Stanford University

Working Safely with Wild Rodents

Zoonoses are diseases that animals can transmit to humans. The following guide details the occupational hazards associated with wild rodents, as well as the precautions necessary for minimizing the risk of animal-to-human transmission of diseases.

Disease transmission from human to animal may also be a concern, particularly when working with potentially immunocompromised animals. Contacts are provided for further assistance.

How Can I Protect Myself?
  1. When working with wild rodents, take the following protective measures:

    • Always wear gloves and a laboratory coat, or other dedicated protective clothing, such as a scrub suit. In some cases, masks or protective eye wear is also indicated.
    • While working in an animal use area, do not eat, drink, or apply cosmetics.
    • After handling wild rodents, always wash your hands.
    • Unfixed tissues, body fluids, and other materials derived from wild rodents may also pose a risk.

    Bedding, hair, and fur may also exacerbate allergies.

    Contact EH&S at (650) 723-0448 for any concerns or questions you have about working with wild rodents. Contact the Veterinary Service Center at (650) 723-3876 for help with training personnel.

    Note that all personnel working with wild rodents are eligible to enroll in the Laboratory Animal Occupational Health Program (LAOHP). Contact EH&S at (650) 723-0448 for additional information.


If You Work with Wild Rodents
  1. Normally, rodents raised in clean facilities are relatively free of zoonotic diseases, unless they have been experimentally or accidentally infected with a human pathogen. All use of pathogenic organisms must be approved by the Administrative Panel on Biosafety (APB). An APB representative can help you determine the appropriate precautions for safeguarding your health. For more information, contact the Biosafety Officer at (650) 725-1473.

    Note that those working with wild rodents should be especially aware of possible allergic reactions. Reactions are often associated with cage cleaning (due to the dust hazards of bedding) and surface contact with urine.

    Wild rodents may act as carriers for viruses, such as hantavirus and lymphocytic choriomeningitis (LCMV). Additionally, each rodent species may harbor a range of bacterial diseases, such as tularemia and plague. Wild rodents may also carry insects that are vectors for disease.

    The following describes some of the causative agents and potential illnesses associated with wild rodents, along with protective measures, signs of illness, and what to do if an exposure or injury occurs.

    Lymphocytic Choriomeningitis Virus (LCMV)

    What is lymphocytic choriomeningitis?

    Lymphocytic choriomeningitis is caused by the lymphocytic choriomeningitis virus (LCMV), one of a family of viruses called arenaviruses, which are generally associated with rodent-transmitted disease in humans.

    How is LCMV spread?

    The rodent hosts of arenaviruses are chronically infected with the viruses, but they do not appear to cause obvious illness in them. LCMV appears to be passed from mother rodents to their offspring during pregnancy, then remains in the population, generation after generation.

    Human infection is incidental to the natural cycle of the viruses, and occurs when a person comes into contact with the excretions (or materials contaminated with the excretions) of an infected rodent. This can occur through ingestion of contaminated food or by direct contact of abraded or broken skin with rodent excrement. Infection can also occur through inhalation of tiny particles soiled with rodent urine or saliva. Human LCMV infection partly depends upon the prevalence of infected animals in a population and the proximity of contact with them.

    Who is at risk for infection?

    The risk of contact and infection depends on the habits of both humans and rodents. Where the infected rodent species prefers a field habitat, the risk of human infection is associated with agricultural work. In areas where the rodent species’ habitat includes human homes or other buildings, infection is more likely to occur in domestic settings. Pregnant women who are exposed to LCMV have a high risk of fetal transmission.

    Is LCMV infection serious?

    LCMV causes aseptic (non-bacterial) meningitis. A number of arenaviruses cause hemorrhagic fever.

    The clinical spectrum of acquired human LCMV infection ranges from inapparent and asymptomatic to (in rare instances) severely symptomatic, systemic, and fatal central nervous system (CNS) disease. Additionally, pregnancy-related infection has been associated with congenital hydrocephalus, chorioretinitis, and mental retardation.

