Usutu virus: An emerging flavivirus in Europe

Among various arthropod-borne viruses (arboviruses), the flaviviruses stand out with regard to their number, geographic distribution and impor- tance in both human and veterinary medicine. West Nile virus is flavivirus, present endemic in many European countries as well as in Serbia where it circulates in horses, birds, humans and mosquitoes. Usutu virus (USUV) is flavivirus morphologically, antigenically, genetically and ecologically very similar to WNV, which circulates in neighbouring countries (Hungary, Croatia, Austria). The USUV is maintained in transmissible cycle between birds and mosquitoes mainly from the genus Culex. Mammals (humans, horses, rodents) can also be infected. Humans and other mammals are “dead end” hosts. Virus is isolated from numerous bird species. The USUV infections are asymptomatic in wild African birds, while for European birds, the virus is very virulent causing necrotizing focal encephalitis, degenera- tive myocarditis and fatal encephalitis. It is assumed that the virus was in- troduced into Europe by the migratory birds that have been infected by living or passing through endemic areas in Africa. First human cases were recorded in Italy in 2009. The genome of USUV was detected in cerebrospi- nal fluid of woman suffering from B-cell lymphoma with meningoencepha- litis and in plasma of a female, who was subjected to a liver transplanta- tion and subsequently developed fever, headache, and fulminant hepatitis which progressed to coma. In Austria, USUV infections were confirme in people with a skin rash of unknown aetiology using plaque reduction neutralization test. The circulation of USUV has been proven in humans in many European countries by serological studies (Germany, Italy, and Croa- tia). Serological study performed in 2015 revealed that USUV is present in inhabitants of South Bačka District of Vojvodina, Serbia. Serum samples were tested using commercial ELISA IgG test for USUV and IgG antibodies against USUV were detected in 5% (4/88) of patients. The molecular inves- tigation included 216 pools of mosquitoes collected in the period from June to September, in the South Bačka District. The USUV genome was detected in two mosquito pools (2/216). In human samples tested by RT PCR, USUV genome was not found.