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

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.

Is golden jackal (Canis aureus) the most important indicator species of Trichinella infection in Croatia?

Epidemiologic monitoring of wild animals is always an important step in defining potential zoonoses that can threaten humans. Particular emphasis should be given to those zoonotic agents permanently cycling within wild animal populations and represent a permanent reservoir for other wild or domesticated animals that can be direct sources of disease for humans. In Croatia, there are two European jackal populations: the Dalmatian population (DP) that has been inhabiting the islands and coastal area along the Adriatic Sea since medieval times, and the South East European population (SEEP) that is found in continental Croatia. Research on Trichinella infections in jackal populations in Croatia was conducted from 2008 to 2022. During this 15-year period, we tested 186 jackal samples and confirmed infection in 47 individuals (25.3 %). The dominant species was T. spiralis, identified in 28 samples (60 %), T. britovi was found in 13 samples (28 %), while for six samples (12 %) the PCR test was unsuccessful. In both populations, the Trichinella species of the domestic cycle (T. spiralis) was found, though in varying ratios: in DP the ratio of identified species was 10:6 in favour of T. britovi, as opposed to 22:3 in favour of T. spiralis in SEEP. The frequency of infection with parasites from the genus Trichinella was significantly different in DP (22.9 %) than in SEEP (26.7 %) (p<0.001), while the larval count in analysed tissue did not differ by type of Trichinella species (p=0.1028). Infected jackals were found in nine of ten tested counties. The results were analysed statistically and the origin of tested and positive samples shown on a map of Croatia. Based on these findings, both jackal populations can be considered to represent an exceptionally important indicators of parasites from the genus Trichinella in Croatia, both for the sylvatic and domestic cycles. There is an evident need for epidemiological monitoring for members of both populations.

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.

A Large-Scale Outbreak of Trichinellosis from Infected Wild Boar Meat in Croatia and the Role of Real-Time PCR Assays in Confirming the Source of the Disease

BACKGROUND

Trichinellosis in Croatia posed a significant health concern during the 1990s, followed by a notable improvement in the epidemiological situation. However, in 2017, there was a resurgence, with 37 recorded cases in 3 outbreaks and 3 sporadic cases. The source of this epidemic was homemade meat products derived from wild boar meat, leading to 26 infections.

METHODS

At the beginning of the outbreak and during the treatment of the patients, the medical and epidemiological records prepared throughout the investigation and over the course of patient treatment were reviewed. The recovery of the first-stage (L1) larvae from suspect meat products was achieved by artificial digestion. The molecular identification of the isolated larvae was performed by multiplex PCR. The molecular identification of the meat used to prepare the meat products was performed by real-time PCR assays.

RESULTS

The epidemic started in early 2017. In total, 71 exposed persons were documented: 26 with clinical symptoms and 3 hospitalised in two cities in different counties. The L1 burden in three different meat products was from 5.25 to 7.08 larvae per gram (LPG), and T. spiralis was determined as the aetiological agent of the outbreak. The molecular and biological identification confirmed that implicated meat products were made solely from wild boar meat.

CONCLUSIONS

Although trichinellosis is no longer a frequent occurrence in Croatia, several cases are still registered nearly every year. Wild boar meat poses an important risk factor for human health if compulsory testing is not conducted before consumption, especially if the meat products are consumed without proper thermal processing.

Eleven Years of Health Monitoring in Wild Boars (Sus scrofa) in the Emilia-Romagna Region (Italy)

In recent years, the growth of wild ungulates has increased the focus on their health monitoring. In particular, the health status of wild boars is relevant for the economic impact on the pig industry. The Emilia-Romagna region activated a wildlife monitoring plan to better evaluate the health status of the wild boar population. Between 2011 and 2021, samples of found dead and hunted wild boar have been examined for trichinellosis, tuberculosis, brucellosis, african swine fever, classical swine fever, Aujeszky's disease, swine vesicular disease, and swine influenza A. Trichinella britovi was identified in 0.001% of the examined wild boars; neither M. bovis nor M. tuberculosis were found in M. tuberculosis complex positive samples; 2.3% were positive for Brucella suis; 29.4% of the sera were positive for Aujeszky's disease virus; and 0.9% of the samples were positive for swine influenza A virus. With an uncertain population estimate, the number of animals tested, the number of positives, and the sampling method do not allow us to make many inferences but suggest the need to implement and strengthen the existing surveillance activity, as it seems to be the only viable alternative for safeguarding animal and human health.

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.

Investigation of the Food-Transmitted Parasites Trichinella spp. and Alaria spp. in Wild Boars in Greece by Classical and Molecular Methods and Development of a Novel Real-Time PCR for Alaria spp. Detection

Simple Summary

There are many parasites that may be transmitted to humans via food, and meat is a major source of such infections. Trichinella spp. is one of the most important meat-transmitted parasites, while Alaria spp. may be considered an emerging pathogen, albeit to date rarely reported in humans. Raw and undercooked wild boar meat has been proven as a major source of human infection by both parasites. In the present study, an investigation of the presence of these parasites in wild boar meat was conducted for the first time in Greece. Classical parasitological methods and molecular techniques were implemented for the examination of samples collected from 128 hunted wild boars, and none of them were found positive for Trichinella spp. or Alaria spp. For the detection of Alaria spp., a novel molecular method was developed, offering a powerful complementary diagnostic tool that may be useful for the epizootiological surveillance of the parasite. The epizootiology/epidemiology, clinical implications, and importance of monitoring of these parasitic infections are briefly discussed.

Abstract

Foodborne parasitic diseases represent a major threat to public health. Trichinellosis, caused by the nematode parasite Trichinella spp., is one of the most important foodborne diseases, while alariosis, caused by the trematode parasite Alaria spp., is less common in humans, and rare cases have been reported only in the USA and Canada. Both parasites can infect humans via the consumption of raw or undercooked wild boar meat. In order to investigate the prevalence of these parasites in wild boar meat in Greece, samples from the diaphragm pillars and the region of the mandibular angle from 128 wild boars, hunted in Greece, were collected. The samples were examined by classical parasitological (compression, artificial digestion, and Alaria spp. migration) and by molecular (real-time PCR) methods. For Trichinella spp. an existent real-time PCR detecting all species likely to be present in Greece was applied, while for Alaria spp. a real-time PCR was developed, employing an LNA TaqMan probe targeting the large subunit ribosomal RNA gene. All examined wild boar samples from Greece resulted negative for Trichinella and Alaria species, indicating a low prevalence of infection in the examined population. The novel real-time PCR for Alaria spp. has 81.5% amplification efficiency and is able to detect 0.12 larvae per 50 g of tissue and could be utilized as a complementary to AMT diagnostic tool in surveillance.