Rabies, crazies!
I had a rare child-free morning today, so naturally I got my blood drawn to check my rabies titre. This little task was nudged closer to the top of my to-do-list on the heals of several unsettling Canadian news stories this month: a young Parksville, B.C. man tragically died from rabies, then a few days later, a four year old boy in Hearland, N.B. was bitten by a rabid bat in his room while sleeping.
July 16, 2019 Young man dies from rabid bat encounter
July 20, 2019 Four year old bitten by rabid bat
Although rabies is incredibly rare in Canada, these stories rekindled widespread fear and interest in the disease. Of all the zoonotic diseases (infectious diseases that are transmitted between animals and humans), rabies takes the cake for the worst symptoms and mortality rate (once clinical signs appear). My goals for this article are to explain what rabies is and how it is transmitted, what we can do to prevent it from infecting ourselves and our pets, and what to do if we are exposed to a potential rabies threat.
RABIES DISEASE:
Rabies is the name of the disease that is caused by a group (or variants) of viruses in the genus Lyssavirus. There are different rabies variants within the same species of reservoir hosts that live in different geographical areas. Multiple variants of fox, skunk, raccoon, and bat rabies exist, with most human rabies cases in North America being caused by bat virus variants. In developing countries across the world, dogs (domestic, feral and wild dogs such as coyotes, jackals and wolves) are the most important reservoir host for the disease. Reservoir hosts are those species in which the virus is able to live and reproduce. Vector hosts are those species that transmit the virus to another host. All rabies reservoirs are also it’s vectors, however, not all rabies vectors are reservoirs. For example, cats are effective vectors of rabies, but there are no documented feline rabies variants to date.
Rabies is most often transmitted via the saliva following the bite of an infected animal. The virus is sometimes transmitted by saliva, salivary glands or brain tissue that contacts fresh wounds or mucous membranes. In the case of the young Parksville man, a rabid bat flew into his hand, exposing him though an unnoticeable bite or scratch. Although the vector is usually showing clinical signs of rabies at the time of transmission, some animals can shed the virus for up to 8 days prior onset of clinical signs.
The incubation period (time between catching an infection and clinical signs appearing) for rabies can be long and variable. Typical cases in domestic cats and dogs have an incubation period of two weeks to three months, however sometimes it can be much shorter or longer.
The virus travels up the peripheral nerves to the spinal cord and finally to the brain, causing encephalomyelitis. The virus then migrates down peripheral nerves to the salivary glands, where it is shed in the saliva. Once the virus has replicated sufficiently in the central nervous system, it is disseminated to all innervated organs in the body.
Once in the CNS, rabies causes major behavioural changes in its host, which can look like either the “furious form” or the “paralytic form”. Infected animals with the furious form are often irritable, hyperexcitable, and very aggressive towards other animals, people, and moving objects. They become more uncoordinated, can suffer from seizures, and eventually progressive paralysis leads to death. Wild rabid animals often lose their fear of people and normally nocturnal species can become active during the day. Rabid animals with the paralytic form are uncoordinated, with paralyzed throat and chewing muscles. These animals are unable to chew and swallow food, salivate profusely, and can have a dropped lower jaw. The paralysis progresses to the rest of their body, leading to coma and rapid death. Infected humans can experience spasms, periods of agitation, hallucinations, fear of water and fresh air, difficulty talking and swallowing, progressive paralysis, and coma.
It is important to note that rabies can infect any animal, including livestock such as cattle and horses, and of course bats. In British Columbia, bats are the only known reservoir host of rabies (0.5% of the bat population is infected with the virus). The BC Centre for Disease Control (BCCDC) reports that 13% of BC bats submitted for testing are positive for rabies. There is a higher prevalence of rabies in submitted bats because rabid bats exhibit abnormal behaviours that increase their contact with people and domestic animals.
RABIES PREVENTION:
There are an estimated 70, 000 human deaths worldwide per year from rabies. Although human cases in Canada are exceedingly rare (26 deaths since reporting began in 1924), Canada is not rabies free. Combined efforts from the public, veterinarians, public health and wildlife government departments, and the Canadian Food Inspection Agency (CFIA) are needed to mitigate the spread of rabies in Canada.
Dr. Lucy Kinninmonth and Rachel give Satti her rabies vaccine. Photo credit: Eleanor Stewart
Photo credit: Eleanor Stewart
Veterinarians and the public should work together to ensure that pets are vaccinated for rabies. The Canadian Veterinary Medical Association (CVMA) considers rabies to be a core vaccine for both dogs and cats. Cats in particular are the most commonly affected domestic species in the USA and Canada. Even indoor cats should be vaccinated, as they may escape or come into contact with a bat that enters a house. Rabies vaccines are available for the following additional domestic species: horses, ferrets, cattle, and sheep. Wildlife departments currently use oral vaccinations for mass immunization of wildlife such as raccoons in certain parts of Canada (Ontario) and the USA. Dogs and cats can be vaccinated for rabies as young as 12 weeks of age (in British Columbia, where I practice, most pets are vaccinated for rabies at 16 weeks of age). They receive their first rabies booster 1 year later. Further rabies immunizations are given every 1-3 years, depending on the type of vaccine used. A dog or cat is considered immune 28 days following it’s initial rabies immunization, and immediately immune following additional rabies boosters.
