A Brief Overview of Zoonotic Disease

Last updated January 15, 2021


A zoonotic disease is any disease that may be transmitted from an animal to a human under natural conditions. It is the responsibility of the Principal Investigator (PI) to educate their staff on zoonotic diseases of the animals that they are using in their research or teaching activities. Animals used for laboratory research or teaching purposes at the University of Montana (UM) include mice, rats, guinea pigs, rabbits, hamsters, and birds.  Wildlife species used as research subjects in field studies at UM include, but are not limited to, bats, birds, fish, mammals, amphibians, and reptiles.

Transmission of Zoonotic Diseases

Transmission of zoonotic diseases from animals is primarily by direct contact, fecal-oral contact, indirect contact with invertebrate vectors and contaminated inanimate objects, or inhalation of aerosolized materials. Transmission of zoonotic diseases can be prevented through a variety of means, including use of protective clothing, prevention of bites and scratches, proper sharps handling procedures, medical surveillance and vaccination programs, and post-injury treatment.

  • Handle animals appropriately and safely, (wear appropriate protective equipment) to prevent bites and scratches
  • Thoroughly wash any bite or scratch wounds and report injuries. Rabies exposure is reportable to public health authorities
  • Do not eat, drink, apply makeup or use tobacco products while handling animals or in animal housing areas
  • Wear gloves when handling animals, animal tissues, body fluids, and waste and wash hands after contact
  • Wear dedicated protective clothing such as a lab coat or coveralls when handling animals. Launder the soiled clothing separate from your personal clothes and preferably at the animal facility
  • Wear respiratory protection when appropriate
  • Keep animal areas clean and disinfect equipment after using it on animals or in animal areas. Do not use cleaning techniques such as vacuuming or power washing which aerosolize animal waste and allows for inhalation of possible pathogens

Most importantly, familiarize yourself with the animals that you will be working with and the potential zoonotic diseases associated with each species. If at any time, you suspect that you have acquired a zoonotic disease, inform your supervisor and seek medical care.

Laboratory Animals

A.  Allergens to Laboratory Animals

Allergies to animals are among the most common health problems affecting personnel who care for and use animals in research. Laboratory animal allergies are associated with the inhalation of allergens, such as animal dander and urinary proteins, into the lungs. Although allergies may be associated with any species of animal, in the laboratory most cases are due to contact with small rodents (mice and rats). Pre-existing allergies to dust mites, pollens and molds, and tobacco smoking are risk factors for the development of laboratory animal allergies

  1. Rats: Rats are among the most commonly used laboratory animals. The major sources of rat allergen exposure appear to be urine and saliva. Disturbance of bedding can leave allergens airborne for 15-35 minutes. Exposure concentrations seem to be task-related. Cage cleaning results in a much higher concentration of airborne allergens than does other tasks like weighing, shaving, blood collection, and urine collection.
  2. Mice: This group is also a heavily used laboratory animal, and is another important source of allergen exposure. The major mouse allergen is a urinary protein produced in the liver and saliva and secreted in urine.
  3. Guinea Pigs: Immunogenic studies have identified allergenic compounds in the dander, urine, fur, and saliva of guinea pigs. Urine appears to be the major source of allergen.
  4. Rabbits: People allergic to rabbits normally react to the protein in the animal's urine. The allergic symptoms can include sneezing, coughing, a runny nose, itchy eyes, congestion, and wheezing. In severe cases, contact with a rabbit can also cause a rash on the face, neck and upper chest. Allergic symptoms can appear within 30 minutes of coming in contact with a rabbit, but they can take longer to appear.

B.  Zoonotic Diseases of Laboratory Animals

  1. Mice:  Laboratory mice are bred to exclude all zoonotic agents.  Therefore, unless the laboratory mice are exposed to wild mice (those coming from the natural habitat outside the laboratory), there is limited concern for disease from these research mice.  However, there is always concern about secondary infections that can occur with bites and scratches.  Common skin, intestinal, and soil bacteria present on you or the animal can infect the scratch or bite wound and cause these secondary infections.  Therefore, you should handle all mice with care and always cleanse any wound immediately with soap and water or antiseptic and seek medical consultation for severe wounds.
  2. Rats: Laboratory rats are bred to exclude all zoonotic agents.  Therefore, there is limited concern for disease from these research rats. However, there is always concern about secondary infections that can occur with bites and scratches.  Common skin, intestinal, and soil bacteria present on you or the animal can infect the scratch or bite wound and cause these secondary infections.  Therefore, you should handle all rats with care and always cleanse any wound immediately with soap and water or antiseptic and seek medical consultation for severe wounds.
  3. Birds: The birds used in research colonies are either caught in the wild or acquired from established flocks.  In general, birds are not supplied disease-free, and usually contain a number of microbial agents.  Of zoonotic concern are the diarrheal bacteria, such as Salmonella that cause intestinal illness and the bacteria that causes psittacosis, which can cause a more severe type of infection.
  4. Rabbits: Rabbits can be asymptomatic carriers of the fungus that causes ringworm. In humans.  The disease usually consists of small, scaly, semi-bald, grayish patches with broken, lusterless hairs, with itching. However, other symptoms may appear. It is usually associated with the hair that can be floating around in the room. Prevention of allergic symptomology includes wearing proper clothing and practicing good personal hygiene.
  5. Other Zoonotic Diseases found in Animal Laboratories

