Unwelcome guests: Nematodes of zoonotic and animal health importance in native and invasive carnivores of Hungary

The spread of non-native carnivores such as raccoons (Procyon lotor) and raccoon dogs (Nyctereutes procyonoides) across Europe is becoming an increasing ecological and public health concern. These species, introduced or expanding through human influence, are now widely established and continue to spread throughout the continent. These species can thrive in diverse environments ranging from natural habitats to urban areas, where they can negatively impact native wildlife through predation, competition, and ecosystem disruption. Besides their ecological effects, these invasive carnivores are also gaining attention as potential reservoirs of pathogens of both veterinary and zoonotic importance. Wild carnivores commonly host parasitic nematodes, microscopic worms that can infect internal organs, and several of these parasites pose risks to animal and human health. Some species can cause serious diseases, such as heartworm disease in dogs or eye infections in humans, making their spread a growing concern.

To better understand the role of invasive species in parasite transmission, the authors examined 371 individuals from six wild carnivore species in Hungary, red foxes, badgers, golden jackals, raccoons, raccoon dogs, and beech martens. Using molecular methods and a nationwide collaboration with hunters who voluntarily collected blood and tissue samples, several parasitic nematodes were identified. Badgers showed the highest infection rate (32.0%), followed by red foxes (15.7%), while invasive raccoons also exhibited notable prevalence (13.2%). Among the most frequently detected parasites was Dirofilaria immitis, a mosquito-borne parasite responsible for heartworm disease. Although heartworm is primarily known as a major concern in domestic dogs, wild carnivores can act as important reservoir hosts, contributing to the maintenance and transmission of these parasites. This study documents the first confirmed occurrence of this parasite in Hungarian badgers and provides the first European infection data for invasive raccoons, thereby expanding its known host range in Europe. The study also identified Crenosoma vulpis, the fox lungworm, in raccoons, demonstrating that invasive species can acquire and transmit parasites typically associated with native wildlife. “This highlights that some parasites are not highly host-specific and can infect multiple carnivore species, likely helping their spread. While the fox lungworm primarily affects dogs and is not considered a human health risk, it still represents an important veterinary concern.” said Tamara Szentiványi, the study’s first author.

The researchers also detected Thelazia callipaeda, a zoonotic eyeworm, in red foxes and in an invasive raccoon dog. This is the first record of this parasite in raccoon dogs in Europe. While the parasite is common in raccoon dogs in their native Asian range, it had not previously been identified in this species in Europe, despite being present in native wildlife and domestic animals such as dogs and cats. “Finding Thelazia callipaeda in an invasive raccoon dog in Hungary is significant from both epidemiological and ecological perspectives,” said Tamara Szentiványi. “It suggests that this newly established species could act as a host for native parasites, in its non-native range. As raccoon dogs continue to expand across Central and Eastern Europe, they may contribute to the further transmission of this eyeworm species. This is particularly concerning because T. callipaeda can infect both animals and humans, posing a potential public health risk.”

Importantly, the study points to a broader and more complex picture: invasive host species such as raccoons and raccoon dogs are expanding their range and may play a key role in spillover events, where pathogens move between wildlife, domestic animals, and potentially humans. Furthermore, the spread of invasive mosquitoes in the region may also drive new disease ecology issues, particularly through pathogens such as heartworms. This is of particular importance given the research group’s focus on mosquitoes and mosquito-borne diseases, and leading a national Mosquito Monitor project (mosquitosurveillance.hu). Invasive species, already known for their ecological impacts, may play a larger-than-expected role in disease transmission. Their spread, combined with the expansion of invasive vectors, creates a dual invasion effect: both hosts and vectors are increasing, potentially leading to novel pathogen transmission pathways and likely helping the emergence of certain diseases. This shows the importance of continued monitoring of mosquitoes and wild carnivores, particularly invasive species, to better understand and manage risks to wildlife, domestic animals, and public health.

About the HUN-REN Centre for Ecological Research

The HUN-REN Centre for Ecological Research is a leading Hungarian research institute dedicated to understanding ecological processes and environmental change. Its work focuses on a wide range of disciplines, including biodiversity, ecosystem functioning, conservation biology, and disease ecology. The Centre conducts both fundamental and applied research, with a strong emphasis on addressing global challenges such as climate change, biological invasions, and emerging infectious diseases. It operates major research facilities, including long-term ecological research sites, and collaborates extensively with international partners.