    How can I protect myself?

    • Limit contact with the blood, urine, or feces of potentially infected animals.
    • Wear personal protective clothing and implement secondary containment and engineering controls when handling potentially infected animals.
    • Workers in potentially high-risk settings, such as rural field research, should receive a thorough orientation about LCMV transmission and the symptoms of the disease.
    • If you develop febrile or respiratory illness within 45 days of potential exposure, seek medical attention immediately.
    • Use disinfectants. LCMV is susceptible to dilute hypochlorite solutions (bleach), 70% ethanol, detergents, phenolics, and most general household disinfectants.
    • Wear rubber, plastic, or latex gloves when handling rodents, cages, or traps contaminated by rodents, or whenever you have broken skin. Before removing gloves, wash gloved hands in a disinfectant, then in soap and water. Thoroughly wash hands with soap and water after removing gloves. (If this is not possible, rinse gloves with water, or use a disinfectant wipe.) Wash hands thoroughly at the end of every work period.
    • Pregnant women should avoid contact with wild rodents.

    What are the signs of infection?

    In adults, LCMV is typically a biphasic disease, with symptoms of fever, malaise, myalgias, anorexia, nausea, vomiting, pharyngitis, cough, and adenopathy, followed by defervescence and a second phase of CNS disease. However, CNS symptoms may appear without any prodrome, or may never develop. Meningitis and meningoencephalitis are the most frequent neurologic manifestations.

    What do I do if an exposure or injury occurs?

    Exposure to aerosols, bites, or scratches involving animals, or injuries from objects contaminated with body fluids from animals, require immediate first aid and medical attention. Always notify your supervisor immediately.

    Between 8:00 am and 5:00 pm, proceed to Stanford Occupational Health Clinic at 480 Oak Road, Room B15, 5-5308.

    After 5:00 pm and before 8:00 am, call (650) 723-2670 or proceed to the Stanford Emergency Room, H126 (in the hospital, next to the cafeteria).

    Hantavirus

    What is Hantavirus?

    Hantavirus is the virus that causes Hantavirus Pulmonary Syndrome (HPS), which has only very recently been recognized as a disease in North America. It is fairly uncommon, and the chances of infection are low. However, HPS can be deadly, and immediate intensive care is essential once symptoms appear.

    Since the first detection of HPS, in the Four Corners area (New Mexico, Arizona, Colorado, and Utah) in 1993, it has been found in over half of the United States. Hantaviruses that cause HPS are carried by rodents, and by the deer mouse in particular.

    How is Hantavirus spread?

    Rodents shed the virus in their urine, droppings, and saliva. It is primarily transmitted to people through inhalation of air contaminated with the virus. This happens when fresh rodent urine, droppings, or nesting materials are stirred up (i.e. aerosolization). There are several other ways rodents may spread Hantavirus to people:

    • If you touch something that has been contaminated with rodent urine, droppings, or saliva, then touch your nose or mouth
    • If you eat food that is infected with rodent urine, droppings, or saliva
    • If a hantavirus-infected rodent bites you (rarely)

    The types of Hantavirus that cause HPS in the US cannot be transmitted from person to person, or from animals other than rodents or insects.

    Who is at risk for infection?

    Anyone who comes into contact with wild rodent droppings, urine, or nesting materials is at risk for infection. You may be at risk if your activities or occupation require that you directly handle rodents, their droppings, or their bedding.

    Is Hantavirus infection serious?

    HPS infections can be deadly, and immediate intensive care is essential once symptoms appear.

    How can I protect myself?

