West Nile Virus: Review of the Literature

Abstract

IMPORTANCE Since its introduction in North America in 1999,West Nile virus has produced the 3 largest arboviral neuroinvasive disease outbreaks ever recorded in the United States. OBJECTIVE To review the ecology, virology, epidemiology, clinical characteristics, diagnosis, prevention, and control of West Nile virus, with an emphasis on North America. EVIDENCE REVIEW PubMed electronic database was searched through February 5, 2013. United States national surveillance data were gathered from the Centers for Disease Control and Prevention. FINDINGS West Nile virus is now endemic throughout the contiguous United States, with 16 196 human neuroinvasive disease cases and 1549 deaths reported since 1999. More than 780 000 illnesses have likely occurred. To date, incidence is highest in the Midwest from mid-July to early September. West Nile fever develops in approximately 25% of those infected, varies greatly in clinical severity, and symptoms may be prolonged. Neuroinvasive disease (meningitis, encephalitis, acute flaccid paralysis) develops in less than 1% but carries a fatality rate of approximately 10%. Encephalitis has a highly variable clinical course but often is associated with considerable long-term morbidity. Approximately two-thirds of those with paralysis remain with significant weakness in affected limbs. Diagnosis usually rests on detection of IgM antibody in serum or cerebrospinal fluid. Treatment is supportive; no licensed human vaccine exists. Prevention uses an integrated pest management approach, which focuses on surveillance, elimination of mosquito breeding sites, and larval and adult mosquito management using pesticides to keep mosquito populations low. During outbreaks or impending outbreaks, emphasis shifts to aggressive adult mosquito control to reduce the abundance of infected, biting mosquitoes. Pesticide exposure and adverse human health events following adult mosquito control operations for West Nile virus appear negligible. CONCLUSIONS AND RELEVANCE In North America, West Nile virus has and will remain a formidable clinical and public health problem for years to come.

Climate change impacts on West Nile virus transmission in a global context

“…Serologically, it is a member of the Japanese encephalitis serocomplex. The viruses can be designated into at least five phylogenetic lineages but only lineages 1 and 2 have been associated with significant disease outbreaks in humans [12,13]. The enzootic cycle is driven by continuous virus transmission to susceptible bird species through adult mosquito blood-meal feeding, which results in virus amplification.…”

Effect of Aerial Insecticide Spraying on West Nile Virus Disease—North-Central Texas, 2012

“…However, detection and reporting of WNV neuroinvasive disease cases is believed to be more consistent than for nonneuroinvasive disease because of the considerable morbidity associated with neuroinvasive disease cases. 2 The higher proportion of nonneuroinvasive disease cases reported in the treated areas after aerial spraying might have resulted from increased awareness after media publicity of the outbreak, and more visits to health care providers or increased laboratory testing for persons with febrile illness. Viremic blood donors identified through routine screening of the blood supply can be a useful and possibly unbiased measure of human WNV infections, but the number of viremic blood donors in the four-county area was too low to be useful for this analysis.…”

“…In consideration of the potential variability in the incubation period for WNV disease, we conducted a sensitivity analysis by using minimum and maximum incubation periods of 2 and 14 days. 2 To account for the possible effect of ground-based insecticide applications in the aerially treated and untreated areas, we calculated the square kilometers and proportion of the total area covered by ground-based spraying in each area~3 weeks before and after the cut-off dates, and compared them by fitting a log-linear model to a three-way array formed by the aerial spraying, ground spraying, and timing classifications. For all analyses, a two-sided P 0.05 was considered statistically significant.…”

“…1 Less than 1% of infected persons experience neuroinvasive disease, which typically manifests as encephalitis, meningitis, or poliomyelitis-like acute flaccid paralysis (AFP). 2 The WNV transmission is seasonal. The majority of patients have onset of illness during July-September, and disease incidence usually peaks during August.…”

End-point disease investigation for virus strains of intermediate virulence as illustrated by flavivirus infections

“…Variability in disease outcomes has been reported regularly for WNV infections in humans and certain mouse strains (Graham et al, 2015;Petersen et al, 2013). Particularly relevant in an Australian context, variable end-point disease outcomes have been reported for other Australian WNV strains of intermediate virulence in the Swiss white mouse model (Bingham et al, 2014).…”