results with those of other ongoing investigations, we hypothesize a two-stage model of disease transmission where TB is maintained at very low prevalence in matriarchal groups, with primary dissemination of the disease attributable to the dispersal and movements of bucks (as well as to the large aggregations of animals created by human activities).

Lesion development in white-tailed deer (Odocoileus virginianus) experimentally infected with Mycobacterium bovis

The recent discovery of tuberculosis in free-living white-tailed deer in northeastern Michigan underscores the need for increased understanding of the pathogenesis of tuberculosis in wildlife species. To investigate lesion development in white-tailed deer, 32 deer were experimentally infected by intratonsilar instillation of 300 colony-forming units of Mycobacterium bovis. Three deer each were euthanatized and examined at days 15, 28, 42, and 56 after inoculation, and five deer each were euthanatized and examined at days 89, 180, 262, and 328 after inoculation. Microscopic lesions first were seen in the medial retropharyngeal lymph node and lung 28 and 42 days after inoculation, respectively. Lung lesions were present in 12 (38%) of 32 deer, involving 23 lung lobes. Left caudal and right middle and caudal lobes were involved in 17 (74%) of the 23 affected lung lobes. Lesions in the medial retropharyngeal lymph node first appeared as granulomas composed of aggregates of macrophages and Langhans-type giant cells. Some early granulomas contained centrally located neutrophils. As granulomas developed, neutrophils were replaced with a central zone of caseous necrosis that first showed signs of mineralization 42 days after inoculation. Granulomas increased in size as the zone of caseous necrosis expanded. Peripheral fibrosis, first seen at 56 days after inoculation, progressed to only a thin fibrous capsule by 328 days after inoculation. By the termination of the study, the central necrotic core of the granuloma contained abundant liquefied necrotic material and grossly resembled an abscess. Although tuberculous lesions in white-tailed deer follow a developmental pattern similar to that in cattle, fibrosis is less pronounced and the advanced lesions may liquefy, a change seldom reported in cattle. An understanding of lesion development will aid in the identification of the spectrum of disease that may be seen in this important wildlife reservoir of tuberculosis.