Trichinella spiralis, T. britovi, and T. nativa: infectivity, larval distribution in muscle, and antibody response after experimental infection of pigs

An Update in Knowledge of Pigs as the Source of Zoonotic Pathogens

The available data indicate that the human world population will constantly grow in the subsequent decades. This constant increase in the number of people on the Earth will lead to growth in food demand, especially in food of high nutritional value. Therefore, it is expected that the world livestock population will also increase. Such a phenomenon enhances the risk of transmitting pathogens to humans. As pig production is one of the most significant branches of the world's livestock production, zoonoses of porcine origins seem to be of particular importance. Therefore, in this review, we aim to introduce the latest data concerning, among other things, epidemiology and available preventive measures to control the most significant porcine zoonoses of viral, bacterial, and parasitic origin.

Scheme of Effective Epidemiological Investigations in Trichinella Outbreaks on Pig Farms

Trichinellosis is a parasitic, zoonotic disease caused by larvae of the genus Trichinella. Infection occurs via the consumption of raw or undercooked meat containing this parasite. Symptoms of the disease manifest as intestinal disorders, followed by facial swelling, fever, muscle pain and other symptoms, eventually leading to neurological and cardiac complications and even death. In Europe, trichinellosis is most often associated with the consumption of meat from wild boars, pigs and horses. In recent years, wild boars that are hunted illegally and not tested for Trichinella spp. have been the most common cause of trichinellosis in humans; however, there have also been cases where infected pigs have been the source of infection. When trichinellosis is suspected in humans, epidemiological measures are taken to identify the source. Similarly, an epidemiological investigation should be initiated whenever Trichinella spp. has been detected in pigs. However, commonly used actions do not provide sufficient data to determine the source of infection for pigs and to prevent further transmission. Therefore, in this article, we propose a scheme for effective epidemiological investigations into Trichinella outbreaks on pig farms that can help trace the transmission mechanisms of the parasite and that takes into account currently available testing tools. The proposed pathway can be easily adopted for epidemiological investigations in routine veterinary inspection work.

Trichinella surveillance program in wild birds, Emilia-Romagna (northern Italy), 2006–2021. First report of Trichinella pseudospiralis in western marsh harrier (Circus aeruginosus) in Italy

The nematode Trichinella pseudospiralis is a cosmopolitan parasite capable of infecting both birds and mammals including humans. T. pseudospiralis has a limited zoonotic importance in comparison to that of the other Trichinella species. However, it has been recognized as the etiological agent of two outbreaks of trichinellosis due to the consumption of wild boar meat. The role played by birds in the epidemiology of T. pseudospiralis is still unclear and needs to be deepened. The aim of our work was to show the results of an extensive wild bird surveillance carried out in the Emilia-Romagna (E-R) region, northern Italy, over the last 16 years. As part of the regional wildlife surveillance program, 14,933 raptors and carrion-eating birds’ carcasses were necropsied from 2006 to 2021 and tested for the presence of Trichinella spp. larvae with only one positive result, an adult female of western marsh harrier. The larvae load (LPG) was evaluated on breast (100 LPG), wings (3.6 LPG), shoulder (2 LPG), head (4.5 LPG), thighs (8 LPG), lower legs (2 LPG) and tongue (0.77 LPG). The results of the present study confirm that also in northern Italy T. pseudospiralis has a low prevalence comparing to that of other Trichinella species. However, this study demonstrates that T. pseudospiralis can reach a high parasitic load in infested birds. The large distribution range, probably facilitated by its ability to infest birds, suggests the need for a continuous monitoring program.

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Results of a Trichinella monitoring program in wild birds during the period 2006–2021.

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First report of Trichinella pseudospiralis in a western marsh harrier (Circus aeruginosus) in Italy.

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T. pseudospiralis can reach a high parasitic load in infested birds.

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The highest larval burden (100 LPG) was detected in the breast muscles of the affected marsh harrier.

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The ongoing isolation of this parasite suggests a stable presence of T. pseudospiralis in Italy.

