Trichinosis revisited — Another look at modes of transmission

A review of Trichinella species infection in wild animals in Romania

Nematodes of the genus Trichinella are important zoonotic parasites present throughout Romania. This study aimed to assess the status of Trichinella species in wild animals in Romania over the past 30 years. A literature review of original studies concerning the only two species (out of the four in Europe) of Trichinella (T. spiralis and T. britovi) confirmed in wildlife from Romania was conducted and corroborated with the results of our original research concerning the topic. This review article has shown that, in Romania, European minks were infected with T. spiralis, while wolves, European wild cats, Eurasian lynx, golden jackals, stone marten, and European badgers were infected with T. britovi, respectively. Both Trichinella species have been identified in foxes, bears, wild boars, and ermines, but mixed infections have been found only in European polecats. Trichinella infection is still significantly present in Romania, infecting several wild omnivorous and carnivorous species in an equal manner, with different prevalence rates over the years. Regarding the spatial distribution of T. spiralis and T. britovi in Romania, both species can be found all over the country, but in wild animals, T. britovi is the most prevalent.

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Trichinella spiralis and T. britovi have been confirmed in wild animals in Romania.

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The highest prevalence rates for Trichinella spp. have been found in wolves, bears, and foxes.

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Similar prevalence rates have been identified for T. britovi and T. spiralis in wild omnivores and carnivores.

Vertebrates as uninfected disseminators of helminth eggs and larvae

The passive dispersal of non-mobile organisms by vertebrates (zoochory) is a common mechanism used to explain their often widespread distribution. Transport occurs either internally via the vertebrate digestive tract (endozoochory), or externally be adhering to skin, feathers or fur (ectozoochory), and its success is due to both physiological and ecological factors associated with the disseminating 'hosting' animal. Helminth eggs and larvae are generally non-mobile stages that are largely dependent on the movement of another animal, typically a host, for geographical dissemination. Studies on the zoochory of helminths by vertebrates are extensive and particularly long-standing, stretching back to the 19th century, although this literature is often overlooked when considering the biogeography of parasites. This review assesses the potential of helminths to be dispersed passively by zoochory examining evidence from both laboratory and field studies. The physiological dynamics of the vertebrate intestines and skin surface as hostile environments, as well as the characteristics of eggs and larvae which may facilitate successful transport are evaluated. The various mechanisms of helminth endo- and ectozoochory are presented and the likelihood of long-distance dispersal determined. It is concluded that zoochory is a potentially important means of disseminating parasites.

Trichinella spp. Infection in European Polecats (Mustela Putorius Linnaeus, 1758) from Romania

The European polecat (Mustela putorius Linnaeus, 1758) is in decline in Romania, often living near human settlements, from mountains to lowlands. They feed on a wide variety of small animals, including rodents, such as mice or rats. The occurrence of this parasite in polecats from Romania was mentioned only once in 1991, but the parasite species was not confirmed by molecular biology. The study aimed to investigate the occurrence of Trichinella spp. in European polecats from Romania and to identify the parasite species by molecular tools. A total of 75 wild European polecats were examined by trichinoscopy and artificial digestion. A large number of animals were examined because of their wide distribution in Romanian territory and their presence near human settlements. For species determination, the positive muscle samples and the larvae recovered from artificial digestion were collected for DNA isolation and further processed by means of Multiplex PCR.

Only two polecats from southern Romania tested positive for Trichinella spp. infection. During trichinoscopy examination, 48 (in a polecat from Giurgiu County) and 78 (in a polecat from Ialomița County) cysts were found in the tested (56 samples/animal) tissue samples. Artificial digestion revealed infection with 2466 larvae/100 g of muscle in the polecat from Ialomița and 254/100 g in the polecat from Giurgiu. The Multiplex PCR indicated the occurrence of Trichinella spiralis in the polecat from Giurgiu and a co-infection with T. spiralis and T. britovi in the polecat from Ialomița.

The current study confirms through molecular biology, the occurrence of T. spiralis and T. britovi, as well as the occurrence of co-infection with these two Trichinella species in European polecats from Romania.

Smart carnivores think twice: Red fox delays scavenging on conspecific carcasses to reduce parasite risk

