West-Nile Fever Risk Profile For Estonia

Abstract

West Nile fever (WNF) is a viral zoonosis distributed by mosquitoes, which can affect people, equines and birds. In most cases, the disease have mild symptoms, but occasionally the virus can cause severe neurological fatal illness.WNF is caused by an arbovirus (genus Flavivirus, family Flaviviridae). WNF virus (WNV) is able to multiply in birds, reptiles, amphibians, mammals, mosquitoes and ticks.In Europa in 2013 WNF was registered endemically in animals in Austria, Spain and Italy, and sporadically in Bosnia-Herzegovina, Croatia and Greece. The virus does not infect all species of mosquitoes.Particularly important WNV vectors are Culex pipiens,Cx.quinquefasciatus, Cx.restuans, Cx.salinarius and Cx.tarsalis. In virus transmission also other species may play a role, such as Cx. nigripalpus, Aedes albopictus, A. vexans, mosquitoes of Ochlerotatus family etc. In endemic regions, the virus circulates constantly between birds and mosquitoes. In Estonia, from among important vectors of WNV only Cx. pipiens, A. vexans and 16 species of mosquitoes of Ochlerotatus family are present. Some authors consider the Cx. pipiens as a main vector for WNV in Europe who feeds mostly on birds and spending the winter as imagos. The main potential reservoir hosts for WNV in Estonia are various species of orders Passeriformes, Accipitriformes, Falconiformes, Charadriiformes and Strigiformes. It can be concluded, that the potential reservoir hosts and vectors for WNFV are present in Estonia allowing the spread of the virus in case of effective introduction. It is not possible to avoid introduction of the virus by migratory birds (apparently the main factor for distribution of the virus to longer distances). Import of infected horses pose no risk of introduction as horses are considered to be dead end hosts. Introduction of infectious poultry and domestic birds can be avoided by implication of preventive quarantine measures.