Insight into Trichinella britovi Infection in Pigs: Effect of Various Infectious Doses on Larvae Density and Spatial Larvae Distribution in Carcasses and Comparison of the Detection of Anti-T. britovi IgG of Three Different Commercial ELISA Tests and Immunoblot Assay

There is limited information available on the Trichinella britovi (T. britovi) muscle larvae (ML) distribution in pig muscle and the humoral immune response of pigs infected with moderate doses of this parasite; therefore, this study investigated the infectivity of a Polish strain of T. britovi for pigs, the antibody response of this host to various doses of T. britovi, and the efficiency of three different commercial ELISA kits and an immunoblot assay at detecting anti-T. britovi IgG. No significant differences in terms of the infection level of particular muscles or of whole carcasses between pigs infected with 3000 and those infected with 5000 ML of T. britovi were observed. The highest intensity of T. britovi infection was reported in the diaphragm pillars. The larvae of T. britovi showed homogeneous distribution with respect to the muscle side. Statistically, specific IgG antibodies against excretory–secretory (ES) antigens of Trichinella ML were first detected by all ELISA protocols on day 36 post infection; however, individual pig results showed some differences between the three tests applied. A significant increase in the level of anti-T. britovi IgG was observed between days 36 and 41 post infection, and from day 45 until day 62 after T. britovi infection, production of these antibodies reached its plateau phase. No positive correlation was found between the anti-T. britovi IgG level and the larvae density in 15 different muscles. Sera of T. britovi-infected pigs showed reactivity with T. britovi ML ES antigens of 62, 55, and 52 kDa. The results provide novel information on spatial larvae distribution in muscles and the humoral immune response of pigs exposed to two different doses of a Polish strain of T. britovi, extend knowledge on serological diagnostic tools which may be introduced in veterinary practice for the detection of T. britovi infections in pig production, and offer practical solutions for meat hygiene inspectors in the field at sampling sites when examining pig carcasses for Trichinella.

Reprint of: Comparison between Trichinella patagoniensis and Trichinella spiralis infection in BALB/c mice

In Argentina, trichinellosis is an endemic disease acquired mainly through consumption of raw pork infected with nematodes larvae from the Trichinella genus. For years, the only species involved in outbreaks in humans and pig foci in Argentina was Trichinella spiralis. In 2008 the presence of a new Trichinella taxon from a cougar (Puma concolor) was detected and recorded in the province of Rio Negro, Argentina, and the finding was established as a new species in 2012: Trichinella patagoniensis. To the best of our knowledge, there is no information available on the intestinal phase and antibody response in a susceptible host during T. patagoniensis infection. Therefore, our research has been designed to study experimental infection with T. patagoniensis compared to infection with T. spiralis in BALB/c mice. One hundred and twenty eight BALB/c mice were divided into two groups and individuals in each group were infected per os with 500 larvae of T. patagoniensis or 500 larvae of T. spiralis, respectively. After that, they were euthanized on different days. Adult worm recovery from small intestines and artificial digestion of each carcass was performed. Histopathology of small intestines was performed using hematoxylin-eosin staining. Systemic cytokines and antibody kinetics were evaluated. Intestinal adult worm recovery of T. patagoniensis and T. spiralis took place until day 17 and 25, respectively. Systemic IFN-γ, IL-10, and TNF showed significant variations in T. patagoniensis infected mice. Seroconversion was detected in animals as from 15 days post-infection (pi) for both T. patagoniensis and T. spiralis, reaching the highest OD value at 42 days pi. Similar microscopic lesions were observed in the small intestine from mice infected with the same dose of T. spiralis and T. patagoniensis. Our findings contribute new information regarding the intestinal phase and the antibody kinetics of T. patagoniensis in BALB/c mice.

