Failure to identify non-bovine reservoirs of Mycobacterium bovis in a region with a history of infected dairy-cattle herds

Mongoose (Herpestes auropunctatus) May Not Be Reservoir Hosts for Mycobacterium bovis in Fiji Despite High Population Density and Direct Contact with Cattle

The presence of a wildlife reservoir for Mycobacterium bovis complicates the eradication of bovine tuberculosis (BTB) from domestic cattle populations. For the BTB eradication program in Fiji, there is concern about the small Indian mongoose (Herpestes auropunctatus), which is overabundant and in direct contact with cattle. Consequently, a survey of mongooses trapped on three BTB affected dairy farms led to necropsy of 85 mongooses during January–February 2017. Thirty (35%) mongooses had gross pathological changes including possible granulomas detected at necropsy, and tissues from these animals were taken for histopathological examination. Granulomatous lesions were present in 53% of animals examined histopathologically but acid-fast bacilli were not observed and the majority of lesions in lung and kidney were associated with the nematodes Pulmostrongylus herpestis and Capillaria sp., respectively. Nevertheless, assuming test sensitivity of 35% for the current study, from this sample of 85 mongooses it can be concluded with 95% confidence that if present in the mongoose population susceptible to trapping, M. bovis prevalence was ≤10%. The prevalence of intercurrent lesions raised concerns about gross pathology as a screening test for M. bovis infection in mongooses in Fiji, and therefore pathogen detection methods such as bacterial culture and direct tissue PCR are recommended for future surveys. These are needed to completely rule out the mongoose as a reservoir host for M. bovis in Fiji.

A review of risk factors for bovine tuberculosis infection in cattle in the UK and Ireland

Bovine tuberculosis (bTB) is an important disease of cattle caused by infection withMycobacterium bovis, a pathogen that may be extremely difficult to eradicate in the presence of a true wildlife reservoir. Our objective was to identify and review relevant literature and provide a succinct summary of current knowledge of risk factors for transmission of infection of cattle. Search strings were developed to identify publications from electronic databases to February 2015. Abstracts of 4255 papers identified were reviewed by three reviewers to determine whether the entire article was likely to contain relevant information. Risk factors could be broadly grouped as follows: animal (including nutrition and genetics), herd (including bTB and testing history), environment, wildlife and social factors. Many risk factors are inter-related and study designs often do not enable differentiation between cause and consequence of infection. Despite differences in study design and location, some risk factors are consistently identified, e.g. herd size, bTB history, presence of infected wildlife, whereas the evidence for others is less consistent and coherent, e.g. nutrition, local cattle movements. We have identified knowledge gaps where further research may result in an improved understanding of bTB transmission dynamics. The application of targeted, multifactorial disease control regimens that address a range of risk factors simultaneously is likely to be a key to effective, evidence-informed control strategies.

Environmental Presence of Mycobacterium tuberculosis Complex in Aggregation Points at the Wildlife/Livestock Interface

The members of the Mycobacterium tuberculosis complex (MTC) cause tuberculosis (TB). Infection is transmitted within and between livestock and wildlife populations, thus hampering TB control. Indirect transmission might be facilitated if MTC bacteria persist in the environment long enough to represent a risk of exposure to different species sharing the same habitat. We have, for the first time, addressed the relationship between environmental MTC persistence and the use of water resources in two TB endemic areas in southern Spain with the objective of identifying the presence of environmental MTC and its driving factors at ungulates' water aggregation points. Camera-trap monitoring and MTC diagnosis (using a new MTC complex-specific PCR technique) were carried out at watering sites. Overall, 55.8% of the water points tested positive for MTC in mud samples on the shore, while 8.9% of them were positive in the case of water samples. A higher percentage of MTC-positive samples was found at those waterholes where cachectic animals were identified using camera-trap monitoring, and at the smallest waterholes. Our results help to understand the role of indirect routes of cross-species TB transmission and highlight the importance of certain environmental features in maintaining infection in multihost systems. This will help to better target actions and implement control strategies for TB at the wildlife/livestock interface.

Respiratory tract infection caused by Mycobacterium bovis in a black swan (Cygnus atratus)

A 3-year-old male black swan (Cygnus atratus), belonging to a private collection, died suddenly and was subjected to post mortem examination. At necropsy, caseous exudate was observed in the lungs and air sacs; granulomatous lesions characterized by epithelioid macrophages and abundant mycobacteria were observed microscopically. Avian tuberculosis associated with Mycobacterium bovis was confirmed by bacteriologic isolation, biochemical tests and molecular methods. The organism was identified as spoligotype SB0140, which is frequently found in cattle and people in North America. In this case, interspecies transmission could have been the source of infection because the swan cohabited with cattle.

