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Rabies is transmitted through the bite or scratch of an infected animal. It is usually passed from animal to animal and rarely affects humans.
Rabies is a virus that causes neuroencephalitis and death in humans. It is transmitted via the saliva of infected animals. In Ontario, animals most at risk for having rabies are raccoons, foxes, skunks, and bats. In some areas of the world, rabies in domestic dogs and livestock poses a considerable risk.
Rabies is nearly always fatal but can easily be prevented by encouraging people to vaccinate their pets, avoid touching or interacting with any unknown animals, and seeking proper care for any animal bites or scratches.
Signs & Symptoms
Symptoms usually appear approximately 3 to 8 weeks after an exposure, but they can appear as soon as nine days or as long as seven years after a bite. Rabies is usually fatal unless post-exposure prophylaxis is given before symptoms would have appeared.
Early symptoms of rabies may include discomfort, paraesthesia, or pain at the exposure site, as well as headache, malaise, fever, and fatigue, and possibly psychological symptoms such personality changes or apprehension. More specific symptoms develop after an average of 4 days (up to 10) of prodrome. The fully developed illness typically presents in one of two ways. The more common furious form presents with symptoms of hydrophobia (fear of drinking, difficulty swallowing, foaming at the mouth caused by severe laryngeal or diaphragmatic spasms that cause a sensation of choking when attempting to drink or swallow), aggression and other behavioural changes. The paralytic (or dumb) form of the disease manifests as progressive flaccid paralysis. Both forms of the disease rapidly progress, typically within days, to encephalitis and death.
Risk Assessment
Factors taken into account during risk assessment:
- Severity/depth of bites
- Bites on hands, neck, or face
- Animal saliva exposure to a pre-existing wound, mucous membrane, or respiratory tract
- Abnormal or aggressive behaviour in animal
- Unprovoked attack
- Prevalence of animal rabies in the area
More severe bites may be more likely to suggest the animal is rabid, and these bites may also provide more opportunity for exposure to and transmission of the virus because of increased exposure to saliva.
Bites on the hands and face are considered high risk exposures because of the high density of nerve endings. Bites to the face and neck are also considered higher-risk exposures because of the proximity to cranial nerves leading directly into the brain.
Ottawa Public Health (OPH) will conduct a risk assessment concerning suspected rabies exposures. However, the ultimate decision regarding
administration of rabies post-exposure prophylaxis (RPEP) is based on the informed-consent discussion between the attending health care provider and the patient or parent/guardian.
In situations where patients find a bat in a room in which they have been sleeping, the risk of rabies is considered low if the patient was not woken by direct contact with the bat and there is no identified direct contact and no sign of a bite or scratch or saliva exposure. If the bat was found in the room with a child or adult who is unable to give a reliable history, it may be more difficult to fulfill these criteria and RPEP may be recommended.
Please see Rabies Prevention and Control Protocol, 2022 for further details.
Prevention
Most humans are given rabies post-exposure prophylaxis (RPEP) as a result of exposure to domestic animals, therefore it is important to emphasize keeping rabies vaccinations up-to-date for all domestic cats, ferrets, and dogs. Also, maintaining control of pets by keeping cats and ferrets indoors and keeping dogs under direct supervision outdoors is important to prevent their exposure to wild animals with rabies.
Finally, it is important to call animal control if you encounter a stray animal or sick or injured wild animal. Do not approach, touch, or feed wild or stray animals. Teach children not to touch animals, including dogs and cats, even if they appear friendly.
Advise your patients who are at higher-risk of exposure to consider pre-exposure vaccine for rabies, particularly if they have occupational exposures (such as lab workers, veterinarians, animal control or wildlife workers) or are travellers who will spend more than one month in a country where rabies is endemic.
Pre-exposure prophylaxis of high-risk individuals consists of rabies vaccine administered at Day 0, 7 and 21–28. The vaccine is 100% effective immediately after all the doses have been given and persists for up to 2 years after immunization. (Recall that exposure to a potentially rabid animal still requires two doses of rabies vaccine post-exposure.) However, protection wanes over time, and this varies from individual to individual, which is why post-exposure vaccines are always given and serologic testing is required every two years for individuals at ongoing high risk of exposure. A booster shot is necessary if antibody titres fall below 0.5 IU/mL.
