Infection: Rabies

Definition
Description
Demographics
Causes and Symptoms
Diagnosis
Treatment
Prognosis
Prevention
The Future
For more information

Definition

Rabies is defined by the Centers for Disease Control and Prevention (CDC) as a preventable viral disease most often transmitted to humans through the bite of an infected animal.

Description

Rabies is a zoonosis, which means that it belongs to a group of diseases that can be transmitted to humans from infected animals. For most of human history, rabies was associated with infected dogs and was uniformly fatal until Louis Pasteur's discovery of an effective vaccine in 1885. As of the early 2000s, however, dogs kept as pets are no longer the primary source of rabies in the United States and Canada, being responsible for only 5 percent of cases. Other animal species that cause greater concern to public health doctors include:

• Wolves, coyotes, jackals, foxes, and other animals in the canine family.
• Bats. Most cases of rabies in the United States in recent years were traced to infected bats; at least thirty of the thirty-nine species of North American bats have been shown to carry rabies. Bat bites are dangerous partly because they are small and may go unnoticed.
  
  Several cases have been reported of children bitten during sleep by bats that had gotten into their bedrooms.
• Raccoons and skunks. All the states along the Eastern seaboard of the United States as well as Vermont, Pennsylvania, West Virginia, and Ohio have reported rabies in these animals.

Domestic cats and ferrets are considered low-risk species because they as well as dogs can be vaccinated against rabies. Rats, mice, and other rodents are also considered even lower-risk species for carrying rabies.

Demographics

Rabies causes about 30,000 to 50,000 deaths each year worldwide, according to the World Health Organization (WHO), and is probably underreported, particularly in developing countries. In the United States, about fifty people died from rabies each year until about 1940, when widespread vaccination of dogs was put into practice. Between zero and three cases of rabies are documented each year in the United States as of the early 2000s, according to the Centers for Disease Control and Prevention (CDC). Between 16,000 and 39,000 people receive post-exposure treatment for rabies each year in the United States and Canada.

Although deaths from rabies are now rare in North America, the CDC estimates the annual cost of rabies prevention and control exceeds $300 million.

People of all ages, both sexes, and all races are equally likely to get rabies if bitten by an infected animal.

Pasteur Finds a Treatment

Rabies was a universally fatal disease until 1885, when Louis Pasteur (1822–1895), the French chemist and microbiologist, successful treated Joseph Meister (1876–1940), a nine-year-old boy who had been mauled by a rabid dog on July 4, 1885. The boy's mother brought her son to Paris on July 6. At that point Pasteur and his assistant, Emile Roux, had been experimenting with a rabies vaccine made from the dried spinal cords of infected rabbits in order to immunize domestic dogs against the disease. He had tested the vaccine on only eleven dogs.

Pasteur, not a physician, took a personal risk in giving the child the new, intried vaccine. He consulted with several physicians who examined the boy's severe wounds and urged Pasteur to go ahead with the vaccination because Meister faced certain death otherwise. Pasteur gave Meister thirteen injections of the vaccine over a ten-day period. Three months later, when it was clear that the boy was completely healthy, Pasteur reported the case to the French Academy of Medicine.

Causes and Symptoms

The disease agent that causes rabies is a virus that seeks out the tissue of the nervous system. It is, however, easily killed by drying, detergents, and ultraviolet light. The virus is most commonly transmitted in the saliva of an infected animal and enters the human body through a bite; however, people have also been infected by nasal secretions from an animal entering the body through an open cut or wound. In a few rare cases, people have contracted the rabies virus through organ transplantation.

The course of the disease can be divided into four phases:

• Incubation. The length of the incubation period usually varies from twenty to ninety days, depending on the closeness of the bite to the central nervous system; bites on the head or neck have the shortest incubation periods. In a few cases the incubation period has lasted as long as nineteen years. The body does not develop antibodies to the virus during the incubation period.
• Prodrome. Warning symptoms of infection appear. The virus moves into the central nervous system and multiples rapidly; this phase lasts from two to ten days. About half of patients experience pain or tingling at the site of the bite; most will also have headaches, fever, loss of appetite, chills, nausea, diarrhea, insomnia, anxiety, and depression.
• Acute phase. This phase lasts from two to seven days. The patient may hallucinate, try to bite others, thrash around, and have seizures. Spasms of the throat muscles prevent swallowing water even though the patient is thirsty; he or she may drool large amounts of saliva, sometimes described as “foaming at the mouth.” The patient is usually calm in between seizures but may die during this phase from paralysis of the breathing muscles. Some human cases, as well as dog cases, can present as “dumb” rabies where there are no signs of overactivity.
• Coma and death. About ten days after the onset of symptoms, the patient slips into a coma and dies of heart failure or paralysis of the breathing muscles.

Diagnosis

Diagnosis begins with reporting an animal bite to the doctor. The patient should describe what type of animal caused the bite and what he or she was doing when bitten. If a pet caused the bite, the patient should tell the doctor whether the cat or dog had been vaccinated against rabies. If the animal can be captured, it can be kept for ten days of observation or put to sleep at once to have its brain tissue examined.

Humans who have developed symptoms of rabies are tested by having samples of blood serum, saliva, and spinal fluid analyzed; a small piece of tissue from the nape of the neck may also be analyzed.

Treatment

Patients who have already developed symptoms of rabies cannot be helped by immune globulin (an agent used to stimulate the immune

system) or vaccine. They can be given supportive care in an intensive care unit before death.

