Trend analysis of Trichinella in a red fox population from a low endemic area using a validated artificial digestion and sequential sieving technique

From wildlife to humans: The global distribution of Trichinella species and genotypes in wildlife and wildlife-associated human trichinellosis

Zoonotic nematodes of the genus Trichinella are foodborne parasites that have a global distribution in wild carnivores and omnivores, with spillover and spillback into domestic livestock and people, with concomitant trade and health consequences. Historically, most human cases were linked to domestic pigs infected with Trichinella spiralis, but under current high biosecurity swine production in many countries, wildlife have become a more important source of human trichinellosis. The aim of this review is to update the global distribution of Trichinella species and genotypes reported in wildlife, as well as reported human outbreaks from the consumption of wildlife. Using several online databases and by "snowballing" references, hundreds of reports of Trichinella spp. in wildlife published between January 1991 and December 2023 provide an important update to the host and geographic range for each of the recognized 13 species/genotypes, grouped by continent. Surveillance effort was highest in Europe and North America, while Africa, Asia, Central and South America have had limited surveillance, in some instances with human cases serving as sentinels of transmission in a region. Dozens of human outbreaks are described, with wild boars (Sus scrofa) being the most frequently implicated wildlife species in human outbreaks globally. Bears are an important source of infection in North America, for wildlife tourism, and importation of bear meat has also been implicated in multicountry outbreaks. The largest study limitation was the dearth of molecular identification of larvae in both wildlife surveillance studies and human outbreaks, particulary in under-studied regions. We highlight the need for enhanced molecular epidemiological approaches to outbreaks of this important foodborne parasite, and emphasize the need for a One Health approach to manage Trichinella spp. which transmit among terrestrial and marine wildlife (including migratory birds), pigs, horses, and people, often across large geographic scales and borders.

Detection of Spirocerca lupi and an unknown Trichinella-like nematode in raccoon (Procyon lotor)

The raccoon Procyon lotor (Carnivora: Procyonidae) is an invasive species of growing importance for the introduction of alien pathogens or as additional hosts for autochthonous pathogens in Europe, including zoonotic parasites. As the population is steadily increasing and outcompeting the red fox (Vulpes vulpes) in Germany, the consumption of raccoon meat raises concerns about pathogens they may transmit. Therefore the presence of Trichinella larvae was here investigated in muscle samples (n = 904) of raccoons from northern Germany. No Trichinella larvae were found, thus confirming the general low occurrence of this parasite in Germany. However, Spirocerca lupi (n = 12) and an unidentified Trichinella-like nematode (n = 1) were accidently detected in the examined samples. The first is not a zoonotic parasite but has a high veterinary relevance as it can cause severe diseases in dogs. It is the first documented autochthonous infection of this nematode in Germany. The larvae of an unidentified Trichinella-like nematode were found in high abundance in all examined muscles of one raccoon, though they could not be identified to species level. Histological investigation revealed intramuscular cystic structures. This is the largest study investigating muscular parasites of raccoons in Europe so far, which suggests that this invasive animal species is infected by S. lupi and by a yet unknown Trichinella -like parasite.

Identification of Trichinella taxa by ITS-1 amplicon next-generation sequencing with an improved resolution for detecting underrepresented genotypes in mixed natural infections

BACKGROUND

Amplicon-based next-generation sequencing (NGS) has rapidly gained popularity as a powerful method for delineating taxa in complex communities, including helminths. Here, we applied this approach to identify species and genotypes of zoonotic nematodes of the Trichinella genus. A known limitation of the current multiplex PCR (mPCR) assay recommended by the International Commission on Trichinellosis is that it does not differentiate Trichinella nativa from T. chanchalensis.

METHODS

The new assay entails deep sequencing of an amplified variable fragment of the ribosomal cistron's (rDNA) internal transcribed spacer 1 using the Illumina platform. The assay was evaluated using first-stage larvae (L1) of select laboratory strains of various Trichinella taxa mixed in known proportions and then validated using archived L1 from 109 wildlife hosts. The species/genotypes of these L1 isolates from wildlife were previously determined using mPCR.

