Section 5: Zoonoses


Zoonoses are diseases of animals that are transmissible to humans. They may be a significant exposure hazard in some laboratories where animals are used for research. Fortunately, many laboratory animal species today are bred to be free of zoonoses that were once more common in these animals. However, there remain zoonotic agents associated with laboratory animals, some which can be life-threatening. Field research with wild species also remains a clear source of zoonoses exposure. Prevention of exposure to these animal-related illnesses requires knowledge of the zoonoses related to the animals with which you will be working. In the sections that follow, the zoonotic agents listed for each animal species are those that may be present in the animals being used. If you are exposed through bite, scratch, aerosol droplet, mucosal secretion, feces or urine, there is the potential for you to become infected, and medical consultation through the Concentra Medical Center is highly recommended.


Mice and Rats

Laboratory Mice:

Modern laboratory mice are bred to exclude all zoonotic agents. 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.

Wild Mice:

Wild mice or laboratory mice that have been exposed to wild mice may have the potential of carrying a variety of zoonotic bacteria and viruses that can be passed on to those handling them. Tests are completed on wild mice when they are received in Baylor labs to screen for these zoonotic agents. Although this provides reasonable assurance that mice will be free of zoonotic infections, the screening does not guarantee infection-free mice. Therefore, because of the serious consequences of becoming infected, you must always follow good personal hygiene and animal handling procedures and use the provided PPE to protect yourself from exposure.

Mice that have originated from the wild or have had contact with wild mice could be infected with one or more of the illness agents described here:

Hantavirus

Hantavirus is transmitted through inhalation of dried rodent feces and urine when such material is raised into the air from disturbed bedding or nesting material. Transmission can also occur through rodent bites and contamination of broken skin or mucous membranes. The infection progresses from flu-like symptoms to respiratory complications and has resulted in death over 50% of the cases, particularly when medical care was not quickly obtained. You can prevent exposure through the use of provided PPE, good personal hygiene, and wet, properly ventilated handling of waste bedding material.

Lymphocytic Choriomeningitis (LCM) Virus

LCM virus is transmitted to humans by inhalation, broken skin or mucous membrane exposure to blood, urine, feces, and other body secretions from infected mice. The infection results in flu-like symptoms 1 to 3 weeks after exposure. More severe symptoms of meningitis and encephalitis can result. There is a special risk of exposure during pregnancy because the fetus can become infected.

Because mice are well-screened and provided from virus-free sources, the potential for exposure in Baylor University animal facilities is very limited. Again, use of proper PPE, such as disposable gloves and a lab coat along with careful hand washing will further reduce the likelihood of exposure.

Rats

Modern laboratory rats are bred to exclude all zoonotic agents. Therefore, unless the laboratory rats are exposed to wild rodents (those coming from the natural habitat outside the laboratory), 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.

Historically, rats have been known to carry the bacteria that cause ,b>Rat-Bite Fever. However, these bacteria have not been found in laboratory rats for decades due to the special efforts of commercial suppliers to eliminate this bacterium from breeding colonies.


Rabbits, Birds and Fish

Rabbits

Modern laboratory rabbits contain few infectious pathogens. Of concern are scratches that can be inflicted with their strong hind legs and sharp claws or from bites. Secondary infection with common skin, intestinal, and soil bacteria present on you or the animal can result, so always cleanse wounds immediately with soap and water or antiseptic and seek medical consultation for severe wounds.

Historically, laboratory rabbits have been known to harbor the bacteria for human Tularemia (Rabbit Fever). Although this zoonotic agent remains present in wild rabbit populations, modern laboratory rabbits are free of this illness bacterium.

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.

Salmonella

Salmonella bacteria is a common contaminate of fecal droppings and eggs. When ingested by humans, this bacterium has the potential for causing severe intestinal disease. Use of good personal hygiene measures, including effective and thorough hand washing along with the proper PPE, such as disposable gloves and lab coat, will greatly reduce the likelihood of infection when handling birds and materials in their environment.

Psittacosis

The bacteria Chlamydia psittaci is the cause of psittacosis, and it is found most widely in large, imported psittacine birds (i.e. parrots, parakeets, cockatoos, macaws). Human infection is most often the result of exposure to these imported birds. The risk of exposure from domestic birds is very low. However, because this bacteria is highly infectious, there is some potential that any bird or mammal may be infected. Acute infection in animals causes such symptoms as reddening of the eyes (conjunctivitis), difficulty breathing pneumonia), swollen painful joints (arthritis), and reproductive problems. After the acute infection, those animals that survive enter a period without symptoms during which stress can cause the animal to shed the bacteria. (Stress can result from such things as the importation process or birds being handled in their new environment.) Humans can be infected when coming in contact with the bird's body secretions, or feces. In humans, the symptoms include fever, headache, muscle pain, chills. If left untreated, the infection may cause pneumonia, liver, heart, and brain inflammation.

