A 38-year study on Trichinella spp. in wild boar (Sus scrofa) of Latvia shows a stable incidence with an increased parasite biomass in the last decade

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.

A framework for the design, implementation, and evaluation of output-based surveillance systems against zoonotic threats

Output-based standards set a prescribed target to be achieved by a surveillance system, but they leave the selection of surveillance parameters, such as test type and population to be sampled, to the responsible party in the surveillance area. This allows proportionate legislative surveillance specifications to be imposed over a range of unique geographies. This flexibility makes output-based standards useful in the context of zoonotic threat surveillance, particularly where animal pathogens act as risk indicators for human health or where multiple surveillance streams cover human, animal, and food safety sectors. Yet, these systems are also heavily reliant on the appropriate choice of surveillance options to fit the disease context and the constraints of the organization implementing the surveillance system. Here we describe a framework to assist with designing, implementing, and evaluating output-based surveillance systems showing the effectiveness of a diverse range of activities through a case study example. Despite not all activities being relevant to practitioners in every context, this framework aims to provide a useful toolbox to encourage holistic and stakeholder-focused approaches to the establishment and maintenance of productive output-based surveillance systems.

Trichinella britovi in wild boar meat from Italy, 2015-2021: A citizen science approach to surveillance

As a result of the increase of game meat intended for human consumption through Europe, a plethora of food-borne diseases, including trichinellosis, may occur in consumers, posing a relevant public health threat. Thus, this study aims to a citizen science approach to monitor the occurrence of Trichinella spp. in wild boar meat intended for human consumption, evaluating the risk of infection for consumers. Following the European Regulation 2015/1375 (laying down specific rules on official controls for Trichinella in meat), from 2015 to 2021, hunters (n = 478) were involved to collect diaphragm pillar samples of wild boars from mainland southern Italy, which were tested for Trichinella spp. L₁ larvae via HCl-pepsin digestion and Multiplex PCR. Overall, 139,160 animals were collected (average of 19,880 per year), being 14 (i.e., 0.01%) tested positive to Trichinella britovi by the combined biochemical and molecular approach. An average larval burden of 28.4 L₁ per gram of meat was found (minimum 3.2 - maximum 132.6). A statistically significant difference was found in the prevalence according to hunting seasons (p < 0.01, with higher values in 2016 and 2021) and regions of the study area (p < 0.01). No statistically significant decrease in the prevalence of T. britovi throughout the study period was found (p = 0.51), except in Apulia region (p < 0.01). These findings revealed a stable prevalence of T. britovi in wild boar meat intended for human consumption, suggesting a risk of infection for consumers, especially hunters and local markets users. Citizen science surveillance models could be promoted to improve trichinellosis control and prevention in a One Health perspective.

Trichinella spiralis and T. britovi in North-Eastern Romania: A Six-Year Retrospective Multicentric Survey

Simple Summary

The genus Trichinella includes roundworm parasites with a wide geographical spread that can cause illness in humans and animals. In this context, an epidemiological study of Trichinella infection was carried out in the northeastern part of Romania to investigate for the first time its prevalence in pigs, horses, wild boars and bears, the geographical distribution of Trichinella species and the natural reservoir of the parasites. Between 2010 and 2015, a total of 166,270 animals were examined by specific methods in order to calculate the prevalence of Trichinella infection, the involved species, and their geographical distribution. The overall prevalence of Trichinella infection in animals was 0.188%. But the specific prevalence varied as follows: in pigs 0.096%, horses 0.021%, wild boar 1.46% and bears 36.76%. The geographical distribution showed that T. spiralis was dominant, occupying the entire northeastern part of Romania, being identified in pigs, horses, wild boars and bears. T britovi occupied five mountain counties, being identified only in wild boars and bears. These results validate the presence of T. spiralis and T. britovi in domestic and game animals in northeast Romania and warn about the risk of human infection in the region.

