The rabies virus is 70nm to 150nm in diameter and has a unique bullet-like shape. The surface of the virus is covered by spikes of Glycoprotein (G protein). The virus is highly resistant to dryness, decay and cold, and it can be active in dead bodies for a long time. However, sunlight, formaldehyde, antiseptics and lipid solvents can make it inactive.
The virus enters the blood stream of an animal or human through saliva by the bite of a rabid animal. In almost 99% of the cases the transmission of rabies is through saliva of the rabid animal. The average incubation period (the period from infection to showing of symptoms) of rabies is four weeks.
In US, almost 90% of rabies cases in humans and 20% of rabies cases in animals are reported due to bat bites. Raccoons, skunk, coyote, fox, wolf, jackal and mongoose are other animal reservoirs of rabies virus in US. In Asia and Africa, most of the rabies cases are attributed to dogs and cats.
There are two forms of rabies – furious or encephalitic form and paralytic or dumb form. The characteristic features of furious form are hydrophobia, hallucination, aerophobia, agitation, extreme irritability, increased salivation and perspiration. The characteristic features of paralytic form are similar to those of Guillain-Barre syndrome exhibiting weakness in limbs, paralysis, depression and coma.
Animals also display the two forms of rabies. Predator animals mostly show the furious form, while non-predator animals show the paralytic form of rabies.
Causes of Rabies:
Rabies is transmitted almost exclusively via a rabid animal bite. However, transmittal of virus through contact with infected brain matter and infected saliva, scratches upon the skin, and organ transplantation have also been reported. In US, rabies cases have been reported in individuals who inhaled the air in bat caves.
After a bite, the virus enters the blood stream and attaches itself to nerve cells, moves along the spinal cord and reaches the brain. This movement is known as the centripetal spread. After reaching the brain the virus replicates and causes encephalitis.
From brain, the virus spreads to other parts of the body, but most prominently to the salivary glands. This movement is known as the centrifugal spread. After entering the salivary glands the virus further replicates and increases the secretion of saliva. This is the end stage of the disease at which the victim starts to show symptoms. Death usually occurs within a few days after this stage.
Symptoms of Rabies:
Patients may display the following initial (prodromal) symptoms.
- The area around the bite may burn along with pain and tingling sensation.
- Other symptoms such as headache, sore throat, diarrhea, loss of appetite, nausea and vomiting, low-grade fever, increase in saliva secretion, increase in perspiration and tears, dilated pupils, low blood pressure and painful spasms in throat muscles may develop.
As the disease develops the patient may show the following symptoms:
- Mental confusion, including fear of death, irritability, anger, agitation and depression.
- Sensitive to touch, cold draught of air, loud noises and bright light.
- Hydrophobia. Even though, the patient has extreme thirst, he or she cannot drink water due to acute pain while swallowing. The diaphragm and muscles contract violently with sudden jerks when the patient attempts to swallow the liquids. Patients become terrified due to these violent spasms and develop intense fear of water. This phobia is not displayed by animals.
- Aerophobia. Some patients develop fear of air in motion due to painful and violent spasms of neck muscles and pharynx.
- Extreme salivation, loss of muscle tone and dehydration.
Diagnosis of Rabies:
The diagnosis of rabies is done by the following tests and procedure:
- Fluorescent antibody test. In this test, a small patch of skin is taken from the back of patient’s neck and tested for the presence of antibodies particular to the rabies virus. If antibodies are present, then they attach themselves to the fluorescent dye and become visible.
- Virus isolation test is conducted on the saliva or throat culture from the patient.
- Cornea impressions are tested for the presence of rabies virus. Cornea impressions are taken by pressing a swab on the cornea of the eye.
- Cerebrospinal fluid (CSF) analysis. In this test, CSF is obtained from the area surrounding the spinal cord and tested. CSF is obtained by a procedure called the lumbar puncture in which a needle is inserted, and fluid is drawn. CSF analysis does not confirm the presence of rabies, but it excludes other possible causes for the patient’s conditions.
Treatment of Rabies:
World Health Organization (WHO) has given clear guidelines for the treatment of rabies. The recommendations of WHO are as follows:
- Pre Exposure Vaccination
- Post Exposure prophylaxis
- Post Exposure treatment of persons already vaccinated
Pre Exposure vaccination or rabies shot:
Pre exposure vaccination or rabies shot is given to high-risk group individuals such as veterinarians, wild life personnel, rabies testing lab personnel, pet owners, dog handlers, rural postmen, taxidermists, slaughter house workers, medical staff that handles rabies patients, and frequent travelers to rabies endemic areas.
