Rabies: An overview

Abstract

Rabies is a fatal disease caused by rabies virus, a neurotropic virus and a prototype of Lyssavirus of Rhabdoviridae family. It is transmitted to human beings through infected saliva of dogs and cats during bite. Dog is the cause of more than 90% of human rabies in India. The incubation period is 4-8 weeks (but it may vary from 5 days to 7 years). There are two clinical types of rabies - encephalitic (furious) and paralytic (dumb) types. In the encephalitic (furious) form, the principal malfunction is in the brain stem and limbic system. Patient has hydrophobia in the full-blown form, but the mind remains clear till the end. Death occurs within a week after the onset of symptoms. Paralytic rabies resembles Guillain-Barre syndrome. Diagnosis is mostly clinical. However, direct fluorescent antibody test is used to identify the antigen in skin biopsy from the nape of neck. In the postmortem specimen, demonstration of Negri bodies in the brain confirms the diagnosis. Anti-rabies vaccine is used for pre- and post-exposure prophylaxis. The commonly used intramuscular (IM) regimen is being superseded by intradermal (ID) vaccine because it makes the treatment economical. Whereas touching of animal or lick on intact skin does not require vaccination, any transdermal bite with bleeding requires immediate administration of rabies immunoglobulin (RIG) and simultaneous vaccination with a tissue culture vaccine (TCV). Minor abrasion without bleeding may require only vaccination and no RIG. Rabies human monoclonal antibody (RMAb) is the newest entry in the prophylaxis of rabies which may ultimately replace RIG. Prognosis is grave since there are just six reports of survivors. Treatment is mainly palliative with heavy sedation and/or therapeutic coma (Milwaukee protocol).