Rabies is a viral infection. Its widely feared because it has the highest death rate of any human infectious disease. People with rabies develop severe neurological symptoms. These symptoms include:
- Hyperactivity with muscle spasms
- Drooling from excess saliva production
- Fear of drinking water (hydrophobia)
- Numbness and tingling
- Weakness and later paralysis
The disease can rapidly progress to coma and death over days to weeks. Only a few people who were not vaccinated before developing symptoms are known to have survived rabies.
About 60,000 people in the world die of rabies each year, mostly in developing countries. In these countries, dogs do not receive routine vaccination. And treatment for humans with rabies vaccine and rabies immune globulin is not available after potential rabies exposure.
In resource-poor countries, human rabies is caused by dog bites 90% of the time. But in the United States, rabies among dogs has nearly been eliminated.
In the past 20 years, only one or two cases are reported annually in the U.S. Most cases happen from a bat bite. Other wild animals that carry rabies include raccoons, skunks and foxes. A couple of Americans have been bitten by rabid dogs while travelling outside the United States.
Rabies is nearly always spread through the bite or (less likely) scratch of an infected animal. The risk of getting rabies is highest with multiple bites, or bites to the head or neck area. When the bite penetrates the skin, the virus is deposited in the peripheral nerves. The virus then moves back up the nerves to the spinal cord and brain at the rate of about Ό to ½ inch per day.
The rabies virus can still be contained while it is in the peripheral nerves or spinal cord. That is, if the patient is treated promptly with vaccines and rabies immune globulin. However, once the virus reaches the brain, it reproduces rapidly and spreads throughout the body. By then, the treatment is usually not effective.
In extremely rare cases, rabies has been spread through non-bite exposure. However, for this to happen, saliva or nerve tissue that is infected with rabies must come into contact with either broken skin or mucous membranes (such as the mouth or nasal passages).
The rabies virus cannot penetrate healthy, unbroken, human skin. And it is rapidly killed by exposure to ultraviolet light and desiccation (drying). For this reason, there has never been a case of rabies infection spread from environmental surfaces or towels, bedding, etc.
Although nearly impossible, someone with broken skin in close contact with an infected animal could theoretically get rabies. The rabies-infected saliva could penetrate the skin wound and the peripheral nerves.
It is also possible to get rabies by inhaling the virus into the nasal passages, throat, or lungs. There have been a few cases of laboratory workers and explorers of bat-filled caves who could have become infected by inhaling the virus.
There have been a couple reported cases where rabies was spread through an organ transplant. Several people who received organs from the two infected donors died of rabies. It is likely that the rabies virus was present in the nerve tissue of the transplanted organs. And the people who received the organs already had weakened immune systems. Then they rapidly developed the disease.
For this reason, it is important to determine the cause of death among organ donors. In these cases, both donors had rabies symptoms before death.