RESULTS

NGS data analysis for Trichinella laboratory strains selected as representative of North American fauna revealed a sequence representation bias. Trichinella pseudospiralis, a non-encapsulated species, was the most underrepresented when mixed with T. spiralis, T. murrelli, T. nativa and Trichinella T6 in equal quantities. However, five L1 of T. pseudospiralis were readily revealed by NGS in a mix with 2000 L1 of T. nativa (1:400 ratio). From naturally infected wildlife, all Trichinella taxa revealed by mPCR were also identified by NGS in 103 of 107 (96.3%) samples amplified on both assays. NGS identified additional taxa in 11 (10.3%) samples, whereas additional taxa were revealed by mPCR in only four (3.7%) samples. Most isolates comprised single or mixed infections of T. nativa and Trichinella T6. On NGS, T. chanchalensis (T13) was detected in combination with Trichinella T6 in a wolverine (Gulo gulo) and in combination with T. nativa and Trichinella T6 in a marten (Martes americana) from the Northwest Territories, Canada.

CONCLUSIONS

This new NGS assay demonstrates strong potential as a single assay for identifying all recognised Trichinella taxa as well as improved sensitivity for detecting under-represented and novel genotypes in mixed infections. In addition, we report a new host record for T. chanchalensis in American marten.

Wild Mesocarnivores as Reservoirs of Endoparasites Causing Important Zoonoses and Emerging Bridging Infections across Europe

Mesocarnivores are small- or mid-sized carnivore species that display a variety of ecologies and behaviours. In Europe, wild mesocarnivores are represented by the red fox (Vulpes vulpes), the golden jackal (Canis aureus), the European wildcat (Felis silvestris), the Mustelidae of the genera Meles, Martes, Mustela, Lutra, the invasive species of raccoon dog (Nyctereutes procyonoides), raccoons (Procyon lotor), and American mink (Neogale vison). These abundant animals thrive in various habitats and often develop their activity close to human settlements. Thus, they may play an important role in the introduction, maintenance, and transmission of major parasitic zoonoses and promote bridging infections with domestic animals. Against this background, this article reports and discusses some of the most important endoparasites of wild mesocarnivores living in Europe, on the basis of their actual role as reservoirs, spreaders, or sentinels. The data derived from epizootiological studies in different European countries, and the proven or speculated implications of the detected endoparasites in human and domestic animals' health, are discussed. Through older and recent literature review, the state-of-the-art knowledge on the occurrence and prevalence of the parasites under consideration is presented, showing further, warranted investigations and the need for surveillance and vigilance.

Zoonotic Pathogens in Eurasian Beavers (Castor fiber) in the Netherlands

Successful repopulation programs of Eurasian beavers (Castor fiber) have resulted in an increase in beaver populations throughout Europe. This may be of public health relevance because beavers can host multiple zoonotic pathogens. From March 2018 to March 2020, opportunistic testing of dead beavers was performed for hepatitis E virus, orthohantavirus, Anaplasma phagocytophilum, Bartonella spp., extended-spectrum-betalactamase or AmpC (ESBL/AmpC-)-producing Enterobacteriaceae, Francisella tularensis, Leptospira spp., Neoehrlichia mikurensis, Babesia spp., Echinococcus multilocularis, Toxoplasma gondii, and Trichinella spp. From the 24 beavers collected, three zoonotic pathogens were detected. One beaver was positive for T. gondii, one was positive for ESBL/AmpC-producing Enterobacteriaceae, and one was positive for N. mikurensis. The latter finding indicates that beavers can be bitten by Ixodes ricinus and be exposed to tick-borne pathogens. The detected ESBL/AmpC-gene was blaCMY-2 in an Escherichia coli ST6599. The findings suggest that the role of beavers in the spread of zoonotic diseases in the Netherlands is currently limited.

