Trichinella nativa and Trichinella T9 in the Hokkaido island, Japan

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 T9 in wild bears in Japan: Prevalence, species/genotype identification, and public health implications

In Japan, the recent series of sporadic outbreaks of human trichinellosis caused by Trichinella (Nematoda: Trichocephalida) has occurred owing to the consumption of raw or insufficiently cooked meat from wild bears. However, the infection status and molecular characteristics of Trichinella larvae in Japanese wild bears remain poorly understood. This study investigated the prevalence of Trichinella spp. in brown bears (Ursus arctos) from Hokkaido, and Japanese black bears (Ursus thibetanus japonicus) from three prefectures (Aomori, Akita, and Iwate) in northern Japan, between April 2019 and August 2022. Trichinella larvae were detected in 2.5% (6/236) of the brown bears and 0.9% (1/117) of the Japanese black bears. Sequence analysis using two genetic loci, the internal transcribed spacer region of nuclear ribosomal DNA and the mitochondrial cytochrome c oxidase subunit I gene, revealed that the larvae collected from the seven infected bears were identical to one of the two haplotypes of Trichinella T9. The prevalence of Trichinella T9 is low but is maintained in bears in the Hokkaido and Iwate prefectures suggesting that undercooked meat from these animals could cause human infection. Thus, continued health education campaigns are needed to raise awareness of the potential risk of trichinellosis among hunters, meat suppliers, consumers, and local governmental health agencies.

Prevalence of Trichinella T9 in Japanese black bears (Ursus thibetanus japonicus) in Iwate prefecture, Japan

Trichinellosis is a meat-borne zoonotic disease caused by nine Trichinella speices and three unclassified genotypes. In Japan, four domestic outbreaks of human trichinellosis are reported sporadically and were associated with the consumption of wild bear meat. This study examined Trichinella prevalence and its species in black bears, Ursus thibetanus japonicus in Iwate prefecture, Japan. Trichinella T9 larvae identified molecularly were first detected in 1.4% (2/144) of the masseters of black bears examined, and their densities were low (1 and 0.3 larvae /g muscle, respectively). Two cytochrome C oxidase I (COI) haplotypes (sequences) of Trichinella T9 were found in distinct bear populations, suggesting that Trichinella T9 populations isolated genetically by bear populations would occur in Japan.

Outbreak of Trichinella T9 Infections Associated with Consumption of Bear Meat, Japan

An outbreak of trichinellosis occurred in Japan in December 2016. All case-patients had eaten undercooked bear meat, from which Trichinella larvae were subsequently isolated. DNA sequencing analysis of the mitochondrial genes cytochrome c-oxidase subunit 1 and internal transcribed spacer 2 confirmed that Trichinella T9 had caused the outbreak.

Present status of trichinellosis - a neglected zoonosis in India

Trichinellosis is a meat-borne helminthic zoonosis, caused by different species of the genus Trichinella. The disease is cosmopolitan in distribution and affects around 10,000 people annually around the globe. Based on genetic, biochemical and biological variability, 9 valid species (T. britovi, T. murrelli, T. nativa, T. nelsoni, T. papuae, T. patagoniensis, T. pseudospiralis, T. spiralis and T. zimbabwensis) and 3 genotypes (Trichinella T6, T8 and T9) of the parasite have been recognized. These species infect around 100 mammalian species including domestic and wild pigs, horses, game animals and wild carnivores. The infection starts with consumption of raw or undercooked meat or meat products containing encysted muscle larvae of the parasite. Most of the infections or outbreaks have been associated with the consumption of meat or meat products of pigs, wild boars, horses, crocodiles, walruses and dogs. Trichinoscopy is used in the veterinary inspection of pork in slaughterhouses and meat-packing facilities in many countries. It is a rapid process, but low in sensitivity and fails to detect mild infection. The muscle digestion method using HCl-pepsin is more sensitive and thus preferred. Recent outbreak of trichinellosis in Uttarakhand state opened up issues related to rapid diagnosis and lack of consumer awareness regarding safe cooking habits of meat of pig origin. This status report is an attempt to compile the information on Trichinella spp. infection in animals and humans in India at one place to draw the attention of medical and veterinary personnels involved in disease investigation and active research on zoonotic diseases.

Molecular identification and phylogenetic analysis of Trichinella isolates from different provinces in mainland China

Polymerase chain reaction (PCR) and sequencing are useful for species identification of Trichinella spp., especially when their morphological characteristics useful for identifying taxa are lacking. In the present study, nine Trichinella isolates from different provinces in mainland China were identified by the PCR-based method using the 5S ribosomal DNA intergene spacer region (5S ISR) and the mitochondrial large subunit ribosomal DNA genes as molecular markers. The results indicated that eight isolates originating from domestic pigs and one isolate originating from civet cat (Paguma larvata) showed identical DNA banding pattern to Trichinella spiralis. Sequence analysis of the 5S ISR gene further confirmed that the nine Trichinella isolates were T. spiralis and revealed the intraspecies genetic variation within T. spiralis.

World distribution of Trichinella spp. infections in animals and humans

The etiological agents of human trichinellosis show virtually worldwide distribution in domestic and/or wild animals, with the exception of Antarctica, where the presence of the parasite has not been reported. This global distribution of Trichinella and varying cultural eating habits represent the main factors favouring human infections in industrialised and non-industrialised countries. Human trichinellosis has been documented in 55 (27.8%) countries around the world. In several of these countries, however, trichinellosis affects only ethnic minorities and tourists because the native inhabitants do not consume uncooked meat or meat of some animal species. Trichinella sp. infection has been documented in domestic animals (mainly pigs) and in wildlife of 43 (21.9%) and 66 (33.3%) countries, respectively. Of the 198 countries of the world, approximately 40 (20%) are small islands far from the major continents, or city-states where Trichinella sp. cannot circulate among animals for lack of local fauna (both domestic and wild). Finally, information on the occurrence of Trichinella sp. infection in domestic and/or wildlife is still lacking for 92 countries.

Epidemiology, histopathology, and muscle distribution of Trichinella T9 in feral raccoons (Procyon lotor) and wildlife of Japan

The prevalences of Trichinella T9 in trapped raccoons (Procyon lotor) and several other potential mammalian reservoirs in Hokkaido, Wakayama, and Nagasaki Prefectures were investigated. Muscle samples were collected from 2003 to 2006 from 1,080 raccoons, 113 raccoon dogs including 2 species (Nyctereutes procyonoides albus and N. p. viverrinus), 41 wild boars (Sus scrofa leucomystax), 14 martens (Martes melampus), 10 badgers (Meles meles), 5 Siberian weasels (Martes sibirica coreana), 7 mink (Mustela vison), and 1 red fox (Vulpes vulpes japonica). The samples were digested, and the prevalence and mean intensity of infection with the Trichinella muscle larvae were determined. The prevalence and intensity of the muscle larvae were 0.9% and 93.3 larvae/g (range 0.4-201.8) in raccoons, and 1.6% and 61.6 larvae/g in raccoon dogs, respectively. The infected animals were captured in different areas in Hokkaido Prefecture. These results confirmed that raccoons, which have been introduced from North America since the 1970s, are involved in the sylvatic cycle of Trichinella in Japan. In raccoons, the muscle density of Trichinella T9 larvae was highest in the tongue, and larvae were not found in the heart muscle or diaphragm. This is the first report of Trichinella T9 infection of feral raccoons in Japan.