Zoonotic diseases are those acquired by humans from contact with animals. The risk to a veterinary employee depends on the type and extent of animal contact and the prevalence of disease in those animals. Those at risk in the workplace include companion and large animal veterinary staff and avian and exotic species veterinary staff.
The Veterinary Nurse plays an important role in educating clients on preventative health issues for their pets and may be required to provide current information on the risks associated with pet ownership relating to zoonotic diseases.
Training and development of staff in the practice must include aspects of public health and safety of staff in relation to working with sick animals. To minimise any potential exposure to zoonotic diseases, nursing and kennel staff must be aware of the importance of maintaining high standards in hygiene.
Principles of Zoonotic Disease Prevention
Detergent and hot water are extremely effective against killing the majority of zoonotic pathogens. Hands should be washed with detergent and hot water before and after handling animals, animal feed, bedding and equipment.
A working knowledge of the correct disinfectants to use in the presence of a zoonotic disease is required. This ensures that the cleaning component of the husbandry techniques will be effective. Educating staff in appropriate handling of chemicals is essential. Material Safety Data Sheets must be made available to all staff working with chemicals.
Microorganisms in order of increasing resistance to disinfection:
Aerosols and Droplets
In many cases high-pressure hoses are the preferred method of cleaning animal wards, kennels and runs. However, this can create infectious aerosols and droplets, which have the potential to increase exposure to staff. In addition to human health risk, aerosolisation also creates a potential environment for cross contamination within animal facilities.
Personal Protective Equipment
Restraint gloves and work apparel of a quality that affords protection to the staff are essential. Facemasks, and in some cases eye wear, must be made available to staff to wear when handling aggressive animals. In situations where a known zoonotic disease is present, protective apparel may become compulsory attire as a part of a protocol when cleaning the environment.
Baffle boards, nets, catching poles, pole syringes and pet packs must be maintained in good condition to ensure the animal can be restrained or medicated at a distance to reduce the incidence of bites and scratches.
Diet preparation areas for animals must be separate from areas where staff prepare and consume food. In areas where meat products are prepared, hot water and detergent must be available to clean all chopping boards and knives. Colour coded chopping boards provides visual identification of boards for meat verses those for fruit and vegetables.
Veterinary managers have an ethical responsibility to appropriately advise staff members of any known risks in the environment at work. In addition, providing information to clients on owning and working with pets if they are known to be immunocompromised is appropriate.
Following is a synopsis of the more common zoonotic diseases that a clinic may be exposed to.
Cat and Dog Bites
Common organisms found in infected bite wounds are: Staphylococcus spp., Klebsiella spp., Enterobacter spp., Pasteurella spp., Bacteroides spp. and Fusobacterium spp. Pasteurella multocida is the most common isolate found and can cause severe cellulitis with erythema, pain and swelling. Infection is generally more aggressive from cat bites, with problems occurring when there is a delay in appropriate wound cleaning. Due to the risk of subsequent wound colonisation with Clostridium tetani a tetanus booster is recommended immediately after such injury.
Bartonellosis (Cat Scratch Disease)
There are a number of bacteria involved in CSD but the most common is Bartonella henselae. Kittens are the primary source but adult cats and fleas are also responsible for transmitting CSD. Fleas inoculate cats via the intradermal route. Cats inoculate their claws whilst grooming and then transfer the bacteria via a scratch or by licking an abraded area of skin or an open wound on a person.
Dermatophytes are the group of fungi known to cause Ringworm infection in animals and humans. Microsporum canis is the most common species of dermatophyte that infects humans. Cats and dogs are natural reservoirs, and cats in particular can be asymptomatic carriers.
Infected cats--organism produces large number of infective spores and these contaminate the environment and infect other cats and humans.
Uninfected cats (carrier cats)--carry small numbers of infective spores and are much reduced in their threat to infect other cats and humans.