The recent SARS-CoV-2 epidemic has highlighted the need to prevent emerging and re-emerging diseases, which means that we must approach the study of diseases from a One Health perspective. The study of pathogen transmission in wildlife is challenging, but it is unquestionably key to understand how epidemiological interactions occur at the wildlife-domestic-human interface. In this context, studying parasite avoidance behaviours may provide essential insights on parasite transmission, host-parasite coevolution, and energy flow through food-webs. However, the strategies of avoiding trophically transmitted parasites in mammalian carnivores have received little scientific attention. Here, we explore the behaviour of red foxes (Vulpes vulpes) and other mammalian carnivores at conspecific and heterospecific carnivore carcasses using videos recorded by camera traps. We aim to determine 1) the factors influencing the probability of foxes to practice cannibalism, and 2) whether the scavenging behaviour of foxes differ when facing conspecific vs. heterospecific carcasses. We found that red foxes were generally reluctant to consume mesocarnivore carrion, especially of conspecifics. When recorded, consumption by foxes was delayed several days (heterospecific carcasses) or weeks (conspecific carcasses) after carcass detection. Other mammalian scavengers showed a similar pattern. Also, meat-borne parasite transmission from wild carnivore carcasses to domestic dogs and cats was highly unlikely. Our findings challenge the widespread assumption that cannibalistic or intra-specific scavenging is a major transmission route for Trichinella spp. and other meat-borne parasites, especially for the red fox. Overall, our results suggest that the feeding decisions of scavengers are probably shaped by two main contrasting forces, namely the nutritional reward provided by carrion of phylogenetically similar species and the risk of acquiring meat-borne parasites shared with these species. This study illustrates how the detailed monitoring of carnivore behaviour is essential to assess the epidemiological role of these hosts in the maintenance and dispersion of parasites of public and animal health relevance.

High prevalence, intensity, and genetic diversity of Trichinella spp. in wolverine (Gulo gulo) from Yukon, Canada

Background

Species of Trichinella are globally important foodborne parasites infecting a number of domestic and wild vertebrates, including humans. Free-ranging carnivores can act as sentinel species for detection of Trichinella spp. Knowledge of the epidemiology of these parasites may help prevent Trichinella spp. infections in northern Canadian animals and people. Previous research on Trichinella spp. in wildlife from Yukon did not identify risk factors associated with infection, or the diversity and identity of species of Trichinella in regional circulation, based on geographically extensive sampling with large sample sizes.

Methods

In a cross-sectional study, we determined the prevalence, infection intensity, risk factors, and species or genotypes of Trichinella in wolverine (Gulo gulo) in two regions of Yukon, Canada, from 2013–2017. A double separatory funnel digestion method followed by mutiplex PCR and PCR-RFLP were used to recover and identify species of Trichinella, respectively.

Results

We found larvae of Trichinella in the tongues of 78% (95% CI 73–82) of 338 wolverine sampled. The odds of adult (≥ 2 years) and yearling (1 year) wolverine being Trichinella spp.-positive were four and two times higher, respectively, compared to juveniles (<1 year). The odds of Trichinella spp. presence were three times higher in wolverine from southeast than northwest Yukon. The mean intensity of infection was 22.6 ± 39 (SD, range 0.1–295) larvae per gram. Trichinella T6 was the predominant genotype (76%), followed by T. nativa (8%); mixed infections with Trichinella T6 and T. nativa (12%) were observed. In addition, T. spiralis was detected in one wolverine. Out of 22 isolates initially identified as T. nativa in multiplex PCR, 14 were analyzed by PCR-RFLP to distinguish them from T. chanchalensis, a recently discovered cryptic species, which cannot be distinguished from the T. nativa on multiplex PCR. Ten isolates were identified either as T. chanchalensis alone (n = 7), or mixed infection with T. chanchalensis and T. nativa (n = 2) or T. chanchalensis and Trichinella T6 (n = 1)].

Conclusions

Wolverine hosted high prevalence, high larval intensity, and multiple species of Trichinella, likely due to their scavenging habits, apex position in the food chain, and wide home range. Wolverine (especially adult males) should be considered as a sentinel species for surveys for Trichinella spp. across their distributional range.

Epidemiology and hypothetical transmission cycles of Trichinella infections in the Greater Kruger National Park of South Africa: an example of host-parasite interactions in an environment with minimal human interactions

Knowledge on the epidemiology, host range and transmission of Trichinella spp. infections in different ecological zones in southern Africa including areas of wildlife-human interface is limited. The majority of reports on Trichinella infections in sub-Saharan Africa were from wildlife resident in protected areas. Elucidation of the epidemiology of the infections and the prediction of hosts involved in the sylvatic cycles within specific ecological niches is critical. Of recent, there have been reports of Trichinella infections in several wildlife species within the Greater Kruger National Park (GKNP) of South Africa, which has prompted the revision and update of published hypothetical transmission cycles including the hypothetical options based previously on the biology and feeding behaviour of wildlife hosts confined to the GKNP. Using data gathered from surveillance studies and reports spanning the period 1964-2019, confirmed transmission cycles and revised hypothesized transmission cycles of three known Trichinella species (T. zimbabwensis, Trichinella T8 and T. nelsoni) are presented. These were formulated based on the epidemiological factors, feeding habits of hosts and prevalence data gathered from the GKNP. We presume that the formulated sylvatic cycles may be extrapolated to similar national parks and wildlife protected areas in sub-Saharan Africa where the same host and parasite species are known to occur. The anecdotal nature of some of the presented data confirms the need for more intense epidemiological surveillance in national parks and wildlife protected areas in the rest of sub-Saharan Africa to unravel the epidemiology of Trichinella infections in these unique and diverse protected landscapes.

