West Nile virus is found in tropical as well as temperate areas, is from the Flaviviridae family, and was discovered in 1937. The virus primarily infects birds. If the virus is transmitted to a human, the so-called West Nile fever develops, a disease that causes no symptoms in 80 percent of cases. However, in less than 1 percent of all cases, West Nile fever is fatal.
What is West Nile fever?
The genome of West Nile virus is (+)ssRNA linear and belongs to the Baltimore 4 group. The symmetry is icosahedral. The virus is contained in an envelope. It belongs to the Flaviviridae family or Flavivirus group. Birds are usually infected, although humans, horses, and other mammals can also be infected by the virus.
Occurrence, distribution, and characteristics
There are different indications that already Alexander the Great was infected with the West Nile virus and subsequently died of West Nile fever. Early official records indicate that West Nile virus was discovered as early as 1937. In 1957, the virus appeared in Israel; in 1960, in Egypt as well as France. In recent years, there has been an increasing number of cases in which West Nile virus was detected and subsequently West Nile fever was diagnosed. These cases have occurred in Algeria, Romania, the Czech Republic, Russia, North America, the Democratic Republic of Congo, and Israel. In 2004, there were several cases in Hungary, and in 2008 in Austria. In 2010, 37 deaths occurred in Greece; in 2011, there were more infections, but in other parts of Greece. After West Nile virus was discovered in North America in 1999, it also received media attention. In the U.S., mainly the areas around New York City were affected. Today, it is clear that the virus was flown in from Israel; a plane flying from Tel Aviv to New York carried an infected mosquito. The first indication that it might be West Nile virus was the phenomenon of dead birds in Central Park. A few days later, mostly elderly people fell ill; Deborah Asnis, a tropical medicine physician from the Bronx, notified the researching military doctors that it could sometimes be West Nile virus. The virus spread throughout the North American continent; in 2004, it reached the West Coast, and in 2012, after experts had already assumed that the virus had disappeared, another epidemic followed, with more than 5,000 people infected.
Diseases and ailments
West Nile virus infects birds and mammals, including humans. In this case, the virus is transmitted via mosquitoes. The mosquitoes are those of the genera Aedes, Culex, and Ochlerotatus. The Asian tiger mosquito, which is already native to Europe, can also transmit West Nile virus. Transmissions based on smear or droplet infections are possible but extremely rare. After infection, a distinction is made between primary and secondary viremia. In primary viremia, infection occurs through the skin. Subsequently, a local reaction is seen. There is a presumed accumulation in the so-called dendritic Langerhans cells. The virus spreads within three to seven days and migrates via the lymphocytes directly into the lymph nodes. In secondary viremia, the body forms the first antibodies after ten to 14 days. This involves the increased use of cytoplasm. If the virus overcomes the blood–brain barrier, glial cells as well as neurons can be affected. In 20 percent of all cases, patients complain of flu-like symptoms. The main symptoms are headache, aching limbs and fever. Meningitis and encephalitis are possible and can sometimes be fatal. 80 percent of all persons infected with West Nile virus do not notice the infection. However, for less than 1 percent, the infection actually becomes a life-threatening illness. Patients complain of muscle weakness, disorientation, drowsiness, cramps, a stiff neck and high fever. Sometimes the onset of coma and, subsequently, death is possible. There are no specific treatments; mainly only the symptoms can be relieved. Since there is no vaccine against West Nile virus, the only option is protection against mosquitoes. Every year, around 200 cases are documented in Europe.Predominantly, these are infections contracted by vacationers in tropical regions.
