Reducing the risk of rabies

FDA Consumer, July-August, 2005 by Linda Bren

* Deadly Virus

* Human Rabies Vaccines

* Animal Rabies Vaccines

* Keep Your Distance

A Suffolk, Va., couple didn't know they were being followed when they drove into their garage one evening in April 2005. When the man and woman got out of the car, they saw their stalker: a gray fox. The animal sprang at the woman, wrapped itself around her legs, and then tangled with the cat that came out of the house to greet its owners.

The fox was killed and found to have rabies. The woman, who had been scratched, received a series of rabies vaccinations and was fine. But sadly, the family cat was euthanized because it had not received its preventive rabies shot, says Calvin Jones, the environmental health manager for the Western Tidewater Health District in Virginia's Department of Health (VDH).

"The way we handled the case would have been different if the cat had a current rabies vaccination," says Jones, adding that the pet would have been revaccinated and confined for 45 days for observation. But to protect the public health, an unvaccinated pet exposed to rabies must be euthanized immediately or placed in strict isolation for six months with no direct human contact, says Jones.

Thanks to increased vaccination of pets and advances in human vaccines, the number of human deaths from rabies in the United States in the last century has decreased from 100 or more per year to an average of one to two per year, according to the Centers for Disease Control and Prevention (CDC). Yet rabid animals are found each year in every state except Hawaii.

In 2003, the CDC received reports of more than 7,000 cases of rabies in animals in the United States and Puerto Rico. More than 90 percent of the cases occurred in wild animals, mostly raccoons, skunks, bats, and foxes. Reports of domestic animals with rabies that year included 321 cats and 117 dogs.

Just three cases of rabies in humans were reported to the CDC in 2003, but more than 40,000 people may have been spared from the deadly disease by getting vaccinated after they were potentially exposed. The Food and Drug Administration has approved vaccines to prevent rabies in humans, and the U.S. Department of Agriculture (USDA) has licensed vaccines to prevent rabies in many animals.

"It's critical to keep current on rabies vaccinations to protect pets," says Suzanne Jenkins, V.M.D., M.P.H., epidemiologist and state public health veterinarian for Virginia, "and, more importantly, so they cannot transmit rabies to people."

If a person is exposed to rabies, "the sooner treatment is begun after exposure, the better," says Robin Levis, Ph.D., regulatory coordinator in the FDA's Office of Vaccines Research and Review.

Deadly Virus

Rabies is caused by a virus that attacks the brain. The virus enters the body through the saliva of an infected animal, usually by a bite, but it can also be transmitted if infected saliva gets into an open wound or splashes into mucous membranes such as those in the eyes, nose, or mouth. From the saliva's point of entry, the virus travels along nerve cells to the brain. It replicates there and moves to the salivary glands. In a rabid animal, the cycle is repeated when the animal bites a person or another animal.

Rabid animals may be aggressive and vicious, or lethargic and weak. In people, early rabies symptoms of fever, headache, and fatigue are followed by confusion, agitation, hallucination, and paralysis. Once symptoms begin, the disease is almost always fatal, says the CDC.

Only mammals get rabies--birds, reptiles, amphibians, and fish do not get the disease.

Human Rabies Vaccines

The FDA has approved several injectable products that are effective in preventing rabies in people who have been exposed to the virus. This post-exposure treatment consists of one injection of proteins that fight the infection (rabies immune globulin) and five injections of rabies vaccine over a 28-day period. The vaccine works by stimulating a person's immune system to produce antibodies that neutralize the virus. "The person develops a protective immune response before the virus reaches the brain and begins to actively replicate," says Levis.

Rabies immune globulin contains antibodies from blood donors who were given rabies vaccine. The antibodies provide interim protection until an exposed person's own antibodies develop in response to the vaccine. "In addition, injecting rabies immune globulin at the site of injury reduces the amount of virus that is able to enter the nerve cells and potentially initiate an active infection," says Levis.

No test can detect rabies in humans at the time of a bite. People who may have been exposed should immediately wash all bite wounds and scratches with soap and water to decrease the chance of infection. If the suspect animal cannot be captured and tested or observed for symptoms, the vaccine regimen should be started promptly. According to the CDC, no one in the United States has developed rabies when the currently recommended post-exposure treatment regimen was followed.