Module 04 - Occupational Health and Safety

Biological Hazards of Working with Experimental Animals

Zoonoses

Definition: The CCAC Guide defines zoonosis as a disease of animals that may under natural conditions be transmitted to humans. What this really means is a disease that it is communicable between animals and humans.

The list of potential zoonoses related to working with animals in research, teaching or testing is quite long, and numerous books have been written on the subject. (See Appendix VII Zoonoses of Volume 1 of the CCAC Guide to the Care and Use of Experimental Animals) However, in reality the risks are very low when dealing with the common small laboratory animal species in the laboratory. There are several reasons for this low risk. Firstly, commercial suppliers of laboratory animals have done an excellent job of producing disease-free animals. As well, institutions generally have developed good occupational health and safety programs that include active veterinary monitoring and care programs.

The risk of exposure to zoonotic diseases is greater for those who work with experimental animals from random sources (including cats, dogs and most livestock), and for field researchers studying wild animals in their habitat. Working with non-human primates in the laboratory is a special case because of the many zoonotic concerns.

A few of the most common zoonoses in each of these areas of animal research will be presented as examples. For more information on zoonoses, and for more information about specific disease organisms, the Material Safety Data Sheets (MSDS) for individual organisms published by Health Canada Office of Laboratory Security can be consulted.

Routes of Exposure

Common routes of exposure to infectious organisms are:

• aerosol (inhaling the organisms)
  
• ingestion (swallowing the organisms)
  
• absorption through the skin, through mucus membranes or skin wounds
  
• injection (accidental, in research)

The use of appropriate equipment, including personal protective equipment appropriate to the route of exposure for a particular infectious organism, and appropriate practices, will minimize the risk of exposure.

Zoonoses Associated with Commercially Produced Laboratory Animal Species

As noted above, the risk of exposure to a zoonosis while working with common small laboratory animals that are commercially reared is very small. One example is presented here: Rat bite fever.

Rat Bite Fever

• Organism name, and synonyms: Streptobacillus moniliformis, a Gram-negative bacteria. Synonyms: Rat-bite fever, Haverhill fever.
  
• Reservoir: Rats. Commensal in the mouth and pharynx.
  
• Mode of Transmission: Animal bite, direct contact with secretions of the mouth, nose, eye of an infected animal.
  
• Incubation Period: 3-10 days.
  
• Clinical Disease: Initial bite wound usually heals. Sudden onset of fever, chills, vomiting, headache and joint pains, rash.
  
• Epidemiology: Uncommon in North America.
  
• Communicability: Not directly transmitted from person to person.

Zoonoses Associated with Random Source Laboratory Animal Species

Ringworm

Ringworm is a fungal infection of the skin that can occur in a wide range of animals including humans.

• Organism names, and synonym: Microsporum spp., Trichophyton spp., fungal organisms. Synonyms: Ringworm, dermatomycosis, tinea.
  
• Reservoir: Most domestic and wild animals, and humans. May be latent in hair of some species.
  
• Mode of Transmission: Direct or indirect contact with skin lesions or infected hair, or fomites (brushes, clippers, etc.).
  
• Incubation Period: 4-10 days.
  
• Clinical Disease: The fungi infect keratinized areas of the body - hair, skin and nails. Signs include round lesion of scaling skin, hair loss or breakage, sometimes reddened and crusting of infected skin.
  
• Communicability: Communicable from person to person when infective lesions are present.
  
• Diagnosis and Prevention: Monitoring for typical signs, confirmed by skin scrapings and culture. Many treatments are available.

Rabies

Rabies can infect any mammal, including humans. Purpose-bred laboratory animals are not a likely source of rabies. However wild animals, animals obtained from random sources, or livestock, may carry rabies. Many institutions have rabies vaccination policies for at-risk personnel.

• Organism name, and synonym: Rabies - a rhabdovirus, Rabies, Hydrophobia.
  
• Reservoir: Wild and domestic animals (e.g., dogs, cats, foxes, coyotes, skunks, racoons) and bats.
• Livestock and rodents may be secondary hosts if infected by a biting animal.
  
• Mode of Transmission: Most commonly by a bite which introduces the virus from the saliva of a rabid animal. May be airborne in caves inhabited by infected bats.
  
• Incubation Period: Usually a few weeks, but may be up to a year or longer. The virus propagates in nerves. Thus the site of the wound (distance from the brain), presence of nerves at the wound, etc., influence the incubation period.
  
• Clinical Disease: Once clinical signs appear, the clinical course is short - usually less than 10 days with death due to respiratory paralysis. Signs include apprehension, behavioural changes, spasms of swallowing muscles, delirium, weakness progressing to paralysis.
  
• Epidemiology: Worldwide distribution with some rabies free areas. All mammals susceptible.
  
• Communicability: Infected animals shed virus for a few days before clinical signs appear. From then until the death of the animal, it is infectious.
  
