The raccoon roundworm, Baylisascaris procyonis, which can cause serious diseases in humans including fatal brain damage, has become established in nine European countries and continues to spread, according to a new study by the ZOWIAC collaborative project at Goethe University Frankfurt. The research, published in Parasitology Research, presents the first comprehensive analysis of the parasite’s presence across Europe.
The roundworm originally arrived in Europe with raccoons imported from North America at the beginning of the 20th century. Since then, both raccoons and their parasites have spread widely across Central Europe, with Germany now considered the main distribution area for both species.
Humans are at risk of infection by accidentally ingesting eggs found in soil, water, or on objects contaminated with raccoon feces. Young children are especially vulnerable due to frequent hand-to-mouth contact.
Anne Steinhoff from Goethe University Frankfurt and first author of the study said: "If the larvae enter the central nervous system, the disease can have severe consequences. Due to frequent hand-to-mouth contact, young children are primarily affected." Most documented cases occur in North America where permanent neurological damage or death has been reported.
Klimpel added: "Furthermore, it is assumed that many cases remain undetected or are misdiagnosed due to non-specific symptoms. In Europe, diagnosis in humans is further complicated by the lack of specific diagnostic testing options." At present, definitive diagnosis is only possible at specialized centers such as those operated by the Centers for Disease Control and Prevention (CDC) in North America.
The research team examined 146 raccoons from Germany through necropsy and combined these findings with data from other European studies. They found that 66.4 percent of raccoons tested were infected with Baylisascaris procyonis—77.4 percent in Hesse, 51.1 percent in Thuringia (with prevalence data for this region reported for the first time), and 52.9 percent in North Rhine-Westphalia.
Klimpel explained: "The results show both an expansion of the roundworm's distribution area and stable infection occurrence at high levels in German raccoon populations." The analysis also showed that wild raccoons carrying this parasite are now present across nine European countries—mainly Central Europe—with some areas showing extremely high infection rates. In three other countries infections were detected among captive animals.
"The studies show a steady expansion of the distribution area in Europe. The distribution of the roundworm is linked to the steady spread of its definitive host, the raccoon, which now occurs throughout Europe," Klimpel continued. "The actual distribution of the roundworm is likely significantly underestimated due to insufficient or absent data collection."
There have been three documented cases of baylisascariasis—the human infection caused by this parasite—in Europe so far; all resulted in permanent visual impairment.
Klimpel concluded: "The results of this study make it clear that further research on the raccoon roundworm in Europe is urgently needed – particularly in light of growing raccoon populations and their increasing adaptation to urban habitats."
