How an alien virus can change animal behavior
The African swine fever virus (ASF) is a viral disease of pigs and wild boars that causes high mortality in infected animals. Typical signs of ASF are fever, abortions, hemorrhages and sudden death. The virus, harmless to humans, causes significant socio-economic hardship in many countries. Areas affected by ASF suffer significant economic losses due to the death of animals, restrictions on the movement of pigs, wild boars and their products, and the cost of control measures. Eradication of the disease can take several years. There are no vaccines or effective treatments.
ASF is endemic in sub-Saharan Africa. In Europe, between 1995 and 2007, ASF was confined to Sardinia. In 2014, the first outbreaks were reported in the European Union, among wild boars in the Baltic States and Poland. Since then, the disease has spread to other EU countries and neighboring third countries. In recent years outbreaks have also occurred in Asia, Oceania and some American countries.
The wild boar (Sus scrofa) has been extremely affected by the ASF, which caused several outbreaks leading to a drastic decline of populations in Europe.
On the other side, the wolf: a carnivorous opportunistic species with a wide choice of prey, which populations can significantly affect the dynamics and distribution of ungulates, including the wild boar.
A recent study carried out in Estonia showed a shift in the wolves’ winter diet to a higher proportion of roe deer and other less typical food sources after the emergence of ASF.
The shortage of regular food (e.g. wild boar) can be detrimental to wolf population as it may consume more mammalian predators, such as the raccoon dog, invasive alien species of Union concern, potentially infected by parasites such as Baylisascaris procyonis. As a result, wolves get more frequently infected and unable to hunt for a regular prey, and come closer to human settlements. Wolves may be brought close to human settlements due to prey availability. For instance, roe deer can concentrate near settlements as a response to a very high predation pressure by wolves and also by lynx, for which roe deer has been a staple food in Estonia. The number of wolves seen around settlements has been steadily increasing in a study area and elsewhere in the country.
This behavior has also been shown in other areas of Europe, such as Italy, with the decline of wild boar populations. The town of Parma, is visited by wolves preying on Myocastor coypu, species of Union concern, infesting canal and rivers.
The presence of wolves in urban areas is recorded by several newspapers headlines: “Milan, wolf ends up in the Naviglio: saved by firefighters” or “Wolves are getting closer to the city center…near thehighway…”, creating unjustified apprehension among the population.
These examples show how the effect of an alien species, such as the ASF, can have an impact at multiple levels of the food chain.