Horse trichinellosis, an unresolved puzzle

Horsemeat consumption in France: Determinants and sustainable market perspectives

In France, the horsemeat market has been declining for about 50 years and has become a specialized market. Our study aims to understand this decline with regard to the drivers and practices of consumers and non-consumers of this meat, in order to estimate the potential for this market development. To study horsemeat consumption, we analyze two sets of data: two large-scale surveys carried out on the French general population, and one ad-hoc survey focusing more specifically on the representations of horses and horsemeat. Our results underline the potential for increasing horsemeat consumption from a sustainability perspective. The question of moral acceptance remains a determining factor in the consumption of this meat. Once this factor is taken into account, horsemeat appears relevant in the diversification of animal protein consumption because of its particular nutritional and environmental properties and similar culinary use to that of other red meats. Horsemeat can thus lay claim to becoming a sustainable alternative to beef consumption.

Validation Parameters of the Magnetic Stirrer Method for Pooled Sample Digestion for Trichinella spp. in Horse Meat Based on Proficiency Tests Results

Meat of horses may be infested with nematodes of the genus Trichinella spp. and can cause serious disease in humans. Rules for the carcasses sampling of species susceptible to Trichinella spp. infection and examination are laid down in Commission Regulation 1375/2015, where the magnetic stirrer method for pooled-sample digestion is recommended (Commission Regulation 1478/2020). All personnel involved in the examination should be properly trained and participate in quality control programs. Proficiency tests (PTs) play a key role in the quality verification process. This paper presents the results of PTs organized for 68 Polish laboratories in 2014-2019. Results were assessed qualitatively at three levels of sample contamination (0, 3, 5 larvae) and quantitatively at one level (5 larvae). The laboratories have achieved the average correct qualitative results 100%, 96.2% and 96.8% for the samples contaminated with 0, 3 and 5 larvae, respectively. In the quantitative evaluation, an average 94.1% of the reported results were correct. The data from PTs enabled us to define, for the first time, validation parameters of the digestion method for the horse meat matrix in a large-scale experiment including: specificity (100%), sensitivity (95.6%), accuracy (97.1%), the limit of detection (LOD) (1.14 ≈ 1) and the limit of quantification (LOQ) (3.42 ≈ 3).

Zoonotic Diseases from Horses: A Systematic Review

Background: Worldwide, horses play critical roles in recreation, food production, transportation, and as working animals. Horses' roles differ by geographical region and the socioeconomic status of the people, but despite modern advances in transportation, which have in some ways altered humans contact with horses, potential risks for equine zoonotic pathogen transmission to humans occur globally. While previous reports have focused upon individual or groups of equine pathogens, to our knowledge, a systematic review of equine zoonoses has never been performed. Methods: Using PRISMA's systematic review guidelines, we searched the English literature and identified 233 previous reports of potential equine zoonoses found in horses. We studied and summarized their findings with a goal of identifying risk factors that favor disease transmission from horses to humans. Results: These previous reports identified 56 zoonotic pathogens that have been found in horses. Of the 233 articles, 13 involved direct transmission to humans (5.6%).The main potential routes of transmission included oral, inhalation, and cutaneous exposures. Pathogens most often manifest in humans through systemic, gastrointestinal, and dermatological signs and symptoms. Furthermore, 16.1% were classified as emerging infectious diseases and thus may be less known to both the equine and human medical community. Sometimes, these infections were severe leading to human and equine death. Conclusions: While case reports of zoonotic infections directly from horses remain low, there is a high potential for underreporting due to lack of knowledge among health professionals. Awareness of these zoonotic pathogens, their disease presentation in horses and humans, and their associated risk factors for cross-species infection are important to public health officials, clinicians, and people with recreational or occupational equid exposure.

International Commission on Trichinellosis: Recommendations on post-harvest control of Trichinella in food animals

Domestic and wild animals which consume meat are at risk of becoming infected with Trichinella and therefore may pose a public health risk. Among domestic livestock, pigs are most commonly associated with Trichinella infection, but human outbreaks have also resulted from consumption of horsemeat, wild boar, bear, walrus and other wild animals. For animals that are not produced under controlled management conditions and for wild animals, specific steps should be taken to prevent human exposure to Trichinella. These steps include appropriate testing of individual carcasses to identify those that pose a public health risk, post-slaughter processing to inactivate Trichinella in meat that might be infected, and education of consumers regarding the need for proper preparation methods for meat that might contain Trichinella larvae. The International Commission on Trichinellosis recognizes three (3) acceptable means of treatment to render potentially Trichinella-infected meats safe for consumption: 1) cooking, 2) freezing (for meat from domestic pigs), and 3) irradiation. Proper use of these methods is described here, along with specific cautions on use of other methods, including curing and heating with microwaves.

