Rabies Disease Facts

Rabies is a zoonotic disease that the Center for Disease Control (CDC) and Environmental Epidemiology Division state “the primary reservoirs for rabies are bats and skunks.” The State of Colorado is experiencing an increase in the occurrence of rabies and other zoonotic diseases, rabies at the top of the list of statewide concerns. The vast majority of rabies cases reported to the Centers for Disease Control and Prevention (CDC) each year occur in wild animals like bats, raccoons, skunks, and foxes. Rabies virus infects the central nervous system, causing encephalopathy and ultimately death. Symptoms of rabies in humans are initially nonspecific, consisting of fever, headache, and general malaise. As the disease progresses, neurological symptoms appear and may include insomnia, anxiety, confusion, slight or partial paralysis, excitation, hallucinations, agitation, hyper salivation, difficulty swallowing, and hydrophobia (fear of water). Death usually occurs within days of the onset of symptoms. There is no treatment for rabies after symptoms of the disease appear. However, an extremely effective rabies vaccine can provide immunity to rabies when administered after an exposure (post exposure prophylaxis) or for protection before an exposure occurs (pre- exposure prophylaxis).”

Rabies is a viral infection to which all mammals, including man, are susceptible. The disease occurs when there is direct contact to infectious saliva and occasionally other bodily fluids through bites, scratches, broken skin. The incubation period ranges in general between 2 and 3 month (2 weeks to 6 years are reported) depending on the site of infliction, the amount of virus and the virus strain. It causes an acute and almost invariably fatal infection of the brain both in animals and humans.

It is one of the oldest known animal diseases transmissible to humans. It has been present throughout the recorded history, and literature, and very likely predates the evolution of humans. The first description of the disease dates from the 23rd Century BC in the Eshuma Code of Babylon. Democritus provided a clear description of animal rabies in about 500 BC. Antiquity, did know rabies as well as the link between human disease and animals, especially dogs. But, it is a famous Italian scholar, Girolamo Fracastoro, born in Verona, who described the human disease, which obviously he had seen in many patients, and its routes of transmission in 1530, i.e. 350 years before Louis Pasteur. According to records, wound cauterization (burning) was the preferred treatment in the 1st Century AD, and this had remained the only real therapy for a long time. Another ‘remedy’ that remains part of popular culture (with little) recognition of its origin) was the hair of the dog that bit the patient.

In medieval villages, people bitten by wolves were tied to poles, and given only solid food (using long sticks, to avoid contact). Those who started begging for water were considered uninfected, since fear of water is one of the symptoms of rabies in humans. Hence the alternate name “hydrophobia”.

In the 19th Century, canine or street rabies was a scourge everywhere, especially in Europe. Fear of rabies, related to the mode of transmission, the absence of any efficacious treatment, was almost irrational. Patients killed themselves or were killed when bitten by a dog believed to be rabid.In this world of irrational terror the first post-exposure treatment in 1885 gave Louis Pasteur an international aura that his previous major scientific works had not been able to provide. A 9-year-old boy was the first person to have received an effective shot for rabies. In 1885, Joseph Meister was bitten by a rabid dog. His parents went to the famous French microbiologist Louis Pasteur. They begged him to help their son. Pasteur thought that if he injected a weak form of virus from one rabid animal into another, the second animal might be able to fight off the disease. He tried this hypothesis out on Joseph. The boy survived and lived a long life. That was how people starting giving shots for rabies. After this success other rabies vaccines were made.

In animals, during the course of the illness there are disturbances of behaviour, which in some affected species, such as dogs, cause them to attack and bite other animals and occasionally humans. In many parts of the world (but not in the British Isles, some other parts of Western Europe and Australasia) rabies is found in terrestrial wildlife species. In Asia, Africa and Central and South America it also commonly infects domesticated animals such as dogs and cats, but rabies in domestic animals is very rare in Europe and North America. Bites from any of these animals can transmit the infection to other domestic and farm animals, and man. However, more than 99.9 % of human deaths from rabies reported worldwide result from the bite of a rabid dog. Bats can also transmit rabies and rabies-like viruses by bite or scratching. A rare route of infection is the inhalation of infected bat secretions in caves inhabited by bats.