a.  Salmonellosis: Salmonella is a bacterial disease that occurs in a multitude of animal species, including non-human primates, cows, horses, and pigeons. It is transmitted through the feces. Animals may not show signs of the disease but can still infect other animals. Disease can range from very mild to severe diarrhea, stomach pain, fever, chills, headache, nausea and vomiting.

b.  Tetanus: Tetanus is caused by a bacterium called Clostridium. Clostridium can live in environments of low oxygen. The Public Health Service Advisory Committee on Immunization Practices recommends immunization against tetanus. It is suggested that you keep your tetanus vaccination up to date at all times. Any puncture wound may require a booster

Wildlife Species

A.  Zoonotic Dieseses of Wildlife Species

1.  Bats

a.  Histoplasmosis: Histoplasmosis is a disease caused by the fungus Histoplasma capsulatum. The histoplasmosis fungus lives in soil, especially soil and material that is contaminated with and enriched by heavy accumulations of bat or bird droppings. Spores become airborne when contaminated soil is disturbed. Breathing the spores causes infection. The disease is not transmitted from an infected person to someone else. Infection with histoplasmosis is common, but the disease is rare. Most infected persons have no apparent ill effects and infection clears on its own without treatment. As many as 80 percent of persons living in U.S. areas where the fungus is common have a positive skin test, meaning they have had the infection in the past. However, most of these people do not have a history of histoplasmosis symptoms. When people develop symptoms, it usually involves the lungs and is characterized by weakness, chills, fever, muscle aches, chest pains, and a dry cough. Chronic lung infections can resemble tuberculosis and may progress over months or years.  Before disturbing potentially-contaminated soil or debris, thoroughly mist-spray the material to control dispersion of dust and soil into the air. Wear protective, disposable coveralls, gloves, and a dust mask.

b.  Rabies: Rabies is a fatal viral infection that can be transmitted by bites, scratches and mucus membrane exposure from an infected animal. Bats, humans and other mammals acquire the rabies virus through direct contact, bites or scratches from other infected animals and rarely via inhalation of infected bat guano (fecal material) in bat roosts or caves. Bats will develop symptoms and typically die once infected but may shed the rabies virus for a period before any symptoms are apparent. The clinical symptoms are depression, anorexia with possible neurological symptoms and unusual behavior. Persons working with bats require rabies vaccination and routine assessment of their rabies titer. They should wear protective clothing and thick protective gloves when handling bats to prevent exposure. If a person is bitten or scratched by a suspect bat, the animal should be euthanized and tested for rabies.  Persons with exposure to rabies must seek post-exposure rabies prophylaxis from a medical professional. Bat bites and scratches and wound and mucous membrane exposure to bat saliva are the ways in which rabies can be transmitted.

c.  Salmonellosis and yersiniosis: Salmonella is acquired by contact and ingestion of fecal material from infected animals. Histoplasmosis, cryptococcosis and blastomycosis are fungal infections that occasionally infect bats and can be present in bat guano. Animals infected with these bacterial and fungal diseases typically have diarrhea but some animals may show no symptoms of disease. Avoid direct contact with feces and urine and use gloves and hand-washing to avoid accidental ingestion of animal waste. When cleaning, avoid aerosolization and possible inhalation of pathogens. Any animal with diarrhea should be suspect of having a zoonotic disease.

2.  Birds

a.  Newcastle Disease: Newcastle Disease is a reportable, viral disease with some virulent strains associated with birds. Some Newcastle disease strains do affect people, causing flu-like symptoms. Exposure, although unlikely, could occur from a wild bird exhibiting general debility, diarrhea, respiratory, or nervous system signs. The disease can be transmitted from birds to humans generally through the virus getting into your eye. Face masks and washing afterwards should help to prevent it.

b. Psittacosis:  Psittacosis is a bacterial disease (Chlamydophila psittaci) that has been identified in over 400 species of birds including chickens, turkeys, pet species and pigeons. Birds may not show signs of the disease but can still transmit it through their feathers, excreta, etc. Birds with an active infection typically will exhibit symptoms of an upper respiratory infection: discharge from the nares, eyes, and may cough, sneeze and wheeze. Avoid contact with obviously infected birds. When working with birds, wear your protective clothing including a mask and gloves.