Trichinellosis surveillance in wildlife in northeastern argentine patagonia

Trichinellosis is a food-borne parasitic disease produced by different nematodes of the genus Trichinella. In Argentina, it is an endemic zoonosis and an important public health problem. The infection has been detected in domestic and wild animals. Trichinella spp. muscle larvae have anaerobic metabolism, which allows their survival in decaying tissues. The aim of this study was to evaluate the presence of Trichinella spp. in carnivorous and/or scavenger wild vertebrates - birds, mammals and reptiles - in northeastern Argentine Patagonia. Skeletal muscle samples from 141 animals, which were found killed on northeastern Argentine Patagonia roads, were analyzed by the artificial digestion method. None of the 141 samples were positive for larvae of Trichinella. These results suggest that Trichinella does not use these species to complete its cycle in this region of the continent and the absence of a significant alteration in the study area makes it difficult to transmit parasitic diseases. However, due to the limited number of samples assessed for some species, this could not be confirmed. The relevance of this study resides in the fact that it is the first systematic study in South America that considers birds, reptiles and mammals as potential hosts for Trichinella.

Epidemiological studies on trichinellosis in pigs (Sus scofa) in India

The present study was conducted to determine the prevalence of trichinellosis in domestic pigs (Sus scrofa) in India. A total of 319 tissue and 279 serum samples were collected from 279 slaughter pigs. The samples were collected from small slaughter shops located in Assam, Chandigarh (Union territory), Punjab and Uttarakhand states of the country. The presence of Trichinella spp. antibodies in serum was determined using a commercially available enzyme-linked immunosorbent assay (ELISA) kit and tissue samples were digested using the OIE recommended pepsin-HCl digestion method. The overall seroprevalence of trichinellosis was found to be 2.87 %. The age wise seroprevalence was found to be 2.83 % in pigs aged more than 6 months and 3.12 % in pigs <6 months of age. The seroprevalence was more in male (3.38 %) than female (1.96 %) pigs. None of the samples were found positive using pepsin-HCl digestion method. Since none of the samples was found positive for Trichinella, PCR assay could not be employed in the current study. The age, sex and management practices of the animals were not significantly (p > 0.05) associated with seroprevalence. The current research confirms that trichinellosis remains a rare zoonosis in India. However, extensive studies must be carried out in wildlife to identify reservoir hosts in the country.

High prevalence of Trichinella spp. in sylvatic carnivore mammals of Latvia

Trichinella spp. are zoonotic parasites transmitted to humans by the consumption of raw or insufficiently cooked meat of different animal species. Carnivore mammals are important reservoir hosts of these nematodes. The aims of this work were to establish the prevalence of Trichinella spp. and infection intensity in sylvatic carnivore mammals of Latvia, to identify the etiological agents at the species level and their circulation in the Latvian regions. From 2010 to 2014, muscle samples were collected from 1286 hunted animals (2 European badgers, 137 pine martens, 24 stone martens, 4 golden jackals, 394 raccoon dogs, 668 red foxes, 23 grey wolves, and 34 Eurasian lynxes). Trichinella spp. larvae were isolated by muscle digestion. Overall, 633 animals (49.2%; 95% CI 46.5%-52.0%) belonging to all the eight investigated species, tested positive for Trichinella spp. larvae. Trichinella britovi was the most common species (94.0%; 95% CI 91.7%-95.7%). Trichinella nativa was detected in 30 animals as single (6, 1.1%; 95% CI 0.4%-2.3%) or mixed infection (24, 4.4%; 95% CI 2.9%-6.4%) with T. britovi. Trichinella spiralis was detected in only three animals as mixed infection with T. britovi. The high prevalence of Trichinella spp. infection in sylvatic carnivore mammals suggests that they are good indicators for the risk assessment of Trichinella spp. in Latvia.

Trichinellosis in the European union: epidemiology, ecology and economic impact

Trichinellosis, one of the most widespread helminthic zoonoses, is still endemic in most countries of the European Union. In the past few years, advanced biotechnology has been used to re-examine the taxonomy, epidemiology and life cycles of aetiological agents, providing additional information on the main factors contributing to the maintenance of these parasites in Nature. The old concept that pigs and rats are the main hosts of Trichinella spiralis, as still reported in many books, has been re-evaluated thoroughly. In this review, Edoardo Pozio summarizes the epidemiology and ecology of human and animal trichinellosis, quantifies the economic impact of this zoonosis and suggests methods of controlling this infection that would result in a great reduction in costs.

