THE WEST NILE IN THE ROCKY MOUNTAINS


By: Brittan Durham, MD

September 02, 2003

A 48 year old female presents to a local medical facility in Boulder Colorado this summer complaining of severe general weakness, mailaise, nausea, and headache for 3 days. This if her second visit with increased symptoms; a previous evaluation revealed a normal routine blood count and electrolyte panel. Serum antibodies were tested and were found to be positive the West Nile Virus (WVN). The patient recovered from the illness and has no long lasting complications. WNV has become endemic in Colorado; this state has reported the most cases this summer (263) including one of this patient?s neighbors.

Nationwide in the USA, the Western Nile Virus has been reported in more than 4,000 human cases last year, including 277 deaths. Since its first detection in the USA in 1999, the WNV has spread from its origin in New York City across the nation westward to the Rocky Mountains and is now found in 44 states and the District of Columbia. To date, there has been no reported illness in California involving locally acquired WNV. This summer the state of California reported its first case of imported WNV virus in an Alameda County woman who had been infected while visiting Colorado.

The WNV is transmitted to humans and animals through a mosquito bite. The virus is maintained in a bird-mosquito-bird cycle. Although human-to-human transmission does not occur, infections have been documented by way of human blood transfusions and organ transplants. Many infected individuals may not experience any illness, while others will have variable mild to moderate symptoms such as fever, headache, myalgias, anorexia, nausea and rash. Eye pain, severe general weakness and lymphadenopathy have also been frequently reported. The incubation period ranges from 3 to 14 days, with symptoms ranging from 3 to 7 days.

Severe illness from WNV occurs in less than 1% of infections and is associated with neurological disease. The neurological presentations include ataxia, altered mental status, focal neurological abnormalities, optic neuritis, acute flaccid paralysis, seizures and severe general weakness. Most deaths are associated with encephalitis with advanced age being the most significant risk factor for developing severe neurological disease. Myocarditis, pancreatitis, and hepatitis have been reported but are considered to be rare. Treatment is generally supportive: intravenous fluids, respiratory support and prevention of secondary infections. Ribovrin and interferon have been found to be useful in vitro, but no controlled studies have been completed. Although a WNV vaccine has been developed for horses, human vaccine is presently under investigation.

The WNV was first isolated in 1937 in a patient in the West Nile District of Uganda. The virus has spread extensively throughout Africa, Middle East and some parts of Europe. Recent outbreaks over the past 4 years have revealed a rapid geographic expansion of the virus to Russia, Asia, and North America. The California Department of Health Services has established a comprehensive surveillance program that monitors WNV in California. While there have been no documented locally acquired human WNV cases, the first evidence of endemic WNV in California has been discovered recently in mosquitoes collected in Imperial County.

The first incursion of the WNV into North America caused an outbreak of meingoencephalitis leading to 7 deaths in 1999. By 2002, another outbreak resulted in over 4,000 infections in the Mississippi Valley and Ohio region. Now Colorado reports the highest incidence of the virus this summer. The West Nile has spread to the Rocky Mountains and is poised to invade western North America. The WNV is on the list of designated reportable diseases. Timely identification may result in augmentation of the public health response. With the arrival of the WNV to California, it is important to promote mosquito precautions and for clinicians to adopt a high index of clinical suspicion and vigilance.