Mycobacterium bovis in California dairies: a case series of 2002-2013 outbreaks

From 2002 to 2013, bovine tuberculosis (bTB) caused by Mycobacterium bovis (M. bovis) has been detected on numerous dairies in California. In total, twelve herds had bTB detected and are included in the case series which describes these recent outbreaks and discusses potential pathways of introduction. Epidemiological investigations to determine the initial source of bTB in each herd included obtaining data on likely pathways of pathogen introduction. Pathways included purchasing cattle, use of heifer-raising operations, commingling of cattle at greater risk of exposure to infected cattle with cattle destined for California dairies, contact with infected wildlife, exposure to humans with bTB infections, community and neighboring herds and others. Epidemiologic and molecular typing data confirmed the source of infection in 3 herds and probable sources of infection in 2 herds. In the 7 remaining herds described in this case series an epidemiologic link to a source could not be determined and molecular typing results did not associate M. bovis isolates acquired from these herds with another specific U.S. herd or U.S.-born animal. Preventing new introductions of M. bovis onto California dairies will require rigorous epidemiologic investigation of all the potential pathways of introduction discussed here. The root cause(s) of bTB on California dairies is certainly multifactorial with complex interactions of herd management practices, importation of cattle at greater risk of exposure to infected cattle, and the potential of human M. bovis exposure. The extensive use of molecular typing has improved epidemiologists' ability to narrow the scope of potential sources.

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.

An Effort to Isolate Mycobacterium bovis from Environmental Substrates during Investigations of Bovine Tuberculosis Transmission Sites (Cattle Farms and Wildlife Areas) in Michigan, USA

Deer movements on cattle farms, wildlife feeding, and livestock management practices in Michigan are thought to create opportunities for indirect transmission of Mycobacterium bovis via environmental substrates. To confirm the presence of viable M. bovis in the environment, substrates were collected from 13 farms with culture-confirmed M. bovis in cattle and 5 sites with high prevalence of M. bovis in free-ranging deer. None of the samples processed for mycobacterial culture were positive for M. bovis. Agent, host, and landscape-level factors decrease the probability of detecting M. bovis in the environment using conventional mycobacterial culture. Molecular techniques that increase the probability of M. bovis detection in environmental substrates should be applied to known sites of M. bovis transmission in Michigan. In the interim, epidemiological investigations informed by experimental studies will be most effective in characterizing M. bovis persistence in the environment and its role in the indirect interspecies transmission of M. bovis.

Epidemiology of bovine tuberculosis in Mexico, bordering the United States, at establishment of controlling strategies

A case-control study was carried out for determining epidemiological patterns at the beginning of the Mexican campaign against bovine tuberculosis (BTB) in the State of Tamaulipas, Mexico, bordering the United States of America. From January 1995 to March 1998, 599 direct tissue smears of cattle from routine slaughterhouse inspection were analyzed for the presence of Mycobacterium bovis acid-fastness with Ziehl-Neelsen stain. BTB status was associated with year of diagnosis, age, breed, geographical origin of cattle, and type of slaughterhouse using the odds ratio (OR) (95% confidence level). The prevalence at slaughterhouse surveillance was 15.36%, which was considerably higher in 1995 (41.38%, OR=5.78, P<0.0001), in comparison with 8.09%, 14.42%, and 10.14% for the years 1996, 1997, and 1998, respectively. BTB was associated with cattle from the State of Tamaulipas (19.73%, OR= 4.438, P=0.01), adult cattle (19.13%, OR=2.19, P<0.0001), Bos taurus (22.54%, OR=2.135, P<0.0001) and B. taurus x B. indicus cross bred animals (29.31%, 2.769, P<0.0001), and cattle slaughtered at federal inspected abattoir (17.58%, OR=1.23, P<0.0001).