Cats that have a history of injection-site sarcomas believed to be associated with a rabies vaccine should not be re-vaccinated for rabies, if possible. Feline injection-site sarcomas are aggressive tumors that can very rarely result from the injection of any substance into the space under the skin. Although a specific cause has not yet been established, it is currently thought that the inflammation related to injectable products can lead to the formation of sarcomas. For most cats, however, the risk of contracting a deadly zoonotic disease such as rabies outweighs the possibility of an injection-site sarcoma (which is currently documented to occur at a rate of 1 case per 10, 000 to 30, 000 vaccinations). Many veterinarians take additional precautions by vaccinating pets in locations that would make tumor removal easier, should an injection-site sarcoma occur (eg. placement low on a leg or in the tail instead of the area between shoulder blades). A small, firm lump can develop under the skin following a vaccination. This lump should disappear several weeks after vaccination. If it persists beyond 3 weeks, owners are advised to contact their veterinarian.
Our old-lady, Luna
When I was in vet school, I adopted an old-lady cat during an external rotation at the Winnipeg Humane Society (WHS). Several weeks after her adoption, I discovered a persistent and firm nodule on her right shoulder (exactly where she was vaccinated for rabies at the WHS). One of my 4th year classmates surgically removed the nodule, which was biopsied and came back as non-specific inflammation. I’ve always wondered whether the nodule would have turned into a sarcoma, had I not addressed it early on. When in doubt, it is always better to be safe than sorry! This old gal lived on for another four years, when she finally succumbed to chronic kidney disease and end-stage osteoarthritis.
In the last decade, I have noticed an increasing trend of adopting pets (mostly dogs) that have been imported from developing countries. It is so important that prospective adopters ensure that their newly acquired pets are vaccinated for rabies prior to being imported. Most of these developing countries have a higher prevalence of rabies in domestic cats and dogs. Although the CFIA and Canada Border Service Agency require imported dogs and cats to have their rabies vaccinations, sometimes these pets arrive with fraudulent documents. Despite importation laws in both Canada and the USA, there has been a rise in illegally imported underage puppies from high-risk countries. In addition to posing a public health threat from rabies, these puppies can carry other zoonotic diseases (eg. parasites, MRSA, Brucellosis) that are especially harmful to children, elderly people, and to other immunocompromised individuals. See the following articles for more details on these importation concerns:
Canada not doing enough to prevent disease from imported dogs
If your pet has been exposed to a potentially rabid animal (any wild animal or domestic animal showing clinical signs of rabies), take your pet to a veterinarian promptly. Your vet will most likely update your pet’s rabies vaccine, regardless of your pet’s vaccination status. Further actions will depend on the exposed pet’s vaccination status at the time of exposure and whether there has been concurrent human exposure. Detailed guidelines for veterinarians can be found on the BCCDC website BC rabies guidelines for veterinarians and by logging into the CVBC website.
If you find a wild animal which may be rabid, do not touch the animal. Contact a the BC Wildlife Veterinarian at 250-953-4285
If someone has been bitten or scratched by a bat in BC, the bat should be tested for rabies. If the bat is alive and can be captured, please contact the Community Bat Programs of BC at 1-855-9BC-BATS (1-855-922-2287) and your local public health unit Immunize BC for assistance. Further instructions can be found at BCCDC. Immediately following a potential rabid animal exposure, it is important to:
Wash the wound with soap and running water for 15 minutes, followed by further flushing with water.
Call you doctor or local public health unit Immunize BC
It is imperative to receive post-exposure rabies treatment within 7 days of exposure.
All seriousness aside, today my 4 year old came home with a bite mark from one of his daycare “friends” (apparently this is a common behaviour among small children at daycares!). Bless his little soul, he asked me very seriously, “Mommy, will I get rabies now?”.
SOURCES:
American Veterinary Medical Association. https://www.avma.org/Pages/home.aspx
BC Centre for Disease Control. http://www.bccdc.ca/health-info/diseases-conditions/rabies
Canadian Veterinary Medical Association. https://www.canadianveterinarians.net/
Journal of Feline Medicine and Surgery (2013) 15, Supplementary File: Rabies, Disease Information Fact Sheet
Merck Veterinary Manual. https://www.merckvetmanual.com/