Trichinella infections in animals and humans in sub-Saharan Africa: a review

The aim of this review is to provide information on Trichinella infection in humans, livestock and wildlife in sub-Saharan Africa mainly focusing on geographical distribution of species/genotypes, biology, host range, life cycles and to identify research gaps. Trichinella britovi, Trichinella nelsoni and Trichinella zimbabwensis and one genotype (Trichinella T8) are known to occur in sub-Saharan Africa. Distinct geographic ranges with overlapping of some taxa in some areas have been observed. Genetic variants of T. nelsoni has been reported to occur among parasites originating from Eastern and Southern Africa and sequence heterogeneity also occurs among T. zimbabwensis isolates originating from different regions of Zimbabwe and South Africa. Field observations so far indicate that sylvatic Trichinella infections in the region are common in carnivores (mammals and reptiles) and to a lesser extent in omnivores. Cannibalism, scavenging and predation appear to be the most important routes of transmission and maintenance of the sylvatic cycles of the Trichinella taxa. To date, human trichinellosis has been documented in only four sub-Saharan countries (8.7%, 4/46). Bushpigs and warthogs have been the source of human infection with T. britovi and T. nelsoni being the aetiological agents. An increase in bushmeat trade and the creation of Transfrontier Conservation Areas (TFCAs) may have increased the risk of human trichinellosis in the region. With the creation of TFCAs in the region, sampling of wildlife hosts from protected areas of most sub-Sahara African countries is required to fully map the distribution of Trichinella species/genotypes in this region. More structured field surveys are still needed to determine the sylvatic host distribution of the different Trichinella taxa. Biological data of the Trichinella taxa in both wild and domestic animals of sub-Saharan Africa is very limited and further research is required.

Determination of Trichinella spiralis in pig muscles using Mid-Fourier Transform Infrared Spectroscopy (MID-FTIR) with Attenuated Total Reflectance (ATR) and Soft Independent Modeling of Class Analogy (SIMCA)

The aim of this work was to study the feasibility of detection of Trichinella spiralis in swine meat using Middle Infrared Spectroscopy Fourier Transform with Attenuated Total Reflectance (ATR) and Soft Independent Modeling of Class Analogy (MID-FTIR-ATR-SIMCA). Five male Pigs were orally infected at different larvae concentrations (13,000, 6500, 3500, 1625, 812 larvae/pig) and after 24 weeks the animals were euthanized. Five types of muscles were studied (leg, loin, rib, masseter, and diaphragm). Results showed that MID-FTIR-ATR-SIMCA was useful to determine the presence of T. spiralis in the samples, as the interclass distance between infected and non infected muscles varied from 13.5 to 36.8. This technique was also useful to discriminate among pig muscles, where masseter showed the largest interclass distance, while rib presented the smallest one. In all cases the recognition and rejection rates were 100%, which means that the methodology is capable of accurately separating T. spiralis infected from non infected swine meat.

Immunoparasitological evaluation of Trichinella spiralis infection during human pregnancy: a small case series

The clinical background, vertical transmission of Trichinella spiralis and helminthotoxic activity of sera were evaluated in four pregnant women infected at different gestation times. Parasitological and immunological parameters were analyzed. Patients presented clinical symptoms and a seroconversion pattern typical of Trichinella infection, independently of the gestation trimester. All patients, including one patient treated with mebendazole, gave birth to healthy infants at full term. Studies performed in placentas and umbilical cords by artificial digestion and/or immunofluorescence did not reveal the presence of parasites or parasite antigens. Specific antibodies were found in placental extraction and maternal sera by immunofluorescence, ELISA and/or immunoelectrotransfer blot assay. Specific IgG, IgE and IgA were found in the umbilical cord sera. One umbilical cord demonstrated immune-complexed specific IgM and circulating parasite antigens were found in the corresponding infant up to 10 months after birth. Patients' sera were able to kill newborn larvae in cytotoxicity assays, even in the absence of specific antibodies; this effect was abrogated by mifepristone. The results suggest that in human trichinellosis during pregnancy there is an enhanced helminthotoxicity to newborn larvae, dependent in part on progesterone, leading to a mild or moderate course of the infection. The results also indicate that the transplacental passage of migrating larvae is possible.

Trichinella zimbabwensis in wild reptiles of Zimbabwe and Mozambique and farmed reptiles of Ethiopia

In 1995, a new species of Trichinella (Trichinella zimbabwensis) was discovered in farmed Nile crocodiles (Crocodylus niloticus) in Zimbabwe, where the mode of transmission was the consumption of the meat of slaughtered crocodiles, used as feed. To determine whether T. zimbabwensis affects poikilotherm vertebrates in the wild, monitor lizards (Varanus niloticus) and Nile crocodiles were collected in Zimbabwe and Mozambique. In 5 (17.6%) of the 28 monitor lizards from Zimbabwe, T. zimbabwensis larvae were identified. For the wild Nile crocodiles from Mozambique, species-level identification was not possible, yet immunohistochemical analysis revealed that 8 (20%) of the 40 animals harboured non-encapsulated Trichinella sp. larvae, which probably belonged to T. zimbabwensis. This is the first report of T. zimbabwensis in wild reptiles, and the findings are consistent with reports that vertebrates with scavenger and cannibalistic behaviour are the most important hosts of Trichinella spp. The wide distribution of monitor lizards and crocodiles in Africa and the development of national crocodile breeding programs in many African countries should be taken into consideration when evaluating the risk of transmission of this parasite to mammals, including humans.