A review on Trichinella infection in South America

Trichinella spp. causes human trichinellosis by means of the consumption of raw or inadequately treated meat from domestic or game animals. In the Americas, as well as in other continents, Trichinella infection is a health issue for humans and has a negative impact on the pork meat market, generated by people's fear of becoming infected with the parasite. The distribution of human cases and the sources of this disease in humans and animals were analysed in this report, which summarizes the information available regarding Trichinella infection in animals and humans in South America. Within South America, human infection with Trichinella was documented in Argentina and Chile during the period 2005-2019. Trichinellosis is endemic in these countries for, with human cases and foci in domestic and wild animals. In Argentina, human cases occur throughout the country, with foci found in pigs and wild animals. In Argentina, during the period 2012-2018, the number of suspected human cases reached 6,662. T. spiralis was identified in one South American sea lion (Otaria flavescens) from Patagonia, Argentina, for the first time in the region in 2018. In Chile, 258 human cases of trichinellosis were confirmed during the period 2005-2015; out of those 258 cases, most samples which tested positive for Trichinella spp. (29.5 %) were detected in the Metropolitan district (Santiago de Chile and outskirts), and 17.4 % in The Lake district. Regarding age brackets, people between 30-49 years of age showed the most cases (40.1 %). In Brazil, the infection is absent in domestic species but it has been found in wild boars (Sus scrofa) but limited to one or more region of the country. Within the animal species destined for food in South America, those that showed higher parasitical loads were pigs and wild boars, while armadillos (Chaetophractus villosus) and peccaries (Tayassu tajacu) showed very low Trichinella spp. larvae loads (0.04-0.1 larvae/g). Antibodies against Trichinella spp. have been detected in pigs from Ecuador and Bolivia. In Bolivia, antibodies were also found in humans. Peru, Colombia and Uruguay have no documented presence of Trichinella spp. in animals and humans. There is insufficient information regarding the presence of Trichinella spp. in domestic and wild animals, as well as in humans, since only a very limited number of surveys have been carried out. No papers with information on Trichinella spp. circulating in animals or humans have been published regarding the situation in Guyana, Surinam, French Guiana, Venezuela and Paraguay. Considering the growth of the guinea pig meat market in the Andean region, and the high prevalence of the disease reported in free range pigs and wild boars, as well as other game animal species, it is important to focus on the role of biosecurity and risk management, while improving meat market regulations, and detection of infection prior to consumption, in order to reduce the risk of transmission of this zoonotic disease to humans.

Distribution of Trichinella spiralis, Trichinella britovi, and Trichinella pseudospiralis in the Diaphragms and T. spiralis and T. britovi in the Tongues of Experimentally Infected Pigs

There is little or even no data in the global literature on the distribution of different species of Trichinella in the individual parts of the diaphragms and tongues in infected pigs. This is of particular importance from the food safety point of view and for the conduct of routine testing of pig carcasses for Trichinella as well as epidemiological surveys. Therefore, the aim of the present study was to evaluate the distribution of Trichinella spiralis (T. spiralis), Trichinella britovi (T. britovi), and Trichinella pseudospiralis (T. pseudospiralis) ML in various parts of the diaphragm (the pillars, costal, and sternal part) and the distribution of encapsulated species of Trichinella (T. spiralis and T. britovi) in various parts of the tongues (the tip, body, and root) of experimentally infected pigs. The diaphragm pillars were the most heavily parasitized part of the diaphragm both in groups of pigs infected with particular species of Trichinella and in groups of pigs presenting different levels of infection; however, statistical differences were observed only in the group of pigs with moderate (21–35 larvae per gram-lpg) or moderately high (35–55 lpg) intensity of Trichinella spp. infection in the entire diaphragm. In all groups of pigs, regardless of the infecting Trichinella species or infection level, larvae showed a homogeneous distribution on both sides of the diaphragm and excluding those of T. pseudospiralis, also in all three parts of the tongue. Histological examination showed features of a differential inflammatory response around larvae of the different Trichinella species. This study confirmed that for mandatory examination of pig carcasses using a pooled-sample digestion assay in which each pig is intended to be represented by a 1 gram sample taken from the diaphragm pillars, if that tissue is not available, the mass of the sample taken from the remaining diaphragm parts (costal or sternal) should be at least double that from the pillars. Histological findings confirmed that the inflammatory pattern of pig muscles varies depending on the Trichinella species triggering the infection and is less intense in the case of infections with T. pseudospiralis than in infections with encapsulated species of Trichinella (T. spiralis and T. britovi).

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.

Acute phase protein pattern and antibody response in pigs experimentally infected with a moderate dose of Trichinella spiralis, T. britovi, and T. pseudospiralis

