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Veterinarian Technician January 2013 (Vol 34, No 1)

Zoonosis: What’s All the Fuss About?

by Ann Wortinger, BIS, LVT, VTS (ECC, SAIM, Nutrition)

    Zoonosis is defined as “an infection that is known in nature to infect both humans and lower vertebrate animals.”1 For people working with animals, zoonosis is a unique occupational hazard, but it is also a risk for veterinary clients. While zoonoses are typically assumed to be transmitted from animals to humans, humans can transmit disease to their companion animals; human-to-animal transmission is commonly referred to as anthroponosis, anthropozoonosis, or reverse zoonosis.2

    More than 800 human pathogens are known to be zoonotic; 20 to 30 of these can be transmitted by dogs or cats.3,4 TABLE 1 lists several important zoonoses in the United States.3 An estimated 75% of emerging diseases, which are primarily viral, are zoonotic.2,5

    Transmission of Pathogens

    Disease transmission requires a source of infection, host susceptibility, and a route of transmission. Animal sources of infection can include endogenous microflora that are pathogenic to humans. Routes of transmission include any way in which an organism can enter the body. The main routes are direct contact, aerosolization, and vector-borne transmission.3

    Direct Transmission

    Direct transmission of pathogens can occur through ingestion, a puncture wound (e.g., a needlestick, a bite, a scratch), or mucous membrane exposure. Zoonoses are primarily transmitted through direct contact. Therefore, the best way to prevent transmission is by following veterinary standard precautions3 (see “Veterinary Standard Precautions” below) for minimizing the spread of zoonoses from recognized and unrecognized sources. Dog and cat bites and scratches, as well as kicks, scratches, and crush injuries from any species, account for most occupational injuries in veterinary personnel. According to one report, approximately 3% to 18% of dog bite wounds and 28% to 80% of cat bite wounds become infected with a mix of aerobic and anaerobic bacteria.3 Needlestick injuries are the most frequent accidents in the veterinary workplace. These injuries usually involve inadvertent injection of a vaccine but also result in inoculation of bacteria from fine-needle aspirates.

    Zoonoses associated with direct transmission include mite infestation, dermatophyte infection, cutaneous larva migrans (hookworms), visceral larva migrans (roundworms), Pasteurella infection, Bartonella infection, Salmonella infection, Escherichia coli 0157:H7 infection, sporotrichosis, and rabies.3 Dermatophytes, Salmonella spp, and E. coli 0157:H7 can also be transmitted from fomites (indirect transmission). Ingestion of Toxocara or Salmonella spp can lead to infection. Humans can contract Bartonella henselae infection (cat-scratch fever) through a scratch or bite from an infected cat; B. henselae is typically transmitted to cats through ingestion of infected fleas.6

    Indirect Transmission

    Indirect transmission of pathogens can occur through aerosol transmission or exposure to fomites, such as when cleaning cages and equipment or handling dirty laundry. Staphylococcus spp, Leptospira spp, Tularemia spp, Bacillus anthracis (anthrax), and Yersinia pestis (plague) can be transmitted from fomites.3 In aerosol transmission, a pathogen travels through the air in (1) droplets that are deposited on mucous membranes or (2) small particles that are inhaled. Droplets can be generated by coughing, sneezing, and vocalization. Exposure can also occur through procedures (e.g., lancing of abscesses, dental procedures) in which infected material is mixed with water and aerosolized (dispersed into the air). Particles may also be aerosolized through (1) the use of suction units, bronchoscopy, and high-pressure spray washers, (2) sweeping, and (3) vacuuming. Influenzavirus A, Hantavirus spp, Cryptococcus spp, and B. anthracis are candidates for aerosol transmission. Zoonoses associated with aerosol transmission include Bordetella infection, influenza, pneumonic plague (Y. pestis infection), and tuberculosis.3 In general, the risk of aerosol transmission increases with decreasing distance from the source and increasing duration of exposure.3 Once aerosolized, certain pathogens may remain infective over long distances. This depends on particle size, the nature of the pathogen, and environmental factors such as temperature and humidity.3

    Vector-borne Transmission

    Vector-borne transmission occurs when an infected vector such as a flea, mosquito, or tick transmits infection during its normal feeding activities. Working outdoors (e.g., large animal veterinary professionals) increases the risk of exposure to insects and other biologic vectors.3 Zoonoses associated with this route include Lyme disease, plague, anthrax, and Rocky Mountain spotted fever.3


