symptomology and outcome
prevention and management
The incubation period for rabies virus is usually 1 to 2 months, but it can vary from a few days to a few years. Rabies is a very variable disease, and incubation time can depend on the site of inoculation and its proximity to the CNS, quantity of virus introduced, host age and immune status.
Rabies is transmitted by the bite of an infected (rabid) animal; virus does not enter through intact skin. Human-to-human transmission is not a significant form of spread, and only mammales are significant natural hosts. Reservoirs include: dogs, foxes, jackals, coyotes, raccoons, skunks, mongooses, and bats. Domestic dogs are the principal hosts and major vector throughout the world, and bat rabies appears to be mostly a New World phenomenon.
Epidemiology is influenced by host species distribution, abundance, demographics, behavioral ecology, dispersal, and interactions with humans. Rabies is enzootic (endemic in the animals) in all major regions of the world except for Antarctica. Hawaii has historically been the only rabies-free state in the United States, mostly because of its isolation.
Wild animals are the main reservoir in Europe and North America now, but in southeast Asia, Latin America, and Africa, dogs continue to be the principal cause of human cases. Japan and the United Kingdom claim to have eliminated rabies by eliminating infected terrestrial animals, but bats can reach great distances and thus could reintroduce the virus.
SYMPTOMOLOGY and OUTCOME
Rabies infection follows a centripetal course from site of bite, where the virus initially replicates. An immune response comes only after replication and dissemination.
There are three phases of clinical rabies:
1: prodromal period- 2-10 days, mild and nonspecific symptoms: general malaise, chills, fever, headache, photophobia, anorexia, nausea, vomiting, diarrhea, sore throat, cough, and musculoskeletal pain. Patient may also have abnormal sensation around the bite site such as itching, burning, numbness, or paresthesia.
2: acute neurologic phase: nervous system dysfunction: anxiety, agitation, dysphagia, hypersalivation, paralysis, and episodes of delirium; priapism and increased libido may occur.
‘Furious rabies’ is characterized by hyperactivity. In paralytic or ‘dumb’ rabies paralysis dominates. It is a flaccid paralysis, usually in the bitten extremity. Paresthesia and weakness develop into paralysis and paraplegia or quadriplegia.
Hydrophobia is the pathognomic sign of rabies. This response probably comes from an exaggerated respiratory tract protective reflex. These episodes last one to five minutes and are usually triggered by attempts to drink or a variety of tactile, auditory, visual, and olfactory stimuli.
3: coma preceding death: For furious rabies: 2-7 days of neurologic period leads to coma or sudden death from respiratory or cardiac arrest. For paralytic rabies: less rapid progression, some patients can live up to 30 days without intensive care; then coma lasting 3-7 days and then death.
PREVENTION and MANAGEMENT
There is no successful treatment of clinical rabies, and it is almost 100% fatal, so prevention is key.
Post-exposure prophylaxis is available for rabies. Post exposure vaccinations involves: (1) washing out the wound with soap and water, (2) passive immunization with the hyperimmune globulin, (3) and active immunization with the antirabies vaccine- five doses on days 1,3, 7, 14, and 28 are recommended.
A pre-exposure vaccine is also available, but the cost is rather high.
Virus may replicate in the muscular tissue before proceeding into the PNS, so amputation or cauterization of the infected limb may reduce mortality if post-exposure prophylaxis is not available.
Survival one rabies develops may be prolonged for weeks with respiratory assistance, but this will not prevent death.
As for controlling the virus in the environment, systematic surveillance is useful in defining rabies in species of the region. Vaccinating dogs is a major form of management. Containing or killing (euthanasia) of any animal that is known or suspected to be infected, as well as stray animal management, leash laws, responsible pet ownership, can be effective in reducing rabies in an area. Population reduction of free-range mammals is not really cost-effective, ecologically sound, or humane, or even effective, though. Oral consumption of vaccine by wild animals by impregnating bait has been tried, with some success.
Back to Rhabdo home
Knipe DM and Howley PM, eds. Fields Virology, Fourth Edition. Philadelphia: Lippincott Williams & Wilkins, 2001. pp. 1245-1267.