Systemic and ophthalmic manifestations of West Nile virus infection

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Abstract

The first cases in the USA of infection with the mosquito vector-borne West Nile virus (WNV) – an enveloped, single-stranded RNA – occurred in 1999 in New York. Since then, it has moved westward and now affects people in nearly every state, with most annual cases appearing in late summer. Suspected infection can be confirmed by ELISA and reverse transcriptase PCR. The incubation period of WNV prior to the onset of symptoms can be as long as 2 weeks. Three clinical categories of infection have been defined: asymptomatic, West Nile fever (WNF) and West Nile meningoencephalitis. The most common symptoms of WNF are flu-like and include fever, headache, myalgia, malaise, diarrhea, vomiting and fatigue. In less than 1% of cases, individuals develop severe, potentially fatal neurologic disease that has been variously classified as West Nile meningitis, West Nile encephalitis and West Nile poliomyelitis (acute flaccid paralysis). The most commonly reported ocular features of WNV infection are multifocal, bilateral chorioretinal lesions characteristically found in either a scattered or linear pattern. Other features include anterior uveitis, retinal vasculitis, optic neuritis and vitritis; less commonly, nystagmus, abducens nerve palsy, optic disc edema and absence of corneal reflex have been reported. Patients were also reported to present with blurred vision, floaters, redness, visual field defects and diplopia. Ocular symptoms of WNV are generally self limited; however, in some notable cases, reduced visual acuity and field loss may persist. Many of the ocular symptoms of WNV infection are associated with numerous viral, bacterial and parasitic diseases, highlighting the importance of differential diagnosis in confirming WNV infection. The fact that ophthalmic manifestations associated with WNV have only been recognized relatively recently makes the long-term prognosis in patients difficult to predict. However, most patients presenting with chorioretinitis show improvement over time, with visual acuity returning to baseline after a few months. There are currently no approved treatments for WNV, although recombinant vaccines are under development.

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