• Diagnosis and Prevention: Pre-exposure immunization of all individuals at high risk (those who will handle animals, including laboratory workers, veterinarians and other animal handlers) should be used. The human diploid cell vaccine (HDCV) is currently used. Post-exposure treatment includes immediate first aid by generously flushing the wound and washing with soap and/or antiseptics, and providing post-exposure treatments as directed by the physician (e.g. rabies immune globulin, and vaccination).

Zoonoses Associated with Farm Animal Species

Q Fever

Q Fever may be contracted from working with sheep or goats, particularly ewes during lambing. The placenta and fetal fluids contain high levels of the organism in infected ewes.

• Organism name, and synonyms: Coxiella burnetii, an intracellular bacteria. Synonyms: Q Fever, Query fever, Rickettsia
  
• Reservoir: Most common in sheep, cattle, goats. Infected domestic animals usually asymptomatic but shed massive numbers of organisms at parturition, in the placenta and placental fluids.
  
• Mode of Transmission: Direct contact with infected animals and their birth fluids; inhalation of organisms in dust from contaminated premises; wool from sheep.
  
• Incubation Period: Usually 2-3 weeks.
  
• Clinical Disease: Sudden onset fever, chills, headache, weakness, malaise, severe sweats; pneumonia, usually self-limiting. Chronic infection mainly involves endocarditis. Up to half of infections are asymptomatic.
  
• Epidemiology: Worldwide distribution. Occurs in laboratories using sheep for research; cases in research staff, exposed hospital patients.
  
• Communicability: Direct transmission from person to person very rare.
  
• Prevention: Use of appropriate protective clothing including masks. Serologic monitoring of ewes of limited value. Appropriate sanitation procedures. Vaccination available.

Zoonoses Associated with the Non-human Primates

As noted earlier, non-human primates are a potential source of many zoonotic diseases, and special facilities, equipment and procedures are required to work with them safely. The zoonosis discussed here - Herpes B infection - is the one that most people will have heard about.

Herpes B virus Infection

Herpesvirus simiae (B virus) causes a fatal ascending encephalitis in humans infected from old world non-human primates. The disease in the host non-human primates is usually mild or asymptomatic.

Rhesus monkey infected with Herpesvirus simiae. Note the ulcers in the inner mucosal surface of the lower lip.

• Organism name and Synonym: Herpesvirus simiae, a DNA herpesvirus. Synonyms: B virus, Monkey B virus, Simian B disease.
  
• Reservoir: Common in old world monkey of the macaque group (most common in rhesus and cynomolgus macaques), both wild and captive colonies.
  
• Mode of Transmission: Latent infection in macaques with periodic episodes of oral lesions and shedding of virus in saliva. Transmission after a bite or direct or indirect contact with infected saliva or tissues. Laboratory infections from infected tissues can occur. Aerosol exposure minimal.
  
• Incubation Period: 3 days to a month.
  
• Clinical Disease: Acute, usually fatal, ascending encephalomyelitis; fever with headache, lesions at site of exposure. Death in 1 day - 3 weeks after onset of symptoms in over 70% of cases.
  
• Epidemiology: Occurs in veterinarians, laboratory workers and others handling old world monkeys or tissue cultures derived from these species.
  
• Communicability: Transmission from person to person rare.
  
• Prevention: Appropriate use of protective laboratory clothing (long sleeved lab coats, face shields or surgical masks and goggles or glasses), proper methods of restraint.

Zoonoses Associated with Wild Animals and Field Studies

Hantavirus Infection

Deer mouse - Peromyscus sp. The main rodent reservoir for Hantavirus infection in humans.

• Organism name, and synonym: Hantavirus, an RNA virus in the Bunyavirus family. Synonyms:
  hantavirus, hantavirus pulmonary syndrome (HPS), Sin Nombre Virus (SNV) in North America.
  
• Reservoir: Wild rodents such as Peromyscus (deer mouse) and Microtus species in the Americas.
  
• Mode of Transmission: Inhalation of the virus in the dust from areas where infected rodent excreta (urine and feces) are present is the most common route. Rodent bites may transmit the disease.
  
• Incubation Period: Average two to four weeks but may be shorter or longer.
  
• Clinical Disease: Hantavirus Pulmonary Syndrome (HPS) is characterized by a sudden onset fever, pain, vomiting, and onset of respiratory distress and prostration. Mortality rates are high despite symptomatic treatment.
  
• Epidemiology: Occurs throughout much of North America including the western provinces.
  
• Communicability: Not thought to be communicable between persons.
  
• Diagnosis and Prevention: Use of personal protective equipment to avoid inhaling the dust particles with virus, and other direct contact in high risk areas should be used. Field biologists and persons working in previously "contaminated" buildings are at risk. Guidelines for protection against infection and for decontaminating facilities are available at this web site.