Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.
Mary D. Nettleman, MD, MS, MACP is the Chair of the Department of Medicine at Michigan State University. She is a graduate of Vanderbilt Medical School, and completed her residency in Internal Medicine and a fellowship in Infectious Diseases at Indiana University.
What is the history of rabies, and what is the cause of rabies?
Rabies has been noted in history since about 2000 BC when owners of rabid
dogs were cautioned against getting bitten. The word rabies is derived from
the Latin word rabies, which meant "madness or rage." For many centuries, it
was common practice to kill any animal or human that showed symptoms of the
disease. Rabies has been a problem in many countries, even into the 21st century
as China developed a "one-dog" rule for people in Beijing to better control an
increasing rate of dog rabies in 2006. Although the U.S. has had no people
infected by dogs in years, there is an increasing incidence in wild animals,
especially in the southern states since the 1970s.
In the 15th century, Italian physician Girolamo Fracastoro studied rabies
and concluded that it was a communicable disease transmitted to people by direct
contact with saliva from infected animals. He termed the disease "rabies." In
1895, after studying the data presented by Fracastoro centuries before, Louis
Pasteur was able to produce a vaccine against the disease-causing viruses
without actually discovering or isolating the viruses
The virus that causes rabies is Lyssavirus (Lyssa is the Greek goddess of
madness, rage, and frenzy) rabies, a cylindrical or bullet-shaped virus that is
enveloped and contains a negative-sensed RNA that makes up its genetic material.
Figure 2: CDC diagrams of the bullet-shaped rabies virus. The top image is the longitudinal view, and the bottom image is the cross-sectional view of the viral structure. SOURCE: CDC
The virus is termed a neurotropic virus because it proliferates in nerve
tissues, especially the brain tissues of humans and animals. It proceeds from
the bite or entrance wound along nerves to eventually infect the brain. The
treatment use of human immune globulin and vaccine is designed to interrupt and
kill the virus before it makes the journey to the brain. The virus enters nerve
cells, takes over the cells systems, and develops virus replicating sites (termed
Negri bodies that can be seen microscopically inside cells) that produce new
viruses to continue viral spread to other body sites like the brain and, most
important for spreading the viruses to other animals, the salivary glands. The
rabies life cycle is relatively simple; the virus is transmitted to a wild
animal by bites or saliva, the virus replicates in the bitten animal that, in
turn, bites another animal and the cycle is completed. Humans are incidentally
infected and rarely transmit the virus so humans play almost no role in the
rabies life cycle.
How is rabies transmitted?
Almost every person who gets rabies has the virus transmitted to them by the
bite of an infected animal. The transmission of rabies from human to human is rare;
the highest number recorded happened when corneal transplants that were unknown
before transplant to contain rabies virus caused rabies in eight patients.
Aerosols of infected saliva or bat guano may also transmit rabies. In developing
countries, the majority of people are infected by rabid dogs. Rabid dogs are
often aggressive and sometimes are drooling, but in other cases, they act very withdrawn.
Figure 3: Rabid dog drooling saliva onto teeth and lower lip. SOURCE: CDC
In underdeveloped and developed countries, there are a number of animals that
can transmit rabies to humans. Bats, foxes, coyotes, skunks, raccoons, cats,
wolves, opossums, and other animals are some of the prevalent wild or feral
animals that may become infected. In Mexico, cows have become infected from bat
bites and can transmit the virus to humans via a bite or saliva if the human skin
is abraded or cut. Currently, in the U.S., bats and raccoons cause the most bites
that may lead to rabies. Readers should note that drooling saliva is not always
present in wild or domestic animals with rabies. Any animal (domestic or wild)
that acts strangely (for example, unusually aggressive or docile, unusual gait,
has seizure-like activity) should be suspected of having rabies.
Anxiety is a feeling of apprehension and fear characterized by physical symptoms. Anxiety disorders are serious medical illnesses that affect approximately 19 million American adults.
Headaches can be divided into two categories: primary headaches and secondary headaches. Migraine headaches, tension headaches, and cluster headaches are considered primary headaches. Secondary headaches are caused by disease. Headache symptoms vary with the headache type. Over-the-counter pain relievers provide short-term relief for most headaches.
Muscle spasms are involuntary muscle contractions that come on suddenly and are usually quite painful. Dehydration, doing strenuous exercise in a hot environment, prolonged muscle use, and certain diseases of the nervous system may cause muscle spasms. Symptoms and signs of a muscle spasm include an acute onset of pain and a possible bulge seen or felt beneath the skin where the muscle is located. Gently stretching the muscle usually resolves a muscle spasm.
Itching can be a common problem. Itches can be localized or generalized. There are many causes of itching to include: infection (jock itch, vaginal itch), disease (hyperthyroidism, liver or kidney), reactions to drugs, and skin infestations (pubic or body lice). Treatment for itching varies depending on the cause of the itch.
Stress occurs when forces from the outside world impinge on the individual. Stress is a normal part of life. However, over-stress, can be harmful. There is now speculation, as well as some evidence, that points to the abnormal stress responses as being involved in causing various diseases or conditions.
Although a fever technically is any body temperature above the normal of 98.6 degrees F. (37 degrees C.), in practice a person is usually not considered to have a significant fever until the temperature is above 100.4 degrees F (38 degrees C.). Fever is part of the body's own disease-fighting arsenal: rising body temperatures apparently are capable of killing off many disease- producing organisms.
Dysphagia or difficulty in swallowing, swallowing problems. Dysphagia is due to problems in nerve or muscle control. It is common, for example, after a stroke. Dysphagia compromises nutrition and hydration and may lead to aspiration pneumonia and dehydration.
There are millions of dogs living in the United States, and thus many cases of dog bites. Annually, hundreds of people seek emergency medical care for dog bites. Treatment for a dog bite depends on how deep the injury is and the amount of tissue damage. Dog bites can be prevented by employing preventative measures.
Tetanus is an often-fatal disease caused by nerve toxins produced by the common bacteria Clostridium tetani. In a seven-day period after infection, a person experiences muscle spasms, restlessness, headache, irritability, then lockjaw, and the lungs stop functioning. Tetanus is treatable with antibiotics and drainage. Sedation is often give to stop muscle spasms.
Insomnia is the perception or complaint of inadequate or poor-quality sleep because of difficulty falling asleep; waking up frequently during the night with difficulty returning to sleep; waking up too early in the morning; or unrefreshing sleep. Secondary insomnia is the most common type of insomnia. Treatment for insomnia include lifestyle changes, cognitive behavioral therapy, and medication.
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