Western Nile Fever
P.K.Ghatak,MD
In 1999 the first case of West Nile fever was identified in New York City. Out of 183 cases were detected, 84 had meningoencephalitis and 40 died. The disease quickly spread to other states, and Louisianan had the worst outcome. In 2002 outbreak 4,156 cases were confirmed in the USA and 2,354 cases of meningoencephalitis and 288 had died. That was the worst outbreak in anywhere in the western world. It was due to virus becoming more neurotrophic. The neurotropism was probably acquired in the Romanian outbreak during 1996.
The West Nile virus was initially isolated in 1937, from the blood of a febrile patient who came from West Nile district of Uganda. During 1951 to 1954, the disease was prevalent in the Mediterranean countries. Several large outbreaks occurred in the Nile Delta of Egypt. 60 % of population of Egypt became seropositive.
The virus:
The West Nile virus belongs to Flaviviridae family of viruses. This virus is closely related to St. Louis encephalitis virus, and Japanese B encephalitis virus There is serological similarity among these group viruses.
Vector: Culex mosquitoes.
Reservoir of West Nile virus: Crows, Ravens, Blue Jays and many other bird species, and dogs and horses.
Present risk of West Nile Fever in the USA:
The people in the Great Plains and western states are at risk of contacting West Nile fever. In 2023, 13 confirmed cases were recorded and 8 of them had neurological complication.
Incubation period : 2 to 14 days, usually 4 to 6 days.
Initial symptoms: Flu like.
Susceptible population : Over 60 years of age and in diabetics and immunocompromised patients.
Clinical types:
Minimal. From asymptomatic to a few days of flu like symptoms followed by full recovery. 70 to 80 % of patients belong to this group.
Encephalitis, meningitis and other neurological features, use to occur 1 in 200 infections: now incidence of encephalitis had gone considerably up.
Viremia: Generally the virus can be grown from blood of the patients within 24hrs. and viremia may persist for 6 to 12 days.
Diagnosis, treatment, surveillance and sequela are in the same line as other arboviruses.
Man to man transmission does not happen and no vaccine is available.