HERBIVORES AS ACCIDENTAL HOSTS FOR TRICHINELLA: SEARCH FOR EVIDENCE OF TRICHINELLA INFECTION AND EXPOSURE IN FREE-RANGING MOOSE (ALCES ALCES) IN A HIGHLY ENDEMIC SETTING

Herbivores can be accidental hosts for the zoonotic nematode parasites Trichinella spp., which are endemic at high prevalence in wildlife in northeastern Europe. Using direct and indirect detection methods for Trichinella spp., we investigated samples from 463 wild moose (Alces alces) harvested by hunters in Estonia in 2015. A total of 460 moose were tested directly by artificial digestion of diaphragm muscle, 463 moose were tested indirectly by enzyme-linked immunosorbent assay (ELISA), and 34 moose also by western blot. Positive-control reference sera were from other host species. Nematode larvae were found in six muscle samples; five of which were pooled samples. None of the larvae were identified as Trichinella spp., based on their morphology and molecular analyses. Twelve moose (2.6%) were positive by ELISA, but none were positive by the western blot test. Trichinella spp. infection was not detected, but ELISA results may suggest Trichinella spp. exposure in a small proportion of moose in Estonia.

Predators in northern Germany are reservoirs for parasites of One Health concern

Urbanisation and invasion of wildlife into urban areas as well as human leisure activities create diverse wildlife-domestic animal-human interfaces, increasing the risk of (zoonotic) parasite spillover from sylvatic to domestic and synanthropic cycles. This study investigated the endo- and ectoparasite fauna, emphasising on parasites of One Health Concern, of the most common predators in northern Germany between November 2013 and January 2016. Eighty red foxes (Vulpes vulpes), 18 stone martens (Martes foina) and nine raccoon dogs (Nyctereutes procyonoides) were available for the study. Overall, 79 (73.8%) of the examined predators (n=107) harboured at least one endoparasite. The most frequently detected endoparasites in red foxes were Toxocara canis (43.8% positive individuals), Capillaria spp. (36.3%), Alaria alata (25.0%), Echinococcus multilocularis (26.3%) and Uncinaria stenocephala (25.0%). Furthermore, Toxascaris leonina, Trichuris vulpis, Taenia ssp., Mesocestoides spp. and coccidian oocysts were observed. The endoparasite species richness in raccoon dogs was comparable to red foxes, while in stone martens, only Capillaria spp. were found. Muscle digestion for detection of Trichinella spp. and antigen testing for Giardia spp. did not show positive results. Ectoparasite analyses revealed infestations with ticks species of the genus Ixodes as well as Dermacentor reticulatus. Scabies mites were not present in digested skin samples, while Demodex spp. mites were observed by faecal flotation in one red fox. Furthermore, fleas (Archaeopsylla erinacei and Chaetopsylla globiceps) were observed in the fur of red foxes, while lice were not present in any predator species. However, infestation frequency with ectoparasites was with 19.2% generally low in available predator skins (n=99). Overall, the present study showed that predators in northern Germany serve as reservoirs for parasites of One Health concern, with four of the five most frequent endoparasites being zoonotic, highlighting the need of parasite surveillance in wildlife predators in order to implement measures avoiding spillovers to domestic animals and humans.

Trichinella pseudospiralis in a wolverine (Gulo gulo) from the Canadian North

Species of Trichinella are a globally distributed assemblage of nematodes, often with distinct host ranges, which include people, domestic, and wild animals. Trichinella spp. are important in northern Canada, where dietary habits of people and methods of meat preparation (drying, smoking, fermenting as well as raw) increase the risk posed by these foodborne zoonotic parasites. Outbreaks in the arctic and subarctic regions of Canada and the United States are generally attributed to T. nativa (T2) or the T6 genotype, when genetic characterization is performed. We report the discovery of Trichinella pseudospiralis (T4), a non-encapsulated species, in a wolverine (Gulo gulo) from the Northwest Territories of Canada. This parasite has been previously reported elsewhere from both mammals and carnivorous birds, but our findings represent new host and geographic records for T. pseudospiralis. Multiplex PCR and sequencing of fragments of Cytochrome Oxidase Subunit I (COI) and D3 rDNA confirmed the identification. Phylogenetically, Canadian isolates linked with each other and others derived from Palearctic or Neotropical regions, but not elsewhere in the Nearctic (continental USA). We suggest that migratory birds might have played a role in the dispersal of this pathogen 1000's of km to northwestern Canada. Wolverines are not typically consumed by humans, and thus should not pose a direct food safety risk for trichinellosis. However, the current finding suggests that they may serve as an indicator of a broader distribution for T. pseudospiralis. Along with infection risk already recognized for T. nativa and Trichinella T6, our observations emphasize the need for further studies using molecular diagnostics and alternative methods to clarify if this is a solitary case, or if T. pseudospiralis and other freeze susceptible species of Trichinella (such as T. spiralis) circulate more broadly in wildlife in Canada, and elsewhere.

