Disease is described as a decrease in performance of normal functions of an individual caused by many factors, which is not limited to infectious agents. [1] Furthermore, wildlife disease is a disease when one of the hosts includes a wildlife 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. [2] 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. [2] 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. [3] 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.
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. [4] [5]
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.
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.
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. [6] This can include places such as wet markets as well as the illegal trade of both live and dead animals and their body parts. [7]
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. [8]
The challenges associated with wildlife disease management, some are environmental factors, wildlife is freely moving, and the effects of anthropogenic factors. Anthropogenic factors have driven significant changes in ecosystems and species distribution globally. The changes in ecosystems can be caused by introduction of invasive species, habitat loss and fragmentation, and overall changes in the function of ecosystems. [3] Due to the significant changes in the environment because of humans, there becomes a need for wildlife management, which manages the interactions between domestic animals and humans, and wildlife. [9]
Wildlife species are freely moving within different areas, and come into contact with domestic animals, humans, and even invade new areas. These interactions can allow for disease transmission, and disease spillover into new populations. Disease spillover can become of great concern when considering outbreaks, not only in humans but in other wildlife species raising a concern for species preservation.
Wildlife disease is detected primarily through surveys, for example taking samples from wildlife populations in an area to determine the prevalence of disease within a population. Prevalence is define as the percentage of a population that is diseased at a particular time. [10] There are limitations to using this to detect disease within wildlife populations, such as all host may not show signs of disease, the sample distribution, and the disease distribution. Diseases in wildlife tend to form patches of disease throughout an entire population, which can affect the prevalence of the disease within a population. Sampling is assumed to be random, but is often opportunistic. Another form of disease detection is through observation of diseased hosts. However if some hosts within a species do not show signs of disease, this can influence the prevalence of disease detection within a wildlife population.
The reservoir of wildlife disease can also be a challenge when considering wildlife disease detection. An example of a challenge identifying the pathogen is the mass mortality event in bald eagles in southeastern United States in 1994. [11] The challenge identifying the causative agent of disease was due to the neurotoxin being isolated from the areas of outbreak, but not when grown in the laboratory until a brominate metabolite was used. [11] The management of wildlife diseases involve many factors, which should are all important to consider when determining the persistence of a pathogen within a population.
Programs have begun to survey wildlife populations to better understand transmission and health impacts in the affected wildlife communities. [12] Tools such as the Geographical Information System (GIS) can be utilized in order to keep track of individual occurrences of disease in order to create an overall image of disease prevalence and spread in a given area. [13] Major zoonotic diseases such as rabies, COVID-19, influenza, and hemorrhagic fever are monitored to ensure both human health and safety as well as mitigation of impacts on wildlife. [14] Proactive intervention can increase the likelihood of species survival while simultaneously preventing emerging pathogens from escalating to an epidemic. [15] [16]
Disease outbreaks in wild animals are sometimes controlled by killing infected individuals to prevent transmission to domestic and economically important animals. [17] [18] While easy and quick for disease management, culling has the consequence of disrupting ecosystem function and reducing biodiversity of the population due to the loss of individuals. [19] Animal rights advocates argue against culling, as they consider individual wild animals to be intrinsically valuable and believe that they have a right to live. [20] Activists favor humane methods of prevention such as vaccination or treatment via rehab centers, as these are non-lethal forms of management.
Wild animal suffering, as a result of disease, has been drawn attention to by some authors, [21] who argue that we should alleviate this form of suffering through vaccination programs. [22] [23] Such programs are also deemed beneficial for reducing the exposure of humans and domestic animals to disease and for species conservation. [24]
The oral rabies vaccine has been used successfully in multiple countries to control the spread of rabies among populations of wild animals and reduce human exposure. [25] Australia, the UK, Spain and New Zealand have all conducted successful vaccination programs to prevent Bovine Tuberculosis, by vaccinating badgers, possums and wild boar. [26]
In response to the COVID-19 pandemic, it has been proposed that, in the future, wild animals could be vaccinated against coronaviruses to relieve the suffering of the affected animals, prevent disease transmission and inform future vaccination efforts. [27]
Wild animals, domestic animals and humans share a large and increasing number of infectious diseases, known as zoonoses. [28] 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. [29] [30] Contemporary diseases of zoonotic origin include SARS, Lyme disease and West Nile virus. [31]
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. [32] 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. [33]
When an epidemic strikes a population of organisms, the loss of individuals can be detrimental to already fragile or fragmented populations. Many disease epidemics have largely reduced the population of their host organisms, some even increasing the possibility of an endangered or extinct status.
