According to a current publication of the European Centre for Prevention and Control of Diseases (ECDC), this year’s total number of cases exceeds the total number of West Nile fever (WNF) cases in Europe of the past five years by far.
WNV belongs to the most widely distributed flaviviruses. West Nile fever (WNF), caused by WNV is a zoonosis endemic on all continents. The virus is distributed in Africa, Israel, West Turkey, the Middle East, India, parts of Southeast Asia and by now also in North America and parts of Central America. In Europe, there have been seasonal outbreaks or isolated transmissions.
WNV is mainly transmitted to birds living in the wild by a number of mosquitoes (mainly species of Culex, but also Aedes and Mansiona). Infected mosquitoes may also pass the virus on to mammals (mostly horses) or humans. WNF outbreaks are closely related with favourable conditions for the vectors. Frequently, an increased number of cases in horses or birds raises awareness and leads to closer monitoring of possible transmissions to humans.
In 2018, 1,670 cases of WNF in humans were registered, e.g. in Italy, Greece, Rumania, Hungary, Croatia, France, Austria, Bulgaria, Slovenia and Czech Republic (ECDC, beginning of October 2018). In 2017, however, only a total 260 cases of WNF were reported in Europe. Of the human WNV cases in 2018, 142 were fatal. There has also been an increase in WNV infections in horses in Europe compared to the previous year.
WNV in Germany
Vectors which may transmit the virus are distributed also in Germany. At the end of September 2018, WNV was detected in 7 birds (three owls in captivity, three birds of prey and one thrush) and one ill horse. The breeding places or locations of the animals were in Bavaria, Saxony, Berlin and Mecklenburg-Vorpommern. These infections, especially of the animals kept in captivity, clearly indicate an autochthonous transmission between birds and at least one case from bird to horse.
Autochthonous human cases had until now been unknown in Germany. According to ProMED (Program for Monitoring Emerging Diseases), however, there is evidence of the first WNF case acquired in Germany. ProMED refers to a statement of the Bundeswehr Institute of Microbiology (Munich, Germany). According to this statement, a male veterinarian had become infected with WNV following contact with an infected bird.
Symptoms of WNF
Infections with WNV in humans are usually asymptomatic. Only around 20% of infected persons develop a feverish, flu-like disease which persists for approximately 3 to 6 days. The infection is accompanied by symptoms such as nausea, chills, headaches, back, joint and muscle pains and other unspecific symptoms such as loss of appetite, coughing and a sore throat.
25 to 50% of symptomatic cases also include exanthema on the chest, back and upper extremities and swelling of the lymph nodes. Severe clinical courses of WNV infections are characterised by myocarditis, pancreatitis and hepatitis, as well as by neurological symptoms. The latter start after a short feverish stage and manifest in the form of encephalitides and meningoencephalitides. WNF usually heals without any complications. In patients with encephalitis, however, sequelae are relatively frequent. The lethality of encephalitis caused by WNV infection amounts to 15 to 40%. Mainly older patients are affected.
EUROIMMUN products for WNV diagnostics
WNV infections are diagnosed by direct virus detection or the detection of specific antibodies. Since IgM antibodies may persist over a longer period of time, the additional determination of low-avidity IgG antibodies is recommended for the differentiation of acute and past infections.