rabies

rabies
Name	Rabies
Caption	Transmission electron micrograph of the rabies virus
Field	Infectious diseases, neurology, veterinary medicine
Symptoms	Fever, fear of water, confusion, excessive salivation, hallucinations, paralysis
Complications	Coma, cardiac arrest
Onset	1–3 months post-exposure
Duration	Almost always fatal after symptoms begin
Causes	Rabies virus and Australian bat lyssavirus
Risks	Animal bites, particularly from dogs, bats, raccoons, foxes, skunks
Diagnosis	Post-mortem: direct fluorescent antibody test on brain tissue. Pre-mortem: saliva, serum, cerebrospinal fluid tests.
Prevention	Rabies vaccine, animal control, pre-exposure prophylaxis
Treatment	Post-exposure prophylaxis (wound cleansing and vaccination)
Medication	Rabies immunoglobulin, human diploid cell vaccine
Prognosis	Nearly 100% fatal if untreated before symptom onset
Deaths	~59,000 annually (WHO estimate)

rabies. Rabies is a viral zoonosis that causes acute encephalitis in mammals. It is caused by lyssaviruses, most commonly the rabies virus, and is almost invariably fatal once clinical symptoms appear. The disease is primarily transmitted through the saliva of an infected animal via bites, and it remains a significant public health concern in many parts of the developing world.

Overview

The causative agent, the rabies virus, belongs to the genus Lyssavirus within the family Rhabdoviridae. Historically documented since ancient times, descriptions of the disease appear in texts from Mesopotamia and were later detailed by scholars like Celsus and Louis Pasteur. The virus has a characteristic bullet shape and primarily infects the central nervous system, leading to severe neurological dysfunction. The World Health Organization and the World Organisation for Animal Health list it as a neglected tropical disease of major importance.

Transmission and pathogenesis

Transmission typically occurs when the virus-laden saliva of a rabid animal enters the body, usually through a bite wound. The primary reservoirs vary geographically: dogs are the main source in Africa and Asia, while wildlife such as raccoons, skunks, foxes, and various species of bats are significant vectors in the Americas and Europe. After entry, the virus replicates locally in muscle tissue before traveling along peripheral nerves to the spinal cord and brain. This retrograde axonal transport is a hallmark of its pathogenesis.

Signs and symptoms

The incubation period is highly variable, ranging from weeks to years. The initial prodromal phase includes nonspecific symptoms like fever and paresthesia at the exposure site. This progresses to one of two clinical forms: furious or paralytic. Furious rabies is characterized by hydrophobia, aerophobia, hyperactivity, and autonomic dysfunction. Paralytic rabies, often associated with bat bites, presents with ascending paralysis. Both forms ultimately progress to coma and death, usually from respiratory failure.

Diagnosis

A definitive diagnosis is often made post-mortem via the direct fluorescent antibody test on brain tissue samples from the brainstem or cerebellum. Ante-mortem tests are less sensitive and can involve detecting viral antigen or RNA in samples of saliva, skin biopsy from the nuchal region, or cerebrospinal fluid. The Centers for Disease Control and Prevention and national reference laboratories like the Institut Pasteur are central to diagnostic confirmation and surveillance.

Prevention

Prevention is the cornerstone of control. For humans, pre-exposure prophylaxis with modern cell culture vaccines is recommended for high-risk groups like veterinarians and laboratory workers. For animals, widespread vaccination of dogs is the most cost-effective strategy, as promoted by the World Health Organization. Other measures include animal control programs and public education. The oral rabies vaccination of wildlife, pioneered in Switzerland, has been successfully deployed in regions like North America and Europe.

Treatment and prognosis

Once symptoms manifest, the disease is nearly always fatal, with only a handful of documented survivors, such as the patient treated with the Milwaukee protocol. Therefore, immediate post-exposure prophylaxis is critical. This involves thorough wound cleansing with soap and water, infiltration of rabies immunoglobulin around the wound, and a series of intramuscular vaccinations. The Essen regimen and Zagreb regimen are common vaccination schedules. Prognosis is excellent if PEP is administered promptly after exposure.

Epidemiology

Rabies causes an estimated 59,000 human deaths annually, with the vast majority occurring in rural areas of Africa and Asia, particularly in countries like India. Children are disproportionately affected. While canine rabies has been eliminated in many Western European nations, the United States, and Japan through coordinated programs, wildlife rabies remains endemic in specific regions. Global elimination efforts are coordinated by entities like the World Health Organization, the Food and Agriculture Organization, and the Global Alliance for Rabies Control.

Category:Infectious diseases Category:Zoonoses Category:Viral diseases Category:Neglected tropical diseases