Wildlife diseases that pose a risk to small ruminants and their farmers☆
Introduction
Diseases of wildlife are presented with a variety of clinical manifestations, in a wide range of animal species and with significant diversity in demographic and population characteristics. Infectious pathogens of wildlife origin have gain interest and are considered to be of increasing importance worldwide, mainly because of their role on livestock health and productivity, as well as their zoonotic potential.
Apart from being zoonotic, a large number of pathogens (61% of the 1415 identified human pathogens within 313 different genera) also infect multiple animal species (Taylor et al., 2001). In fact, these agents predominate among animal and human emerging diseases. For instance, 90% of emerging diseases in cattle are caused by multi-host infectious agents. All multi-host pathogens that include by definition all zoonotic agents, pathogens that infect more than one taxonomic order and pathogens that infect wildlife hosts have a higher relative risk for emergence than species-specific pathogens (Cleaveland et al., 2001). Furthermore, diseases, when expressed in free-ranging animals, can have a significant effect on wildlife ecologies. While the disturbance caused in the wildlife ecology and the consequences in domestic animal and human health can remain of limited importance for years. They can lead to sudden outbreaks, epizooties or even pandemic infections characterized by high morbidity and mortality (Wobeser, 1994).
Studies on zoonotic diseases revealed the importance of wildlife as hosts of zoonotic pathogens as 619 of the 800 zoonotic diseases currently identified are caused by pathogens that affect wildlife (77%). Moreover, 113 of the 125 emerging zoonotic diseases also affect wildlife (90%). Moreover, approximately 75% of all diseases, including zoonoses, which have emerged in the last few decades, are of wildlife origin (Jones et al., 2008).
In contrast to livestock where feeding, reproduction and movements depend on human activities and manipulations (Artois et al., 2006), disease in wild animals is strongly associated with environmental factors. Certain environmental and ecological parameters are constantly changing and could subsequently induce modifications in transmission of the pathogens. On the other hand, diseases can influence ecological factors, which are of major importance in the dynamics of wild populations altering their survival rate and fecundity (Wobeser, 2007). Changes in disease incidence result from economic and climate changes, as well as from microbiological alterations. Moreover, close interaction of humans and livestock with wild animals has led to an increased frequency of zoonotic and epizootic infections.
Appearance and spread of new diseases is partially attributed to modifications in ecosystems, either naturally occurring or resulting from human interventions (Williams et al., 2002). A well-documented association between introduction of a disease into a new previously unaffected region and ongoing forest clearances has been reported, while movement of animals or animal products have been identified as contributing factors, which pose significant risks. Natural climatic changes can increase host abundance and transmission of pathogens. The incidence of the disease is further affected by climatic changes, due to alterations in land use or altered livestock rearing practices and movement or changes in distribution of animal reservoirs or insect vectors. Naïve populations can be significantly affected by movement of pathogens within animal hosts. Interaction of wild and domestic species can result in serious outbreaks of disease in wildlife. Movement of pathogens has also been associated with the emergence of wildlife diseases in new areas. In the case of vector borne diseases, movement of vectors can be implicated in the appearance of diseases in wildlife reservoirs (Williams et al., 2002). 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.
Apart from their hosts, carriers and the reservoirs the pathogens are also subjected to severe changes, such as mutations and re-combinations than can give rise to new pathogens or modification of existing ones. Pathogen evolution may occur in response to changes of which man is not aware and remain unnoticed, especially those currently being poorly monitored. Furthermore, this evolution may affect the extent to which established methods of diagnosis can successfully identify presence of infectious agents. The increase in the incidence of endemic diseases in different areas is of various and largely unknown reasons. Gaining information on the prevalence of the diseases in a wide range of hosts will enhance our understanding on these reasons.
The study of the diseases in wildlife, due to their role in the epidemiology of small ruminant and human health problems, as a source of diseases via various transmission routes, will contribute to better recognize epidemiology, pathogenicity and host–pathogen interactions.
Section snippets
European wildlife health surveillance
Recent studies in infections of wildlife in Europe have highlighted an impact on small ruminants, as well as on their farmers.
Mycobacterium tuberculosis complex infection has been reported in wild ungulates in Spain, France, Slovakia and the Czech Republic. M. tuberculosis complex has been reported in wild boars, in red deer (Cervus elaphus), in fallow deer (Dama dama) and, less frequently, in roe deer (Capreolus capreolus) (Vicente et al., 2006, Martin et al., 2011). Individual cases have been
Concluding comments
Wildlife may be carriers of several pathogens, which can be transmitted to domestic ruminants, as well as to their farmers. There is a need to increase sampling and testing from other countries to ensure a broader evaluation of the epidemiological role of wildlife.
Conflict of interest
The author declares that he has no conflict of interest with the contents of this paper in any respect.
Acknowledgements
The research leading to these results received partial funding from the European Union Seventh Framework Programme (2007–2013) under grant agreement no. 222633 (WildTech).
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This paper is part of the special issue entitled “Lectures of the 1st European Conference on Small Ruminant Health Management”, held in Athens, Greece, October 2011. Guest Edited by G.C. Fthenakis.