The rabies virus is an enveloped, bullet‑shaped RNA virus of the genus Lyssavirus that causes fatal encephalitis in mammals, including humans.
Explanation
The rabies virus belongs to the family Rhabdoviridae and has a single‑stranded negative‑sense RNA genome encapsidated within a helical nucleocapsid and surrounded by a lipid envelope studded with glycoprotein spikes. Infection is usually transmitted through the saliva of an infected animal via a bite or scratch. After replication in muscle cells at the inoculation site, the virus travels retrograde along peripheral nerves to the central nervous system, where it replicates extensively and causes progressive neurological disease. Clinical manifestations in humans include fever, anxiety, hydrophobia, agitation and progressive paralysis, culminating in coma and death without timely intervention. Two clinical forms are recognised: furious rabies, characterised by hyperactivity and hallucinations, and paralytic (dumb) rabies, marked by flaccid muscle weakness. The incubation period ranges from weeks to months, influenced by the site of exposure and inoculum size.
Transmission and Control
Globally, domestic dogs remain the primary reservoir for human rabies, accounting for most cases in Asia and Africa. In the Americas and Europe, wildlife species such as bats, raccoons, skunks and foxes are important reservoirs. Virus excretion in saliva begins a few days before symptom onset, making seemingly healthy animals infectious. Post‑exposure prophylaxis with wound cleansing, administration of rabies immunoglobulin and vaccination is highly effective if initiated promptly after exposure. Pre‑exposure vaccination is recommended for individuals at high risk, such as veterinarians and travelers to endemic areas. Mass vaccination of dogs has dramatically reduced human rabies in many countries. The Milwaukee protocol, involving induced coma and antiviral therapy, has been attempted in a few human rabies survivors but remains controversial. Beyond disease, attenuated rabies virus is used as a neural tracer in research due to its ability to travel retrograde along axons.
The rabies virus illustrates the importance of zoonotic disease control and the power of preventive vaccination. Although invariably fatal once symptoms appear, rabies is preventable through animal vaccination and timely post‑exposure treatment.
Related Terms: Lyssavirus, Negri body, Post‑exposure prophylaxis, Encephalitis, Vaccine