The aim of the present study was to evaluate the acute-phase protein (APP) response in three groups of pigs experimentally infected with a moderate infective dose, i.e. 1000 muscle larvae (ML) of Trichinella spiralis, 3000 ML of Trichinella britovi, and 2000 ML of Trichinella pseudospiralis. Over a 62-day period of infection, we examined the serum level and kinetics of the haptoglobin (Hp), C-reactive protein (CRP), serum amyloid A (SAA), and pig major acute-phase protein (pig-MAP). In addition, to better understand the immune response of pigs experimentally infected with three different species of Trichinella, the kinetics of IgG and IgM antibodies against excretory-secretory (ES) antigens of Trichinella ML were also investigated. In order to assess anti-Trichinella IgG dynamics, we used a commercial and an in-house ELISA based on both heterologous (T. spiralis) and homologous (T. spiralis, T. britovi, and T. pseudospiralis) Trichinella species ES antigens. Among the four APPs analyzed, the concentration of CRP and pig-MAP significantly increased only in T. britovi-infected swine when compared with control pigs. This took place as early as 6 days post-infection (dpi). Hp was the only APP whose concentration significantly increased in pigs infected with T. pseudospiralis, this occurring as late as on day 62 pi. Despite the statistical differences found, increases in pig-MAP, CRP, and Hp levels were rather mild and transitory; none of these proteins were found to be elevated in the serum of all experimental groups of pigs at the same time point after infection. Specific IgG antibodies against ES antigens of Trichinella ML were first detected by the commercial and in-house T. spiralis ML ES-antigen ELISAs on days 30, 36 and 36 pi in pigs experimentally infected with T. spiralis, T. britovi, and T. pseudospiralis, respectively. However, seroconversion in pigs experimentally infected with T. britovi was detected slightly earlier (30 dpi) when the ELISA based on homologous rather than heterologous ES antigens was applied. In serum samples from pigs infected with T. spiralis, statistically significant increases in the level of specific IgM antibodies against T. spiralis ML ES antigens were first detected on day 30 pi and after this time, their concentration began to decrease. No changes in the level of anti-Trichinella IgM were observed in T. britovi- or T. pseudospiralis-infected pigs throughout the entire period of the experiment.

Comparison between Trichinella patagoniensis and Trichinella spiralis infection in BALB/c mice

In Argentina, trichinellosis is an endemic disease acquired mainly through consumption of raw pork infected with nematodes larvae from the Trichinella genus. For years, the only species involved in outbreaks in humans and pig foci in Argentina was Trichinella spiralis. In 2008 the presence of a new Trichinella taxon from a cougar (Puma concolor) was detected and recorded in the province of Rio Negro, Argentina, and the finding was established as a new species in 2012: Trichinella patagoniensis. To the best of our knowledge, there is no information available on the intestinal phase and antibody response in a susceptible host during T. patagoniensis infection. Therefore, our research has been designed to study experimental infection with T. patagoniensis compared to infection with T. spiralis in BALB/c mice. One hundred and twenty eight BALB/c mice were divided into two groups and individuals in each group were infected per os with 500 larvae of T. patagoniensis or 500 larvae of T. spiralis, respectively. After that, they were euthanized on different days. Adult worm recovery from small intestines and artificial digestion of each carcass was performed. Histopathology of small intestines was performed using hematoxylin-eosin staining. Systemic cytokines and antibody kinetics were evaluated. Intestinal adult worm recovery of T. patagoniensis and T. spiralis took place until day 17 and 25, respectively. Systemic IFN-γ, IL-10, and TNF showed significant variations in T. patagoniensis infected mice. Seroconversion was detected in animals as from 15 days post-infection (pi) for both T. patagoniensis and T. spiralis, reaching the highest OD value at 42 days pi. Similar microscopic lesions were observed in the small intestine from mice infected with the same dose of T. spiralis and T. patagoniensis. Our findings contribute new information regarding the intestinal phase and the antibody kinetics of T. patagoniensis in BALB/c mice.