    • Practice good personal hygiene at all times. Wash your hands with soap and water or with a disinfectant wipe after working with animals.
    • Workers in potentially high-risk settings, such as rural field research, should receive a thorough orientation about Hantavirus transmission and the symptoms of the disease.
    • If you develop febrile or respiratory illness within 45 days of potential exposure, seek medical attention immediately.
    • Use disinfectants. Hantaviruses are susceptible to dilute hypochlorite solutions (bleach), 70% ethanol, detergents, phenolics, and most general household disinfectants.
    • Wear rubber, plastic, or latex gloves when handling rodents, cages, or traps contaminated by rodents, or whenever you have broken skin. Before removing gloves, wash gloved hands in a disinfectant, then in soap and water. Thoroughly wash hands with soap and water after removing gloves. (If this is not possible, rinse gloves with water, or use a disinfectant wipe.) Wash hands thoroughly at the end of every work period.
    • Workers may need to wear respirators when handling field-caught rodents or contaminated traps or cages, or when disturbing rodent burrows and nests. Until the infectivity of Hantavirus is better understood, respirators should be used to minimize exposure to airborne particles of rodent excreta during procedures that generate aerosols. The proper use of respirators will provide protection against airborne particles. However, the incorrect use or care of respirators may increase, rather than decrease, the risk of exposure to harmful agents. If respirators cannot be maintained in a sanitary condition, do not use them.

    What are the signs of infection?

    The length of the incubation period is likely between one and five weeks. Universal symptoms include fatigue, fever, and muscle aches, especially in the large muscle groups (e.g. thighs, hips, back, and shoulders).

    Symptoms may also include headache, dizziness, chills, and abdominal problems, such as nausea, vomiting, diarrhea, and abdominal pain. About half of all HPS patients experience these symptoms.

    Four to 10 days after these early symptoms, patients usually develop coughing and shortness of breath.

    What do I do if an exposure or injury occurs?

    Exposure to aerosols, bites, or scratches involving animals, or injuries from objects contaminated with body fluids from animals, require immediate first aid and medical attention. Always notify your supervisor immediately.

    Between the hours of 8:00 am and 5:00 pm, proceed to Stanford Occupational Health Clinic at 480 Oak Road, Room B15, 5-5308.

    After 5:00 pm and before 8:00 am, call (650) 723-2670 or proceed to the Stanford Emergency Room, H126 (in the hospital, next to the cafeteria).

    Tularemia

    What is tularemia?

    Caused by the bacteria Francisella tularensis, tularemia is a highly infectious disease that can affect both animals and humans. It is particularly associated with rabbits, but may also be carried by rodents, deer, pets, and many other animals. Those whose occupations put them into frequent contact with these animals, particularly wild animals, are at the greatest risk for contracting tularemia.

    How is tularemia spread?

    There are two common ways that humans can contract tularemia:

    • From the bite of an infected tick, deerfly, or mosquito
    • When blood or tissue from infected animals (especially rabbits) comes into contact with the eyes, mouth, or cuts or scratches on the skin

    It is also possible to contract tularemia by drinking contaminated water, or by breathing dust that contains the bacteria. The disease is not transmitted from person to person.

    Who is at risk for infection?

    Anyone can get tularemia if they spend time in outdoor areas near infected animals, deerflies, or ticks. Rabbit hunters, trappers, and laboratory workers who work with rabbits are at higher risk.

    Is tularemia infection serious?

    Without treatment, tularemia lasts for two to three weeks, with a prolonged convalescence. Antibiotics can be used to eliminate the infectious bacteria. If you suspect that you have been infected, seek care from a medical professional immediately.

    How can I protect myself?

    • Wear face masks, gowns, and rubber gloves when handling animals or working with cultures or infective material in a laboratory.
    • If you are doing field work that involves handling wild animals, use insect repellent containing 20 to 30% DEET. Wear long pants and long-sleeved clothes.
    • Thoroughly wash hands after handling animals.
    • Sanitize lab and surgical areas after animal work.
    • Use disposable supplies whenever possible.

    What are the signs of infection?

    Symptoms of tularemia may appear within one to 14 days, but usually within three to five days. Flu-like symptoms of fever, chills, headaches, muscle aches, chest pain, and coughing are common.