Abstract

The genus Trichinella includes species with a wide geographical spread that cause pathology in humans and animals. In this context, an epidemiological study of Trichinella infection was carried out in the northeastern part of Romania to investigate for the first time the prevalence of this infection in pigs, horses, wild boars and bears, the geographical distribution of Trichinella species and the natural reservoir of Trichinella infection. Between 2010 and 2015, a total of 166,270 animals were examined by the method of artificial digestion, in order to calculate the annual and general prevalence of Trichinella infection, according to the host and the Trichinella species involved, the Pearson correlation coefficient (r), trendline and geographical distribution of species of the genus Trichinella. Taxonomic framing was performed by the multiplex PCR method. The overall prevalence of Trichinella infection in animals was 0.188%. Within the host species, the prevalence varied as follows: in pigs 0.096%, horses 0.021%, wild boar 1.46% and bears 36.76%. The geographical distribution showed that T. spiralis was dominant, occupying the entire northeastern part of Romania, being identified in pigs, horses, wild boars and bears. T britovi occupied five mountain counties, being identified only in wild boars and bears. These results validate the presence of T. spiralis and T. britovi in domestic and game animals in the northeastern part of Romania.

The International Trichinella Reference Centre database. Report on thirty-three years of activity and future perspectives

The International Trichinella Reference Centre (ITRC) is the official laboratory of the International Commission on Trichinellosis, of the World Organization for Animal Health and of the European Union Reference Laboratory for Parasites. The ITRC was established in 1988 as a repository of Trichinella strains and a source of reference materials and information for international scientific research. To date, more than 8000 Trichinella isolates collected throughout the world have been identified at the species or genotype level by the ITRC staff and the information has been stored in a freely accessible database providing the largest collection of data available for scientists involved in the systematics and epidemiology of this parasite. This paper presents a summary of the data collected over 33 years of activity and describes the database functionalities. It finally advocates the potential of the database to improve knowledge of the epidemiology and taxonomy of Trichinella, which in turn may help the international surveillance of Trichinella species.

High prevalence, intensity, and genetic diversity of Trichinella spp. in wolverine (Gulo gulo) from Yukon, Canada

Background

Species of Trichinella are globally important foodborne parasites infecting a number of domestic and wild vertebrates, including humans. Free-ranging carnivores can act as sentinel species for detection of Trichinella spp. Knowledge of the epidemiology of these parasites may help prevent Trichinella spp. infections in northern Canadian animals and people. Previous research on Trichinella spp. in wildlife from Yukon did not identify risk factors associated with infection, or the diversity and identity of species of Trichinella in regional circulation, based on geographically extensive sampling with large sample sizes.

Methods

In a cross-sectional study, we determined the prevalence, infection intensity, risk factors, and species or genotypes of Trichinella in wolverine (Gulo gulo) in two regions of Yukon, Canada, from 2013–2017. A double separatory funnel digestion method followed by mutiplex PCR and PCR-RFLP were used to recover and identify species of Trichinella, respectively.

Results

We found larvae of Trichinella in the tongues of 78% (95% CI 73–82) of 338 wolverine sampled. The odds of adult (≥ 2 years) and yearling (1 year) wolverine being Trichinella spp.-positive were four and two times higher, respectively, compared to juveniles (<1 year). The odds of Trichinella spp. presence were three times higher in wolverine from southeast than northwest Yukon. The mean intensity of infection was 22.6 ± 39 (SD, range 0.1–295) larvae per gram. Trichinella T6 was the predominant genotype (76%), followed by T. nativa (8%); mixed infections with Trichinella T6 and T. nativa (12%) were observed. In addition, T. spiralis was detected in one wolverine. Out of 22 isolates initially identified as T. nativa in multiplex PCR, 14 were analyzed by PCR-RFLP to distinguish them from T. chanchalensis, a recently discovered cryptic species, which cannot be distinguished from the T. nativa on multiplex PCR. Ten isolates were identified either as T. chanchalensis alone (n = 7), or mixed infection with T. chanchalensis and T. nativa (n = 2) or T. chanchalensis and Trichinella T6 (n = 1)].