Except through corneal transplantation, transmission of the virus from a human case to another human is unknown and there is no evidence that infected patients are a hazard to their families or health care workers looking after them, though vaccine should be offered to these close contacts.

The incubation period in man is usually three to eight weeks, but may be as long as several years. The range of non-descript symptoms in patients, are numerous. Early symptoms may include itching, pain or numbness around the site of the bite (which has usually been healed by the time the first symptoms appear), fever, headache, and general malaise. General symptoms may then develop such as fever, tiredness, headache, muscle ache, anxiety, depression. The patient then develops either furious or paralytic rabies. However, such clinical symptoms are not always observed. Feurious rabies is the most common presentation in humans. The patient develops periods of generalised arousal characterised by agitation, aggression and hallucinations. These periods alternate with clear intervals. The patient is often unable to swallow the saliva, which is usually abundant and viscid, so that it hangs about the mouth and is expelled with difficulty. Vomiting is common.

In “dumb” rabies, the initial symptoms are followed by paralysis of the muscles and eventual paralysis of the respiratory muscles. Hydrophobia is not usually a feature of dumb rabies. In either form, the symptomatic course usually runs 2 to 14 days before coma supervenes. Once symptoms have developed rabies is almost invariably fatal. Death occurs an average of 18 days after the onset of symptoms, but the range is broad. Only two patients have been reported who recovered and a further four patients survived with severe neurological defects.

How is rabies infection diagnosed?

During the incubation period, no diagnostic studies in the patient are useful. Once symptoms develop, a number of diagnostic tests are available, including testing serum or cerebral spinal fluid, skin (nape of neck) or brain biopsies. Due to the nature of the disease progression it is necessary to test multiple samples over a period of days and weeks. Rabies is endemic in most countries of the world.

The World Health Organization has estimated the annual number of human rabies deaths to be between 40,000 and as high as 70,000. Most of these deaths take place in developing countries, particularly in South and South East Asia.

Pre-exposure rabies prophylactic treatment (rabies vaccination) is not a general requirement for travel to any country. Based on the local incidence of rabies in the country to be visited, the availability of appropriate anti-rabies biological, and the intended activity and duration of stay rabies vaccination may be recommended for international travelers. Travelers with extensive unprotected outdoor exposure in rural areas, such as people engaging in certain occupational activities (veterinarians, animal workers, etc) or tourists with activities like trekking, bicycling, camping, hiking, etc might be at high risk in rabies-endemic regions even if their trip is brief. Therefore travelers visiting rabies-endemic countries are advised to seek advice on the need for pre-exposure rabies vaccination.

The standard pre-exposure vaccination schedule is administered on days 0, 7 and 28, but more rapid courses can be given if necessary. Regardless of whether a traveler receives pre-exposure vaccination (s)he should be advised to seek medical attention if bitten by a mammal. Anyone who regularly handles bats should also be vaccinated against rabies. Pre-exposure vaccination does not eliminate the need for additional medical attention after a rabies exposure but simplifies post-exposure prophylaxis in populations at risk by eliminating the need for rabies immune globulin and by decreasing the number of doses of vaccine required.

The cornerstone of rabies prevention is wound care, potentially reducing the risk of rabies by 90%. Therefore, any animal bite or scratch one should receive prompt treatment by thorough cleansing of the wound with soap and water; this local treatment will substantially reduce the risk of rabies as the virus. Those who have received pre-exposure vaccination will receive a further two doses following a potential rabies exposure. Such persons do not require rabies-specific immune globulin.

Those who have not received pre-exposure vaccination require a five dose, post-exposure vaccination schedule plus rabies immune globulin. Any person who has been bitten by a bat or any wildlife should be considered to be at risk of developing rabies. After the incident it is very important that the wound is flushed and thoroughly washed with soap and water or alcohol.

If you find a bat do not handle it. If it seems to be injured or sick, or needs to be moved, seek advice from a local Wildlife professional.