    However, more specific symptoms depend on how the bacteria entered the body. If tularemia is caused by the bite of an infected insect, or from bacteria entering a cut or scratch, it usually causes a skin ulcer and swollen glands. If it is caused by eating or drinking food or water containing the bacteria, it may produce a throat infection, stomach pain, intestinal pain, diarrhea, and vomiting. Breathing dust containing the bacteria may cause a pneumonia-like illness.

    What do I do if an exposure or injury occurs?

    Exposure to aerosols, bites, or scratches involving animals, or injuries from objects contaminated with body fluids from animals, require immediate first aid and medical attention. Always notify your supervisor immediately.

    Between 8:00 am and 5:00 pm, proceed to Stanford Occupational Health Clinic at 480 Oak Road, Room B15, 5-5308.

    After 5:00 pm and before 8:00 am, call (650) 723-2670 or proceed to the Stanford Emergency Room, H126 (in the hospital, next to the cafeteria).

    Plague

    What is plague?

    Plague is caused by infection with the bacterium Yersinia pestis, which is carried by rats, other rodents, and their fleas. It is manifested in bubonic and pneumonic forms. Human infections are initially transmitted from rodents by rat fleas, but the disease may shift into the pneumonic form, then spread from person to person.

    How is plague spread?

    Plague is transmitted to humans primarily through the bite of infected rat fleas. It is also possible to contract bubonic plague when cuts or other breaks in the skin come into direct contact with the body fluids or tissues of infected animals. In bubonic plague, the bacilli spread from a local abscess at the flea bite site to draining lymph nodes. Person to person transmission can occur through fleas, but much more commonly occurs via respiratory droplets in the pneumonic form.

    Who is at risk for infection?

    Anyone who is exposed to fleas from diseased rodents is at risk for infection, as is anyone who has close contact with infected animals. This includes travelers to rural areas with large numbers of plague-infected rats, and laboratory workers who have close contact with infected or potentially infected animals, or who work with the Yersinia pestis bacterium itself.

    Is plague infection serious?

    Plague infection is extremely serious, and early clinical diagnosis is essential. If untreated, the fatality rate is 60% (bubonic) to 100% (septicemic or pneumonic). With antibiotic treatment, the chances of survival are greatly increased.

    How can I protect myself?

    The best way to protect yourself against plague is to be aware of its signs and symptoms. You should also avoid wild rodents as much as possible. Note that some species may be more susceptible to infection with Yersinia pestis than others.

    What are the signs of infection?

    Symptoms of plague include general malaise, high fever, and pain or tenderness at the regional lymph nodes. The lymph nodes become hot, swollen, tender, and hemorrhagic, giving rise to characteristic black buboes. This swelling of the lymph nodes, along with skin blotches and delirium, can occur within a few days of infection. Once the infection enters the bloodstream, the liver, spleen, and lungs are affected, and the patient develops a severe bacterial pneumonia. Septicemia can also develop, with or without lymph node involvement.

    What do I do if an exposure or injury occurs?

    Exposure to aerosols, bites, or scratches involving animals, or injuries from objects contaminated with body fluids from animals, require immediate first aid and medical attention. Always notify your supervisor immediately.

    Between the hours of 8:00 am and 5:00 pm, proceed to Stanford Occupational Health Clinic at 480 Oak Road, Room B15, 5-5308.

    After 5:00 pm and before 8:00 am, call (650) 723-2670 or proceed to the Stanford Emergency Room, H126 (in the hospital, next to the cafeteria).


Who Is at Risk for Infection?
  1. Bites or scratches involving wild rodents, or injuries from objects contaminated with body fluids from wild rodents, require immediate medical attention. Always notify your supervisor in these cases.

    Between 8:00 am and 5:00 pm, Monday through Friday, contact the Stanford University Occupational Health Center (SUOHC) at (650) 725-5111 for immediate phone triage and to schedule an urgent drop-in appointment time.

    For immediate, life-threatening injuries, or when SUOHC is closed, go directly to the Stanford University Medical Center Emergency Department.



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