Molecular characterization of Trichinella species from wild animals in Israel

Genetic structure of Trichinella britovi populations in wildlife of north and northeast Iran

Trichinella britovi is a parasite prevalent in the temperate regions of the vast Palearctic realm, including Iran. In this study, we investigated Trichinella infection in road-killed animals and carcasses in northern and northeastern Iran by artificial digestion. We assessed species identification and intraspecific genetic diversity using the markers 5S ribosomal DNA intergenic spacer (5S rDNA), internal transcribed spacer I (ITS1), and cytochrome c oxidase subunit I (COXI). Of the 80 encountered carcasses, 10 had Trichinella infection, including seven golden jackals, one wolf, one wild cat, and one wild boar. BLAST analysis exhibited the highest similarities with T. britovi sequences in the GenBank database, at 99.79%, 99.84%, and 100% for COXI, 5S rDNA, and ITS1, respectively. All 5S rDNA sequences were identical, while analysis using DnaSP software identified eight haplotypes in the ITS1 region and six haplotypes in the COXI sequences. The phylogenetic analysis based on the COXI marker clustered all T. britovi sequences, including those from Iran, into a distinct clade. Furthermore, this marker revealed shallow branching, dividing T. britovi sequences into two subclades. The first subclade, the "European" group, consisted exclusively of haplotypes from Poland. In contrast, the second subclade, "Euro-Asiatic," included haplotypes of Asian and European origins. The Euro-Asiatic and European populations exhibited a 0.52% genetic distance while showing 0.59% and 0.15% intrapopulation divergence, respectively. Further studies involving specimens from other regions of Iran, particularly the southeast adjoining the Oriental zoogeographical zone, could provide additional insights into the molecular identity and population structures of T. britovi and potentially other species in Iran.

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, Oceania, 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.

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.

First report of Trichinella pseudospiralis in a wolf (Canis lupus italicus)

Within the genus Trichinella, Trichinella pseudospiralis is the only recognized non-encapsulated species known to infect mammals and birds. In October 2020, larvae recovered from muscle tissues of a wolf (Canis lupus italicus) originating from Molise Region, Central Italy, were molecularly confirmed as those of Trichinella britovi and T. pseudospiralis. This is the first detection of T. pseudospiralis from a wolf. In Italy, this zoonotic nematode was detected in a red fox (Vulpes vulpes), three birds (Strix aluco, Athene noctua, Milvus milvus) and five wild boars (Sus scrofa), and was also identified as the etiological agent of a human outbreak of trichinellosis in 2015. Since T. pseudospiralis is rarely reported from carnivore mammals in comparison to the encapsulated species frequently detected in these hosts, this finding opens the question of the role of carnivores as reservoirs for this parasite.

Genotyping and Phylogenetic Position of Trichinella spiralis Isolates from Different Geographical Locations in China

In China, the nematode Trichinella spiralis is the main aetiological agent of human trichinellosis. We performed multi-locus microsatellite typing of T. spiralis isolates to improve the current knowledge of the evolution and population diversity. First, seven polymorphic microsatellite loci were used to infer the genetic diversity of T. spiralis collected in 10 endemic regions. Then, a Bayesian model-based STRUCTURE analysis, a clustering based on the neighbor-joining method, and a principal coordinate analysis (PCA) were performed to identify the genetic structure. Finally, the phylogenetic position of Chinese isolates was explored based on six mitochondrial and nuclear genetic markers (cox1, cytb, 5S ISR, ESV, ITS1, and 18S rDNA) using the maximum likelihood and Bayesian methods. In addition, the divergence time was estimated with multiple genes using an uncorrelated log-normal relaxed molecular-clock model. A total of 16 alleles were detected in 2,310 individuals (1,650 muscle larvae and 660 adult worms) using seven loci. The STRUCTURE analysis indicated that the T. spiralis isolates could be organized and derived from the admixture of two ancestral clusters, which was also substantiated through the clustering analysis based on the allelic data. PCA separated most samples from Tiandong, Guangxi (GX-td), and Linzhi, Tibet (Tibet-lz), from the remaining isolates. However, both maximum likelihood and Bayesian inference supported the close relationship between Xiangfan, Hubei (HB-xf), and GX-td. The molecular dating analysis suggested that the Chinese isolates started to diverge during the Late Pleistocene (0.69 Mya). Generally, T. spiralis was observed to harbor low genetic variation, and further investigation with deeper sampling is needed to elucidate the population structure.

The Golden jackal (Canis aureus) as an indicator animal for Trichinella britovi in Iran

Nematodes of the genus Trichinella are zoonotic parasites causing trichinellosis. In Iran, these parasites occur in several animal species and rare cases have been recorded in humans. To monitor the epidemiological pattern of these parasites in the Khorasan-e-Razavi province, Northeastern Iran, muscle tissues were collected from the tongues of roadkill animals between 2016 and 2017: 295 stray dogs, one red fox (Vulpes vulpes), 12 golden jackals (Canis aureus), and one wild boar (Sus scrofa). Trichinella spp. larvae were retrieved using the artificial digestion method and identified to the species level by multiplex PCR. Larvae identified as Trichinella britovi were detected in five stray dogs (1.7%) and one golden jackal (8.3%). The results confirm the circulation of T. britovi in animals of the Khorasan-e-Razavi province, as previously documented. A review of the literature on Trichinella spp. in animals in Iran showed that these parasites were previously detected in 20.02% and 0.04% of carnivore and omnivore mammals, respectively, and that golden jackals can be screened as indicator animals for these zoonotic nematodes. Convenient sampling of Trichinella susceptible roadkill animals may provide a suitable method of monitoring the circulation of these parasites within any given region.