Which important epizootic diseases of farm animals are currently transmitted by wildlife animals in Europe?
In Europe classical swine fever, avian influenza, and rabies are the most important epizootic diseases, which are transmitted by wildlife.
Which important epizootic diseases of farm animals could potentially be transmitted by wildlife animals in Europe?
At present African swine fever (ASF) is now endemic in several sub-Saharan African counties, Sardinia, Georgia and neighbouring countries. During the last 50 years it has caused epidemics in several European and overseas counties. It might cause epidemics or endemics in Western Europe when introduced into the wild boar population. Foot-and-mouth disease (FMD) has been eradicated in Europe (outbreaks in United Kingdom 1967, 2001, 2007). In case of an introduction cloven-hoofed wildlife would be at risk, e.g., wild boar; deer, roe deer.
The most relevant arthropod transmitted diseases are the arbovirus infections Bluetongue and West nile fever as well as Equine infectious anemia. The latter is only mechanically transmitted by insects, while genuine arboviruses replicate in arthropodes. Other arbovirus infections being endemic in southern countries, e.g. Rift valley fever, Chikungunya, West Nile fever are permanent threats for Europe.
In general wild rodents might play a role in disease transmission either by spreading infectious agents mechanically or by accidentally getting infected. Animal experiments have shown that rodents could play a role in the transmission of pseudorabies and foot-and-mouth disease.
The eradication and control of epizootic diseases in wildlife (as far as possible) is important in order to protect farm animals from infected wildlife. In order to eradicate rabies and classical swine fever hunting and vaccination campaigns have been used very successfully. The eradication of epizootic diseases in wild birds is much more difficult. Therefore, when outbreaks of diseases like avian influenza or Newcastle disease occur, the housing of poultry is an important protective measure.
Migratory birds can transport diseases over long distances. They might introduce epizootic diseases, e.g avian influenza (low or high pathogen strains) or Newcastle disease, at any time.
Most Member States of the European Union have successfully eradicated Classical swine fever from the domestic pigs and wild boar. However, CSF was recently or still is currently present in parts of the wild boar population in several regions of EU Member States. Wild boar and domestic pigs can get infected by direct contact with infected animals or indirectly by contaminated food garbage. But also other routes of transmission are possible (see questions and answers about CSF). In many European countries the number of wild boar has increased to a level at which CSF once introduced may become endemic. In areas where CSF is endemic there is a constant threat of transmission from infected wild boar to domestic livestock and vice versa.
CSF can only be eradicated from a wild boar population when the transmission rate R0<1, i.e. an infected animal infects less than 1 other susceptible animal. Therefore a low number of susceptible animals is crucial for the success of control measures. Older animals that have survived CSF infection are immune, whereas young animals that have no longer maternal antibodies against CSFV are susceptible. In dense wild boar populations a large number of susceptible young animals maintains the infection, i.e. this age class acts as a virus reservoir. The reduction of susceptible animals can be achieved in two ways: Selective hunting of young wild boar: In case hunters can be motivated to selectively shoot young wild boar, the number of susceptible animals will decrease. However, for ethical and economical reasons there is often resistance by hunters to shoot young wild boar. In addition effective hunting of wild boar is difficult and tedious. Oral vaccination: Oral vaccination has been shown to be an effective tool to increase the number of immune animals thereby decreasing the rate of susceptible animals. However vaccination of young animals might be problematic because they are not attracted by (large) baits. Usually CSF in dense wild boar populations can be eradicated using a combination of selective hunting and oral vaccination.