Zoonotic nematodes of wild carnivores

For a long time, wildlife carnivores have been disregarded for their potential in transmitting zoonotic nematodes. However, human activities and politics (e.g., fragmentation of the environment, land use, recycling in urban settings) have consistently favoured the encroachment of urban areas upon wild environments, ultimately causing alteration of many ecosystems with changes in the composition of the wild fauna and destruction of boundaries between domestic and wild environments. Therefore, the exchange of parasites from wild to domestic carnivores and vice versa have enhanced the public health relevance of wild carnivores and their potential impact in the epidemiology of many zoonotic parasitic diseases. The risk of transmission of zoonotic nematodes from wild carnivores to humans via food, water and soil (e.g., genera Ancylostoma, Baylisascaris, Capillaria, Uncinaria, Strongyloides, Toxocara, Trichinella) or arthropod vectors (e.g., genera Dirofilaria spp., Onchocerca spp., Thelazia spp.) and the emergence, re-emergence or the decreasing trend of selected infections is herein discussed. In addition, the reasons for limited scientific information about some parasites of zoonotic concern have been examined. A correct compromise between conservation of wild carnivores and risk of introduction and spreading of parasites of public health concern is discussed in order to adequately manage the risk of zoonotic nematodes of wild carnivores in line with the 'One Health' approach.

Trichinella spp. biomass has increased in raccoon dogs (Nyctereutes procyonoides) and red foxes (Vulpes vulpes) in Estonia

BACKGROUND

Raccoon dogs and red foxes are well-adapted hosts for Trichinella spp. The aims of this study were to estimate Trichinella infection prevalence and biomass and to investigate which Trichinella species circulated in these indicator hosts in Estonia.

METHODS

From material collected for evaluating the effectiveness of oral vaccination program for rabies eradication in wildlife, samples from 113 raccoon dogs and 87 red foxes were included in this study. From each animal, 20 g of masseter muscle tissue was tested for the presence of Trichinella larvae using an artificial digestion method. The Trichinella larvae were identified to species level by multiplex polymerase chain reaction method.

RESULTS

The majority of tested animals were infected with Trichinella spp. The parasite species identified were T. nativa and T. britovi. The apparent infection prevalence was 57.5% in raccoon dogs and 69.0% in red foxes, which were higher than previous estimates. In addition, the larval burden had also increased in both hosts. We estimated that in 2011-2012, the Trichinella spp. biomass was more than 15 times higher in raccoon dogs and almost two times higher in red foxes than in 1992-2000 (based on mean larval burden), and almost 20 times higher in raccoon dogs and almost five times higher in red foxes than in 2000-2002 (based on median larval burden).

CONCLUSIONS

Raccoon dogs and red foxes are relevant reservoirs for Trichinella spp. in Estonia. The biomass of Trichinella circulating in sylvatic cycles was substantial and had increased: there is substantial infection pressure in the sylvatic cycle.

First findings of Trichinella spiralis and DNA of Echinococcus multilocularis in wild raccoon dogs in the Netherlands

The recent invasion of the raccoon dog in the Netherlands may be associated with the risk of introduction and spread of zoonotic pathogens. The aim of this study was to assess whether Echinococcus multilocularis and Trichinella spp. infections are present in Dutch raccoon dogs. Between 2013 and 2014, nine raccoon dogs, mainly road kills, were collected for necropsies. One raccoon dog tested repeatedly positive in the qPCR for E. multilocularis. The positive raccoon dog was collected in the province of Flevoland, which is not a known endemic region for E. multilocularis. Another raccoon dog tested positive for Trichinella spiralis by the digestion of the forelimb musculature and the tongue. Trichinella spiralis has not been reported in wildlife since 1998 and thus far was not found in wild carnivores in the Netherlands. It shows that despite the small raccoon dog population that is present in the Netherlands and the limited number of raccoon dogs that were tested, the raccoon dog may play a role in the epidemiology of E. multilocularis and Trichinella spp. in the Netherlands.

