Wild boars meat as a potential source of human trichinellosis in Poland: current data

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.

Trichinella spiralis Infecting Wild Boars in West, Southwest, and Northwest of Romania: Evidence of an Underrated Risk

The species of the genus Trichinella are etiological agents distributed all over the world and are able to infect mammals, birds, and reptiles. Trichinella spiralis is the species most adapted to domestic and wild pigs and is also the most important etiological agent of trichinellosis. The wild boar (Sus scrofa) is a nocturnal omnivorous mammal belonging to the Suidae family. S. scrofa has a great appetite and its diet includes a variety of small prey such as mice, rats, and other rodents, as well as carcasses of larger animals. The aim of this study was the identification and the molecular characterization of Trichinella larvae isolated from the muscle tissue of S. scrofa specimens collected in different counties of Romania. The muscle samples were examined by artificial digestion and the larvae identified at the species level by multiplex PCR. T. spiralis, a species that is able to infect a considerable number of different host species including humans, was identified. In Romania, S. scrofa is an important reservoir species for T. spiralis and plays an important role in linking the domestic and the wild cycle of Trichinella, with serious repercussions for human health.

Immunomodulatory in vitro effects of Trichinella cystatin-like protein on mouse splenocytes

Trichinella parasites have developed specific mechanisms allowing successful completion of their life cycle. These mechanisms are in a great part involved in immunomodulation and studying them may provide a valuable insight into the functioning of the immune system. Trichinella products may be also used as potential therapeutic agents to treat immune diseases. This study investigates the immunomodulatory potential of recombinant multi cystatin-like protein (CLP) derived from T. britovi to determine whether CLP has anti-inflammatory properties in vitro. CLP is a highly antigenic glycoprotein present in Trichinella excetory-secretory (ES) products. AlphaFold structure prediction confirms that it consists of three type-two cystatin-like domains. Mouse splenocytes were stimulated in vitro with lipopolysaccharide (LPS) and co-stimulated with recombinant CLP. The culture supernatants were collected and tested for secreted cytokine levels using ELISA. CLP was found to reduce LPS-induced secretion of inflammatory cytokines TNFα and IL-6. On the contrary, in some experimental groups, co-stimulation with CLP resulted in increased secretion of the regulatory cytokine IL-10. The obtained results indicate that CLP has anti-inflammatory properties and future research on its function is advisable, specifically in the context of the therapy of inflammatory disorders.

Analysis of a Trichinellosis Outbreak in Poland after Consumption of Sausage Made of Wild Boar Meat

An outbreak of trichinellosis due to the consumption of sausage made from wild boar meat unexamined for the presence of Trichinella spp. was reported in Poland in December 2020. The outbreak affected eight people. Examination of the sausages made of wild boar meat collected during epidemiological investigation indicated a high level of Trichinella spp. Larvae per gram (>30 lpg) and therefore the threat of an infection in humans after consumption of such product was significant. Over the years, the main source of trichinellosis in Poland has been wild boar meat, and the majority of trichinellosis cases were related to the consumption of traditional raw meat products such as Polish sausage. Taking this into account, there is the need for better education of consumers in the Trichinella spp. endemic regions and among cultures consuming traditional raw meat products.

Trichinella Outbreaks on Pig Farms in Poland in 2012-2020

Trichinella nematodes continue to circulate in various hosts both in the domestic and sylvatic cycles. In the majority of countries in Europe, wild boars have been noticed as a primary source of Trichinella spp. infections in humans. However, in some regions, the meat of pigs containing Trichinella spp. larvae can still be a cause of trichinellosis. Therefore, in the present study, we aimed to determine and present actual data on the occurrence of Trichinella spp. on pig farms (Sus scrofa f. domestica) in Poland. In this study, over 194 million pigs, slaughtered for commercial and personal purposes between 2012 and 2020, were tested with a digestion method according to the official rules for Trichinella control. Positive results were noticed in 172 pigs which gives an overall prevalence of 0.000088%. On seven farms, rats (Rattus norvegicus) infected with Trichinella spp. were also discovered. The species identification showed pigs were infected with Trichinella spiralis on 26 farms, and on four farms pigs with Trichinella britovi infections were found. Therefore, it is important to constantly monitor pigs for the presence of these parasites, especially in view of the growing interest in organic meat originated from ecological farms.

Immunoproteomic analysis of Trichinella spiralis and Trichinella britovi excretory-secretory muscle larvae proteins recognized by sera from humans infected with Trichinella

The present study compares the immunogenic patterns of muscle larvae excretory-secretory proteins (ML E-S) from T. spiralis and T. britovi recognized by Trichinella-infected human sera. Samples were analyzed using two-dimensional electrophoresis (2-DE) coupled with 2D-immunoblot and liquid chromatography-tandem mass spectrometry LC-MS/MS analysis, two ELISA procedures and a confirmatory 1D-immunoblot test. Sera were obtained from nine patients with a history of ingestion of raw or undercooked meat who presented typical clinical manifestations of trichinellosis and from eleven healthy people. Specific anti-Trichinella IgG antibodies were detected in all samples tested with the Home-ELISA kits, but in only four samples for the commercially-available kit. The 1D-immunoblot results indicated that all nine serum samples were positive for T. spiralis ML E-S antigens, expressed as the presence of specific bands. In contrast, eight of the serum samples with T. britovi E-S ML antigens were positive, with one serum sample taken from a patient at 33dpi (days post infection) being negative. To identify immunoreactive proteins that are specifically recognized by host antibodies, both species of ML E-S proteins were subjected to 2D-immunoblotting with human serum taken at 49 dpi. The sera recognized 22 protein spots for T. spiralis and 18 for T. britovi in 2D-immunoblot analysis. Their molecular weights (MW) ranged from 50 to 60 kDa. LC-MS/MS analysis identified both common and specifically-recognized immunoreactive proteins: transmembrane serine protease 9, serine protease, antigen targeted by protective antibodies and Actin-1 partial were shared for both Trichinella species; hypothetical protein T01_7775 and P49 antigen, partial those specific to T. spiralis; deoxyribonuclease-2-alpha and hypothetical protein T03_17187/T12_7360 were specific to T. britovi. Our results demonstrate the value of 2-DE and 2D-immunblot as versatile tools for pinpointing factors contributing to the parasite-host relationship by comparing the secretomes of different Trichinella species.