Prognosis

Without preventive treatment, the prognosis is death within days. Only six cases have been recorded of people surviving rabies after developing symptoms of the disease; five of the six patients had received some kind of preexposure or postexposure treatment before their symptoms appeared. The sixth survivor, a young woman from Wisconsin, is still being studied to determine what factors may have helped her survive without vaccine treatment.

Prevention

The prevention of rabies is known as post-exposure prophylaxis or PEP. It should begin as soon as possible after a bite or other known exposure to the rabies virus. In the United States, PEP consists of one dose of rabies immune globulin, which provides temporary antibodies against the disease. It is injected in part around the site of the bite. The patient also receives five injections of rabies vaccine over a twenty-eight-day period, given in the muscle of the upper arm; the vaccine stimulates the body to produce its own antibodies against the rabies virus.

There are several measures that people can take to prevent exposure to rabies:

• Have pet cats, dogs, and ferrets vaccinated against rabies and keep their shots current.
• Avoid contact with wild or strange animals, whether alive or dead.
• Report stray animals or any animals that look sick or are acting strangely to animal control or the local police.
• Since most of the animals likely to carry rabies, except for dogs and cats, are nocturnal, any animals seen during the day and seemingly not afraid of humans should be avoided.
• Have the house batproofed according to instructions from the CDC or Bat Conservation International (BCI).
• Teach children not to pet or handle wild or unfamiliar animals.

To prevent getting rabies after exposure to a potentially rabid animal, people should:

• Wash the wound immediately with one part soap to four parts of water.

• Go to the emergency room as soon as possible after cleaning the wound.
• Contact the local animal control and public health authorities to have the animal trapped and evaluated for rabies.

People who work with animals, such as veterinarians, animal control workers, scientists who work with bats or other animals known to carry rabies, and some laboratory workers should be immunized against rabies before they are exposed, and have a booster shot every two years.

The Future

The case of the young woman who survived rabies without vaccine has interested researchers in studying the treatment that was given to her to see whether it might benefit others. She had been placed in a coma to protect her brain as well as given a combination of drugs and vitamin replacement therapy. It is not yet known, however, whether the treatment was effective, whether she had been infected by an unusually weak strain of the rabies virus, or whether her survival resulted from both factors.

SEE ALSO Encephalitis; Toxoplasmosis

WORDS TO KNOW

Negri bodies : Round or oval bodies found within the nerve cells of animals infected by the rabies virus. They were first described by Dr. Adolchi Negri in 1903.

Postexposure prophylaxis (PEP) : A treatment given after exposure to the rabies virus. It consists of one dose of rabies immune globulin and five doses of rabies vaccine.

Prodrome : A period before the acute phase of a disease when the patient has some characteristic warning symptoms.

Zoonosis : A disease that animals can transmit to humans.

For more information

BOOKS

Kienzle, Thomas E. Rabies. New York: Chelsea House Publishers, 2006.

Roueché, Berton. The Incurable Wound and Other Narratives of Medical Detection. New York: Berkley Medallion, 1966. First published in 1957 in the

New Yorker, the title chapter in this book is a classic study of rabies. Roueché was one of the first popular medical writers to describe cases of rabies transmitted by bats.

PERIODICALS

Centers for Disease Control and Prevention (CDC). “Recovery of a Patient from Clinical Rabies—Wisconsin, 2004.” Morbidity and Mortality Weekly Report 53 (December 24, 2004): 1171–1173. Available online at http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5350a1.htm (accessed on April 8, 2008). This is the CDC's report of the only known case of a human to survive rabies after developing symptoms without either preexposure or postexposure treatment.

Pasteur, Louis. “Method for Preventing Rabies after a Bite.” Bulletin de l'Académie de Médecine, second series, 14 (October 27, 1885): 1431–1439. Available online at http://pyramid.spd.louisville.edu/~eri/fos/Rabies.html (accessed on April 8, 2008). This is an English translation of Pasteur's landmark report of his successful treatment of Joseph Meister.

“Soul Survivor: A Journey of Faith and Medicine.” Milwaukee Journal Sentinel Online, http://www.jsonline.com/story/index.aspx?id=373532 (first posted June 2005; accessed on April 6, 2008). This is an archived series of news stories and videos about the recovery of Jeanna Giese, the first known human to survive rabies without vaccine.

WEB SITES

American Veterinary Medical Association (AVMA). What You Should Know about Rabies. http://www.avma.org/communications/brochures/rabies/rabies_brochure.asp (revised 2006; accessed on April 10, 2008). Includes information about protecting household pets against rabies and advice about what to do if a pet bites someone.

Bat Conservation International (BCI). FAQ—Public Health Issues. http://www.batcon.org/home/index.asp?idPage=91&idSubPage=62 (accessed on April 8, 2008). The BCI Web site is recommended by the CDC as a good source of information about batproofing one's house as well as answering questions about rabies in bats. The Web site includes a PDF file of the fifty-three confirmed cases of death from rabies caused by bats from 1951 through March 2008, available at http://www.batcon.org/dfs/rabieschart.pdf.

Centers for Disease Control and Prevention (CDC). Rabies. http://www.cdc.gov/rabies/ (accessed on April 8, 2008). This is a gateway Web site with a menu of specific topics about rabies, including information about the disease itself as well as special problems involving bat-related rabies and a kids' page about the disease.

Mayo Clinic. Com. Rabies. http://www.mayoclinic.com/health/rabies/DS00484 accessed on April 8, 2008).