Wildlife Diseases and Health Concerns

Disease Types

Rabies is an acute disease, caused by a virus (rhabdovirus), that can infect all warm-blooded animals, and is usually fatal. Certain carnivorous mammals and bats are the usual animal hosts. Rabies occurs throughout most of the world; only Australia and Antarctica are free of it. Most human cases have been contracted from rabies-infected dogs.
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Hantavirus includes a group of viruses that can cause a febrile illness in humans which can be accompanied by kidney, blood, or respiratory ailments and can sometimes be fatal. The febrile illness includes fever, headache, muscle aches, nausea, vomiting, and lower back pain.

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Trichinosis may result in diahrrea, sudden edema of the upper eyelids, photophobia, muscle soreness and pain, skin lesions, thirst, sweating, chills, and weakness. Other respiratory and neurological symptoms may appear if treatment is delayed.

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Mosquito-borne Encephalitis
Encephalitis is a disease caused by mosquito-borne viruses (arboviruses) that affect the central nervous system. Infections range from unapparent to mild, nonspecific illnesses (fever, headache, musculoskeletal pain, and malaise) to occasionally severe illness of the central nervous system resulting in permanent neurologic damage and possibly death.

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Plague is an acute disease caused by the bacteria Yersinia pestis. Humans usually become infected by the bites of infected fleas but also directly from exposure to tissues or body fluids from diseased animals, especially when skinning animals.

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Murine Typhus Fever
Murine typhus fever is caused by Rickettsia typhi, a rickettsial organism that occurs throughout the southeastern and Gulf Coast states and southern California. Rats are the reservoir animals from which the disease reaches many humans by way of rat fleas.

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Rat-bite Fever
Rat-bite fever is caused by the bacteria Streptobacillus moniliformis, which is found on the teeth and gums of rats. It is transferred from rats to humans by the bite of the rat.

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The Salmonella group of bacteria exists nearly everywhere in the environment and, unfortunately, several serotypes are pathogenic to humans and other animals. Salmonellosis can lead to severe cases of gastroenteritis (food poisoning), enteric fever septicemia (blood poisoning), and death.

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Leptospirosis is a mild to severe infection that is seldom fatal. Human cases of the disease result from direct or indirect contact with infected urine of rodents and other animals.

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Rickettsialpox is a mild nonfatal disease resembling chicken pox.

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Colorado Tick Fever
Colorado tick fever (CTF) is an acute and rather benign disease caused by a virus (coltivirus) that is transmitted to humans by ticks. Symptoms are usually limited to high fever, headache, muscle aches, and lethargy, but the symptoms are frequently biphasic and recurring.

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Tularemia is caused by the bacteria Francisella tularensis and is characterized by sudden onset of high fever and chills, joint and muscle pain, and prostration. Slow-healing sores or lesions develop at the site of entry of the bacteria (or arthropod bite).

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Rocky Mountain Spotted Fever
Rocky Mountain spotted fever (RMSF) is a moderate to severe illness caused by a rickettsia (Rickettsia rickettsii). The disease is distinguished by a sudden onset of high fever, severe headache, muscle pain, and a red rash starting on the extremities about 3 to 6 days after onset of symptoms and extending to the palms of hands and soles of feet and then to the rest of the body.

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Relapsing Fever
Relapsing fever can be caused by several Borrelia spirochete bacteria, which are related to the Lyme disease spirochete and are transmitted by soft ticks (Argasidae). Symptoms resemble Lyme disease except for the absence of the diagnostic rash and the presence of recurring fever.

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Lyme Disease
Lyme disease is caused by a spirochete bacterium (Borrelia burgdorferi) that is transmitted to humans by hard ticks. Early symptoms include a flu-like illness with headache, slight fever, muscle or joint pain, neck stiffness, swollen glands, jaw discomfort, and inflammation of the eye membranes.

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Other Tick-borne Diseases
Three other tick-borne diseases occur in the United States. Human ehrlichiosis is a recently recognized disease caused by a rickettsia, Ehrlichia chaffeensis.

