West Nile Virus: The First Pandemic of the Twenty-First Century

Prior to the 1999 New York City outbreak few had ever heard of West Nile virus. That changed rapidly once the illness caused by the virus resulted in deaths, hospitalizations, and early fears of the unknown etiology of the disease. In some ways it was like Legionnaire's Disease all over again. This review, although not extensive, will cover many of the medical, biological, epidemiological, diagnostic, and public health considerations regarding this new entry onto the list of disease agents seen in the United States. It is important that each of us is knowledgeable regarding new scientific information. It is all too easy for misinformation to be disseminated to the public by news media and word of mouth. Scientific societies must be ready to protect the public from this misinformation and to add perspective to the issue. OHIO J SCI 102 (5):9&-101, 2002 INTRODUCTION The purpose of this review is to provide the membership of the Ohio Academy of Science who may be unfamiliar with the biological, clinical, and preventive aspects of West Nile virus (WNV) and its infectious process in humans, information that will be both interesting and useful. Isolation of WNV first occurred in 1937 from an infected person living in the West Nile area of Uganda (Smithburn and others 1940). Since that time, outbreaks have occurred in endemic areas that include Africa, the Middle East, southern Europe, southwest and central Asia, and Oceania (Mandell and others 2000). The virus is most commonly transmitted by mosquitoes of the genus Culex (Brooks and others 2001). After being bitten by an infected female mosquito, the virus spreads throughout the body of the human host. If symptoms appear they are typically an acute, usually mild febrile disease often accompanied by malaise, anorexia, nausea, vomiting, and headache (Table 1). Transient meningeal involvement may occur at this time. Fatal cases associated with severe neurological manifestations have been seen in the elderly or debilitated person (Table 2). Until 1999, this was our understanding of West Nile virus and the associated infection. At that time the virus caused an outbreak in New York City (Nash and others 2001). It should not be surprising that since 1999, our knowledge of West Nile virus has increased as the virus has spread across the country. WHAT IS WEST NILE VIRUS? West Nile fever is caused by an arbovirus of the family Flaviviridae and the genus Flavivirus (Brooks and others 2001). The virus is commonly called West Nile virus. The virus is spherical, with a diameter of about 50.0 nm. The nucleic acid is single-stranded RNA with a positive sense (that is, the viral RNA acts like a messenger RNA in host cells). The virus has a viral hemagglutinin TABLE 1 Signs and symptoms during the West Nile virus epidemic, New York City, 1999*. Sign/Symptom Percent Cases Observed