Wild animals are not immune to illness, facing constant health challenges. This contrasts with a common perception of wildlife as inherently healthy and untouched by disease. This article explores common illnesses, their causes, consequences for wildlife and ecosystems, and what to do if you encounter a sick animal.
Do Wild Animals Get Sick?
Wild animals are susceptible to a diverse range of illnesses and injuries. Their lives are continuously influenced by pathogens, environmental factors, and physical trauma. Natural selection favors disease resistance, but illness still occurs within wild populations.
They contend with the same biological threats that affect other living organisms. Many wild animals, with immune systems similar to humans, can succumb to diseases caused by viruses, bacteria, and parasites. Wild animals often die younger than zoo animals, partly because captive animals receive treatment for pathogens that would be fatal in the wild. This highlights the constant health risks wild animals navigate in their natural state.
Common Illnesses in Wild Animals
Wild animals are affected by a wide spectrum of diseases, categorized broadly into infectious and non-infectious conditions. Infectious diseases are caused by microscopic organisms and can spread among individuals. Non-infectious conditions arise from factors like environmental toxins or physical harm.
Viral diseases are prevalent in wild animal populations. Examples include rabies, which affects the central nervous system of mammals, including humans, and canine distemper. West Nile virus, spread by mosquitoes, also impacts various wildlife species and can affect humans. Other viruses, like those causing foot-and-mouth disease, can infect wild ruminants and other hoofed animals.
Bacterial infections are also common in wildlife. Tuberculosis, caused by Mycobacterium bovis, is a chronic bacterial disease found in many mammal and bird species. Leptospirosis is another bacterial disease affecting both humans and animals, often transmitted through contaminated water or contact with infected urine. Salmonellosis, caused by Salmonella bacteria, can be carried by various animals, including rodents and reptiles.
Parasitic diseases are widespread. External parasites include mange mites (Psoroptes spp., Sarcoptes spp.) and ticks, which can cause skin infestations. Internal parasites, such as various species of worms and protozoa, are frequently found in wild ruminants. Giardia, an intestinal parasite, can cause diarrhea and is carried by wildlife such as beavers, muskrats, and deer.
Beyond infections, wild animals also experience non-infectious conditions. Nutritional deficiencies can occur if food sources are scarce or lack essential nutrients. Environmental toxins, such as lead poisoning from discarded ammunition or fishing tackle, can severely impact wildlife health. Pesticide exposure and agricultural runoff can also introduce harmful chemicals into their environments. Physical injuries are a frequent threat, often resulting from falls, collisions with objects or other animals, or getting trapped. These injuries can range from minor bruising to severe fractures or internal damage.
Causes of Wildlife Sickness
Various factors contribute to wild animals getting sick, often interacting in complex ways. The presence and transmission of pathogens are fundamental. Contact with viruses, bacteria, parasites, and fungi directly leads to infection. These pathogens can spread through direct contact, contaminated food or water, or via vectors like mosquitoes and ticks.
Environmental stressors play a significant role in weakening animals’ immune systems and increasing their susceptibility to disease. Habitat loss and fragmentation, often due to human development, can isolate animal populations and reduce their gene flow, potentially leading to increased disease susceptibility. Climate change also impacts disease dynamics by altering ecosystems, shifting the distribution of disease vectors, and causing extreme weather events. Warmer temperatures can increase the survival and reproduction rates of pathogens and vectors, while changes in precipitation affect breeding sites.
High population density within a species can facilitate rapid disease transmission. When animals are crowded, pathogens can spread more easily from one individual to another, leading to outbreaks. This is particularly evident in urban areas where wildlife populations may be concentrated around human-provided resources.
Human activities are increasingly recognized as major drivers of wildlife sickness. Urbanization, deforestation, and agricultural expansion create new interfaces where humans, livestock, and wildlife interact more frequently. This increased contact can lead to the introduction of novel pathogens into wildlife populations or the amplification of existing ones. For instance, the wildlife trade and trafficking can bring animals into close contact, creating opportunities for disease transmission. Additionally, pollution from industrial waste and agricultural runoff can directly harm wildlife or suppress their immune systems, making them more vulnerable to infections.
Consequences of Disease in Wildlife
The impacts of disease in wildlife extend beyond individual animals, affecting entire populations and the broader ecosystem, with potential relevance to human health. At the individual level, illness causes suffering and can impair an animal’s ability to forage for food, evade predators, or reproduce. This often leads to reduced fitness and can result in mortality.
At the population level, diseases can cause significant declines in animal numbers. Outbreaks can affect breeding success and reduce genetic diversity, making populations less resilient to future threats. For example, infectious diseases have caused an increase in wildlife mortality over the last fifty years, posing serious conservation challenges.
Disease also influences ecosystem health. Changes in wildlife populations due to illness can alter predator-prey dynamics and disrupt other ecological processes, such as nutrient cycling. The loss of certain species due to disease can impact ecosystem services, like pollination or pest control, that benefit the environment and humans.
A significant consequence of wildlife disease is the emergence of zoonotic diseases, which are transmissible from animals to humans. About six out of ten infectious diseases in humans are zoonotic, and three out of four new or emerging infectious diseases are of zoonotic origin. Examples include rabies, Lyme disease, West Nile virus, and hantavirus. Human activities, such as wildlife trade, habitat encroachment, and climate change, increase the risk of these diseases spilling over from animals to humans, posing substantial public health implications.
Encountering a Sick Wild Animal
If you encounter a wild animal that appears sick or injured, it is important to prioritize both your safety and the animal’s well-being. Maintaining a safe distance is crucial, as sick or injured animals can behave unpredictably and may pose a risk of injury or disease transmission. Even animals that seem healthy can carry germs.
Attempting to intervene directly can be dangerous for both you and the animal. Wild animals often hide their pain or illness, and approaching them can cause further stress or provoke a defensive reaction. Handling wild animals improperly can also spread diseases to other species.
Instead, contact your local animal control, a wildlife rehabilitation center, or your state wildlife agency. These organizations have trained professionals equipped to assess the situation safely and provide appropriate care. They can determine if the animal needs intervention and how to proceed.
Reporting observations of sick or deceased wildlife is also important for disease monitoring and surveillance. Information about unusual animal behavior or deaths can help authorities track disease outbreaks and understand their spread, contributing to broader wildlife and public health efforts.