RABIES

Electron Microscope Image of the Rabies Virus
(Photocredit: Norden, a Smith-Kline Company via Wikimedia Commons)

Descriptions of rabies go back thousands of years as rabies has classically been one of the most feared infections of all time. It is because of rabies that dog ownership requires a license and documentation of rabies vaccination. There is still no reliably effective treatment for rabies infection once symptoms have started.

The virus does not survive outside of the infected host very long so direct contact with fresh secretions is required for transmission. In most cases, disease is transmitted via bite wound and it is mostly wildlife that gets infected. When wildlife starts coming into contact with the pet population, then pets become infected and when pets get infected, human infection is not far behind. Because this infection has nearly 100% mortality, prevention of infection in pets becomes crucial to preventing human disease. Of course, people can get infected by wildlife contact as well. Despite vaccination being readily available, every year the U.S. reports approximately 50 canine deaths, 250 feline deaths and several human deaths from rabies. Worldwide, some 55,000 human deaths occur annually from rabies even now in the 21st century.

The most common wildlife species to spread rabies to domestic animals and humans in the Northern Hemisphere are the skunk, bat, raccoon, fox, and coyote. It should be noted that wildlife (especially bats) are able to gain access to indoor areas where they can come in close contact with both pets and people. Indoor pets are not without risk.

MANY PEOPLE DO NOT REALIZE HOW FAST DEATH OCCURS FROM RABIES.

While it may take a long time for the virus to incubate, once even mild symptoms begin, death occurs within 10 days.
The injection treatment most people have heard of only works during the incubation period; once symptoms have started, survival chances are slim.

COURSE OF THE DISEASE

Virus present in the infected animal's saliva enters the victim's tissues during the bite. The virus attaches to the local muscle cells for a couple of days before penetrating to local nerves and beginning its slow ascent to the brain. Once within nervous tissue, the virus is not accessible to the immune system and may safely proceed towards the brain. The journey is slow and can take up to a year but the average time is 3-8 weeks depending on the species. Virus ultimately reaches the brain and in two to three days more is evident in all body secretions including the saliva. At this point, the disease becomes transmissible and symptoms begin.

PRODROMAL STAGE  (the first 2-3 days after symptoms have started) - A change in personality is noted. Friendly animals become shy etc. The larynx begins to spasm and a voice change may be noted (especially true in rabid cattle). Most infected animals will actively lick or scratch the site of the original bite.

EXCITATIVE OR FURIOUS STAGE (Next 1-7 days) Classically, this would be the "mad dog" stage, though in reality most dogs skip this phase altogether. The animal has no fear and suffers from hallucinations. If confined, the animal often attacks the bars of the cage.

PARALYTIC OR DUMB STAGE (Next 2 - 4 days) Weakness/paralysis sets in. The larynx is paralyzed resulting in an inability to swallow thus drooling and "foaming at the mouth" result. The animal dies when the intercostal muscles (which control breathing) are paralyzed. It is from animals in this stage where most human exposure occurs. There is no treatment for animals or humans once clinical signs appear.

Once the virus has been released to body secretions, it is again accessible to the immune system; however, the patient dies before an adequate immune response is mounted.

The classical symptoms of rabies described above may not be obviously recognizable
making diagnosis difficult if not impossible in the living animal.
Long quarantines are often needed to determine if infection has occurred.

When human exposure to the animal in question is involved, what happens depends on an assortment of criteria. If the animal in question is dead, its brain can be tested for rabies. There is no test for rabies in a living animal but since we know that death follows quickly after the virus becomes contagious, a living animal can be confined for 10 days. If the animal is still alive 10 days after biting a person, then the bite could not have transmitted rabies.

TREATMENT FOR HUMANS ("POST EXPOSURE PROPHYLAXIS" OR "PEP")

As mentioned, once symptoms have started, treatment can be attempted but truly there is little chance of survival. The only way to survive rabies is to exploit the long incubation period and basically get vaccinated quickly. Doing this involves a very big piece of information: knowing you were (or may have been) exposed. Every year a small number of people die of rabies in the U.S. Most of these people were bitten by a dog, bat, or some other animal and did nothing other than basic first aid. Recall that it takes many weeks for the rabies virus to reach the brain. This allows time for vaccine to be administered so that when the virus "comes out" of its neurologic hiding place and is ready to infect the brain, a substantial immunologic response is waiting. The virus is foiled and clinical rabies does not result.

