Wildlife diseases that pose a risk to small ruminants and their farmers

Abstract

Infectious pathogens from wild animals have become increasingly important throughout the world in recent years, as they have had a substantial impact in livestock and human health. A large number of pathogens (61% of the 1415 currently identified human pathogens within 313 different genera) are zoonotic and can infect multiple animal species. Multi-host pathogens are predominant among animal and human emerging diseases. Multi-host pathogens (including all zoonotic agents, pathogens that can infect more than one taxonomic order and pathogens that can infect wildlife hosts) have a higher relative risk for emergence than species-specific pathogens. Of 800 zoonotic diseases currently identified, 619 (77%) are caused by pathogens that affect wildlife; of 125 emerging zoonotic diseases, 113 (90%) affect wildlife. Of the diseases that have emerged in the last few decades around 75% are of wildlife origin. Many factors influence changes in disease incidence, including economic, climatic and microbiological effects. Increasingly, close interaction of humans and livestock with wild animals has led to increased frequency of zoonotic infections. Forest clearance and movement of animals or animal products are factors, which pose significant risks of introducing disease into a new region. Changing climate affects disease incidence by changes in land use or animal production practices, as well as by movement or changes in distribution of animal reservoirs or insect vectors. Local increases in biting midges or mosquito numbers, changes in the distribution of known vector species and/or recruitment of novel vector species, have increased the risk of spread or introduction of diseases. Pathogen evolution may occur in response to changes of which humans are not aware. The evolution may be occurring in many hosts, currently poorly monitored. Microbial evolution may affect the extent to which established methods of diagnosis can detect infectious agents. Other endemic diseases may also change in incidence for largely unknown reasons. Increased information on prevalence in a wide range of hosts will increase our understanding of these reasons. Wildlife can play an important role in the epidemiology of small ruminant and human diseases, by representing a source of disease via various transmission routes. Recent studies in infections of wildlife in Europe have highlighted the impact on small ruminant health. In Greece, blood/organ samples were collected from 60 wild deer and 140 wild boars (2006-2011). Serum samples were tested for presence of antibodies against Toxoplasma gondii,Neospora caninum, Mycobacterium avium subsp. paratuberculosis, Chlamydophila, Salmonella and Trichinella spirallis, by using appropriate immunodiagnostic techniques. Tissue samples were examined for Mycobacterium bovis by using PCR. In serum samples from deer, antibodies against T. gondii, N. caninum and Chlamydophila were detected in 15%, 5% and 5% of samples, respectively. In serum samples from wild boars, antibodies against Salmonella, T. gondii and T. spirallis were detected in 15%, 5% and 5% of samples, respectively. No M. bovis was found in tissue samples. In Spain, Bluetongue virus, Brucella spp., Coxiella bumetii and M. avium were detected in many wild cervid species. Spanish wild boars have been found to be greatly exposed to Salmonella spp., an important small ruminant intestinal pathogen. In Austria, Spain and Poland, Anaplasma phagocytophilum has been detected in various cervids. Finally, in Poland and Spain, wild deer and wild boars were found to be exposed to T. gondii and N. caninum. The results indicate that wildlife may be carriers of several pathogens, which can be transmitted to domestic small ruminants and their farmers. It is noteworthy that samples from many European countries will be collected and tested to ensure a broader evaluation of the epidemiological role of wildlife. (C) 2012 Elsevier B.V. All rights reserved.