    The first steps in preventing zoonoses are (1) remembering that diseases can be transmitted between humans and animals and (2) knowing the various means of transmission. The next step is educating veterinary personnel and clients. A 1999 study involving 327 veterinarians and 322 physicians was performed to determine how frequently they encounter zoonoses and educate the public on them.7 The results revealed that veterinarians encounter zoonoses and discuss them with their clients more frequently than do physicians. Small animal practitioners encounter or discuss zoonoses more frequently (approximately once a week) than do large animal veterinarians. Physicians indicated that “veterinarians should play an equal or greater role in advising patients about zoonotic diseases” and “veterinarians should be involved not only in controlling zoonotic disease pathogens in animals but also in providing information for patients and physicians.” However, the study revealed an almost complete lack of communication between physicians and veterinarians about zoonotic issues.7 Physicians and veterinarians need to initiate discussions about zoonoses with their patients and clients, respectively, to advise them on how to reduce the zoonotic risks associated with pet ownership.

    As the incidence of zoonoses rises, the legal consequences for veterinary professionals are likely to increase. Veterinarians are increasingly concerned about the threat of legal liability for failing to (1) diagnose and treat animals with zoonoses or (2) educate clients on zoonotic risks.7 There is no legal definition for zoonosis, and only one case has demonstrated the risk of legal action against a business after a person acquired a zoonosis.7 In the case, a child in New Haven, Connecticut, sustained permanent vision loss due to ocular larval migration of a Toxocara organism transmitted by a puppy. The pet store that sold the puppy settled out of court with the child’s family for $1.5 million. Until the settlement, the prosecution had handled the case as a product liability issue: the puppy was a product, and the pet store could be liable for injury due to the product. The store owner was allegedly negligent for failing to deworm the puppy, have a deworming program, and keep medical records of the pets it sold.

    To help prevent legal action regarding zoonoses, veterinary professionals need to have a proactive approach:

    • Identify resources to educate the entire veterinary staff about zoonoses, especially those transmitted by parasites.

    • Educate clients about the health risks of zoonoses associated with pet ownership. Reinforce this message with client handouts.

    • Develop effective parasite control programs and recommend them to clients.

    • Keep a record of all medical treatments you provide and all recommended treatments and diagnostic tests that clients decline.

    • Ensure that your parasite-detection system is as accurate as possible. Ensure that test samples are fresh and representative of the patient’s condition (e.g., if the patient has diarrhea, a formed part of the stool should not be used for the fecal examination). Use the most accurate diagnostic method (e.g., centrifugation rather than gravity flotation, as recommended by the Companion Animal Parasite Council). Ensure that the staff is trained to accurately identify microscopic findings.

    • Have each client sign a form releasing the veterinarian from liability if the client does not consent to recommended treatments and diagnostic procedures, such as deworming.8

    Veterinary Standard Precautions

    Veterinary standard precautions should be used whenever personnel have nonintact skin or may be exposed to potentially infectious materials, including feces, blood, bloody fluid, or exudate.3 These precautions include strategies to reduce the potential for bites and other trauma that may result in exposure to zoonotic pathogens. For more information, see “Guidelines for Reducing Pathogens in Veterinary Hospitals: Disinfectant Selection, Cleaning Protocols, and Hand Hygiene” (Compendium, May 2010).

    Consistent, thorough hand washing is the most important measure for reducing the risk of disease transmission. In veterinary practice, hand washing is preferred to using antimicrobial lotions or rubs because veterinary personnel are routinely exposed to organic materials such as blood, feces, and exudate. Most disinfectants do not penetrate or remove organic material, which can harbor infective organisms. Hand washing with plain (non-antibacterial) soap and running water mechanically removes organic material and reduces the number of bacteria on the skin. Hands should be washed for a minimum of 20 seconds each time.3 To help reduce the opportunity for cross-contamination, liquid or foam soap is recommended over bar soap.3 Refillable containers should be emptied, cleaned, and refilled to prevent creation of a bacterial reservoir. Autoclavable containers provide even better protection against resistant bacteria. The use of a moisturizing soap can help improve compliance and maintain skin integrity by helping to prevent dry, cracked skin.3

    Alcohol-based rubs or lotions are highly effective against bacteria and enveloped virusesa but should be used only if hands are not visibly soiled with organic matter. These products are not as effective against nonenveloped viruses (e.g., parvovirus), bacterial spores (e.g., Clostridium spp), or protozoal parasites (e.g., coccidia, Cryptosporidium spp). When using a rub or lotion, apply it to one hand and rub it over all the surfaces of the hands and fingers. The hands should be rubbed together until the product has dried completely.3