3.  Fish and Aquatic Amphibians

Aquatic species can carry pathogenic bacteria such as Klebsiella and other gram negative and gram positive bacteria, although these rarely lead to human infections under normal conditions. In addition, Edwardsiella tarda and atypical Mycobacteria species, carried by aquatic species are known human pathogens.

4.  Mammals

a.  Babesia:  Babesia(caused by the intracellular parasite Babesia microti) is a protozoan parasite commonly infecting many species of rodents including mice, rats, and voles. The infection in humans causes flu-like illness that usually lasts for 1 or 2 weeks, that is commonly a self-limiting hemolytic disease transmitted by tick bite (the deer tick commonly). In its mildest form it causes fever, spleen enlargement and a mild fever. Individuals who have had to have their spleen removed for any reason develop a very serious anemia disease compared to other people.

b.  Hantavirus Pulmonary Syndrome:  HPS is believed to result primarily from transmission of aerosolized excreta or saliva from rodents infected with hantavirus. Transmission via a bite from an infected rodent is also a probable means of transmission. Hantaviruses are readily killed by contact with common disinfectants (e.g.10% bleach, 3% Lysol) or exposure (>30 min) to direct sunlight or heat >60°C.

  • All handling of rodents known to transmit viruses that cause HPS should be done in the open air with the rodent (or trap containing the rodent) held away from the face and positioned such that direct wind (and wind vortices) do not blow aerosolized particles from the rodent toward the investigator.
  • Live traps containing rodents known to transmit viruses that cause HPS should not be transported within a vehicle unless they are securely isolated in intact plastic bags (e.g. large garden bags) or otherwise placed in an area in which air circulation is separate from that of the driver and any passengers.
  • Researchers should avoid direct contact with urine, feces, saliva, blood, and internal organs of rodent species associated with HPS. Eye protection and rubber, latex, vinyl, or nitrile gloves are recommended when handling or doing invasive procedures with rodents that potentially transmit Hantavirus.
  • Appropriate training should prioritize safe and secure handling of small mammals to avoid being bitten or scratched. Rodents can be anesthetized or euthanized by placing the trap containing the rodent inside a disposable plastic bag containing the anesthetic agent. For mark-and-release studies, smaller rodents (<100 g) can be removed from traps using disposable plastic or washable cloth bags and handled safely and securely by grasping them firmly at the nape of the neck.
  • In the unlikely event that a field researcher is bitten, scratched, or comes into direct contact with the fluids of rodents that potentially transmit Hantavirus, the affected area should be washed thoroughly with soap and water, then disinfected with an alcohol-based hand sanitizer or a similar disinfectant, such as Lysol or Clorox  hand wipes.
  • All researchers should be fully aware of the symptoms of HPS, which include severe muscle aches, fever, and headaches. If these flu-like symptoms appear within 1-5 weeks after fieldwork, the person should see a physician immediately and report that he or she might have been exposed to Hantavirus.
  • All field mammalogists should visit the CDC website regularly to get updates on hantaviruses (www.cdc.gov/hantavirus/), HPS, and other rodent-borne diseases (www.cdc.gov/rodents/diseases/)

c.  Lyme Disease:  Lyme disease (Borrelia burghdorferi) is a bacterium commonly infecting deer, white-footed mice, and possibly other species that is transmitted to humans by ticks or occasionally by direct contact with the infected vertebrate. You must have a tick drinking your blood for at least 16 hours to contract this disease. Removal of a tick before that length of time is preventative. A reddish halo (bull’s eye ring around the bite) sometimes forms approximately 2-12 weeks following a tick bite, and is the earliest sign of Lyme disease. After this, severe illness may develop including: heart inflammation with arrhythmia, arthritis, and nervous system disorders including peripheral nerve dysfunction.

d.  Plague: Plague is caused by the bacterium, Yersinia pestis. The pathogen is transmitted by fleas but it also can be transmitted from human to human in its pneumonic form (a lung infection).  Plague primarily is a disease of rodents. However, in Montana, the bacteria thrive in prairie dog fleas. Once infected, prairie dogs contract a form of plague and die within days.  Other animals in Montana known to carry the disease are deer mice, rats, badgers, coyotes, bobcats and antelope.  Fleas that have fed on plague-infected animals become infected. Plague bacilli multiply in the gut of the flea, and, if humans are in close association with infected rats, the fleas may attempt to feed on them. During feeding, the plague bacilli are introduced into the victim. In humans, after the bacteria are introduced, the onset of the disease usually occurs in three to four days. The disease is characterized by a rapid rise in temperature to approximately 41oC. Headaches and delirium quickly follow. The infection then spreads from the lymph nodes to the bloodstream, and then to the liver and spleen. A secondary pneumonia may develop because of the deposit of bacteria in the lung tissues. A patient may die in less than 24 hours.

