Wildlife disease is an abnormal health condition affecting a wild animal species. In many cases, wildlife hosts can act as a reservoir of diseases that spillover into domestic animals, people and other species. Wildlife diseases spread through both direct contact between two individual animals or indirectly through the environment. Additionally, human industry has created the possibility for cross-species transmission through the wildlife trade. Furthermore, there are many relationships that must be considered when discussing wildlife disease, which are represented through the Epidemiological Triad Model. This model describes the relationship between a pathogen, host and the environment. There are many routes to infection of a susceptible host by a pathogen, but when the host becomes infected that host now has the potential to infect other hosts. Whereas, environmental factors affect pathogen persistence and spread through host movement and interactions with other species. An example to apply to the ecological triad is Lyme disease, where changes in environment have changed the distribution of Lyme disease and its vector, the Ixodes tick. The recent increase in wildlife disease occurrences is cause for concern among conservationists, as many vulnerable species do not have the population to recover from devastating disease outbreaks.
Transmission
Indirect Wildlife may come in contact with pathogens through indirect vectors such as their environment by consuming infected food and water, breathing contaminated air, or encountering virulent urine or feces from an infected organism. This type of transmission is typically associated with pathogens that are able to survive prolonged periods, with or without a host organism. The most recognizable wildlife disease that indirectly spreads are prion disease. Prion diseases are indirectly spread due to their longevity in the environment, lasting for several months once released from a host via their excretions (urine or feces). Notable animal prion diseases include chronic wasting disease in cervids, scrapie in sheep and goats, and various types of spongiform encephalopathy including bovine (also known as mad cow disease), mink, feline, and ungulate.
Direct Disease can be spread from organism to organism through direct contact such as exposure to infected blood, mucus, milk (in mammals), saliva, or sexual fluids such as vaginal secretions and semen. A prominent example of direct infection is facial tumor disease in Tasmanian devils, as these marsupials will repeatedly bite other individuals in the face during the breeding season. These open wounds allow transmission via blood and saliva in the devil's orifices.
Wildlife Trade A major driver for transmission between species recently is wildlife trade, as many organisms that do not typically encounter each other naturally are in close proximity. This can include places such as wet markets as well as the illegal trade of both live and dead animals and their body parts. The most notable example of wildlife trade impacting both animal and human health is COVID-19, originating in a wet market in Wuhan, China. The originating species has been a topic of debate as it is unclear due to the variety of species found at the market, however pangolins and bats both have been absolved of blame despite initial claims.
Zoonoses Wild animals, domestic animals and humans share a large and increasing number of infectious diseases, known as zoonoses. The continued globalization of society, human population growth, and associated landscape change further increase the interactions between humans and other animals, thereby facilitating additional infectious disease emergence. Contemporary diseases of zoonotic origin include SARS, Lyme disease and West Nile virus. Disease emergence and resurgence in populations of wild animals are considered an important topic for conservationists, as these diseases can affect the sustainability of affected populations and the long-term survival of some species. Examples of such diseases include chytridiomycosis in amphibians, chronic wasting disease in deer, white-nose syndrome, in bats, and devil facial tumour disease in Tasmanian devils.
Wildlife Disease Management
Wildlife disease management serves to protect not only the animals at hand but also the very delicate equilibrium that favors ecosystems, and in turn, the planet's health. Wildlife diseases have gained recognition as a big issue, increasingly so in the present with greater human impacts on the environment, and this concern is shared by conservationists and all those who cherish biodiversity: Managing wildlife diseases is complex and requires to have the understanding of the science and the heart to realize that wildlife health sometimes becomes intermingled with other health issues concerning environment and humans.
Role of humans
Human impact has put in place both direct and indirect pathways of propagating disease through wildlife populations. Habitat destruction, climate change, and the increasing footprint of humans in landscapes formerly reserved for wildlife contribute to increasing susceptibility of wildlife to pathogens. For example, deforestation can bring previously isolated species into close contact with each other and us, creating new interfaces for disease jump from animals to humans. Climate change compounds the problem by altering the habitat of vectors and reservoirs of many diseases, like ticks, that transmit Lyme disease to both animals and humans. Environmental changes and human encroachment upon wild spaces increase human-wildlife interactions: agriculture, construction, wildlife trade, etc. These interactions are accelerating interspecies transmission of disease, sometimes triggering devastating outbreaks.
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