Detection of natural Trichinella murrelli and Trichinella spiralis infections in horses by routine post-slaughter food safety testing

Trichinella spiralis typically infects domestic swine, wild boar and occasionally horses, has a cosmopolitan distribution, and consequently is most frequently associated with food-borne outbreaks of trichinellosis in humans. Trichinella murrelli is typically found in wild carnivores in temperate areas of North America, where it has been responsible for outbreaks of human trichinellosis due to consumption of infected wild game. There has previously been only indirect evidence of natural infection with T. murrelli in a horse originating from Connecticut and implicated in an outbreak of trichinellosis in France in 1985. We describe a T. murrelli infection detected during routine testing of a horse from the USA imported to Canada for slaughter and export to the European Union (EU). Approximately 5 or more larvae per gram were recovered from digested tongue and diaphragm samples and identified as T. murrelli by PCR. This case provides the first direct evidence of naturally acquired T. murrelli infection in a horse, and further supports the potential food safety risk posed by this parasite species. It is the first instance in Canada of the detection of a Trichinella-infected horse via routine post-mortem testing. Trichinella spiralis-infected horses have been similarly detected by regulatory testing in France, and further details of two such previously reported cases are also provided here. The cases described herein underscore the importance of continued vigilance in quality assured food safety testing of horse meat to mitigate the risk of human trichinellosis.

Trichinella spp. imported with live animals and meat

Nematodes of the genus Trichinella are widely distributed throughout the world in omnivorous and carnivorous animals (mammals, birds, and reptiles) and in incidental hosts. To prevent the transmission of these zoonotic parasites to humans, meat samples from Trichinella spp. susceptible animals are tested at the slaughterhouse or in game processing plants. The aim of the present review was to collect documented cases on Trichinella infected animals, meat, or meat derived products which reached the international trade or were illegally introduced from one to another country in personal baggage. In the course of the last 60 years in the international literature, there have been 43 reports of importation of Trichinella spp. infected animals or meat, most of which (60%, 26/43) related to live horses or their meat. Meat or meat derived products from pigs, wild boar and bears, account only for 18.6% (8/43), 4.7% (3/43), and 14.3% (6/43), respectively. However, only live horses or their meat intended for human consumption, meat from a single wild boar, and live polar bears caught in the wild for zoos, were imported through the international market; whereas, meat from pigs, wild boars and bears were illegally introduced in a country in personal baggage. Trichinella infected animals or meat which were officially or illegally introduced in a country were the source of 3443 Trichinella infections in humans in a 40-year period (1975-2014). Most of these infections (96.8%) have been linked to horsemeat consumption, whereas meat from pigs, wild boars and bears accounted only for 2.2%, 0.7% and 0.3% of cases, respectively. This review shows the Trichinella spp. risk in the international animal and meat trade has been linked mainly to horses and only one time to wild boar, if they carcasses are not adequately tested, whereas pigs and other wild animals or their derived products infected with Trichinella spp. are unlikely to reach the international market by the official animal and meat trade.

Epidemiology of trichinellosis in Germany, 1996-2006

The epidemiology of trichinellosis in Germany was investigated by analyzing national surveillance data from 1996-2006. During this period, 95 laboratory-confirmed infections and 12 outbreaks were reported. The highest mean annual incidence was found in immigrants from southeast European countries (0.3 cases/100,000 vs. 0.01 cases/100,000 in the German population) with an incidence rate ratio of 26.0 (95% confidence interval 11.6-51.8). The predominant clinical symptom was muscle pain in 79 patients (83%). Mean diagnostic delay was 49 days. Among patients with reported source of infection (85%; n = 81), the consumption of pork (mostly originating from endemic countries) represented the most frequent exposure (93%; n = 75). In addition, trichinellosis cases were associated with both indigenous (n = 1) and imported (n = 5) wild boar meat. Although domestic pigs in Germany are practically free from Trichinella spp., the parasite was found in German wild animals such as wild boars, foxes, and racoon dogs. We conclude that trichinellosis still remains a public health issue in Germany, especially among individuals with a migrational background. Immigrants from endemic countries need to be educated about the risks of consuming raw or inadequately cooked pork and wild boar products from their homeland. In addition, German healthcare providers need to be aware of trichinellosis, especially in areas with a large immigrant population.