e.  Rabies:  Rabies is caused by a virus and occurs throughout the United States. It can infect virtually all mammals, including humans. PIs or their staff and students working with wild animals in field studies may be at risk of exposure to rabies. The rabies virus can be transmitted through bite wounds or contact with saliva.  Rabies is endemic in wild carnivores. Wild rodents, metatherians (opposums), foxes, skunks and lagomorphs (rabbits) can also contract rabies. If you plan to work with high-risk species (e.g. raccoons, foxes, skunks, or bats), then you must receive vaccination against this disease. You should have an antibody titer determined after vaccination to be assured that you are protected.  Wear suitable clothing to protect against injuries, particularly mammalian animal bites. As soon as possible after receiving a bite from a mammal that breaks the skin clean, scrub the wounded area with disinfectant soap, and soak for 30 minutes in a disinfectant solution afterwards (a 5% dilution of household bleach in tap water is excellent for this purpose). Prompt and judicious wound care is the single most important prevention of contracting any disease from an animal bite. In “true rabies exposures,” where bite wounds are incurred by any abnormally behaving mammal, contact the local health department for immediate prophylactic vaccination. If the animal that bit you is available, either alive or dead, it is a valuable source for the health department to check to see if it truly harbored rabies. Eye protection should be worn when dissecting any mammal that may have died under unexplained circumstances.

f.  Rocky Mountain Spotted Fever:  Rocky Mountain Spotted Fever (Rickettsia rickettsii) is a disease requiring a tick vector for people to become infected. Human symptoms generally occur 5-10 days after a tick bite and include: fever, headache, vomiting, muscle pain, severe headache followed several days later by abdominal pain, diarrhea and a skin rash. The organism that causes Rocky Mountain spotted fever is transmitted by the bite of an infected tick. The American dog tick (Dermacentor variabilis) and Rocky Mountain wood tick (Dermacentor andersoni) are the primary arthropods (vectors) which transmit Rocky Mountain spotted fever bacteria in the United States.

g.  Roundworms:  Roundworms (Baylisascaris procyonis & B. columnaris) are parasitic nematode roundworm parasites carried by skunks and raccoons. Contact with feces-contaminated water or plants can pass the sticky and environmentally durable eggs to humans. Contracting this disease occurs by accidental ingestion of the eggs (i.e., in the absence of hand washing or gloves). Infection of humans can lead to larval parasite migration to the brain with the development of highly variable neurological symptoms.

h.  Tularemia:  Tularemia (caused by Franciella tularensis) is a severe bacterial disease carried by rodents and lagomorphs (rabbits) that is readily transmissible to humans by inhalation of infected aerosol, exposure of mucous membranes (the eyes), ingestion, and inoculation into skin wounds.  Field dissection of infected animals is a common cause of exposure, as is contact with contaminated food, water, or hands in the eyes. Also, the bacterium is unusual in that it can penetrate intact undamaged skin. In humans and other species, the agent rapidly grows in the blood, produces high fever, and can lead to death if it goes untreated.

i.  Yersiniosis:  Yersiniosis (caused mainly by the bacterium Y. enterocolitica in people) is an organism carried by wild birds and mammals that concentrates in water bodies under conditions of cold wet weather. Individuals drinking from that water source can be exposed to very high doses of bacteria. The agent causes diarrhea, enlarged lymph nodes in the gastrointestinal tract and is a cause of appendicitis.

5.  Reptiles and Chelonians

All reptiles (herbivore, omnivore, or carnivore) can carry the Salmonella species of bacteria. Contact with reptiles has been directly implicated in human Salmonellosis outbreaks. Reptiles carrying the pathogenic agent typically exhibit no signs of illness themselves. Washing hands after handling reptiles and chelonians, (or avoiding contact with reptiles if you have children under 5 years of age, are pregnant, or if you are immunocompromised) are typical CDC recommendations. Hand-washing after handling is prudent. Cleaning potentially soiled reptile utensils, capture tools or housing accoutrements in human food preparation areas is to be avoided. Symptoms of Salmonellosis can be variable from mild diarrhea to fulminant dysentery with fever, muscle soreness, and hepatitis.