What is West Nile virus?

Updated: Apr 02, 2018
  • Author: Jess D Salinas, Jr, MD; Chief Editor: Elizabeth A Moberg-Wolff, MD  more...
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The West Nile virus is one of the many members of the genus Flavivirus that are known to cause human disease. The life cycle of the West Nile virus involves the microbe's transmission from nonhuman animals to humans by way of Aedes, Culex, or Anopheles mosquitoes. The West Nile virus can infect horses, birds, dogs, and other mammals. [1, 2, 3] However, wild birds are apparently the optimal hosts for harboring and replicating the virus.

The West Nile virus has been reported in Africa, Asia, Europe, the Middle East, and North America. In 1999, the first cases of West Nile virus disease were reported in New York City, and the infection has been spreading throughout the North American continent ever since. [4]

The West Nile virus causes serious manifestations in approximately 1% of persons who are infected, with increased morbidity and mortality in individuals older than 50 years. In hospitalized patients in New York City, neurologic sequelae of the West Nile virus included severe muscle weakness, with approximately 10% of patients developing a complete flaccid paralysis. [5, 6, 7] One in 150 West Nile virus infections results in encephalitis or meningitis, and the mortality rate for persons with severe illness is 3-15%. Individuals older than 75 years are at particular risk. [2]

As the elderly population increases and the distribution of the West Nile virus spreads nationwide, a growing number of infected individuals may require comprehensive inpatient rehabilitation to overcome the virus's disabling effects. [8]

A study by Hadler et al suggested that many US states may no longer have adequate surveillance systems for detecting and responding to outbreaks of West Nile virus. The investigators stated that although by 2004, with the aid of federal funding, well-developed West Nile virus surveillance systems existed in almost every state, by 2012, following a 61% decrease in federal funding, many health departments had reduced such surveillance and lacked a systematic, disease-based surveillance system for other arboviruses. [9]

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