Presidential address of ICT12 Conference: "Trichinella and trichinellosis--a never ending story"

Trichinellosis remains an important zoonotic disease on a global basis, related primarily to the consumption of pork as well as variety of wild life species and horsemeat. This disease is still present in eastern Europe, China, and Argentina, and huge outbreaks have emerged in Turkey and Laos. Many advances have been made in the understanding and the prevention of the parasite and the disease. New proteins interfering with the cell cycle and maintaining the nurse cell have been identified. Trichinella is a fascinating model for immunologists and biochemists: description of new mediators, chromosomal mapping of host resistance, antibodies recognising heart-specific antigens and inducing myocarditis, identification of early stage antigens, alleviation of respiratory flu infection or of autoimmune diabetes in mice. New regulations for meat inspection and efficient quality control programs have been discussed and implemented. The members of the International Commission on Trichinellosis regularly convene to discuss the latest scientific issues dealing with this parasitic zoonosis.

Larval viability and serological response in horses with long-term Trichinella spiralis infection

The horse is considered an aberrant host for the nematode parasite Trichinella spiralis, and many aspects of the biology and epidemiology of Trichinella infection in the horse are poorly understood. It has been reported that experimentally-infected horses produce a transient serological response to infection and that muscle larvae are cleared more rapidly than in parasite-adapted hosts such as the pig and humans. However, limited numbers of animals have been studied, and both the longevity of larvae in horse musculature and the immune response to Trichinella larvae remain unclear. In this study, we infected 35 horses with 1000, 5000, or 10,000 T. spiralis muscle larvae and followed the course of infection for 1 year, assessing larval burdens in selected muscles, the condition and infectivity of recovered larvae, and the serological response of infected horses. The results demonstrated that T. spiralis establishes infection in horses in a dose dependent manner. Anti-Trichinella IgG antibodies peaked between weeks 6-10 post-inoculation. Viable, infective larvae persisted in horse musculature for the duration of the study (12 months), and exhibited no apparent reduction in muscle burdens over this period. Encapsulated larvae showed no obvious signs of degeneration in histological sections. Larval capsules were surrounded by infiltrates consisting of mature plasma cells and eosinophils. Macrophages were notably absent. Given the lack of a detectable serological response by 26 weeks p.i. and the persistence of infective muscle larvae for at least 1 year, parasite recovery methods are currently the only suitable detection assays for both meat inspection and epidemiological studies of Trichinella infection in the horse.

Viability and infectivity of Trichinella spiralis muscle larvae in frozen horse tissue

Many aspects of the biology and epidemiology of Trichinella infection in the horse are poorly understood, including survival of Trichinella spp in horse muscle. In this study, we have assessed the freeze tolerance of T. spiralis in horse meat stored at 5, -5, and -18 degrees C for 1 day to 24 weeks. Results demonstrate a steady reduction in the number of live ML recovered from the cold stored meat samples. On Day 1, recovery of live larvae had been reduced by 18.6%, 50.1%, and 37.2%, and by 4 weeks, recovery of larvae had been reduced by 65.4%, 66.5%, and 96.2% in samples stored at 5, -5, and -18 degrees C, respectively. Infectivity results (measured as reproductive capacity index (RCI)) from mice inoculated with larvae recovered from non-frozen meat samples at day 0 was 23.5. Following storage at -18 degrees C for one and two days, the RCIs were 2.09 and 0.99, respectively. Small numbers of infective larvae were still present in meat samples stored at -18 degrees C for 4 weeks. The RCI of ML recovered from meat samples stored at -5 degrees C was 14.99 and 6.36 at 2 weeks and 4 weeks respectively; the RCI of samples stored at 5 degrees C was 23.1 at 8 weeks, and fell rapidly thereafter (12 week RCI 1.33; 0 at 24 weeks). These data demonstrate that infective T. spiralis, a non-freeze tolerant species, can survive for at least 4 weeks in horse tissue frozen at -5 or -18 degrees C, and that the numbers of infective larvae decrease substantially by day 2 at -18 degrees C and by week 4 at -5 degrees C.