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Histoplasmosis is a respiratory disease in humans caused by inhaling spores from the fungus Histoplasma capsula-tum. Birds do not spread the disease directly — spores are spread by the wind and the disease is contracted by inhalation.

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The Salmonella group of bacteria can also be transmitted by birds. Refer to Commensal Rodent-borne Diseases (above) for additional information.

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Ornithosis is an infectious respiratory disease caused by Chlamydia psittaci, a viruslike organism that affects humans, pets, and livestock. It usually leads to a mild pneumonia-or flu-like infection, but it can be a rapidly fatal disease (less than 1% of the cases reported in the United States).

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Other Bird-borne Diseases
Pigeons, starlings, sparrows, blackbirds, and other types of birds have been implicated in the transmission of various diseases of significance to humans or livestock. Starlings have been shown to be vectors of transmissible gastroenteritis (TGE) of swine.

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Diseases of wildlife can cause significant illness and death to individual animals and can significantly affect wildlife populations. Wildlife species can also serve as natural hosts for certain diseases that affect humans (zoonoses). The disease agents or parasites that cause these zoonotic diseases can be contracted from wildlife directly by bites or contamination, or indirectly through the bite of arthropod vectors such as mosquitoes, ticks, fleas, and mites that have previously fed on an infected animal. These zoonotic diseases are primarily diseases acquired within a specific locality, and secondarily, diseases of occupation and avocation. Biologists, field assistants, hunters, and other individuals who work directly with wildlife have an increased risk of acquiring these diseases directly from animal hosts or their ectoparasites. Plague, tularemia, and leptospirosis have been acquired in the handling and skinning of rodents, rabbits, and carnivores. Humans have usually acquired diseases like Colorado tick fever, Rocky Mountain spotted fever, and Lyme disease because they have spent time in optimal habitats of disease vectors and hosts. Therefore, some general precautions should be taken to reduce risks of exposure and prevent infection.


Use extreme caution when approaching or handling a wild animal that looks sick or abnormal to guard against those diseases contracted directly from wildlife. Procedures for basic personal hygiene and cleanliness of equipment are important for any activity but become a matter of major health concern when handling animals or their products that could be infected with disease agents. Some of the important precautions are:

  • Wear protective clothing, particularly disposable rubber or plastic gloves, when dissecting or skinning wild animals.
  • Scrub the work area, knives, other tools, and reusable gloves with soap or detergent followed by disinfection with diluted household bleach.
  • Avoid eating and drinking while handling or skinning animals and wash hands thoroughly when finished.
  • Safely dispose of carcasses and tissues as well as any contaminated disposable items like plastic gloves.
  • Cook meat from wild game thoroughly before eating.
  • Contact a physician if you become sick following exposure to a wild animal or its ectoparasites. Inform the physician of your possible exposure to a zoonotic disease.

Precautions against acquiring fungal diseases, especially histoplasmosis, should be taken when working in high-risk sites that contain contaminated soil or accumulations of animal feces; for example, under large bird roosts or in buildings or caves containing bat colonies. Wear protective masks to reduce or prevent the inhalation of fungal spores. Protection from vector-borne diseases in high-risk areas involves personal measures such as using mosquito or tick repellents, wearing special clothing, or simply tucking pant cuffs into socks to increase the chance of finding crawling ticks before they attach. Additional preventive methods include checking your clothing and body and your pets for ticks and removing the ticks promptly after returning from infested sites. If possible, avoid tick-in-fested areas or locations with intense mosquito activity during the transmission season. Reduce outdoor exposure to mosquitoes especially in early evening hours to diminish the risk of infection with mosquito-borne diseases. Equally important preventive measures are knowledge of the diseases present in the general area and the specific habitats and times of year that present the greatest risk of exposure. Knowledge of and recognition of the early symptoms of the diseases and the conditions of exposure are essential in preventing severe illness.