USDA regulations require that testing be performed on all psittacine birds imported from foreign countries during an initial 60 day quarantine period. Such birds are to be quarantined in specially ventilated rooms while testing is done and infected birds require elimination from the colony. If you are handling birds, use of protective apparel and thorough hand washing will reduce the risk of any potential exposure.

Fish and Amphibians

Fish and amphibians used in research colonies are mostly wild-caught or raised on commercial farms. These animals often contain parasites and bacteria. Of zoonotic concern are gram negative bacteria that will cause secondary infection of contaminated wounds and breaks in the skin. These bacteria include Aeromonas, Pseudomonas, Klebsiella, and Mycobacteria. Use of proper PPE, such as disposable gloves, will help prevent contamination of skin surfaces. Likewise, thorough hand washing is very important to further reduce potential for infection.


Bats

Bats

Exposure to wild bat roosts and handling of bats in the field presents a greater potential for exposure to rabies and the fungal disease histoplasmosis. Because the wild bats may have a greater potential to carry rabies virus or generate histoplasmosis spores in fecal-contaminated soil, there is greater need for care in handling of the animals and in disturbing and cleaning of fecal-contaminated roosts.

Bat bites and scratches and wound and mucous membrane exposure to bat saliva are the ways in which rabies can be transmitted. Spores of histoplasmosis can be present in soil and debris enriched with bird and bat droppings. When this dry soil is disturbed, spores can become airborne and cause infection by inhalation. In enclosed spaces where these conditions are present, it is important that protective clothing and dust mask be worn and that potentially-contaminated soil and debris that will be disturbed be moistened with water spray to control dust dispersion.

Rabies

Rabies is a preventable virus disease that causes an inflammation of the brain, and is almost always fatal once symptoms develop. Rabies is transmitted through the saliva of infected, warm-blooded animals. Worldwide, dogs are the most common source of rabies. In the United States, skunks, raccoons, foxes, coyotes, and bats are the main source of rabies infections. Most people who get rabies have been bitten by an infected animal, but getting the infected saliva from an infected animal into an open wound or mucous membrane of eyes, nose, or mouth can also lead to infection. Rabies is not spread by contact with bat feces, blood, or urine.

Rabies virus infects the central nervous system, causing brain inflammation and ultimately death. Early symptoms of rabies in humans are nonspecific, consisting of fever, headache, and general malaise. As the disease progresses, neurological symptoms appear and may include insomnia, anxiety, confusion, slight or partial paralysis, excitation, hallucinations, agitation, hypersalivation, difficulty swallowing, and hydrophobia (fear of water). Death usually occurs within days of the onset of symptoms.

Rabies can be prevented by avoiding contact with infected animals, and providing pre-exposure and/or post-exposure vaccination to those who have high-risk contact with animals presumed to be infected.

Post-exposure treatment should begin as soon as possible after exposure. It begins with a dose of rabies immune globulin given partially in the wound, if possible, and partially in the deltoid shoulder muscle. This is followed by a series of 5 vaccination injections given over 28 days.

A pre-exposure vaccine regimen consisting of 3 inoculations over 28 days is required for those working with laboratory bats. Completing the pre-exposure vaccine series does not eliminate the need for post-exposure treatment; it only reduces the post-exposure regimen.

In the event of a bat bite or mucous membrane exposure to bat saliva, it is critical that the following be done:

  1. Immediately wash the wound thoroughly with soap and water. Flush exposed mucous membranes of eye, nose, or mouth for 15 minutes at an eye wash station, sink drench hose, or hose from a potable water source.
  2. Proceed to Concentra Medical Center for medical evaluation and appropriate post-exposure treatment.

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.

Infection can be prevented by using the following precautionary measures:

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.

Field Studies

Field studies involving wild animal populations can expose workers to a number of additional Zoonoses that may be naturally endemic in some wild species. For those doing field studies involving birds, mice, and other wild species, more careful consideration needs to be given to conscientious use of PPE, good personal hygiene, i.e. hand washing, and appropriate training and application of good animal-handling techniques to minimize exposure to infection or injury.


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