The epidemiology of Mycobacterium bovis infections in animals and man: A review

There are huge numbers of wild animals distributed throughout the world and the diversity of wildlife species is immense. Each landscape and habitat has a kaleidoscope of niches supporting an enormous variety of vertebrate and invertebrate species, and each species or taxon supports an even more impressive array of macro- and micro-parasites. Infectious pathogens that originate in wild animals have become increasingly important throughout the world in recent decades, as they have had substantial impacts on human health, agricultural production, wildlife-based economies and wildlife conservation. The emergence of these pathogens as significant health issues is associated with a range of causal factors, most of them linked to the sharp and exponential rise of global human activity. Among these causal factors are the burgeoning human population, the increased frequency and speed of local and international travel, the increase in human-assisted movement of animals and animal products, changing agricultural practices that favour the transfer of pathogens between wild and domestic animals, and a range of environmental changes that alter the distribution of wild hosts and vectors and thus facilitate the transmission of infectious agents. Two different patterns of transmission of pathogens from wild animals to humans are evident among these emerging zoonotic diseases. In one pattern, actual transmission of the pathogen to humans is a rare event but, once it has occurred, human-to-human transmission maintains the infection for some period of time or permanently. Some examples of pathogens with this pattern of transmission are human immunodeficiency virus/acquired immune deficiency syndrome, influenza A, Ebola virus and severe acute respiratory syndrome. In the second pattern, direct or vector-mediated animal-to-human transmission is the usual source of human infection. Wild animal populations are the principal reservoirs of the pathogen and human-to-human disease transmission is rare. Examples of pathogens with this pattern of transmission include rabies and other lyssaviruses, Nipah virus, West Nile virus, Hantavirus, and the agents of Lyme borreliosis, plague, tularemia, leptospirosis and ehrlichiosis. These zoonotic diseases from wild animal sources all have trends that are rising sharply upwards. In this paper, the authors discuss the causal factors associated with the emergence or re-emergence of these zoonoses, and highlight a selection to provide a composite view of their range, variety and origins. However, most of these diseases are covered in more detail in dedicated papers elsewhere in this Review.

/pdf/the-role-of-wildlife-in-emerging-and-re-emerging-zoonoses-3zvdkx4ima.pdf

The role of wildlife in emerging and re-emerging zoonoses

The long-standing conflict between livestock owners and animal health authorities on the one hand, and wildlife conservationists on the other, is largely based on differing attitudes to controlling diseases of livestock which are associated with wildlife. The authors have attempted to highlight the fact that these disease problems are frequently bi-directional at the wildlife/livestock interface. The different categories of diseases involved are presented. A new dimension being faced by veterinary regulatory authorities is the spectre of emerging sylvatic foci of diseases, such as bovine tuberculosis, bovine brucellosis and possibly rinderpest; these diseases threaten to undermine national and international eradication schemes, which have been implemented and executed with significant success, and at great cost. Conversely, wildlife-based ecotourism world-wide has expanded rapidly over the past decade and is the source of lacking foreign revenue for many developing countries. Traditional subsistence farming is still the largest source of much-needed protein on some continents and this, together with the growth and hunger of historically disadvantaged communities for land, is forcing enterprises and communities with markedly different objectives and land-use practices to operate effectively in close proximity. Some land-users rely exclusively on wildlife, others on livestock and/or agronomy, while yet others need to combine these activities. The net result may be an expansion or intensification of the interface between wildlife and domestic livestock, which will require innovative control strategies that permit differing types of wildlife/livestock interaction, and that do not threaten the land-use options of neighbours, or the ability of a country to market animals and animal products profitably.

Infectious animal diseases: the wildlife/livestock interface.

The United States is the world's largest wildlife importer, and imported wild animals represent a potential source of zoonotic pathogens. Using data on mammals imported during 2000-2005, we assessed their potential to host 27 selected risk zoonoses and created a risk assessment that could inform policy making for wildlife importation and zoonotic disease surveillance. A total of 246,772 mammals in 190 genera (68 families) were imported. The most widespread agents of risk zoonoses were rabies virus (in 78 genera of mammals), Bacillus anthracis (57), Mycobacterium tuberculosis complex (48), Echinococcus spp. (41), and Leptospira spp. (35). Genera capable of harboring the greatest number of risk zoonoses were Canis and Felis (14 each), Rattus (13), Equus (11), and Macaca and Lepus (10 each). These findings demonstrate the myriad opportunities for zoonotic pathogens to be imported and suggest that, to ensure public safety, immediate proactive changes are needed at multiple levels.

/pdf/population-mobility-globalization-and-antimicrobial-drug-1uywmj00t6.pdf

Population mobility, globalization, and antimicrobial drug resistance.

Mycobacterium bovis is emerging as an important pathogen of free-ranging wildlife in which it is a potential source of infection for domestic animals and a threat to valuable wildlife species. This review examines the procedures for the detection, diagnosis and management of M. bovis in wildlife populations. The ante-mortem detection of M. bovis infection in wildlife is difficult, due to the common occurrence of subclinical infections and the deficiencies of the currently available diagnostic tests. Serological tests are insensitive, while tests measuring cell-mediated immune responses show promise, but have not been sufficiently developed for routine use in most species. The diagnosis of M. bovis in free-ranging wildlife relies on post-mortem examination supported by histopathology and microbiology. A feature of M. bovis infections is the variation in the appearance and distribution of lesions in the different host species. Bacterial culture remains the gold standard for diagnosis of tuberculosis, while histopathology is limited by the frequent inability to distinguish lesions caused by M. bovis from those produced by other mycobacterial species. Deoxyribonucleic acid (DNA) fingerprinting and advanced typing techniques are increasingly being used to unravel the epidemiology of mycobacterial infections, including tuberculosis in free-ranging wildlife. An understanding of the epidemiology is essential if procedures are to be developed for the management of tuberculosis in wildlife. Few management options are currently available, especially for protected wildlife. Vaccination is the subject of much research, but further developments are required before it can be used to control tuberculosis in any animals, let alone in free-ranging wildlife.

https://web.oie.int/boutique/extrait/delisle.pdf

Tuberculosis in free-ranging wildlife: detection, diagnosis and management.

The Kafue lechwe population of Zambia numbers90,000 and is divided by the River Kafue into two virtually segregated populations. The south bank population is known to be infected with tuberculosis but the north bank is thought to be free. One hundred and twenty-five south bank lechwe were cropped at random and lesions of tuberculosis were found in45 (36%). Isolates from lung lesions were typed asMycobacterium tuberculosis var.bovis.

Pulmonary tuberculosis in free-living lechwe antelope in Zambia.

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Pulmonary tuberculosis in free-living lechwe antelope in Zambia.