Conclusions

Wolverine hosted high prevalence, high larval intensity, and multiple species of Trichinella, likely due to their scavenging habits, apex position in the food chain, and wide home range. Wolverine (especially adult males) should be considered as a sentinel species for surveys for Trichinella spp. across their distributional range.

Trichinella spp. in Wild Boars (Sus scrofa), Brown Bears (Ursus arctos), Eurasian Lynxes (Lynx lynx) and Badgers (Meles meles) in Estonia, 2007-2014

In this study, we summarize Trichinella findings from four wild, free-ranging host species from Estonia during 2007-2014. Trichinella spp. larvae were detected in 281 (0.9%, 95% confidence interval (CI) 0.8-1.0) of 30,566 wild boars (Sus scrofa), 63 (14.7%, 95% CI 11.6-18.3) of 429 brown bears (Ursus arctos), 59 (65.56%, 95% CI 55.3-74.8) of 90 Eurasian lynxes (Lynx lynx), and three (60.0%, 95% CI 18.2-92.7) of five badgers (Meles meles). All four European Trichinella species were detected: T. britovi in 0.7% of the wild boars, 7.2% of the brown bears, 45.6% of the lynxes, and 40.0% of the badgers; T. nativa in 0.1% of the wild boars, 5.8% of the brown bears, and 20.0% of the lynxes; T. pseudospiralis in 0.02% the wild boars; and T. spiralis in 0.03% of the wild boars and 4.4% of the lynxes. The results include the first description from Estonia of T. britovi in brown bear and badgers, T. pseudospiralis in wild boars, and T. spiralis in wild boars and lynxes. The results indicate high infection pressure in the sylvatic cycles across the years-illustrating continuous risk of spillover to domestic cycles and of transmission to humans.

Trichinella spp. in wild boar (Sus scrofa) populations in Croatia during an eight-year study (2010-2017)

Wild animals represent a constant source of Trichinella spp. infections for domestic animals and humans. To date, four species of Trichinella have been isolated in wild boar populations in Europe: T. pseudospiralis, T. spiralis, T. britovi and T. nativa, in addition to several mixed infection types and one hybrid formation between T. britovi and T. spiralis. Meanwhile, insufficiently thermally processed wild boar meat has been reported to be a source of trichinellosis in humans in several European countries. In Croatia, there have been no reported or proven cases of trichinellosis caused by wild boar meat consumption. The aim of this study was to obtain data on the prevalence of Trichinella species present in Croatia and to anticipated the potential risk of infection for humans in specific Croatian regions based on information obtained over an eight-year surveillance period. A veterinary inspection of wild boar carcasses for Trichinella larvae in Croatia has been mandatory since 1989, and the artificial digestion method was introduced as a compulsory test for wild boar samples in 2008. Based on the official data submitted to the Ministry of Agriculture, Directorate of Veterinary Services, in the period 2010-2017, 303 of 183,184 (0.17%) wild boar meat samples tested positive for Trichinella spp. Infected wild boar were found in 18 of 21 counties. Of these positive samples, 85 were submitted by the authorised veterinary inspectors to the National Reference Laboratory for further examination. The intensity of infection in muscle samples was 0.04-152.66 (mean: 23,37) larvae per gram, and Trichinella species were identified as T. spiralis, T. britovi, T. pseudospiralis and T. spiralis + T. britovi. Genetic analysis of T. pseudospiralis isolates demonstrated their belonging to the Palaearctic population.

