Put rabies on your veterinary clients radar

"Come closer ... I promise I won't bite!" (EBFoto/stock.adobe.com)

Rabies is one of the deadliest diseases on Earth. A viral zoonotic infection of the nervous system, rabies is transmitted when the saliva of an infected animal enters the bloodstream of another animal or human. Transmission usually occurs via a bite or scratch, although the virus can also gain entrance through an existing break in the skin (scratch, wound) or through the mucous membranes (mouth, eyes).

Nationwide efforts in the 1950s to mandate pet rabies vaccinations and implement leash control laws effectively curtailed the incidence of rabies in the U.S., but the disease can and does affect a handful of people and pets every year. That's why it's important for pet owners to be aware of these five facts about rabies.

1. Rabies is more common than most people realize

Rabies has been around for centuries. In the U.S., 4,454 confirmed cases in animals were reported to the Centers for Disease Control and Prevention in 2017-down 9.3% from 2016.1 Of those cases, 276 were cats and 62 were dogs.1

Rabies is relatively rare in people the U.S. today-only one to three human deaths are attributed to the virus annually. Worldwide, though, an estimated 59,000 human deaths result from rabies each year, largely in poor regions of the world with large populations of free-roaming dogs.

The Zero by 30 campaign, launched by a worldwide collaborative partnership called United Against Rabies, has set a global goal to reach zero human deaths from canine rabies by 2030.

2. Bats are the most common reservoir in the U.S.

Any warm-blooded animal can acquire and transmit rabies if exposed to the virus (see sidebar). In the United States, rabies is found primarily in wildlife (bats, raccoons, skunks, foxes and coyotes). Of domestic animals, cats are three to four times more likely than dogs to be reservoirs because many cats are feral, they generally have more contact with wild animals and fewer cats are vaccinated against rabies.2

How the rabies virus does its damage

After the rabies virus enters the body, it travels along the nerves from the infection site to the spinal cord and brain. During this incubation period-which typically lasts three to 12 weeks or longer, depending on the bite or scratch location-the infected animal shows no clinical signs and cannot pass along the virus. When the virus reaches the brain, it multiplies rapidly then invades the salivary glands. This is the point at which progressive clinical signs appear, beginning with generalized weakness, fever or vomiting; moving to cerebral dysfunction, anxiety, confusion and agitation; progressing to delirium, abnormal behavior, hallucinations and hydrophobia; and culminating in death.

Outside the U.S., 90% of rabies cases involve dogs, and it's those exposures that lead to 99% of human rabies deaths worldwide.2

Human deaths in the United States due to rabies are usually caused by bats, largely because a bite from a bat is so small that a person may not realize he or she has been bitten and thus does not seek medical care.

3. A rabid animal may appear docile

When most people picture a rabid dog, they imagine a snarling, crazed animal foaming at the mouth and trying to attack everything in sight (Cujo, anyone?). And this may well be the case … but it may not.

The progression of rabies is similar in animals and people, including early nonspecific signs (general weakness or discomfort, fever, headache), acute neurologic signs and, ultimately, death.3 A normally docile animal may act unusually aggressive, a typically playful animal may appear withdrawn or shy and a nocturnal animal may be found out and about in daylight. Other possible signs and symptoms: appetite loss, pica, difficulty swallowing, hallucinations, hypersensitivity to touch or sound, hydrophobia, seizures and pawing at the mouth, among others.

4. Rabies is not necessarily a death sentence

Although rabies is invariably fatal once signs of the infection appear, the disease is preventable. It's called post-exposure prophylaxis (PEP), and it's pretty simple. About 40,000 people in the United States receive PEP each year following contact with a potentially rabid animal.

The incubation period for rabies is about three to 12 weeks,3 although the virus can lay dormant for more than a year. However, death from rabies is entirely preventable if treatment is initiated before clinical signs occur. Washing a bite or scratch wound immediately with soap and water may prevent the onset of disease.

PEP should be administered as soon as possible following known exposure to the rabies virus. In addition, PEP should be initiated any time a bat is found in the home of someone who was sleeping, incapacitated or unable to speak-even if a bite was not felt or witnessed.

Once upon a time (OK, before the early 1980s), PEP consisted of a series of 21 painful injections into the stomach with a long needle. Today, rabies vaccines are relatively painless and are given in the arm, much like a flu vaccine. The PEP regimen consists of a single dose of human rabies immune globulin and a dose of rabies vaccine as soon as possible after exposure, followed by three additional vaccine doses over a 14-day period.3

Individuals who are at high risk for exposure to rabies, such as veterinary practice personnel, can receive pre-exposure rabies vaccinations. This entails three vaccines administered in the deltoid area over the course of three to four weeks.3

For subsequent exposures, PEP requires only two doses of vaccine, once on the day of new exposure and again three days later.

5. Pet vaccinations are vital

Although people in the U.S. are more likely to be exposed to rabies through wild animals, pet owners may be exposed through a family pet after the pet is exposed to rabid wildlife. Ensuring that pets are up-to-date with rabies vaccination will prevent dogs and cats from acquiring the disease through wild animals and thus decrease the likelihood of transmission to people.

After receiving an initial rabies vaccination, dogs and cats are vaccinated again one year later. They then receive either annual or triennial vaccinations in accordance with the vaccine license and state or municipal regulations.

References

1. Ma X, Monroe BP, Cleaton JM, et al. Rabies surveillance in the United States during 2017. Journal of the American Veterinary Medical Association 2018;253(12):1555-1568.

2. The burden of rabies. Centers for Disease Control and prevention website: https://www.cdc.gov/features/dsrabies/index.html. Reviewed September 25, 2017. Accessed July 22, 2019.

3. Rabies. Centers for Disease Control and Prevention website. https://www.cdc.gov/rabies/index.html. Reviewed June 11, 2019. Accessed July 19, 2019.