Molecular characterization of Trichinella genotypes by inter-simple sequence repeat polymerase chain reaction (ISSR-PCR)

A bulk analysis of inter-simple sequence repeat-polymerase chain reaction (ISSR-PCR) provides a quick, reliable, and highly informative system for DNA banding patterns that permit species identification. The present study evaluates the applicability of this system to Trichinella species identification. After a single amplification carried out on a single larva with the primer 816([CA]nRY) under high stringency conditions, which provide high reproducibility, we were able to identify by consistent banding patterns 5 sibling species: Trichinella spiralis (ISS48), 2 Trichinella britovi isolates (ISS11 and ISS86), Trichinella murrelli (ISS35), Trichinella nativa (ISS71), Trichinella nelsoni (ISS29); 3 additional Trichinella genotypes: T8 (ISS149), T9 (ISS408 and ISS409), and T6 (ISS34); and the nonencapsulated species Trichinella pseudospiralis (ISS13). Moreover, 33 new Trichinella isolates from 2 zoogeographical regions were unequivocally identified. All Trichinella isolates have shown an identical pattern with those produced by the reference strain. According to these data, we have demonstrated that ISSR-PCR is a robust technique that emerges as a useful new application for the molecular identification of Trichinella isolates in epidemiological studies.

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.

Red fox (Vulpes vulpes) cannibalistic behaviour and the prevalence of Trichinella britovi in NW Italian Alps

Food habits of the red fox (Vulpes vulpes) were studied in the Aosta Valley region (NW Italian Alps) and were related to the prevalence of Trichinella infection in the red fox itself and in two Mustelid species (the stone marten (Martes foina) and the badger (Meles meles)). The search of Trichinella by the automatic digestion of muscles samples led us to determine a prevalence of 3.5+/-1.2% in red foxes, 7.9+/-4.3% in stone martens and 1.9+/-1.8% in badgers, with no significant differences among the species. All larvae were identified as Trichinella britovi. The fox diet was assessed through the analysis of both faeces (n=180) and the stomach contents of road-killed animals (n=109). Our results confirmed the opportunistic feeding behaviour of the red fox, which is able to use various trophic resources, both of animal and vegetal origin: e.g. wild and cultivated fruits (F%=47.1; V%=67.3), rodents (F%=22.8; V%=64.8) and carrion (F%=15.6; V%=78.6) formed the bulk of the fox's diet. The frequency of occurrence of potential events of cannibalism was 1.0%, even if the complete absence of undigested remains, other than hairs, suggested the possibility of confusing cannibalism with coat-cleaning. We suggest that intra-specific necrophagy could not represent the unique way of transmission of the nematode in natural conditions.

Spatial Variation of Trichinella Prevalence in Rats in Finnish Waste Disposal Sites

Trichinellosis is 1 of the most widespread parasitic zoonoses in the world and can be lethal to humans. Trichinella spp. are also parasites of considerable economic importance. Because rats may play a role in the transmission of trichinellosis to swine and farmed wild boar, 767 brown rats (Rattus norvegicus Berkenhout) from 13 Finnish waste disposal sites were examined for Trichinella spp. by a HCl-pepsin digestion method. Trichinella spp. were found to be a common parasite in trapped rats (overall prevalence, 19%) detected in 12 of 13 dumps. Significant differences were observed between sites in the prevalence (0-49%) of Trichinella spp. Female rats were more often and more heavily infected than males, but age was not shown to be a risk factor for trichinellosis. In addition, positive correlation was demonstrated between rat population density and prevalence. Trichinella spiralis was identified by multiplex polymerase chain reaction in 28 rats. The median density of infection was 42 (range, 0.5-6,925) larvae/ g of host tissue, but neither the occurrence nor the density of the parasite was related to the physical condition of the animal.