While disease can ravage a population, many wildlife are resilient and can recuperate their population loss. Human intervention can also increase the chances of species recovering from epidemics via various prevention and treatment methods. Individuals that survive epidemics can repopulate, now with disease resistance present in the gene pool of that population. This will result in future generations of a species that are less susceptible to a specific disease. [34]
A human pathogen is a pathogen that causes disease in humans.
A zoonosis or zoonotic disease is an infectious disease of humans caused by a pathogen that can jump from a non-human to a human and vice versa.
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable disease, is an illness resulting from an infection.
Q fever or query fever is a disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals. This organism is uncommon, but may be found in cattle, sheep, goats, and other domestic mammals, including cats and dogs. The infection results from inhalation of a spore-like small-cell variant, and from contact with the milk, urine, feces, vaginal mucus, or semen of infected animals. Rarely, the disease is tick-borne. The incubation period can range from 9 to 40 days. Humans are vulnerable to Q fever, and infection can result from even a few organisms. The bacterium is an obligate intracellular pathogenic parasite.
In medicine, public health, and biology, transmission is the passing of a pathogen causing communicable disease from an infected host individual or group to a particular individual or group, regardless of whether the other individual was previously infected. The term strictly refers to the transmission of microorganisms directly from one individual to another by one or more of the following means:
Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. They are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa. The economic impact of tick-borne diseases is considered to be substantial in humans, and tick-borne diseases are estimated to affect ~80 % of cattle worldwide. Most of these pathogens require passage through vertebrate hosts as part of their life cycle. Tick-borne infections in humans, farm animals, and companion animals are primarily associated with wildlife animal reservoirs. Many tick-borne infections in humans involve a complex cycle between wildlife animal reservoirs and tick vectors. The survival and transmission of these tick-borne viruses are closely linked to their interactions with tick vectors and host cells. These viruses are classified into different families, including Asfarviridae, Reoviridae, Rhabdoviridae, Orthomyxoviridae, Bunyaviridae, and Flaviviridae.
Bartonella is a genus of Gram-negative bacteria. It is the only genus in the family Bartonellaceae. Facultative intracellular parasites, Bartonella species can infect healthy people, but are considered especially important as opportunistic pathogens. Bartonella species are transmitted by vectors such as fleas, sand flies, and mosquitoes. At least eight Bartonella species or subspecies are known to infect humans.
In infectious disease ecology and epidemiology, a natural reservoir, also known as a disease reservoir or a reservoir of infection, is the population of organisms or the specific environment in which an infectious pathogen naturally lives and reproduces, or upon which the pathogen primarily depends for its survival. A reservoir is usually a living host of a certain species, such as an animal or a plant, inside of which a pathogen survives, often without causing disease for the reservoir itself. By some definitions a reservoir may also be an environment external to an organism, such as a volume of contaminated air or water.
An emergent virus is a virus that is either newly appeared, notably increasing in incidence/geographic range or has the potential to increase in the near future. Emergent viruses are a leading cause of emerging infectious diseases and raise public health challenges globally, given their potential to cause outbreaks of disease which can lead to epidemics and pandemics. As well as causing disease, emergent viruses can also have severe economic implications. Recent examples include the SARS-related coronaviruses, which have caused the 2002–2004 outbreak of SARS (SARS-CoV-1) and the 2019–2023 pandemic of COVID-19 (SARS-CoV-2). Other examples include the human immunodeficiency virus, which causes HIV/AIDS; the viruses responsible for Ebola; the H5N1 influenza virus responsible for avian influenza; and H1N1/09, which caused the 2009 swine flu pandemic. Viral emergence in humans is often a consequence of zoonosis, which involves a cross-species jump of a viral disease into humans from other animals. As zoonotic viruses exist in animal reservoirs, they are much more difficult to eradicate and can therefore establish persistent infections in human populations.
