Clinical Pathology: Microbiology, Virology

• Infected mosquitoes are the vector for human West Nile virus (WNV) infection. Person-to-person transmission can occur through blood transfusion, organ transplantation, and from mother-to-child via the intrauterine route and breast feeding.

• WNV may cause asymptomatic infection, low grade fever, or neuroinvasive meningitis or encephalitis. The highest incidence of neuroinvasive disease occurs in individuals aged 70 years.

• WNV was first detected in North America in 1999 during an epidemic of meningoencephalitis in New York City and has since spread across the continental United States. Case numbers peak in the summer and early autumn. Birds are the hosts that amplify WNV.

• There is currently no WNV vaccine for humans or specific antiviral therapy for WNV. Treatment is purely supportive. Diagnosis of acute WNV infection is based on detecting IgM in serum or CSF. Commercial polymerase chain reaction (PCR) testing for WNV is also available.

• Prevention measures include the use of mosquito repellents, wearing protective clothing when outdoors, and eliminating standing water where mosquitoes can breed. Vector mosquito control by targeted spraying in areas with new or persistent levels of WNV activity is another potential public health measure.

Campbell GL, Marfin AA, Lanciotti RS, Gubler DJ: West Nile virus. Lancet Infect Dis 2002;2:519-529.

2012 DOHMH Advisory #18. First human case of West Nile virus in NYC 2012. July 30, 2012.

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