Trichinella papuae and Trichinella zimbabwensis induce infection in experimentally infected varans, caimans, pythons and turtles

The discovery of Trichinella zimbabwensis in farm crocodiles of Zimbabwe has opened up a new frontier in the epidemiology of the Trichinella genus. The objective of the present study was to investigate the infectivity of encapsulated species (T. spiralis, T. nativa, T. britovi, T. murrelli and T. nelsoni) and non-encapsulated species (T. pseudospiralis, T. papuae and T. zimbabwensis) in caimans (Caiman crocodilus), varans (Varanus exanthematicus), pythons (Python molurus bivittatus) and turtles (Pelomedusa subrufa) raised at their natural temperature range (26-32 degrees C). Mice and chickens were used as controls. At 6 days post-infection (p.i.), adult worms were detected in the small intestine of reptiles infected with T. papuae and T. zimbabwensis, of chickens infected with T. pseudospiralis and of mice infected with all encapsulated and non-encapsulated species. At 60 days p.i., T. papuae and T. zimbabwensis adult worms were collected from the intestine of varans and caimans and larvae from muscles of the four reptile species, T. pseudospiralis larvae from muscles of chickens, and larvae of all Trichinella species from mouse muscles. The highest reproductive capacity index of both T. papuae and T. zimbabwensis was observed in varans. The results show that T. papuae and T. zimbabwensis are able to complete their entire life-cycle in both poikilothermic and homoiothermic animals.

New patterns of Trichinella infection

Human and animal trichinellosis should be considered as both an emerging and reemerging disease. The reemergence of the domestic cycle has been due to an increased prevalence of Trichinella spiralis, which has been primarily related to a breakdown of government veterinary services and state farms (e.g., in countries of the former USSR, Bulgaria, Romania), economic problems and war (e.g., in countries of the former Yugoslavia), resulting in a sharp increase in the occurrence of this infection in swine herds in the 1990s, with a prevalence of up to 50% in villages in Byelorussia, Croatia, Latvia, Lithuania, Romania, Russia, Serbia, and the Ukraine, among other countries. The prevalence has also increased following an increase in the number of small farms (Argentina, China, Mexico, etc.) and due to the general belief that trichinellosis was a problem only until the 1960s. The sylvatic cycle has been studied in depth at both the epidemiological and biological level, showing the existence of different etiological agents (Trichinella nativa, Trichinella britovi, Trichinella murrelli, Trichinella nelsoni) in different regions and the existence of "new" transmission patterns. Furthermore, the role of game animals as a source of infection for humans has greatly increased both in developed and developing countries (Bulgaria, Canada, Lithuania, some EU countries, Russia, USA, etc.). The new emerging patterns are related to non-encapsulated species of Trichinella (Trichinella pseudospiralis, Trichinella papuae, Trichinella sp.), infecting a wide spectrum of hosts (humans, mammals including marsupials, birds and crocodiles) and to encapsulated species (T. spiralis, T. britovi, and T. murrelli) infecting herbivores (mainly horses). The existence of non-encapsulated species infecting mammals, birds and crocodiles had probably remained unknown because of the difficulties in detecting larvae in muscle tissues and for the lack of knowledge on the role of birds and crocodiles as a reservoir of Trichinella. On the other hand, it is not known whether horse and crocodile infections existed in the past, and their occurrence has been related to improper human behavior in breeding. The problem of horse-meat trichinellosis is restricted to France and Italy, the only two countries where horse-meat is eaten raw, whereas mutton and beef have been found to be infected with Trichinella sp. only in China.

Epidemiology of trichinellosis in Mexico, Central and South America

Trichinella species are widely distributed throughout the world and are found in a large number of carnivorous animals, humans and incidental hosts. The data presented in this review show that Trichinella infection has been reported in both humans and animals in Mexico, Argentina and Chile since the end of the 19th century, and more recently in Bolivia. This parasitic infection is still a public health problem in countries such as Argentina and Chile. Although efforts have focused on the control and prevention of trichinellosis in these countries, there were still human cases and outbreaks of trichinellosis reported. Diagnosis of infection in animals such as pigs still includes, in many endemic areas, the use of trichinoscopy. In Argentina, however, artificial digestion has been recently introduced in slaughterhouses to detect Trichinella infection in pigs. In some endemic areas in Mexico, the use of serological assays for human trichinellosis and pig infections have resulted in improved detection. Most of the outbreaks of human trichinellosis in Mexico, Argentina and Chile have occurred as a result of the consumption of undercooked pork or pork products from animals raised under poor hygienic conditions and which are clandestinely slaughtered. In several studies, rats, dogs and cats have been found to be infected with Trichinella and may be considered a risk for transmission of the infection to pigs or other animals intended for human consumption. Another potential source of transmission of Trichinella to humans is horsemeat; however, information related to horse trichinellosis in Latin-American countries is scarce. In most cases the etiological agent of human trichinellosis in Central and South America has been reported to be Trichinella spiralis; however, only in a few cases has the parasite species been properly identified. Based on the reports available, it is clear that there is a need to carry out better controlled epidemiological studies to determine the true prevalence of the infection in this region of the world. Also, more sensitive methods of diagnosis and improvements in conditions for pig production as well as better sanitary inspection systems, are needed for controlling and preventing transmission of trichinellosis in these countries.