Factors influencing farmers' concerns regarding bovine tuberculosis in wildlife and livestock around Riding Mountain National Park

Despite intensive efforts over the last century to eradicate bovine tuberculosis (TB) in North America, several hotspots of infected wildlife and livestock remain, raising concerns that the disease will never be eradicated. The stress and frustration for a farmer caused by having a herd test positive for TB or living in an infected region can be substantial. The goal of this study was to investigate the concerns of farmers around Riding Mountain National Park (RMNP) regarding the presence of TB in wildlife and livestock and conduct an exploratory analysis of causal factors. Data were collected from 786 farmers within 50 km of RMNP using a mail-back questionnaire. Overall, farmers indicated a high level of concern toward diseases in both wildlife and cattle relative to other concerns. The spatial variables that had the greatest influence on TB concern were both the distance of farms to the RMNP boundary and distance of farms to previous cases of TB. The most important aspatial factor associated with high TB concern was the frequency with which farmers observed elk on their land. These results underscore the important differences between 'objective' measures of risk, such as epidemiological estimates of disease prevalence, and subjective measures of disease concern, such as risk perception and acceptability of management actions. Written responses suggest that concerns regarding disease may affect how farmers view wildlife on their land and their relationship with neighbouring protected areas. Management activities that reduce the frequency of elk interactions with farms, but also recognize the complex relationship that farmers have with wildlife and protected areas, will be most effective in mitigating farmer concern regarding this important problem.

Experimental inoculation of pigeons (Columba livia) with Mycobacterium bovis

The purpose of this pilot study was to determine if pigeons (Columba livia) are susceptible to infection with Mycobacterium bovis by either oral or intratracheal inoculation and to assess their possible role in the lateral transmission of bovine tuberculosis. Six pigeons were orally inoculated with 1.3 x 10(5) colony-forming units of M. bovis, six pigeons were intratracheally inoculated with the same dose, and six pigeons served as noninoculated controls. The study continued for 90 days postinoculation (PI), with groups of birds necropsied at 30-day intervals, and fecal samples and tissues were collected for mycobacterial culture. Two pigeons, one intratracheally inoculated and one orally inoculated, shed M. bovis in their feces at 1 day PI, and one intratracheally inoculated bird shed M. bovis in its feces 60 days PI. Whereas no illness or weight loss was present during the course of the study, 2 of 12 inoculated birds exhibited microscopic lesions of mycobacteriosis, and the organism was isolated from tissues of three inoculated birds. Pigeons are susceptible to infection with M. bovis after high dose inoculation and can shed the organism in their feces for up to 60 days PI; intratracheally inoculated birds appear more likely to become active fecal shedders of M. bovis. Although these were high dose inoculations under experimental conditions, pigeons may potentially play a role in the lateral transmission of bovine tuberculosis between infected and uninfected mammalian hosts.

The transmission of Mycobacterium bovis infection to cattle

The prevalence of Mycobacterium bovis infection in cattle is increasing rapidly in some countries, including the UK and Ireland. The organism infects a wide range of mammalian hosts, and eradication of the disease is difficult if there is an extensive reservoir in the wildlife population. Existing evidence suggests that wildlife vectors include the European badger in the UK and Ireland, the brush-tailed possum and ferret in New Zealand and ungulates in some other countries. Cattle grazing field boundaries or short swards are at particularly high risk, since the chance of contact with the intermediate host or their excreta is increased. There is evidence that the transmission of the disease between cattle following movement accounts for 10-15% of outbreaks in the British Isles and that transmission can occur across farm boundaries. The prevalence the prevalence of single reactors in herds suggested that within-herd transmission was not common. In herds with infected cattle, spreading slurry is a risk factor, which can be minimised by prolonged storage of the slurry, by spreading it on fields not used for grazing or by soil injection. M. bovis also survives in water and may enter the respiratory tract during drinking. It is concluded that M. bovis infection in cattle can be transmitted by a number of routes, some of which can be controlled by appropriate husbandry, but that circumstantial evidence suggests that the existence of a widespread intermediate host is the greatest contributor to infection in cattle.

Molecular fingerprinting confirms extensive cow-to-cow intra-herd transmission of a single Mycobacterium bovis strain

In this study we have characterized M. bovis isolates from a herd of cattle in Uvalde, Texas in which 52 of the 193 animals selected at random in 1994 from a herd of 331 were caudal fold skin-test positive. Thirty-two of 52 skin-test positive cattle had gross lesions at slaughter, and isolations of M. bovis were made from 29 animals. The herd was comprised of Red Devon cattle purchased between 1978 and 1980 (n = 26) and breeding bulls (n = 3) introduced at later times, and all were tuberculosis test negative at the time of purchase. Other animals were natural additions (offspring) of these cattle. One additional animal, a Holstein present on the ranch at the time of purchase in 1976, was retained to nurse orphaned and weak calves. Using several molecular fingerprinting techniques we have verified a clonal relationship among the M. bovis isolates consistent with infection originating with a single strain. The molecular fingerprint patterns demonstrate the stability of the profiles despite persistence and spread of the organism within the herd for two decades and confirms their use in epidemiological tracing.