Correct!
5. West Nile
encephalitis
The only manner to differentiate between causes of encephalitis/meningitis is diagnostic and serological laboratory tests to identify the specific pathogen causing the symptoms. The CSF IgM serology for West Nile Virus (WNV) was positive at 5.97 (normal < 0.9). Japanese encephalitis virus and Murray Valley encephalitis would present similarly but are limited to Asia (2). Guillain–Barré could initially present similarly but there is no history of ascending muscle weakness. Furthermore, there is an absence of the characteristic markedly elevated CSF protein level (100–1000 mg/dL), without an accompanying increased cell count (absence of pleocytosis) seen in Guillain–Barré. Cat scratch fever can very rarely present with encephalitis but is unlikely. The patient’s antibiotics were discontinued; he was extubated after on his fourth hospital day, and discharged on his sixth.
WNV is a mosquito-borne zooinotic arbovirus (3). It was first described in the Western hemisphere in 1999 in New York City (NYC). Simultaneous clusters of unexplained meningoencephalitis struck NYC hospitals, and fatal bird infections struck the Queens zoo - both found to be caused by WNV. Since then, WNV has spread westward to the Pacific coast, and into Canada and Latin America. The year 2012 was the worst year on record in the US with 268 deaths – the state of Texas was the most hard-hit.
WNV should be suspected in any patient presenting with an acute febrile disease or meningitis, who has been exposed to mosquitoes or blood transfusion in a state with active WNV epidemiology (3). It presents primarily in the summer as mosquitoes become active. Eighty percent of cases are asymptomatic, and 20% present with fever, headache, myalgias, arthralgias, gastrointestinal upset, and rash. Less than one percent suffers meningitis or meningoencephalitis as in our patient. Acute flaccid paralysis can occur secondary to a poliomyelitis-like infection of the anterior horn cells of the spinal column, or from Guillain–Barré syndrome. WNV can be diagnosed by serum or CSF IgM antibodies that are usually detectable 3-8 days after initial symptoms. Most patients recover, but 10% of patients with neuroinvasive disease die, and neurological sequelae can persist. In those that recover, fatigue can persist for months.
The 2013 WNV season is still early, but as of July the CDC is reporting 31 cases from 14 states – mostly in the Midwest and the Southwest (3). Thirty-five percent of the reported cases were neuroinvasive, with 3 fatalities thus far.
One of my mentor’s favorite sayings is that “history-taking is never completed” – this case again confirms his wisdom.
References