Trichinella britovi as a risk factor for alternative pig production systems in Greece and Europe

Trichinellosis is an important zoonosis and the most common source of human infection is meat from pigs and wild boars. The European Union (EU) supports alternative pig production systems (organic and free-ranging) as sustainable farming systems. However, these systems that allow outdoor access for farm animals, may create new or reintroduce old risks to public health. During the last years, alternative pig production systems (free-ranging or organic pig) are growing in popularity in Greece due to the increasing interest of consumers for organic products. The majority of the trichinellosis outbreaks in the EU were associated with pork and meat products including wild boars. In Greece, from 2009 to 2012, 37 Trichinella spp. positive free-ranging pigs were reported in free-ranging pig farms of Northern-Eastern Greece (31 were identified as T. britovi). The recent re-emerging present of the Trichinella spp. infections in free-ranging pigs and wild boars are a high risk for the consumers and should alarm the Public Health Authorities in Greece and the EU. During the last years, the organic or free-ranging pig production systems are growing in popularity in the EU. However, these systems increase the risk of Trichinella spp. infections, since pigs are possible to be infected by feeding on carcasses or the offal of hunted or dead wild animals. For this reason, it is important for Public Health Authorities to be focused on the training of hunters and farmers in order to avoid the transmission among free-ranging pigs and prevent the cases of human infection.

Parasites in the changing world - Ten timely examples from the Nordic-Baltic region

The world is changing, and parasites adapt. The Nordic-Baltic region in northern Europe - including the Nordic countries Denmark, Finland, Iceland, Norway and Sweden, and the Baltic States Estonia, Latvia and Lithuania - is facing new parasitological challenges due to changes in populations of parasites and their hosts and the spread of new parasites to the region due to climate change. Some changes can also be ascribed to increased awareness and detection. In this paper, we review and discuss a convenience selection of ten timely examples of recent observations that exemplify trends and challenges from different fields of parasitology, with particular focus on climate change and potential changes in epidemiology of pathogens in northern Europe. The examples illustrate how addressing parasitological challenges often requires both intersectoral and international collaboration, and how using both historical baseline data and modern methodologies are needed.

A Simple and Rapid Staining Technique for Sex Determination of Trichinella Larvae Parasites by Confocal Laser Scanning Microscopy

The roundworms of Trichinella genus are worldwide distributed and their prevalence in nature is high. Trichinella genus parasites are the causative agents of foodborne zoonosis trichinellosis. The main prevention and control of the infection are meat inspection by the magnetic stirrer method for the detection of Trichinella larvae in muscle samples. The treatment can be effective if the parasite is discovered early in the intestinal phase. Once the Trichinella larva has reached the muscle tissue, the parasite remains therein and there is no treatment for this life cycle stage. The Trichinella species is dioecious with separate male and female individuals. The developed staining technique that uses confocal laser scanning microscopy (CLSM) displays sufficient results for Trichinella larvae examination and this protocol is applicable to study the internal and external structures and for the sex determination of T. britovi and T. spiralis larvae samples. In the present study, a luminescent derivative was synthesized and used for staining of T. spiralis and T. britovi larvae samples for the examination by CLSM. Various fixatives, such as AFA, 70% ethanol, and Bouin's and Carnoy's solutions were tested for sample preparation. The synthesized luminescent compound demonstrates best visualization results for samples fixed in Bouin's fixative.

The subnivium, a haven for Trichinella larvae in host carcasses

Parasite nematodes of the genus Trichinella are transmitted from one host to another through the ingestion of larvae present in striated muscles. The longer the survival of muscle larvae in host carcasses, the higher the probability of being ingested by a scavenging host. Thereby, these nematodes developed an anaerobic metabolism favouring their survival in decaying tissues. In addition, muscle larvae of three taxa, namely Trichinella nativa, Trichinella britovi and Trichinella T6, can survive freezing for several months to several years depending on the taxon. The aim of the present work was to investigate the survival time of T. britovi larvae in naturally infected host carcasses preserved beneath or above the snow. Fox and raccoon dog carcasses naturally infected with T. britovi larvae were preserved beneath or above the snow in a cold mountainous area. Temperature and relative humidity were recorded. Every 14 days, muscle samples collected from each carcass, were digested and larvae were counted and given per os to laboratory mice to evaluate their reproductive capacity index (RCI). The RCI of larvae in carcasses preserved beneath the snow (the subnivium) ranged from 23 to 25 at day 0, to 12–18 after 112 days. In contrast, the RCI of larvae in carcasses preserved above the snow ranged from 22 to 27 at day 0, to 0.0 after 112 days. The difference between the RCIs of larvae beneath the snow and above the snow was statistically significant (P < 0.01). These data corroborate the hypothesis that the subnivium with its environmental stability favours the survival of Trichinella larvae in host muscles, increasing the probability of their transmission to other hosts. On the other hand, the environment above the snow, characterized by sudden temperature variations, causes strong environmental stress for larvae in host carrions causing their death.