Babesia, also called Nuttallia, is an apicomplexan parasite that infects red blood cells and is transmitted by ticks. Originally discovered by the Romanian bacteriologist Victor Babeș in 1888, over 100 species of Babesia have since been identified.
Evolution of Infectious Disease is a 1993 book by the evolutionary biologist Paul W. Ewald. In this book, Ewald contests the traditional view that parasites should evolve toward benign coexistence with their hosts. He draws on various studies that contradict this dogma and asserts his theory based on fundamental evolutionary principles. This book provides one of the first in-depth presentations of insights from evolutionary biology on various fields in health science, including epidemiology and medicine.
Rabies is a viral disease that causes encephalitis in humans and other mammals. It was historically referred to as hydrophobia due to the symptom of panic when presented with liquids to drink. Early symptoms can include fever and abnormal sensations at the site of exposure. These symptoms are followed by one or more of the following symptoms: nausea, vomiting, violent movements, uncontrolled excitement, fear of water, an inability to move parts of the body, confusion, and loss of consciousness. Once symptoms appear, the result is virtually always death. The time period between contracting the disease and the start of symptoms is usually one to three months but can vary from less than one week to more than one year. The time depends on the distance the virus must travel along peripheral nerves to reach the central nervous system.
The prevalence of rabies, a deadly viral disease affecting mammals, varies significantly across regions worldwide, posing a persistent public health problem.
In animals, rabies is a viral zoonotic neuro-invasive disease which causes inflammation in the brain and is usually fatal. Rabies, caused by the rabies virus, primarily infects mammals. In the laboratory it has been found that birds can be infected, as well as cell cultures from birds, reptiles and insects. The brains of animals with rabies deteriorate. As a result, they tend to behave bizarrely and often aggressively, increasing the chances that they will bite another animal or a person and transmit the disease.
In biology, a pathogen, in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.
Spillover infection, also known as pathogen spillover and spillover event, occurs when a reservoir population with a high pathogen prevalence comes into contact with a novel host population. The pathogen is transmitted from the reservoir population and may or may not be transmitted within the host population. Due to climate change and land use expansion, the risk of viral spillover is predicted to significantly increase.
Cross-species transmission (CST), also called interspecies transmission, host jump, or spillover, is the transmission of an infectious pathogen, such as a virus, between hosts belonging to different species. Once introduced into an individual of a new host species, the pathogen may cause disease for the new host and/or acquire the ability to infect other individuals of the same species, allowing it to spread through the new host population. The phenomenon is most commonly studied in virology, but cross-species transmission may also occur with bacterial pathogens or other types of microorganisms.
Groups of animals and humans that live in places with high population density have an increased risk of disease prevalence. In looking at sociality and disease transmission, an examination of how social grouping strategies may reduce or increase the spread of disease is critical for the health of large groups of people. Social groups, community structures, and cultures affect the use of different strategies and behaviors to reduce the spread of disease.
Disease ecology is a sub-discipline of ecology concerned with the mechanisms, patterns, and effects of host-pathogen interactions, particularly those of infectious diseases. For example, it examines how parasites spread through and influence wildlife populations and communities. By studying the flow of diseases within the natural environment, scientists seek to better understand how changes within our environment can shape how pathogens, and other diseases, travel. Therefore, diseases ecology seeks to understand the links between ecological interactions and disease evolution. New emerging and re-emerging infectious diseases are increasing at unprecedented rates which can have lasting impacts on public health, ecosystem health, and biodiversity.
Animal vaccination is the immunisation of a domestic, livestock or wild animal. The practice is connected to veterinary medicine. The first animal vaccine invented was for chicken cholera in 1879 by Louis Pasteur. The production of such vaccines encounter issues in relation to the economic difficulties of individuals, the government and companies. Regulation of animal vaccinations is less compared to the regulations of human vaccinations. Vaccines are categorised into conventional and next generation vaccines. Animal vaccines have been found to be the most cost effective and sustainable methods of controlling infectious veterinary diseases. In 2017, the veterinary vaccine industry was valued at US$7 billion and it is predicted to reach US$9 billion in 2024.