Factors affecting the flow among domestic, synanthropic and sylvatic cycles of Trichinella

Nematodes of the genus Trichinella are maintained in nature by sylvatic or domestic cycles. The sylvatic cycle is widespread on all continents, from frigid to torrid zones, and it is maintained by cannibalism and scavenging behavior of carnivores. Trichinella is primarily a parasite of carnivorous mammals, although one non-encapsulated species, Trichinella pseudospiralis, has also been detected in birds. The anaerobic metabolism of larvae in nurse cells allows their survival in extremely decayed meat. Encapsulated larvae in the decomposing carcass function similarly to the species-dispersing population of eggs or larvae of other nematodes, suggesting that the natural cycle of Trichinella includes a free-living stage when the parasite is no longer protected by the homeothermy of the host. Consequently, environmental temperature and humidity play an important role in the transmission of Trichinella among wildlife. Of the 10 recognized genotypes of Trichinella, only Trichinella spiralis is transmitted and maintained in a domestic cycle, although it can be present also in wildlife. All other genotypes (Trichinella nativa, Trichinella britovi, T. pseudospiralis, Trichinella murrelli, Trichinella nelsoni and Trichinella papuae, Trichinella T6, T8, and T9) are transmitted and maintained only in a sylvatic cycle. This generalization does not preclude sylvatic species of Trichinella from invading the domestic habitat, and T. spiralis may return to this habitat when humans fail in the management of wildlife and domestic animals. However, the presence of sylvatic genotypes of Trichinella in the domestic habitat represents a "dead-end" for the sylvatic cycle. Synanthropic animals (rats, foxes, mustelids, cats, dogs, etc.) contribute to the flow of sylvatic Trichinella genotypes from wildlife to domestic animals and of T. spiralis from domestic to sylvatic animals. Furthermore, human behavior not only influences the transmission patterns of Trichinella genotypes in the domestic habitat, but also it can contribute to the transmission and spread of this infection among wildlife, for example by improper hunting practices.

Influence of temperature on the survival and infectivity of Trichinella spiralis larvae in Sarcophaga argyrostoma (Diptera, Sarcophagidae) maggots

To investigate the role of fleshfly maggots as a paratenic host for Trichinella spiralis larvae, maggots of Sarcophaga argyrostoma (Muscidae, Sarcophagidae) kept at different temperatures (26, 22, 20, 16, 12, 8, and 4 C) were allowed to feed on T. spiralis-infected mouse meat. Trichinella larvae found in maggots kept at 8-26 C were able to cause infection when inoculated in mice. Infective larvae survived in maggots up to 5 days postinfection at 8 C and for shorter periods of time at higher temperatures. The survival time in maggots was negatively related to the temperature of maggot breeding. The results suggest that the role of S. argyrostoma in the dissemination of Trichinella larvae in nature is limited in comparison to the role played by mammals with scavenger and cannibalistic behavior.

Trichinella murrelli n. sp: etiological agent of sylvatic trichinellosis in temperate areas of North America

Trichinella T5, collected from sylvatic carnivores in North America, was identified previously as a different phenotype of Trichinella, with an uncertain taxonomic level due to the availability of only 2 isolates. Cross-breeding experiments carried out with single female and male larvae of 2 strains of Trichinella T5, with single female and male larvae of 2 strains of Trichinella spiralis, Trichinella nativa, Trichinella britovi, Trichinella pseudospiralis, Trichinella nelsoni, and Trichinella T6, showed a reproductive isolation of Trichinella T5. Viable offspring were obtained only when a female of Trichinella T5 was crossed with a male of T. britovi, but not vice versa. Furthermore, the analysis of biological, biochemical, and molecular data of 32 isolates collected from sylvatic animals in the Nearctic region and identified as Trichinella T5 permitted its reassessment at the species level. Trichinella murrelli n. sp. is characterized by the following: distribution in temperate areas of the Nearctic region; newborn larvae production in vitro of 29-36/72 hr; nurse cell development time between 24 and 70 days postinfection; reproductive capacity index in Swiss mice 1.2-9.5, in wild mice 29.5-159.8, in rats 0.7-2.4, and in pigs 0.03-0.0004; no resistance to freezing; ribosomal DNA fragments of 7.2 kb and/or 11.4 kb, plus 2.2 kb and 1.8 kb present after Dra I digested DNA when probed with total T. spiralis RNA; a specific amplicon of 179 bp after polymerase chain reaction (PCR) amplification with the primer set SB147G; a specific fragment of 1,600 bp after PCR amplification with the primer set Ts43CA and Hhb I digestion; long incubation period; and moderate to severe pathogenicity for humans. The new species is most similar to T. britovi, though it differs from T. britovi in the pattern of 2 allozymes, in the patterns of major ribosomal DNA and PCR-restriction fragment length polymorphism fragments, and in geographical distribution.

