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Rabies: Symptoms and diagnosis
The production of large quantities of saliva and tears coupled with an inability to speak or swallow are typical during the later stages of the disease Rabies, this can result in 'hydrophobia', where the patient has difficulty in swallowing
THE PERIOD between infection and the first flu-like symptoms is normally two to twelve weeks but can be as long as two years. Soon after, the symptoms expand to slight or partial paralysis, cerebral dysfunction, anxiety, insomnia, confusion, agitation, abnormal behaviour, paranoia, terror, hallucinations, progressing to delirium.
The production of large quantities of saliva and tears coupled with an inability to speak or swallow are typical during the later stages of the disease; this can result in “hydrophobia,” where the patient has difficulty swallowing because the throat and jaw become slowly paralysed, shows panic when presented with liquids to drink and cannot quench his or her thirst.
The disease itself was also once commonly known as hydrophobia, from this characteristic symptoms. Death almost invariably results two to ten days after the first symptoms; the few humans who are known to have survived the disease were all left with severe brain damage, with the exception of Jeanna Giese (see below). It is neurotropic in nature.
The reference method for diagnosing rabies is by performing PCR or viral culture on brain samples taken after death. The diagnosis can also be reliably made from skin samples taken before death.[26] It is also possible to make the diagnosis from saliva, urine and cerebrospinal fluid samples but this is not as sensitive.
Inclusion bodies called Negri bodies are 100 per cent diagnostic for rabies infection but found only in 20 per cent of cases. The differential diagnosis in a case of suspected human rabies may initially include any cause of encephalitis, particularly infection with viruses such as herpesviruses, enteroviruses, and arboviruses (eg, West Nile virus). The most important viruses to rule out are herpes simplex virus type 1, varicella-zoster virus and (less commonly) enteroviruses, including coxsackieviruses, echoviruses, polioviruses, and human enteroviruses 68 to 71.
In addition, consideration should be given to the local epidemiology of encephalitis caused by arboviruses belonging to several taxonomic groups, including eastern and western equine encephalitis viruses, St Louis encephalitis virus, Powassan virus, the California encephalitis virus serogroup and La Crosse virus.
New causes of viral encephalitis are also possible, as was evidenced by the recent outbreak in Malaysia of some 300 cases of encephalitis (mortality rate, 40 per cent) caused by Nipah virus, a newly recognised paramyxovirus. Similarly, well-known viruses may be introduced into new locations, as is illustrated by the recent outbreak of encephalitis due to West Nile virus in the eastern United States.
Epidemiologic factors (eg, season, geographic location and the patient’s age, travel history and possible exposure to animal bites, rodents and ticks) may help direct the diagnostic workup.
Cheaper rabies diagnosis will be possible for low-income settings according to research reported on the Science and Development Network website in 2008. Accurate rabies diagnosis can be done ten times more cheaply, according to researchers from the Farcha Veterinary and Livestock Research Laboratory and the Support International Health Centre in N'Djamena, Chad.
The scientists evaluated a method using light microscopy, cheaper than the standard tests, and say this could provide better rabies control across Africa.
In non-vaccinated humans, rabies is almost always fatal after neurological symptoms have developed, but prompt post-exposure vaccination may prevent the virus from progressing. Rabies kills around 55,000 people an year, mostly in Asia and Africa.
There are only six known cases of a person surviving symptomatic rabies and only two known cases of survival, in which the patient received no rabies-specific treatment either before or after illness onset.
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