Baylisascaris procyonis (Stefanski & Zarnowski, 1951) Sprent, 1968

Mackenstedt, Ute, Jenkins, David & Romig, Thomas, 2015, The role of wildlife in the transmission of parasitic zoonoses in peri-urban and urban areas, International Journal for Parasitology: Parasites and Wildlife 4 (1), pp. 71-79 : 74

3. Baylisascaris procyonis in Europe

Raccoons are opportunistic carnivores native to North and Central America. They are highly adaptable to various environments and settle in rural, as well as peri-urban and urban areas. Raccoons have been introduced to Europe in the early 20th century and are now known to occur in at least 20 European countries ( Bartoszewicz, 2011; Beltrán-Beck et al., 2012). Stable populations are presently developing in Spain and France and a few raccoons appear occasionally in Denmark and other Scandinavian countries. Raccoons have been released deliberately for hunting purposes (in Russia and Poland), escaped from fur farms or set free by pet owners. High population densities are recorded in Germany and it is estimated that at least 500,000 raccoons are living there. In 2012, the hunting index increased up to 67,000 individuals ( Michler and Michler, 2012). In some urban areas in Germany, raccoons may reach a population density of up to 100 individuals/km 2 due to their adaptable behaviour, their omnivorous feeding habits, their high reproductive potential and the lack of natural predators ( Beltrán-Beck et al., 2012). The high population density of raccoons in some European urban settlements greatly exceeds the known density of other wild carnivores in these environments ( Michler and Hohmann, 2005).

Raccoons are competent hosts for various pathogens ( Beltrán-Beck et al., 2012), but only Baylisascaris procyonis , the common raccoon roundworm, poses a serious threat to humans in Europe. Apart from raccoons, this nematode can also develop into the mature stage in dogs (but not cats) ( Beltrán-Beck et al., 2012). Larvae, however, may start their body migration in a wide range of hosts (birds, reptiles and mammals including humans). The eggs of B. procyonis remain infectious for months in humid soil or water. Raccoons apparently aquire the infection by the uptake of embryonated eggs from contaminated environments, but especially adult raccoons may also become infected by the consumption of thirdstage larvae in intermediate hosts ( Bauer, 2013). Raccoons defecate at latrines close to their resting and sleeping places, and in case of raccoons adapted to peri-urban and urban areas these can be located in barns, lofts, attics, chimneys and garages ( Bauer, 2013). The surroundings of such latrines may become heavily contaminated with B. procyonis eggs, increasing the risk of human infections. In humans, the larval stages may cause ocular and visceral larva migrans, which may become fatal when larvae invade the central nervous system ( Wise et al., 2005). The prevalences of B. procyonis in European raccoon populations vary considerably, as high as 70% in parts of Germany (Hesse) ( Michler and Hohmann, 2005) and as low as 3% in adjacent countries. Although the prevalence of B. procyonis may be very high in ‘urban’ raccoons, human cases of baylisascariosis are rare both in Europe and elsewhere. Infection is usually restricted to patients who had close contact with raccoons, i.e. pet owners ( Küchle et al., 1993). The results of serological studies indicated, however, that many more individuals showed increased antibody levels against B. procyonis , although clinical symptoms were lacking ( Conraths et al., 1996).