Virus 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 in nervous tissue, the virus is not accessible to the immune system and may safely proceed, although the journey is slow taking up to one year (average time between bite and detectable virus in the brain is 20 to 30 days). Virus ultimately reaches the brain and in two to three days more is evident in all body secretions including saliva. At this point, the disease becomes transmissible and symptoms begin.

PRODROMAL STAGE (the first 1.5 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 STAGE (Next 2-3 days)
Classically, this would be the "mad dog" stage. 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 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.

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.

Prevention

Happily, rabies prevention is accomplished with vaccination and limiting exposure to wildlife. The standard killed-virus vaccines are available for both dogs and cats and, after the initial dose, which is good for one year, subsequent doses are generally good for three years. Because of an association with tumor development in cats with killed virus vaccine, a recombinant product is now available that uses a portion of rabies viral DNA cloned into a harmless canarypox virus. This vaccine is just as effective as the traditional vaccines but must be administered annually. Rabies vaccination protocols are typically controlled by municipal regulations. Most communities legally require vaccination of all dogs. The American Association of Feline Practitioners recommends rabies vaccination for all cats.

The Law Regarding Animal Bites

The purpose of the ten-day period is to determine if rabies virus could have been in the animal's saliva at the time of the bite. An animal infected with rabies and shedding virus will certainly be dead within ten days.

If the biting animal is known to have been exposed to wildlife, the situation is different. A vaccinated animal must be re-vaccinated within 48 hours and confined for observation for 30 days. Unvaccinated animals must either be confined for 6 months or be euthanized and tested for rabies. All bites that break the skin are reportable to the health department. All dogs must be vaccinated against rabies. Wildlife/pet incidents leading to bites on the pet are of no concern to public health officials as long as no humans have been bitten.

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

If you are Exposed

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.

If the animal is dead, 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 biting animal is living, its vaccination status should be confirmed as soon as possible and it will need to be confined. The bite wound should be reported to the health department as soon as possible.

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. In this way, when the virus comes out in secretions, a strong immune response is waiting to put down the infection.

For complete details, the CDC has information on post-exposure rabies.

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

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

Quarantines when Traveling

Great Britain, Hawaii, 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 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 listings of what each state requires for entry, the USDA has prepared a Web site with the most recent regulations at:

For travel to another country it is best to check with that country's consulate but guidelines are also available at USDA.

Other Links

The CDC's rabies home page has, in addition to basic information, a children's education area that is particularly helpful for families who go camping.
 

Date Published: 1/1/2001
Date Reviewed/Revised: 9/22/2008