West Nile Virus

Symptoms

The majority of patients (approximately 80%) are asymptomatic or develop only mild symptoms. Approximately 20% experience flu-like symptoms (West Nile fever) such as fever, headache, feeling sick, nausea, vomiting, muscle aches, and skin rashes. Other symptoms such as conjunctivitis, hepatitis, movement disorders or confusion are possible. Less than 1% develop neuroinvasive disease with meningitis, encephalitis, or poliomyelitis. The incubation period ranges from 2-15 days. Patients are contagious 6-7 days before to shortly after disease onset. The duration of the disease varies. In a mild course, it is a few days; in a severe course, it is months. Long-lasting symptoms such as severe fatigue, muscle pain, headache, dizziness and lack of concentration are also possible.

Causes

West Nile virus is an enveloped RNA virus of the flavivirus family (Flaviviridae, genus: Flavivirus), which includes TBE virus and Japanese encephalitis virus. The main reservoir of the virus is birds, mainly passerine birds, which include finches, sparrows, and corvids. Mammals such as humans and horses may occasionally become infected and develop clinical symptoms. However, they represent a dead end for the virus. Certain squirrels, chipmunks, rabbits, other mammals, alligators, and frogs can also be infected. West Nile virus was first isolated in 1937 from the blood of a woman with a fever in Uganda who was participating in a sleeping sickness study.

Transmission

Mosquitoes of the genus , including , the common mosquito, which is common in Europe, are considered the most important vector. Mosquitoes of the genus and are also vectors. Other modes of transmission are possible:

  • Bird droppings
  • Contaminated blood or tissue, for example, from a blood transfusion or organ transplantation
  • In pregnant women via the placenta or in breastfeeding women via breast milk (rare).
  • Infection has been reported after oral ingestion in animals

Differential diagnosis

Meningitis or encephalitis can also be caused by other viral or bacterial agents, among others.

Epidemiology

The virus occurs in numerous regions, including Africa, Israel, the Middle East, Australia, Asia, Europe, the United States, and Canada. In the fall of 1999, the first cases of the disease appeared in New York, presumably introduced from the Middle East. Subsequently, the virus spread throughout the U.S. and neighboring Canada and has led to several thousand infections there since then. In contrast to the USA, the virus has not yet been able to spread extensively in Europe. It has occurred only sporadically in individual countries, including France (Camargue), Italy, Portugal, Spain and some Eastern European countries. Larger outbreaks occurred in Romania in 1996 and in Russia in 1999. However, these remained limited in time and location.

Prevention

In risk areas, mosquito bites should be prevented with rules of conduct (e.g., long-sleeved clothing, mosquito nets, staying outdoors in the evening). Repellents such as DEET are also used for this purpose. Vaccination is not yet available.

Drug treatment

Treatment to date has been symptomatic, for example, with analgesics for fever and pain. Specific antiviral drugs are not yet on the market.