If you are bitten by an animal and its rabies vaccination history is unknown, there are definite steps to take. A fresh bite wound should be washed out with water quickly as this may wash out viral particles. The time it takes for the virus to reach the brain depends on the amount of virus present in addition to the proximity of the wound to the head. This simple step can be life-saving.

If the biting animal is living, its vaccination status should be confirmed as soon as possible and it will need to be confined according to local law. The bite wound should be reported to the health department as soon as possible. Only rodent and rabbit bites are not reportable.

If the animal is dead then its brain can be tested for rabies. The head of the biting animal is submitted to the health department for fluorescent antibody testing for the rabies virus. This process takes a matter of hours so that any bite victims can know right away if they will require rabies treatment.

If the animal is not available or its vaccination status is in question, further treatment may be needed. Hyperimmune (antibody rich) serum is flushed into the wound in hope of inactivating the virus before it may penetrate to the nerves. The patient receives a vaccination on a regular schedule for about a month, as described above.

To report an animal bite in Los Angeles County:

http://publichealth.lacounty.gov/vet/biteintro.htm

PREVENTION FOR OUR PETS

For pets not current on rabies vaccination that have been exposed to biting wildlife, the Texas Post-Exposure Rabies Prophylaxis Protocol has been particularly helpful. In this situation, the pet should be vaccinated for rabies as soon as possible after the wildlife bite with booster vaccines given 3 weeks post-bite and 8 weeks post-bite. The pet should be strictly isolated for 90 days (note that in California, the law requires a 180 day isolation period). This protocol has been extremely successful in preventing rabies symptoms and contagion when normal rabies vaccination had lapsed.

THE LAW IN OUR AREA REGARDING ANIMAL BITES (AGAINST HUMANS)

LAWS REGARDING BITING DOGS AND RABIES VACCINATION ARE HIGHLY REGIONAL.
CHECK WITH YOUR LOCAL ANIMAL REGULATION DEPT.
OR VETERINARIAN TO FIND OUT WHAT YOU NEED TO KNOW

OR VISIT RABIESAWARE.ORG

For complete details, visit the CDC's page on rabies post-exposure:

www.cdc.gov/rabies/medical_care/index.html

ANYONE PURSUING A CAREER WITH ANIMALS SHOULD CONSIDER VACCINATION AGAINST RABIES.

(original graphic by marvistavet.com)

 Veterinarians, for example, have a rabies exposure risk more than 300 times that of the general population.

QUARANTINES WHEN TRAVELING

Great Britain, Hawaii, Japan, New Zealand, and several other island areas have successfully eradicated rabies from their territory. These places are EXTREMELY cautious about allowing potential carriers of rabies in. Because of the long incubation period of rabies, a very long quarantine is needed; however, this must be balanced by the expense associated with quarantine and an owner's reluctance to be separated from his or her pet. Most places that have eradicated rabies have special protocols for avoiding or minimizing quarantine. Typically, a microchip is implanted in the pet for identification purposes, a rabies antibody titer (a measurement of vaccine-induced protection) must be performed at an approved laboratory, and rabies vaccine documentation is necessary.

For links to travel requirements for other states and other countries, please visit our page on Traveling with your Pet.

OTHER LINKS

Click here to visit the CDC's rabies home page, complete with a children's education area (particularly helpful for families that go camping):

www.cdc.gov/rabies/

Did you know there was a rabies outbreak in Los Angeles that involved 847 dogs? Read the history of rabies in Los Angeles County from 1898 to 1987 here:

www.publichealth.lacounty.gov/vet/rabiesmanual/historical.htm

In order to raise awareness of rabies, a World Rabies Day is scheduled annually to call attention to this problem. More information about rabies in both humans and animals can be found at:

www.cdc.gov/rabies/around-world/

Page last updated: 9/10/2024