SCOTTSDALE, ARIZ. — Despite the first known survival of an unvaccinated rabies patient, prophylaxis still is the only proven defense after rabies exposure, Dr. L. Barry Seltz told physicians at a pediatric update sponsored by Phoenix Children's Hospital.
“There is no established, effective treatment,” Dr. Seltz of the University of Arizona in Tucson warned in a talk that addressed misconceptions about human rabies risk and why current thinking discourages vaccination in the gluteal area.
The treatment that saved the Wisconsin teenager (N. Engl. J. Med. 2005;352:2508–14) needs to be duplicated, according to Dr. Seltz. Vaccination can be before or after exposure, he said, but it must be done whenever exposure to the rabies virus is suspected.
Exposure may not be easy to document, however. For Dr. Seltz, a key lesson from the survival of the 15-year-old girl is the importance of taking a good patient history.
“She said she had been bitten by a bat. She didn't think anything of it,” he said, crediting careful questioning by the teenager's primary care physician with unearthing this crucial piece of information after the patient became ill. She had not previously reported the bite.
Despite public fear of rabid dogs and widespread rabies in wild raccoons on the Eastern seaboard, Dr. Seltz said that most human rabies cases in the United States involve bats. From 1990 to 2004, he said there were 47 cases, including 10 cases acquired abroad. Of the 37 infections that originated in this country, 34 were determined to involve a bat variant of the rabies virus. Only one came from a raccoon.
“Bat bites are not dramatic. You may not recognize them when they occur,” Dr. Seltz said. As examples of patients he would vaccinate in the absence of certain exposure, he cited the person who was asleep when a bat flew into a room or a child who cannot give a reliable history.
Other than a bite, he said the virus can be transmitted via “contamination of nonintact skin or mucous membranes with saliva from a rabid animal.”
“Petting a rabid animal is not an exposure. Contact with blood, urine, or feces of an infected animal is not exposure,” he said.
The virus has a 20- to 60-day incubation period in humans. Ten days is adequate for observation of a dog that appears healthy after it has bitten someone in the United States, according to Dr. Seltz. If the dog has been infected, the virus will present itself quickly.
To control rabies in humans, he urged preexposure vaccination of veterinarians, animal handlers, lab workers, people moving to areas where dog rabies is common, and those who make frequent contact with wildlife.
The postexposure protocol is three-pronged, he said: local wound care, active immunization, and passive immunization with immune globulin. “Cleaning [the wound] is critically important,” he said. “Animal studies show that wound cleaning can reduce the risk of rabies by 50%.”
The vaccines available in the U.S. are all inactivated viruses. Do not inject them in the gluteal area, he warned, as it has been associated with prophylaxis failure.
Exposed patients should receive a dose of 20 IU/kg—no more, no less—of immune globulin prepared from the plasma of immunized human donors, Dr. Seltz added.
In five cases of children who died despite receiving the full postexposure protocol for multiple bites, their wounds were not sufficiently infiltrated with immune globulin, according to Dr. Seltz. If a child has multiple wounds, he said to dilute the 20-IU/kg dose in normal saline solution and use the extra volume to make sure all the wounds are infiltrated.
'Petting a rabid animal is not an exposure'—nor is contact with its blood, urine, or feces. DR. SELTZ
Bats vs. Raccoons
Dogs are the first animal that comes to mind when most people think about rabies, but Dr. Seltz said they are not much of a threat in the United States.
In 2004, only 94 rabid dogs were reported in this country, according to Dr. Seltz. Among domestic animals, there were more cases of rabid cats and rabid cattle: 281 and 115 animals, respectively.
Dog bites do account for most of the 50,000 human rabies cases worldwide each year, he said. In the United States, however, 92%–94% of animal rabies comes from wild animals.
The largest concentration of infected animals has been identified to date on the East Coast, Dr. Seltz reported. Nationwide, in 2004, there were 2,400 rabid raccoons, 1,800 skunks, and 1,300 bats. Because bats are more likely to come in contact with people, they are most often implicated in human infections. Squirrels are rarely found to be rabid, he said, as they generally do not survive the initial attack of a rabid animal.