•

The snow cover increases the survival time of Trichinella larvae in host carrions.

•

The subnivium, seasonal refuge of Trichinella larvae in host carcasses.

•

Frequent thermal variations reduce larva survival in host muscles.

•

Muscle putrefaction did not adversely affect the survival of Trichinella larvae.

Wild Boar: A Reservoir of Foodborne Zoonoses

Wild boar populations around the world have increased dramatically over past decades. Climate change, generating milder winters with less snow, may affect their spread into northern regions. Wild boars can serve as reservoirs for a number of bacteria, viruses, and parasites, which are transmissible to humans and domestic animals through direct interaction with wild boars, through contaminated food or indirectly through contaminated environment. Disease transmission between wild boars, domestic animals, and humans is an increasing threat to human and animal health, especially in areas with high wild boar densities. This article reviews important foodborne zoonoses, including bacterial diseases (brucellosis, salmonellosis, tuberculosis, and yersiniosis), parasitic diseases (toxoplasmosis and trichinellosis), and the viral hepatitis E. The focus is on the prevalence of these diseases and the causative microbes in wild boars. The role of wild boars in transmitting these pathogens to humans and livestock is also briefly discussed.

Occurrence of selected zoonotic food-borne parasites and first molecular identification of Alaria alata in wild boars (Sus scrofa) in Italy

Wild boar is a source of human infections with zoonotic pathogens, including food-borne parasites. With the aim of a characterization of the human exposure risk, a survey on wild boars intended for human consumption was planned, selecting three pathogens, Toxoplasma gondii, Alaria alata, and Trichinella spp., as markers of meat infection. Diaphragm muscle samples from 100 wild boars hunted in Piedmont region (Northern Italy) in two hunting seasons (2015-2016) were collected. Concerning T. gondii, a combined approach of antibody detection and molecular techniques with genotyping was performed. For the detection of A. alata and Trichinella spp., the larva migration technique and the magnetic stirrer method were employed, respectively; in addition, molecular confirmation of the morphological identification of the recovered specimen was performed. Anti-T. gondii antibodies were found in meat juice samples (43.3%) and T. gondii DNA (type II) was detected in three animals (7.1%) out of 42 seropositive examined. In none of the sampled wild boars (0%), Trichinella spp. larvae were found, whereas one animal (1%) scored positive to A. alata mesocercariae. The molecular diagnosis proved the morphological identification of the trematode. This is the first finding of A. alata in Italian wild boar population. The present study confirmed the role of wild boars as a source of parasitic zoonotic diseases and thus the risk derived for humans posed by the consumption of game meat. Considering the zoonotic implications, the results underline the importance of monitoring and surveillance of zoonotic parasites in Italian wild boar populations.

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.

Epizootic and Epidemiological Situation of Trichinella sp. Infection in Poland in 2006-2015 in View of Wild Boar Population Dynamics

Introduction

The objective was to evaluate the epizootic and epidemiological situation of Trichinella sp. infection in Poland between 2006 and 2015 against the dynamics of the wild boar population and its primary reservoir host.