Helminth parasites in black rats (Rattus rattus) and brown rats (Rattus norvegicus) from different environments in the Netherlands

BACKGROUND

Rattus norvegicus (brown rat) and Rattus rattus (black rat) are known carriers of bacteria, viruses, and parasites of zoonotic and veterinary importance. Moreover, rats may play a role in the transmission of muscle larvae of the zoonotic nematode Trichinella spiralis to farm animals. We aimed to study the intestinal and intramuscular helminths in wild rats from three different environments to assess the relevance of rats as carrier of zoonotic parasites for public health.

MATERIALS AND METHODS

Wild brown rats (117 individuals) and black rats (44 individuals) were captured at farms, in suburban and in rural environments in the Netherlands. Intestinal helminths were isolated and identified morphologically. Artificial digestion was used to isolate muscle larvae.

RESULTS AND DISCUSSION

Morphological analysis of rat intestinal contents yielded six nematode species (Syphacia muris, Heterakis spumosa, Aonchotheca murissylvatici, Trichuris muris, Nippostrongylus brasiliensis, and Strongyloides sp.), three cestode species (Hymenolepis diminuta, H. nana and Hymenolepis (=Rodentolepis) fraterna), and four trematode species (Plagiorchis muris, Plagiorchis proximus, Echinostoma chloropodis, and Notocotylus imbricatus).Black rats at farms displayed the lowest intestinal helminth species variation (six species) and carried overall on average 0.93 species simultaneously. In comparison, brown rats at farms carried seven helminth species and 1.91 species simultaneously. Brown rats from suburban environments displayed the highest species variation (11 species) at 1.82 simultaneous helminth species. Absence of trematodes from rats at farms may suggest limited exchange of rats between farms and surrounding wet rural environments. We report four species of veterinary (Syphacia muris) or zoonotic relevance (Hymenolepis diminuta, Hymenolepis nana and Plagiorchis muris). We did not find Trichinella muscle larvae, consistent with long-term prevalence in Dutch wild rats.

High prevalence of Trichinella spp. in sylvatic carnivore mammals of Latvia

Trichinella spp. are zoonotic parasites transmitted to humans by the consumption of raw or insufficiently cooked meat of different animal species. Carnivore mammals are important reservoir hosts of these nematodes. The aims of this work were to establish the prevalence of Trichinella spp. and infection intensity in sylvatic carnivore mammals of Latvia, to identify the etiological agents at the species level and their circulation in the Latvian regions. From 2010 to 2014, muscle samples were collected from 1286 hunted animals (2 European badgers, 137 pine martens, 24 stone martens, 4 golden jackals, 394 raccoon dogs, 668 red foxes, 23 grey wolves, and 34 Eurasian lynxes). Trichinella spp. larvae were isolated by muscle digestion. Overall, 633 animals (49.2%; 95% CI 46.5%-52.0%) belonging to all the eight investigated species, tested positive for Trichinella spp. larvae. Trichinella britovi was the most common species (94.0%; 95% CI 91.7%-95.7%). Trichinella nativa was detected in 30 animals as single (6, 1.1%; 95% CI 0.4%-2.3%) or mixed infection (24, 4.4%; 95% CI 2.9%-6.4%) with T. britovi. Trichinella spiralis was detected in only three animals as mixed infection with T. britovi. The high prevalence of Trichinella spp. infection in sylvatic carnivore mammals suggests that they are good indicators for the risk assessment of Trichinella spp. in Latvia.