Epidemiological investigation of trichinellosis in Switzerland

Domestic pigs in Switzerland have been considered Trichinella-free for decades, despite the occurrence of Trichinella in the wildlife cycle. In order to reevaluate the present epidemiological situation, tissue samples from 11226 domestic pigs, 356 wild boars and 452 foxes were examined using the standard artificial digestion method. A simultaneous serological study, extended to include 25239 sera from sows provided by a Swiss pig serum bank, was also undertaken. The results of both studies support the conclusion that Trichinella spp. do not occur within the domestic pig population in Switzerland. Among the fox population, Trichinella was detected in four (0.9%) of the animals tested using the digestion method, and Trichinella britovi was identified as the infecting species by RAPD fingerprint analyses.

Environmental and human influence on the ecology of Trichinella spiralis and Trichinella britovi in Western Europe

Surveys on Trichinella parasites in domestic and sylvatic animals collected in France, Italy, and in the Extremadura region of Spain showed that the distribution of Trichinella spiralis and Trichinella britovi is influenced by both environmental and human behaviour factors. In France, both Trichinella species are prevalent in the fox population from mountain areas and natural parks but are infrequent in wild boars (< 0.001%). In Italy, only T. britovi is present in sylvatic animals (foxes, wolves, and mustelids) living 500 m above sea level. This species is rare in wild boars (< 0.001%) in that area. Sylvatic trichinellosis is found in only 24% and 34% of French and Italian territory, respectively, while lowland areas may generally be considered Trichinella-free, because the domestic cycle is absent. The ecology of T. spiralis and T. britovi in the Extremadura shows a different picture from that observed in France and Italy because of the presence of both domestic and sylvatic cycles. The domestic cycle not only allows the maintenance of T. spiralis in the domestic environment, but it also has a great impact on the prevalence in wild boar populations. It does not influence the prevalence in vulpine populations. These data suggest (1) that domestic trichinellosis occurs only in rural areas of Western Europe in association with traditional swine-rearing practices, but not in industrialized pig farms; (2) that sylvatic trichinellosis occurs only in natural habitats which, in Western Europe, are widespread in mountain areas; (3) that the fox is the primary reservoir in the sylvatic cycle, where the parasite is maintained in a closed circuit and (4) that among sylvatic animals T. spiralis is present at lower altitude than is T. britovi.

Diel locomotory activity of deer mice (Peromyscus maniculatus) infected with Trichinella nativa or Trichinella pseudospiralis

The effects of infection by two species of sylvatic Trichinella on the diel locomotory activity of a wild rodent host, the deer mouse Peromyscus maniculatus, in a familiar environment were investigated in the laboratory using computer-linked activity chambers equipped with an infrared photocell. Locomotory activity data were collected on each mouse prior to and after sham inoculation or inoculation with graded doses of muscle-encapsulating Trichinella nativa or nonencapsulating Trichinella pseudospiralis larvae. Trichinella nativa infections induced activity deficits in deer mice that were proportional to the number of infective larvae recovered, whereas derived indices of locomotory activity of mice infected with T. pseudospiralis remained essentially within the range of those of sham-inoculated control mice. Quantitative differences between T. nativa and T. pseudospiralis in their potential to modulate the host's immune response may account for the observed difference in their effect on locomotory activity of the deer mouse host. Such variation in trichina-induced changes in diel locomotory activity may serve to channel transmission of the parasites to suitable hosts.

Trichinella pseudospiralis in humans: description of a case and its treatment

The first known human case of Trichinella pseudospiralis myositis is described. A 33 years old woman reported 5 years of relatively mild symptoms of tiredness, muscle fatigue and muscle pain after exercise. She had minimal proximal weakness. Creatinine kinase was significantly elevated, and muscle biopsy showed polymyositis and Trichinella larvae. Steroid treatment dramatically worsened the weakness. Treatment with albendazole led to complete resolution of symptoms and laboratory abnormalities. Diagnosis and identification of the parasite were based on the distinctive appearance of the unencapsulated larvae and their movement in fresh muscle, plus clinical and laboratory findings.

Biochemical resolution of European and African isolates of Trichinella nelsoni Britov and Boev, 1972

Isoenzyme analysis was used to characterize 47 isolates of Trichinella nelsoni from Europe (EUR) and two from Kenya and Tanzania (AFR). In all, 27 isoenzymes showed polymorphism within the species. The EUR parasites, isolated from domestic, synanthropic, sylvatic animals and man, showed isoenzymatic profiles different from those exhibited by AFR parasites isolated from sylvatic animals. The EUR parasites showed polymorphism due to three isoenzymes, i.e. ME, MPI and PGM. Euclidean distance and a dendrogram were used to evaluate the relationships among isolates. The Euclidean values showed that EUR and AFR genotypes are distant from each other and from the reference strains T. spiralis s.str. and T. pseudospiralis. The genetic data indicate the absence of gene flow between AFR and EUR isolates. The biochemical results suggest the presence of genetic heterogeneity in T. nelsoni and support the existence of a zoogeographical segregation of the two gene pools. The authors propose that as operational labels, code T3 be assigned to EUR isolates and code T7, to AFR isolates.