A review on Trichinella infection in South America

Trichinella spp. causes human trichinellosis by means of the consumption of raw or inadequately treated meat from domestic or game animals. In the Americas, as well as in other continents, Trichinella infection is a health issue for humans and has a negative impact on the pork meat market, generated by people's fear of becoming infected with the parasite. The distribution of human cases and the sources of this disease in humans and animals were analysed in this report, which summarizes the information available regarding Trichinella infection in animals and humans in South America. Within South America, human infection with Trichinella was documented in Argentina and Chile during the period 2005-2019. Trichinellosis is endemic in these countries for, with human cases and foci in domestic and wild animals. In Argentina, human cases occur throughout the country, with foci found in pigs and wild animals. In Argentina, during the period 2012-2018, the number of suspected human cases reached 6,662. T. spiralis was identified in one South American sea lion (Otaria flavescens) from Patagonia, Argentina, for the first time in the region in 2018. In Chile, 258 human cases of trichinellosis were confirmed during the period 2005-2015; out of those 258 cases, most samples which tested positive for Trichinella spp. (29.5%) were detected in the Metropolitan district (Santiago de Chile and outskirts), and 17.4% in The Lake district. Regarding age brackets, people between 30-49 years of age showed the most cases (40.1%). In Brazil, the infection is absent in domestic species but it has been found in wild boars (Sus scrofa) but limited to one or more region of the country. Within the animal species destined for food in South America, those that showed higher parasitical loads were pigs and wild boars, while armadillos (Chaetophractus villosus) and peccaries (Tayassu tajacu) showed very low Trichinella spp. larvae loads (0.04 - 0.1 larvae/g). Antibodies against Trichinella spp. have been detected in pigs from Ecuador and Bolivia. In Bolivia, antibodies were also found in humans. Peru, Colombia and Uruguay have no documented presence of Trichinella spp. in animals and humans. There is insufficient information regarding the presence of Trichinella spp. in domestic and wild animals, as well as in humans, since only a very limited number of surveys have been carried out. No papers with information on Trichinella spp. circulating in animals or humans have been published regarding the situation in Guyana, Surinam, French Guiana, Venezuela and Paraguay. Considering the growth of the guinea pig meat market in the Andean region, and the high prevalence of the disease reported in free range pigs and wild boars, as well as other game animal species, it is important to focus on the role of biosecurity and risk management, while improving meat market regulations, and detection of infection prior to consumption, in order to reduce the risk of transmission of this zoonotic disease to humans.

Study of Trichinella patagoniensis in wild boars

Trichinellosis is a zoonotic disease, which represents a significant public health concern in some South American countries, such as Argentina and Chile. Its impact is essentially due to absence of adequate control measures on meat from game animals, as well as the presence of illegal slaughterhouses and the trade of meat products without being tested for this parasite. In Argentina, trichinellosis is an endemic disease. At present, Trichinella spiralis, Trichinella patagoniensis, Trichinella pseudospiralis, and Trichinella britovi have been detected in animals from Argentina. Until now, T. patagoniensis had only been found in mountain cougars (Puma concolor) in Argentina but there is limited information available. The present study intends to determine susceptibility, serological response and distribution of muscle larvae in wild boars infected with T. patagoniensis, T. spiralis and T. pseudospiralis. For each of the Trichinella species five wild boars were inoculated with 20,000 muscle larvae. Except for two specimens which died during the experiment, the animals were euthanized 19 weeks post infection (pi). Blood samples were collected throughout the study in order to determine the antibody kinetics. Also, nine muscle samples from each specimen were taken and analysed for determination of larval distribution. Additionally, four muscle samples were used to obtain muscle juices. Wild boars infected with T. patagoniensis showed little to no larvae in the muscle samples analysed while animals infected with T. spiralis and T. pseudospiralis had a significantly high larval load in all the samples analysed. Optical density (OD) values remained above the cut-off value throughout the experiment. This is the first study to characterize the biological aspects of T. patagoniensis in wild boars.

Trichinella infectivity and antibody response in experimentally infected pigs

The objective of the present study was to investigate the infectivity and antibody response of four Trichinella species (Trichinella spiralis, Trichinella britovi, Trichinella pseudospiralis and Trichinella murrelli) in experimentally infected pigs. A total of 120 Large White pigs (30 animals per group) were inoculated with 10,000 muscle larvae (ML) of T. spiralis, T. britovi, T. pseudospiralis, and T. murrelli. The pigs were sacrificed at 12-21 days post-infection (dpi) to examine the viability and infectivity of ML. A total of 54 Large White pigs (6 animals per group) were inoculated with 25, 50, 100, 200, 400, 600, 800, 1000 and 10,000 T. spiralis ML. The pigs were sacrificed, and the average numbers of larvae per gram (lpg) from six different muscle tissues were calculated at 120 dpi. The results showed that the larvae first be detectable for T. spiralis, T. britovi, and T. pseudospiralis at 16 dpi, 17 dpi, and 16 dpi, respectively. Viable larvae and average lpg were significantly increased with time from 17 to 21 dpi. The T. spiralis ML burden was dependent of the inoculation dose with an average lpg of 0.003, 0.005, 0.007, 0.17, 0.82, 2.89, 4.90, 28.30 and 226.18, respectively. The IgG antibody response was dose-dependent to generate and increased throughout the experimental period. And the IgG1 isotype was significantly higher than IgG2a, which meant that T. spiralis infection induced the Th2 immune response. The time of detecting IgM antibodies was significantly earlier than IgG antibody detection. These results provide important information in the primary characterization of pigs infected with Trichinella.

