SPECIAL REPORT

Rabies

Rabies: A neglected zoonotic disease

Rabies is a zoonotic disease (a disease that is transmitted from animals to humans) that is caused by a virus. It is known to be present on all continents except Antarctica and infects domestic and wild animals.

Rabies is spread to people through close contact with infected saliva via bites or scratches. The main route of rabies transmission to humans is the bite of rabid dogs. Most of the deaths occur in the absence of post-exposure prophylaxis. Rabies is nearly always fatal when left untreated.

Although it is a vaccine-preventable disease, rabies still poses a significant public health problem in many countries in Asia and Africa where 95% of human deaths occur even though safe, effective vaccines for both human and veterinary use exist.

Nearly half of those bitten by suspect rabid animals are children under 15 years of age. Although the efficacy and safety of modern cell culture vaccines have been recognized, some countries still produce and use nervous tissue vaccines, which are less effective.

Symptoms 

The incubation period for rabies is typically 1-3 months. This however could vary from 1 week to a year. Initial symptoms of rabies are usually non-specific and suggest involvement of fever and often pain or unusual or unexplained tingling, pricking or burning sensation (paraesthesia) at the wound site.

As the virus spreads through the central nervous system, progressive, fatal inflammation of the brain and spinal cord develops.

Two forms of the disease can follow:

• Furious rabies during which people infected by the virus exhibit signs of hyperactivity, excited behaviour, hydrophobia and sometimes aerophobia. After a few days, death occurs by cardio-respiratory arrest.
• Paralytic rabies accounts for about 30% of the total number of human cases. This form of rabies runs a less dramatic and usually longer course than the furious form. The muscles gradually become paralyzed, starting at the site of the bite or scratch. A coma slowly develops, and eventually death occurs. The paralytic form of rabies is often misdiagnosed, contributing to the underreporting of the disease.

Prevention

The most cost-effective strategy for preventing rabies in people is by eliminating rabies in dogs through vaccination. Vaccination of animals (mostly dogs) has reduced the number of human (and animal) rabies cases in several countries, particularly in Latin America. However, recent increases in human rabies deaths in parts of Africa, Asia and Latin America suggest that rabies is re-emerging as a serious public health issue.

Preventing human rabies through control of domestic dog rabies is a realistic goal for large parts of Africa and Asia, and is justified financially by the future savings of discontinuing post-exposure prophylaxis for people.

Diagnosis 

No tests are available to diagnose rabies infection in humans before the onset of clinical disease, and unless the rabies-specific signs of hydrophobia or aerophobia are present, the clinical diagnosis may be difficult. Post mortem, the standard diagnostic technique is to detect rabies virus antigen in brain tissue by fluorescent antibody test.

Treatment

All cases of suspected exposure to rabies should be treated as soon as possible to prevent the onset of symptoms and death. Post-exposure prevention consists of local treatment of the wound, administration of rabies immunoglobulin (if indicated), and immediate vaccination.

Removing the rabies virus at the site of the infection by chemical or physical means is an effective means of protection. Therefore, prompt local treatment of all bite wounds and scratches that may be contaminated with rabies virus is important.

Recommended first-aid procedures include immediate and thorough flushing and washing of the wound for a minimum of 15 minutes with soap and water, detergent, povidone iodine or other substances that kill the rabies virus.

The recommended post-exposure prophylaxis depends on the type of contact with the suspected rabid animal (see table).

Recommended post-exposure prophylaxis for rabies infection Category of exposure to suspect rabid animal Post-exposure measures Category I – touching or feeding animals, licks on intact skin (i.e. no exposure) None Category II – nibbling of uncovered skin, minor scratches or abrasions without bleeding Immediate vaccination and local treatment of the wound Category III – single or multiple transdermal bites or scratches, licks on broken skin; contamination of mucous membrane with saliva from licks, exposures to bats. Immediate vaccination and administration of rabies immunoglobulin; local treatment of the wound

Other factors that should be taken into consideration when deciding whether to initiate post-exposure prevention include:

• the likelihood of the implicated animal being rabid
• the clinical features of the animal and its availability for observation and laboratory testing.

In developing countries, the vaccination status of the suspected animal alone should not be considered when deciding whether to initiate prophylaxis or not.

                                                                                                                  

                                                        Source: WHO(www.who.int)