Rabies

ByDr. Girish Chandra

 

 

RABIES

(Dr. Girish Chandra)

            Rabies is a serious viral disease that affects central nervous system. It is an infectious disease of animals caused by a bullet-shaped, enveloped RNA virus, 180 x 75 nm. Man is occasionally infected and once infection is established in the central nervous system, the outcome is almost invariably fatal. Typically rabies spreads by way of the saliva of infected animals, usually a rabid dog, that comes in contact with blood through a bite. Once infected, the virus spreads from muscles to peripheral nerves to spinal cord and brain. From initial flu-like symptoms, the illness progresses to convulsions, hallucinations, paralysis or breathing failure and almost always to death. The severity of the bite determines the risk of infection. The disease does not usually spread from man to man.

Incubation

            After inoculation, the virus enters small nerve endings at the site of the bite. The virus slowly travels up the nerve to reach the central nervous system, where it replicates and then travels down the nerves to salivary glands where there is further replication. The time it takes to do this depends upon the length of the nerves. A bite on the foot will have a much longer incubation period than a bite on the face. The incubation period may last from two weeks to six months. Very often the primary wound is healed and forgotten by the time of clinical symptoms appear.  

Clinical Symptoms

 Furious Rabies
            When the virus reaches the central nervous system, the patient suffers from headache, fever, irritability, restlessness and anxiety. This may progress to muscle pains, salivation and vomiting. After a few days to a week the patient may experience a stage of excitement and painful muscle spasms, triggered sometimes by swallowing of saliva or water. Hence they fear water (Hydrophobia). The patients are also excessively sensitive to air blown on the face. The stage of excitement lasts only a few days before the patient lapses into coma and death.
            Once clinical disease manifests, there is a rapid, relentless progression to invariable death, despite all treatment. The symptoms may include: Fever, headache, malaise, insomnia, anxiety and confusion, slight or partial paralysis, excitation, hallucinations, agitation, salivation, difficulty swallowing, convulsions and fear of water (hydrophobia) because of the difficulty in swallowing

 Dumb Rabies
            Starts in the same way, but instead of progressing into excitement, the subject retreats steadily and quietly downhill, with some paralysis, to death. Rabies diagnosis may easily be missed.

ANIMAL RABIES

 

            It is very similar to human rabies. In the stage of excitement the animal may bite vigorously and viciously at anything: sticks, stones, grass, other animals and humans, without provocation. Wild animals may be abnormally tame or appear sick – beware of approaching or picking up such animals.

            An animal infected with rabies carries the virus in its saliva, so if it bites a person, the virus enters into the person’s body. It’s possible to get rabies from an animal scratch, too. People sometimes describe animals that have rabies as "foaming at the mouth." This happens because the animal’s nerves no longer work properly and it can’t swallow its own saliva.

Disease transmission

          Most often rabies transmission occurs through the bite of a rabid animal. Rarely, people contract rabies when saliva from an infected animal comes in contact with their eyes, nose, mouth or a wound. This may occur if you’re licked by an infected animal. Inhaling the rabies virus is another potential route of exposure, but one likely to affect only laboratory workers.

             The disease is endemic in wild animals in most parts of the world although some countries (UK, Australia) have become rabies-free through vigorous control measures and campaign. The wild animal cycle constitutes the natural reservoir. Wild animals may bite and infect domestic animals (cattle, horses, pigs, dogs and cats) which in turn may infect man. Occasionally wild animals may infect man directly. In recent decades, a separate form of dog rabies spread from dog to dog has been recognized as spreading from West Africa eastwards and southwards in Africa and Asia.

            You’re at greatest risk of contracting rabies if your activities bring you into contact with the rabies virus or a potentially rabid mammals. People at risk can include veterinarians, animal caretakers, laboratory workers, hunters, forest rangers and people visiting bat-inhabited caves.

ANIMAL RESERVOIRS

            Mongoose (main reservoir in RSA in the wild), jackals, bats(some evidence to suggest carrier status and droplet infection), foxes (in Europe), skunks, raccoons (in USA) and semi-wild dogs.

 

 

DIAGNOSIS

 

            If you’ve been bitten or have had contact with an animal that may have rabies, certain information may help your doctor determine your risk of contracting rabies and how to treat you. Take note of the following:

 

            Where the incident occurred, a description of the animal and the vaccination status of the domesticated animal should be found out. If the animal can be safely captured to be tested for rabies, then if it survives for 8 days it would not be rabid. Another option is for health professionals to conduct tests on the animal’s brain tissue to determine whether it has rabies. Testing can be done quickly, but only after the animal is dead.

 

            If you have the signs and symptoms of rabies, a number of tests using blood, saliva, spinal fluid, brain tissue or skin tissue taken from the nape of your neck may be required to identify or rule out rabies infection.

 

Prevention

 

            Ways to help prevent exposure to rabies include: Keep your pets and other domesticated animals up-to-date with regular animal rabies shots. Avoid contact with wild or unfamiliar animals, whether they’re alive or dead. Seal or close any openings where animals might find entry into your home. Report stray animals or any that act strangely or sick to your local animal control authorities. Teach your children to never handle unfamiliar animals. If your work or activities might bring you into contact with the rabies virus or a potentially rabid mammal, consider getting a preventive vaccination. This vaccination — called pre-exposure prophylaxis — involves three injections over three or four weeks. A booster shot can maintain the vaccination’s effectiveness

 

 

TREATMENT

 

            If bitten by an animal with rabies, thoroughly wash the wound or area of exposure with soap and water. Quick action is important. Once the earliest signs and symptoms appear, death almost always follows. Promptly contacting the doctor after a potential rabies exposure greatly increases chance of survival.

 

            The treatment — called post-exposure prophylaxis — consists of one dose of rabies immunoglobulin and five doses of rabies vaccine over a 28-day period. Rabies immunoglobulin and the first dose of rabies vaccine are administered as soon as possible after the patient has been exposed. The immunoglobulin is given by injection around the site of bite and into the upper arm muscle.

 

            Immunoglobulins are disease-fighting proteins that provide you with temporary antibodies. The rabies vaccine helps the body to start producing its own antibodies. Antibody production takes time, but the antibodies produced by the body provide longer lasting protection than do the ones contained in rabies immune globulin.

 

            Although the vaccine isn’t painful, there might be mild physical reactions. Watch for reactions such as swelling or redness where the injection was given. Headache, fever, nausea, muscle aches and dizziness are other possible side effects. Contact your doctor if side effects produce discomfort.

 

 

 RABIES VACCINE


            A good but expensive killed virus vaccine (Human Diploid Cell Vaccine, HDCV) grown in human fibroblasts is available for safe use in man. The unusually long incubation period of the virus permits the effective use of active immunization with vaccine postexposure. When used, vaccine has dramatically cut the rabies death rate. (Older killed virus vaccines, made from infected neural tissues, were poorly immunogenic and had allergic encephalitic side effects, but are still used in developing countries.)

Prophylaxis

            High-risk persons, e.g. veterinarians, may be immunized before exposure, and then merely require one or two booster doses if they should be exposed to rabies.

Animal Vaccines
            A range of live and killed virus vaccines are available for domestic animals (farm animals, cats and dogs).