West Nile fever (WNV) (ICD-10 A92.3: West Nile fever) is an infectious disease that belongs to the group of zoonoses (infectious diseases transmissible from animals to humans; epizootics).
The disease belongs to the viral hemorrhagic fever group.
West Nile fever is caused by West Nile virus (WNV), genus Flavivirus, an RNA virus belonging to the Flavivirus group (Flaviviridae). The virus is one of the most widespread flaviviruses.West Nile virus is divided into subtypes 1 and 2.
Pathogen reservoirs are wild bird species.
Occurrence: Infection is endemic worldwide (clustered occurrence of the disease in a limited area). Affected regions are found in India, Israel, the Middle East, western Turkey, Greece (central Greece), parts of Southeast Asia, and North and Central America. Additional endemic areas exist in the tropics. Originally, the virus originated in Africa (West Nile province of Uganda). Through migratory birds, the virus has also reached areas north of the Mediterranean and southern Europe. Seasonal outbreaks are observed there. In 2018, nearly 800 cases of West Nile fever have been registered in Europe. Isolated imported cases (by travelers) have also been detected in Germany. Prolonged summer weather favors the spread of the virus. According to estimates by the Robert Koch Institute, the disease is expected to spread further in Germany. In August 2020, at least 4 people in Germany have been infected with West Nile virus (autochthonous infections).
Transmission of the pathogen (route of infection) occurs via mosquitoes between wild birds. The infected mosquitoes (mainly of the genus Culex, but also Aedes and Mansonia species) can transmit the virus to mammals (especially horses) and humans, who, however, excrete the virus as a virus source (false hosts) due to low-level viremia (presence of virus in the blood).Transmission routes from human-to-human are organ transplants, blood transfusions, and pregnancy and breast milk.
Human-to-human transmission: Yes
Incubation period (time from infection to onset of disease) is usually 2-14 days.
Duration of illness is usually up to 7 days.
Prevalence figures are not available, as the disease is often asymptomatic.
Course and prognosis: West Nile fever occurs repeatedly like an epidemic. In the majority of cases (80%), the disease goes undetected. In other cases, the onset is abrupt with fever and chills. In the further course, the patients suffer from flu-like symptoms. After the first episode of fever, the condition often improves before fever reappears (biphasic course). Towards the end of the fever, an exanthema (skin rash) appears in about 50%, which remains for about a week. The disease usually heals without complications. About every 150th person develops a severe course of the disease. Those affected are usually elderly (> 50 years), immunocompromised or have a previous disease (e.g. diabetes mellitus).After encephalitis (brain inflammation), a residual condition (lasting impairment) can occur in up to 50% of cases.If encephalitis occurs as a complication, the lethality (mortality related to the total number of people affected by the disease) is 15 to 40% (in older people > 70 years.).
Vaccination: A vaccination against West Nile fever is not yet available.
In Germany, the disease is notifiable according to the Infection Protection Act (IfSG). The notification has to be made in case of direct or indirect pathogen detection.