Systematics and epidemiology of trichinella

In this review, we describe the current knowledge on the systematics, ecology and epidemiology of Trichinella and trichinellosis, and the impact of recent research discoveries on the understanding of this zoonosis. The epidemiology of this zoonosis has experienced important changes over the past two decades, especially with regard to the importance of the sylvatic cycle and the sylvatic species. Outbreaks of trichinellosis due to Trichinella spiralis from domestic swine, while still frequent, increasingly are caused by other Trichinella spp. infecting hosts such as horses, dogs, wild boars, bears and walruses. The latter revelations have occurred as a result of a series of discoveries on the systematics of Trichinella spp., facilitated by new molecular tools. As a consequence, the genus is now composed of two clades, an encapsulated group (five species and three genotypes) and a non-encapsulated one (three species). This has sparked renewed investigations on the host range of these parasites and their epidemiological features. Most dramatic, perhaps, is the recognition that reptiles may also serve as hosts for certain species. This new knowledge base, in addition to having an important relevance for food safety policies and protection measures, is raising important questions on the phylogeny of Trichinella spp., the ecological characteristics of the species and their geographic histories. Answers to these questions may have great value for the understanding of the evolutionary biology for other parasitic helminths, and may increase the value of this genus as models for research on parasitism in general.

Recent advances on the taxonomy, systematics and epidemiology of Trichinella

Since Owen first described Trichinella as a human pathogen in 1835, the number of organisms comprising this genus has grown dramatically. Where it was once thought to be a monospecific group, this genus is now comprised of eight species and three additional genotypic variants that have yet to be taxonomically defined. Along with the growth in the genus and description of the parasites has come a concomitant increase in our understanding of the epidemiology and geographical distribution of these organisms. Recent expansion of the non-encapsulated group to include three species biologically defined by their unique host ranges encompassing mammals, birds and reptiles, has raised substantial questions as to the term, 'Trichinella-free' as it applies to geographical localities. A true appreciation of the adaptability of this genus to host and environmental selection factors, as well as its dissemination to the far reaches of the world can best be appreciated by reviewing what we know and what we hope to know about this ancient and elusive parasite. The review herein consolidates our current understanding of the taxonomy, epidemiology, and phylogeny of the genus Trichinella, and identifies areas where data are lacking and our knowledge requires additional clarification.

Re-emergence of trichinellosis in southeastern Europe due to political and economic changes

The countries of southeastern Europe including the Balkan region and bordering countries - Albania, Bulgaria, Bosnia and Herzegovina, Croatia, Greece, Hungary, Macedonia, Romania, Serbia and Montenegro, Slovenia, and the European part of Turkey - occupy a very important strategic position and represent a land bridge between Europe and Asia. In the majority of southeastern European countries, cases of trichinellosis among the human and animal populations were described in the late 19th or early 20th centuries. Trichinella infections among wildlife were also described in the aforementioned countries. Today, the prevalence of trichinellosis is different between the Balkans and bordering countries. A high prevalence of trichinellosis in domestic animals and humans has been reported in Bulgaria, Serbia and Montenegro, Romania and Croatia. A moderate prevalence was found in Bosnia and Herzegovina. In Hungary, human trichinellosis has not been present for a long period of time. However, sporadic cases were recorded in swine over the last 2 years. Trichinellosis has not been found among domestic animals and humans in Greece and Macedonia in recent years while in Turkey and Slovenia human trichinellosis is sporadic. The re-emergence of trichinellosis is connected with the changes in the social and political systems in Bulgaria and Romania. In Serbia and Montenegro as well in Croatia, however, a re-emergence of trichinellosis was due not only to political and social changes but also to wars that took place in these countries during the last years of the 20th century. Social, economic and political factors responsible for the re-emergence of trichinellosis in southeast European countries are discussed in this communication.