Quality Control of Trichinella Testing at the Slaughterhouse Laboratory: Evaluation of the Use of a 400-Micrometer-Mesh-Size Sieve in the Magnetic Stirrer Method

The performance of a 400-μm-mesh-size sieve (sieve400) has not previously been compared with that of a 180-μm-mesh-size sieve (sieve180). Using pork samples spiked with 0 to 10 Trichinella muscle larvae and an artificial digestion method, sieve performance was evaluated for control of Trichinella in meat-producing animals. The use of a sieve400 resulted in 12% lower larval counts, 147% more debris, and 28% longer counting times compared with the use of a sieve180. Although no false-negative results were obtained, prolonged counting times with the sieve400 may have an impact on performance in a high-throughput environment such as a slaughterhouse laboratory. Based on our results, the sieve180 remains the sieve of choice for Trichinella control in meat in slaughterhouse laboratories, according to the European Union reference method (European Commission regulation 2075/2005). Furthermore, the results of the present study contribute to the discussion of harmonization of meat inspection requirements among countries.

Genetic evidence of interspecies introgression of mitochondrial genomes between Trichinella spiralis and Trichinella britovi under natural conditions

Trichinellosis is a zoonotic disease caused by Trichinella muscle larvae (ML) through ingestion of raw or undercooked meat. To date, 12 taxa are recognized in this genus, of which four are circulating in Europe (Trichinella spiralis, Trichinella nativa, Trichinella britovi and Trichinella pseudospiralis). T. spiralis and T. britovi circulate in European wildlife and occur simultaneously in the same host species. The possibility of hybrid formation between T. britovi and T. spiralis has hardly been addressed and so far, results of experimental hybridisation attempts between T. britovi and T. spiralis are inconclusive. The aim of the present study was to analyse molecular polymorphisms of single T. spiralis and T. britovi ML from natural infections based on nuclear 5S rDNA intergenic spacer region (5S rDNA-ISR) and mitochondrial cytochrome c oxidase 1 (CO1) gene sequences. Six haplotypes of the 5S rDNA intergenic spacer region (5S rDNA-ISR) and 14 of the cytochrome c oxidase 1 (CO1) gene were demonstrated in 89 individual T. britovi ML from Latvia and Poland. In contrast, only two haplotypes were observed at both 5S rDNA-ISR and CO1 of 57 individual T. spiralis ML from Polish wild boar and red foxes. Moreover, this study demonstrates hybridisation in eight individual ML between T. britovi and T. spiralis under natural conditions in four Polish wild boar and two red foxes, revealed by combining 5S rDNA-ISR and CO1 sequence information of individual Trichinella ML. To our knowledge, this is the first report of interspecies hybridisation between T. spiralis and T. britovi under field conditions.

The red fox (Vulpes vulpes) plays a minor role in the epidemiology of the domestic cycle of Trichinella in Romania

Nematode worms of the genus Trichinella are zoonotic parasites with a worldwide distribution. The majority of the biomass of these nematodes circulates among wildlife, but when humans fail in the proper management of domestic animals and wildlife, Trichinella infections are transmitted from the sylvatic to the domestic environment. Such failures occur in Romania, where a high prevalence of Trichinella spiralis has been detected in domestic pigs. The aim of the present study was to provide data about the prevalence of Trichinella spp. infections in red foxes (Vulpes vulpes) that are hunted in Romanian counties, in which the prevalences of Trichinella spp. infection in backyard and free-ranging pigs range from 0.17 to 2.5%, to determine the role played by this carnivore species in the transmission of the parasite to domestic cycle. A total of 121 animals from 45 hunting grounds of three counties were screened to detect Trichinella spp. larvae by the digestion method. Infections were detected in 26 (21.5%) foxes from 18 (40%) hunting grounds of the three counties (13/67 in Arad, 1/3 in Hunedoara, and 12/51 in Timiş). The mean larval density was 10.5 larvae per gram. Of the 25 successfully tested samples, the Trichinella larvae from 24 isolates were identified as T. britovi (96%), and the larvae from one isolate were identified as T. spiralis (4%). No mixed infections were recorded. The present results revealed that the red fox should be considered an important T. britovi reservoir in the sylvatic cycle; in contrast, the detection of only a single T. spiralis-positive isolate suggests that red foxes play a minor role in the epidemiology of the domestic cycle in the investigated area of western Romania.