Transmission occurs by direct contact with an infected animal, or indirectly by spores shed into the environment. Kittens with lesions are the most common cause of transmission to people. In a clinic environment, infected animals must be isolated from others until the infection is cleared. All items that come into contact with the animal must be decontaminated using appropriate disinfectant.
The GIT is an important reservoir of organisms which can cause systemic disease in humans. Cats and dogs can be fastidious groomers. If they are allowed to lick humans faces there is a possibility that they may transmit any disease that has a faecal oral route.
Visceral Larva Migrans
Cat and dog Roundworm ova are passed in faeces, and incubate in the soil before being ingested by the secondary host (human). This can occur when children pick up faecal matter outside in the garden. The larvae enters the lymphatic system and can spread to many parts of the body. Preventative health programs, including routine worming and good basic hygiene, minimize this risk.
This protozoal parasite is transmitted by ingestion of the highly infective cysts from food or water contaminated by faeces. There is a greater incidence in dogs and shedding infective cysts may occur more during times of stress.
Echinococcosis (Hydatid Disease)
There are two types of transmission; the Sheep-Dog Cycle and the Sylvatic Cycle. The one veterinary nurses should be aware of is the 'sheep-dog cycle'.
The dog is the definitive host, feeds on sheep offal and ingests Echinococcus sp. Eggs with infective embryos inside them are then passed in the faeces of the dog. Humans then ingest these eggs by oral contact with dog faeces or by contact with contaminated fomites. The eggs hatch and the infective embryos penetrate the intestinal mucosa and migrate to various organs via the lymphatic system. When they reach the various organs, they form hydatid cysts.
Toxoplasmosis is caused by the protozoal parasite T. gondii. The cat is the definitive host but T. gondii can infect a wide range of intermediate hosts too.
Cats are infected through ingestion of small prey such as rodents. The life cycle of T. gondii in the cat will vary depending on if they have ingested tissue cyst stage or oocysts.
Oocysts must sporulate in faeces to become infective, cats excrete oocysts for 2-3 weeks but most are excreted in the first 3 days, cats shed oocysts during their primary infection (usually between 6-12 months of age) but are also thought to have further episodes of shedding later in life. Human infections from direct contact with cats shedding oocysts are rare.
Tissue cysts are found in any organ of the body and may be present for the life of the host. It is believed that the most common source of toxoplasmosis infection in humans is through the contact or ingestion of infected raw or partially cooked meats infected with tissue cysts.
Pregnant women are at most risk during weeks 10-14 of gestation if they are seronegative (have not been exposed before, therefore non immune). Other groups most at risk include people that are immunodeficient.
Wild and domestic pet birds are natural reservoirs of Chlamydophila psittaci (formerly known as Chlamydia psittaci). The bacteria is shed in faeces and in ocular and nasal secretions. Transmission occurs through inhalation of the organism. All bird species can transmit these bacteria. Popular pet birds, including lorikeets, cockatoos and budgerigars have a high prevalence.
Care must be taken when housing sick or injured birds in a hospital if Chlamydophila is suspected.
Salmonellosis and Campylobacteriosis
Salmonella and Campylobacter are just two of the many enteric pathogens that occur in both animals and humans. The causative agents are gram-negative bacteria that inhabits the intestines. Companion animals are rarely the major animal reservoir, but birds and reptiles are considered potential transmitters of serotypes that have human health significance. Salmonellosis and Campylobacteriosis are the most common reptile zoonotic diseases.
Salmonella typhimurium is the most commonly encountered species of salmonella in all wild birds.
Campylobacter jejuni is commonly found as a commensal in the gastro-intestinal tract of many wild and domestic animal species. These reservoirs are the ultimate source for most human infections with Campylobacter.
These enteric pathogens are transmitted to people through the oral faecal route and by contamination of fomites, food or water. Appropriate hygiene standards will ensure that this does not occur.
If staff and clients are aware of standard hygiene and basic principals of prevention, they can minimise risks associated with zoonotic disease.
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