Material and Methods

Boar and porcine trichinosis epizootic analysis was based on General Veterinary Inspectorate data from RRW-6 bulletins. The epidemiological situation was evaluated on the basis of the data supplied by the Department of Epidemiology of the National Institute of Hygiene - National Institute of Public Health. The wild boar hunting harvest and population dynamics were estimated, as these animals remain the basic infection source for humans. Population size and harvest data were obtained from hunting statistics.

Results

The study timeframe showed an almost 2.5-fold increase in Trichinella infection cases in wild boars but a significant decline in human cases. In the domestic pig, the incidence rate did not exceed 0.00037%. The highest infection risk exists in West Pomerania, Greater Poland, and Kuyavian-Pomeranian Provinces. Over the study period, the wild boar population increased more than 1.5-fold, while the hunting harvest more than tripled. During the last two seasons the total hunt surpassed 100% of the spring population.

Conclusion

Wild boar management by increasing the hunting take of the annual population growth should limit that growth and decrease the take in the future. Thereby, over some years intra-species trichinosis spread should reduce, for a substantial safety gain for wild boar meat.

First case of Trichinella nativa infection in wild boar in Central Europe-molecular characterization of the parasite

The examination of wild boars gained in Poland shows for the first time occurrence of Trichinella nativa, freeze-resistant species of Trichinella in this host from the central Europe region. This finding is not only one of several cases of T. nativa invasion in wild boars all over the world but also one of the very few cases of T. nativa detected so far beyond the known boundary of occurrence of this species. The molecular characterization of discovered larvae based on analysis of partial genes: 5s rDNA-ISR and CO1 confirm the findings. Moreover, the analyzed DNA sequences of both genes present new haplotypes of T. nativa in comparison to that described previously.

Proteomic analysis of differentially expressed proteins in the three developmental stages of Trichinella spiralis

Trichinella spiralis, an intracellular parasitic nematode, can cause severe foodborne zoonosis, trichinellosis. The life cycle of T. spiralis consists of adult (Ad), muscle larvae (ML) and newborn larvae (NBL). The protein profiles in different developmental stages of the parasite remain unknown. In the present study, proteins from lysates of Ad, ML and NBL were identified by isobaric tags for relative and absolute quantitation (iTRAQ). A total of 4691 proteins were identified in all the developmental stages, of which 1067 proteins were differentially expressed. The number of up-regulated proteins in NBL was higher than that of the other two groups. The protein profiles from Ad, ML and NBL were compared in pairs. The identified proteins were involved in various functions of T. spiralis life cycle, including sexual maturity, metabolism, utilization of carbohydrates, lipids and nucleotides, and other crucial developmental processes that occur at distinct stages. Further investigation of the transcriptional levels of major sperm protein, serine protease, zinc finger protein, etc. from the different protein profiles using quantitative RT-PCR showed identical results to the iTRAQ analysis. The differentially expressed proteins that are involved in developmental regulation and host-parasite interactions should be further studied.

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.

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.

Trichinella pseudospiralis in the Iberian peninsula

Nematode worms of the genus Trichinella are zoonotic parasites circulating in most continents, including Europe. In Spain, Trichinella spiralis and Trichinella britovi are highly prevalent in wildlife but seldom in domestic pigs. In Portugal, only T. britovi was documented in wild carnivores. In the period 2006-2013 in Spain, 384 (0.0001%) pigs and 1399 (0.20%) wild boars (Sus scrofa) were positive for Trichinella spp. larvae, which were identified as T. spiralis or T. britovi. In 2014, Trichinella pseudospiralis larvae were isolated from a wild boar hunted in the Gerona province, Cataluña region, North-East of Spain, near the border to France. This is the first report of T. pseudospiralis in the Iberian peninsula, which suggests a broad distribution area of this zoonotic nematode in Europe. Since larvae of this Trichinella species do not encapsulate in the host muscles, they can be detected only by artificial digestion of muscle samples. T. pseudospiralis is the only Trichinella species infecting both mammals and birds. Birds can spread this pathogen over great distances including islands triggering new foci of infections in areas previously considered at low risk for this pathogen.