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West Nile Virus

West Nile virus (WNV) is an emerging infectious disease that was first discovered in the African country of Uganda in 1937, and in recent years has spread, causing illness in birds, horses, and humans in Europe and now the United States. It was first discovered in the U.S. in 1999 in New York City. Since that time, WNV has been detected in humans, animals, and mosquitoes in 47 states from coast to coast (1).

Growth of West Nile Virus in the United States
Figure 1. Growth of West Nile Virus in the United States (Credit: Data from Centers for Disease Control and Prevention.http://www.cdc.gov/ncidod/dvbid/westnile/index.htm)

The virus is transmitted through mosquito vectors, which bite and infect birds. The birds are amplifying hosts, developing sufficient viral levels to transmit the infection to other biting mosquitoes which go on to infect other birds (in the Western hemisphere, the American robin and the American crow are the most common carriers) and also humans. The infected mosquito species vary according to geographical area; in the US Culex pipiens (Eastern US), Culex tarsalis (Midwest and West), and Culex quinquefasciatus (Southeast) are the main sources.

West Nile Virus transmission process
Figure 2. West Nile Virus transmission process (from http://www.mayomedicallaboratories.com/articles/communique/2008/07.html)

The genetic material of WNV is a positive-sense, single strand of RNA, of 11,000-12,000 nucleotides long. These genes encode seven non-structural proteins and three structural proteins. The RNA strand is held within a nucleocapsid formed from 12kD protein blocks; the capsid is contained within a host-derived membrane altered by two viral glycoproteins.

Mosquitos carry the highest amounts of virus in the early fall, which is why the rate of the disease increases in late August to early September. The risk of disease decreases as the weather becomes colder and mosquitos die off.

Mosquito (Culex pipiens)
Figure 3. Mosquito (Culex pipiens)

Most people who become infected with West Nile either have no symptoms or experience mild illness such as fever, headache and body aches before fully recovering. Some people develop a mild rash or swollen lymph glands. In some individuals, particularly the elderly, West Nile can cause serious disease that affects brain tissue. In humans with a weak immune system and the elderly, West Nile can cause permanent neurological damage and can be fatal. Healthy adults and children usually have mild reactions.

The most accurate way to diagnose this infection is with a serology test, which checks a blood or CSF sample for antibodies against the virus. More rapid techniques using polymerase chain reaction (PCR) may be used.

There is no vaccine for West Nile Virus, although currently there is a DNA vaccine available for horses, one of the key targets of this disease. DNA vaccines are comprised of DNA plasmids, extracted from the pathogen, and are used for inoculation, instead of the whole virus. They contain the genetic code for the antigens that stimulate the body to produce antibodies. In this way the virus’s natural infection route is replicated without actually triggering the disease (2). DNA virus vaccines are an active area of research for WNV and there are candidates currently in clinical trials (3,4).

 

Reference:

  1. http://www.cdc.gov/ncidod/dvbid/westnile/index.htm
  2. DNA-Based Vaccine Against West Nile Virus Effective Even After Onset Of Disease, http://www.sciencedaily.com/releases/2008/11/081103091033.htm
  3. Schneeweiss, A. et al., (2011) Vaccine, 29; 6352-6357.
  4. Ledgerwood, J.E. et al., (2011) J. Infect. Dis. 203; 1396-1404

 

Selected West Nile Virus Products

 

Catalog #

Product Name

Type

Host

W1018-50K West Nile Virus Mab Mo x
W1018-50L West Nile Virus (WNV) Mab Mo x
W1018-50M West Nile Virus Mab Mo x
W1018-50N West Nile Virus Mab Mo x
W1018-50P West Nile Virus Mab Mo x