Epidemiology of Trichinella infection in the horse: the risk from animal product feeding practices

A discovery in 2002 of a Trichinella spiralis-infected horse in Serbia offered an opportunity to conduct needed epidemiological studies on how horses, considered herbivores, acquire a meat-borne parasite. This enigma has persisted since the first human outbreaks from infected horse meat occurred in then 1970s. The trace back of the infected horse to a farm owner was carried out. Interviews and investigations on the farm led to the conclusion that the owner had fed the horse food waste in order to condition the horse prior to sale. Further investigations were then carried out to determine the frequency of such practices among horse owners. Based on interviews of horse producers at local horse markets, it was revealed that the feeding of animal products to horses was a common practice. Further, it was alleged that many horses, particularly those in poor nutritional condition would readily consume meat. A subsequent series of trials involving the experimental feeding of 219 horses demonstrated that 32% would consume meat patties. To confirm that horses would eat infected meat under normal farm conditions, three horses were offered infected ground pork balls containing 1100 larvae. All three became infected, and at necropsy at 32 weeks later, were still positive by indirect IFA testing, but not by ELISA using an excretory-secretory (ES) antigen. This result indicates that further study is needed on the nature of the antigen(s) used for potential serological monitoring and surveillance of horse trichinellosis, especially the importance of antigenic diversity. The experimentally-infected horses also had very low infection levels (larvae per gram of muscle) at 32 weeks of infection, and although the public health consequences are unknown, the question of whether current recommended inspection procedures based on pepsin digestion of selected muscle samples require sufficient quantities of muscle should be addressed. It is concluded that horses are more willing to consume meat than realized and that the intentional feeding of animal products and kitchen waste is a common occurrence among horse owners in Serbia (and elsewhere?). This is a high risk practice which demands closer scrutiny by veterinary and food safety authorities, including the implementation of rules and procedures to ensure that such feeds are rendered safe for horses, as is now required for feeding to swine.

Social, political, and economic factors responsible for the reemergence of trichinellosis in Serbia: a case study

Over the past decade, eastern Europe has experienced a resurgence of trichinellosis. A recent outbreak in Serbia, Yugoslavia, from December 2001 to January 2002, involving 309 people, revealed many of the causes for this reemergence. Epidemiological investigations indicate that the immediate cause of the recent outbreak was the consumption of smoked sausages produced by a small slaughterhouse or meat processor. However, failure of in-house meat inspection procedures and quality assurance as well as oversight by official veterinary control were also responsible. Further analysis of this breakdown in the food safety net revealed additional general factors that have yielded a seriously deficient veterinary control system, and these are factors that are relevant to the problems experienced throughout eastern Europe and other regions. The recent civil war that led to the breakup of the former Federation of Yugoslavia resulted in severe economic and demographic changes, including high inflation and external economic sanctions. This led to (1) the loss of large numbers of experienced veterinary control officers and their replacement with inexperienced personnel, (2) a change in the swine industry with reduction in the number of large establishments with in-house inspection and replacement with more than 1,000 small abattoirs, too small to afford full-time in-house inspection, and (3) an increase in smallholder pig farming with reduced government oversight to ensure high standards in pig-rearing practices (infection risk management). The consequences of these events have been a 300% increase in Serbian pig infection and a concomittant large increase in human outbreaks. Before 1990, swine trichinellosis in Serbia was confined to 4 small districts, but today about one third of the Republic is considered endemic for trichinellosis. The reemergence of trichinellosis in Serbia illustrates the ability of this zoonosis to "leak" through a poorly maintained food safety barrier and the vulnerability of effective veterinary control to national and international events.

Persistence of Trichinella spiralis in rat carcasses experimentally mixed in different feed

Trichinella spiralis infected rat carcasses were incubated for 6 weeks in several animal feeds to assess how long Trichinella can present a risk for an outbreak in contaminated feeds. In groups of 6, 24 infected target rats were placed in silage, grained barley, propionic acid-preserved feed, and also into simulated pasture conditions. Test environments were sampled after one-, 2-, 4-, and 6-week-incubations. Trichinella larvae were recovered by digestion, and their infectivity was evaluated in rats. A two-week incubation reduced the number of recovered larvae, but still after 6 weeks low numbers were isolated from all feeds except from the experimental group simulating pasture conditions. After 2 weeks storage, the larvae were infective in all storage environments. However, up to 4 weeks, they survived only in the propionic acid-fermented feed and there in small numbers with reduced reproductive capability. This indicates the possibility of farm animals to get infection from rats or other infected material being hazardously mixed with hay or other feed. If silage is stored for at least one month before use, however, the risk from this forage appears to be minimized.