By taking rabies shots individuals can develop active immunity, thus decreasing the requirements of rabies immunoglobulin. Further, instead of six doses only three are required during the post-exposure treatment stage. In addition pre exposure vaccination will make immune system to give a better response when an individual is bitten by a rabid animal or when the post-exposure treatment is delayed due to any reason.
The dosage consists of three injections of cell culture vaccines of at least 2.5 IU (International Units) potency. First injection is given on day 1, second on day 7 and the final one on day 28. Immune system can further be maintained by taking booster injections after one year and then every three years.
Individuals from the high-risk group should undergo regular checkups to know the antibody titer levels. If the titer level falls below 0.5 IU/ml, then the individual shall be revaccinated.
Post Exposure Treatment:
The decision on whether a person should be given post-exposure treatment or not depends on various factors such as the species of animal, prevalence of rabies in the area, type of exposure, availability of the animal for observation, and vaccination status of the animal.
World Health Organization (WHO) gave guidelines on the type of treatment based upon three types of exposures.
Category I exposure involve touching or feeding of animals or licking on unbroken skin. There is no need of any treatment for this exposure.
Category II exposure involve chewing of uncovered skin or minor scratching without any bleeding. For this exposure, vaccination must be administered immediately. There is no need to give RIG (rabies immunoglobulin). The animal should be tested for rabies and kept under observation for 10 days. Treatment should be stopped, if the animal fails to show any rabies-related symptoms or if the laboratory results are negative.
Category III exposure involve single or multiple transdermal (cutting across the layers of skin) scratches or bites, or contamination of the mucous membrane with saliva or exposure to bats. For this type of exposure, both RIG (rabies immunoglobulin) and vaccine should be administered immediately. The treatment should be stopped if the animal does not show any symptoms during the 10 day observation period or if the test results on the animal are negative.
There are three recommended steps in post exposure treatment of rabies.
- Local cleaning of wound
- Passive Immunization and
- Active Immunization
Local cleaning of wound:
The wound should be cleaned immediately with plenty of water and soap and later with ethanol and tincture of iodine. The wound should not be sutured. However, if suturing is unavoidable, then the wound should be first injected by human rabies immunoglobulin.
Passive immunization involves administering of antibodies from already immunized individual through the injection of Human Rabies Immunoglobulin (HRIG). WHO recommended that HRIG should be given to all types of Category III exposures. HRIG is given only once at the start of the treatment. About half of the dosage is injected around the wounded area, and the remaining dosage is injected into the muscle. The recommended dosage of HRIG is 20 IU/Kg of body weight.
Active Immunization of rabies:
Active Immunization involves administering of vaccines such as rabies vaccine adsorbed (RVA) or human diploid cell vaccine (HDCV). These vaccines are given to stimulate the person’s immune system to produce antibodies against the rabies. The dosage should be given on days 1, 3, 7, 14, 28 and 90. The vaccination should be given in the deltoid (shoulder) region and never in the gluteal (buttock) region.
Post Exposure treatment of persons already vaccinated:
As a first-aid the wound should be cleaned with plenty of water and antiseptic soap and later with tincture of iodine. Persons, who underwent complete pre or post exposure treatment with potent vaccine (at least 2.5 IU/dose), should be given only two doses of vaccine on day 1 and day3. There is no need to administer rabies immunoglobulin (RIG).
Individuals who underwent complete pre or post exposure treatment with a vaccine of unproven potency and/or low antibody titer should be given full post exposure treatment, including rabies immunoglobulin.
Prognosis of Rabies:
Rabies is an extremely dangerous and fatal disease if treatment is delayed or untreated properly. The immunization is exceptionally effective if it is given within two days of rabid animal bite. Otherwise, the chances of survival get slim as the days passes without immunization. However, if treated properly and within time the patient can recover.
Prevention of Rabies:
Rabies can be prevented by taking certain precautions while dealing with animals, whether wild or domesticated. Domestic animals such as cats, dogs, ferrets and other household pets should be vaccinated. If a pet is bitten by an animal suspected to be rabid, then the pet should be immediately vaccinated, even if it was previously vaccinated.
Extreme care should be taken while dealing with animals in wild. They should not be touched or petted, especially when they show odd behavior such as not displaying normal fear of humans. Animals such as raccoons and skunks are nocturnal in nature, and so they should be suspected if they are active during the day.
Persons handling animals should wear personal protective gears. Such individuals should also be vaccinated. People should not interfere when animals are fighting. In bats infested areas all the doors and windows should be properly screened.