A cluster of three cases of trichinellosis linked to bear meat consumption in the Arctic

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.

Zoonotic helminths - why the challenge remains

Helminth zoonoses remain a global problem to public health and the economy of many countries. Polymerase chain reaction-based techniques and sequencing have resolved many taxonomic issues and are now essential to understanding the epidemiology of helminth zoonotic infections and the ecology of the causative agents. This is clearly demonstrated from research on Echinococcus (echinococcosis) and Trichinella (trichinosis). Unfortunately, a variety of anthropogenic factors are worsening the problems caused by helminth zoonoses. These include cultural factors, urbanization and climate change. Wildlife plays an increasingly important role in the maintenance of many helminth zoonoses making surveillance and control increasingly difficult. The emergence or re-emergence of helminth zoonoses such as Ancylostoma ceylanicum, Toxocara, Dracunculus and Thelazia exacerbate an already discouraging scenario compounding the control of a group of long neglected diseases.

Wildmeat consumption and zoonotic spillover: contextualising disease emergence and policy responses

Zoonotic diseases are estimated to constitute 75% of all emerging infectious diseases, of which more than 70% come from wild species. The potential threat of zoonotic spillover from the consumption of wildmeat has been the subject of policy and media attention, especially in the context of the COVID-19 pandemic; however, little is known about the actual conditions that contribute to the risk of spillover and associated disease transmission. In this Review, we compile existing evidence from available literature on the conditions of spillover associated with wildmeat consumption, including the types of wild animal and disease, modes of transmission, and the conditions in which spillover is thought to have occurred. We suggest that stronger understanding of the context of spillover from wildmeat is needed to enable more targeted and effective policy responses that reduce the risk of future pandemics of zoonotic origin. Such interventions could also lead to the avoidance of unintended adverse consequences for human communities that rely on wild produce, including wildmeat, as sources of dietary protein, fat, and micronutrients.

A common source for a trichinellosis outbreak reported in France and Serbia in 2017

Trichinellosis is a rare parasitic zoonosis in the European Union. Meat from backyard pigs was the common source for a trichinellosis outbreak caused by Trichinella spiralis, which occurred in France and Serbia in the beginning of 2017. An epidemiological study was conducted in France and Serbia to determine the extent of the outbreak, to identify its source and to implement control measures. Three cases were exposed in Serbia and brought back to France pork delicatessen which they shared with relatives and friends. Around 47 individuals were exposed to the parasitised meat in France and Serbia and 20 cases of trichinellosis were reported (nine in France and 11 in Serbia). Nine of them were female. The diagnosis was delayed, in part because the parasitosis was not known by most physicians, which led to complications in the French cases such as facial paralysis and pulmonary embolism. Health alerts and survey networks are indispensable at a European level to control the disease.

Culture, eating behavior, and infectious disease control and prevention

Humans need to obtain nutrients from foods for survival and health. Culture and belief play important roles in food selection and intake. Throughout human history, dietary factor has been one of the important factors inducing and causing outbreaks of infectious diseases. If unhealthy eating behavior, like eating raw/undercooked food or meat and products from wild animals, are not abandoned, foodborne infectious diseases will remain an important risk factor of outbreaks and epidemics. The misconception of dietary culture is one of the important factors that triggers unhealthy eating behavior. Therefore, it is vital to change people’s conceptions and knowledge about what is healthy to eat, in order to completely eliminate unhealthy eating behavior and prevent the recurrence of foodborne infectious diseases. Meanwhile, many factors such as family, society, region, and religion should be involved in.

Differentiation of Trichinella species (Trichinella spiralis/Trichinella britovi versus Trichinella pseudospiralis) using western blot

BACKGROUND

Trichinellosis is a meat-borne zoonotic disease caused by parasites of the genus Trichinella. To date, 12 taxa have been described. The identification of Trichinella species is crucial in order to identify the possible source of infection, the geographical origin of the parasite and to assess risk of infection for domestic pigs and humans. Specific identification of the etiological agent is not always feasible using direct methods since the source of infection can be untraceable. The aim of this study was to develop a diagnostic tool to infer the causative Trichinella species using western blot patterns of sera derived from infected animal and human hosts.

METHODS

Sera from mice experimentally infected with Trichinella spiralis, Trichinella britovi, Trichinella pseudospiralis and Trichinella papuae were tested by western blot using homologous and heterologous crude worm extracts (CWE) and a highly sensitive detection system based on chemiluminescence. In addition, sera from pigs experimentally infected with T. spiralis, T. britovi and T. pseudospiralis and from patients with confirmed T. spiralis, T. britovi and T. pseudospiralis infections, were also included.

RESULTS

Sera from mice infected with one Trichinella species reacted with CWE proteins from all four investigated species. Likewise, sera derived from pigs and humans infected with one Trichinella species reacted with CWE proteins from all the three investigated species. Using T. spiralis CWE, sera from T. pseudospiralis-infected hosts yielded a characteristic pattern of reactivity using Wb, which differed to that produced by T. spiralis/T. britovi- or T. papuae-infected host sera.

CONCLUSIONS

The present study suggests that western blot using T. spiralis CWE may be a useful tool to distinguish Trichinella infections caused by T. pseudospiralis from those caused by T. spiralis or T. britovi. This method may support epidemiological investigations, particularly when the source of infection is not traceable.

Trichinella and polar bears: a limited risk for humans

In this review, we identified 63 cases reported since World War II of human trichinellosis linked to the consumption of parasitized polar bear (Ursus maritimus) meat. This low number contrasts to the numerous cases of human trichinellosis related to consumption of the meat of black (U. americanus) or brown bears (U. arctos). The prevalence of Trichinella infection is high in bears, but larval muscular burden is usually lower in polar bears compared to other bear species. Polar bears, therefore, seem to play a limited role in the transmission of trichinellosis to humans, as native residents living in the Arctic traditionally consume well-cooked bear meat, and travellers and foreign hunters have only limited access to this protected species due to the declining polar bear population.