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.

Diversity of Trichinella species in relation to the host species and geographical location

Trichinella nematodes still circulate in various hosts in both domestic and sylvatic environments. Recently, in Europe, the transmission of Trichinella spp. to humans has been attributed more to wild animals than to domestic animals. However, domestic animals could still be a source of human infections in some regions. Therefore, our aim was to determine the species composition of Trichinella and the prevalence and intensity of infections in animal populations from the domestic cycle, namely pigs (Sus scrofa f. domestica); the synantropic cycle, in the form of rats (Rattus norvegicus); and the sylvatic cycle, namely wild boars (Sus scrofa) and red foxes (Vulpes vulpes), in Poland. The findings showed that the nematode prevalence in pigs (0.0002 %) and wild boars (0.3 %) was lower than it was in red foxes (4 %). A very high prevalence was found in rats (23.3 %), but it must be emphasized that the investigated rat samples were collected from farms where pigs were infected with Trichinella spp. The mean larval burden was found to be higher in wild boars and pigs (11.48 lpg and 10.19 lpg) than in red foxes and rats (4.09 and 2.30). Trichinella spiralis was the predominant species in pigs (98.6 %), wild boars (77.3 %) and rats (100 %), while in red foxes, this species occurred less frequently (15.5 %). The most frequently occurring species in red foxes was Trichinella britovi (73.2 %). Moreover, in wild boar and red fox coinfections, T. spiralis/T. britovi were detected (3.1 and 9.9 %, respectively). In addition, Trichinella pseudospiralis was detected in a few wild boars (0.5 %) and Trichinella nativa was found in one red fox and one wild boar. Furthermore, different T. spiralis and T. britovi prevalence ratios in various geographical regions were found. In the wild boar population, a higher frequency of T. spiralis (70-85 % of infected animals) was observed in the western and central parts of Poland, while in the eastern part, this dominance was not as evident (46-59 %). In the red fox population, T. britovi was abundant throughout the entire territory; however, its highest prevalence was in the east (90-100 %).

The Immunological Properties of Recombinant Multi-Cystatin-Like Domain Protein From Trichinella Britovi Produced in Yeast

Trichinellosis is a globally-distributed zoonotic parasitic disease caused by nematode worms of the genus Trichinella. One of the most common species of Trichinella known to affect human health is T. britovi; however, it is relatively poorly investigated. A thorough knowledge of the proteins expressed by Trichinella is important when developing immunological detection methods and vaccines and studying its interactions with the host. The present study uses the Pichia pastoris expression system to produce a soluble TbCLP antigen which induces strong antibody responses in the host during natural infection. Our results demonstrate the feasibility of TbCLP antigen production in yeasts, which are able to carry out post-translational modifications such as glycosylation and disulfide bond formation; they also indicate that the glycosylated TbCLP antigen had immunogenic effects in the tested mice and induced a mixed Th1/Th2 response, and was associated with a reduced larval burden after challenge with T. britovi. Subsequent in vitro stimulation of mice splenocytes revealed that TbCLP most likely possesses immunomodulatory properties and may play a significant role in the early phase of infection, affecting host immunological responses.

Seroprevalence of Trichinella spp. infection in bank voles (Myodes glareolus) - A long term study

Rodents play an important role as reservoir hosts of zoonotic diseases. As a component of our long-term programme of monitoring parasitic infections in bank vole populations in three ecologically similar sites in NE Poland, we screened blood samples for signs of a serological response to the presence of Trichinella spp. The overall seroprevalence of Trichinella spp. was 1.52%, but prevalence was largely concentrated in one of our three study sites and confined to the oldest individuals in the study. Seroprevalence of Trichinella spp. did not differ between the sexes. Although a local prevalence of 1.52% may seem low, when this is extrapolated to the national population of bank voles in peak years, perhaps numbering hundreds of millions of animals, the number of infected bank voles on a country wide scale is likely to be huge. Our results suggest that bank voles may be reservoirs of Trichinella spp. However, on the basis of our results we consider their importance as epidemiologically significant hosts for Trichinella spp. to be moderate and their role in this context to require further investigation.

The occurrence of nematodes of the genus Trichinella in wolves (Canis lupus) from the Bieszczady Mountains and Augustowska Forest in Poland

The aim of the present study was to investigate the prevalence of Trichinella infection in wolves (Canis lupus) in two regions in Poland. Muscle samples were collected from 21 wolves between 1999 and 2015 and processed by artificial digestion. In two cases, the muscle larvae (ML) were obtained and stored in alcohol. ML were detected in 12 wolves and genotyped by multiplex PCR. Trichinella britovi was confirmed in 12 wolves (54.5%). The larval burdens in infected animals ranged from 0.009 to 27 larvae per gram. The high prevalence of Trichinella infection in wolves might suggest that this predator is a significant reservoir of Trichinella species in the sylvatic cycle in Poland.