    Facial protection can help prevent the mucous membranes in the eyes, nose, and mouth from being exposed to infectious materials. Facial protection should be used whenever exposure to splashes or sprays is likely, such as during lancing of abscesses, flushing of wounds, dental procedures, nebulization of medications, suction or lavage of wounds, and necropsies. Adequate facial protection includes wearing a surgical mask with goggles or a face shield. Wearing a surgical face mask provides adequate protection during most veterinary procedures that generate potentially infectious, large droplets.3

    Using gloves can help to reduce the risk of pathogen transmission by providing a physical barrier between pathogens and the hands. However, using gloves is not a substitute for hand washing. Gloves should be worn when handling an animal that shows evidence of disease or has an unknown medical history. Gloves should also be worn when skin on the hands is not intact or when contact with feces, blood, body fluid, secretion, excretion, or exudate is likely, including cleaning of cages, litterboxes, and surfaces such as countertops and work tables.3 Gloves should be changed between examinations of individual animals or groups of animals (e.g., litters of puppies or kittens), between clean and dirty procedures performed on a single patient, and whenever a glove is torn or its integrity is questionable. Dirty gloves should be removed promptly after use, and contact between the user’s skin and the outer glove surface should be avoided. Do not reuse disposable gloves! After glove removal, immediately wash the hands to remove possible contamination.

    Protective outerwear such as laboratory coats and coveralls is designed to protect clothes or scrubs from contamination. This type of outerwear is not usually fluid resistant, so it should not be used when splashing or soaking of potentially infectious material is likely. Outerwear should be promptly changed and laundered (using standard laundry detergent and machine drying3) or disposed of when it becomes visibly soiled with feces or body fluids. Outerwear should be changed daily and not worn outside the work environment.3

    Nonsterile gowns provide a better moisture barrier than do laboratory coats and can be used for general care of animals in isolation. Impermeable gowns should be used when splashing or a large amount of fluid is anticipated. Disposable gowns should not be reused. Reusable fabric gowns may be used repeatedly for the same animal in isolation but should be laundered between contact with different animals or when soiled.

    Gloves and gowns should be removed and placed in the garbage or laundry before veterinary personnel leave the animal’s environment. Hands should be washed immediately after leaving.

    To help prevent bite injuries, (1) use effective physical restraint, bite-resistant gloves, muzzles, sedation, or anesthesia and (2) have experienced veterinary personnel rather than clients restrain patients. If an animal is aggressive or unpredictable or has a history of biting, this information should be in the patient record and communicated to attending personnel.

    This discussion of standard precautions is not complete but addresses the most common issues affecting veterinary personnel and clients. Make sure that you know the common zoonoses in your area and the standard precautions for each of them. Give clients gloves and/or surgical masks, when appropriate, to help prevent zoonotic exposure at home.

    aEnveloped viruses have an outer protein layer that (1) facilitates entry into host cells but (2) makes the viruses more susceptible to desiccation (drying), heat, and detergents.

    1. Medicinenet.com. www.medterms.com. Accessed November 15, 2012.

    2. Colville J, Berryhill D. Principles of zoonoses. In: Handbook of Zoonoses: Identification and Prevention. St. Louis, MO: Elsevier; 2007:2-13.

    3. Elchos B, Scheftel J, Cherry B, et al. Compendium of veterinary standard precautions for zoonotic disease prevention in veterinary personnel. J Am Vet Med Assoc 2008;233(3):415-432.

    4. Ford R. Zoonoses: how real the threat? Proc Am Anim Hosp Assoc 2008.

    5. Chomel B, Belotto A, Meslin F-X. Wildlife, Exotic Pets, and Emerging Zoonoses. Centers for Disease Control and Prevention. www.cdc.gov/ncidod/eid/13/1/6.htm. November 15, 2012.

    6. Haubenstricker S. Bartonella infection: an underrecognized threat. Vet Tech 2010;31(9):E1-E5.

    7. Grant S, Olsen C. Preventing Zoonotic Disease in Immunocompromised Persons: the Role of Physicians and Veterinarians. Centers for Disease Control and Prevention. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2627689/. Accessed August 21, 2012.

    8. Zoonotic Diseases 102: the Issue of Liability. VetMedTeam. www.vetmedteam.com. Accessed September 15, 2006.

    References »

    NEXT: Degenerative Joint Disease in Cats


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