Use of meat juice from racoons (Procyon lotor) collected from Central Europe for immunological detection of Trichinella spp

The raccoon (Procyon lotor) is a species native to North America, but which is now spreading throughout Europe. Raccoons have been found to host various Trichinella species. The aim of the present study was to evaluate the effectiveness of using immunological testing of meat juice for determining the occurrence of Trichinella in raccoons. The studies were carried out on 139 animals from three European countries: the Czech Republic, Germany and Poland. Seven meat juice samples were found to be positive for antibodies to Trichinella by ELISA, and another seven were unclear. The ELISA results were confirmed by immunoblot: anti-Trichinella antibodies were identified in 9.35 % of the examined animals. Slight agreement (κ = 0.13) was found between the digestion method and the combined ELISA and immunoblot approach. From the results of our study, we concluded that meat juice may be used as a simple and convenient sample for detection of anti-Trichinella in racoons.

Diversity of Trichinella species in relation to the host species and geographical location

Trichinella nematodes still circulate in various hosts in both domestic and sylvatic environments. Recently, in Europe, the transmission of Trichinella spp. to humans has been attributed more to wild animals than to domestic animals. However, domestic animals could still be a source of human infections in some regions. Therefore, our aim was to determine the species composition of Trichinella and the prevalence and intensity of infections in animal populations from the domestic cycle, namely pigs (Sus scrofa f. domestica); the synantropic cycle, in the form of rats (Rattus norvegicus); and the sylvatic cycle, namely wild boars (Sus scrofa) and red foxes (Vulpes vulpes), in Poland. The findings showed that the nematode prevalence in pigs (0.0002 %) and wild boars (0.3 %) was lower than it was in red foxes (4 %). A very high prevalence was found in rats (23.3 %), but it must be emphasized that the investigated rat samples were collected from farms where pigs were infected with Trichinella spp. The mean larval burden was found to be higher in wild boars and pigs (11.48 lpg and 10.19 lpg) than in red foxes and rats (4.09 and 2.30). Trichinella spiralis was the predominant species in pigs (98.6 %), wild boars (77.3 %) and rats (100 %), while in red foxes, this species occurred less frequently (15.5 %). The most frequently occurring species in red foxes was Trichinella britovi (73.2 %). Moreover, in wild boar and red fox coinfections, T. spiralis/T. britovi were detected (3.1 and 9.9 %, respectively). In addition, Trichinella pseudospiralis was detected in a few wild boars (0.5 %) and Trichinella nativa was found in one red fox and one wild boar. Furthermore, different T. spiralis and T. britovi prevalence ratios in various geographical regions were found. In the wild boar population, a higher frequency of T. spiralis (70-85 % of infected animals) was observed in the western and central parts of Poland, while in the eastern part, this dominance was not as evident (46-59 %). In the red fox population, T. britovi was abundant throughout the entire territory; however, its highest prevalence was in the east (90-100 %).

Comparative Proteomic Analysis of Serum from Pigs Experimentally Infected with Trichinella spiralis, Trichinella britovi, and Trichinella pseudospiralis

Although the available proteomic studies have made it possible to identify and characterize Trichinella stage-specific proteins reacting with infected host-specific antibodies, the vast majority of these studies do not provide any information about changes in the global proteomic serum profile of Trichinella-infested individuals. In view of the above, the present study aimed to examine the protein expression profile of serum obtained at 13 and 60 days postinfection (d.p.i.) from three groups of pigs experimentally infected with Trichinella spiralis, Trichinella britovi, and Trichinella pseudospiralis and from uninfected, control pigs by two-dimensional gel electrophoresis (2-DE) followed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The comparative proteomic analysis of the T. spiralis group vs. the control group revealed 5 differently expressed spots at both 13 and 60 d.p.i. Experimental infection with T. britovi induced significant expression changes in 3 protein spots at 13 d.p.i. and in 6 protein spots at 60 d.p.i. in comparison with the control group. Paired analyses between the group infected with T. pseudospiralis and the uninfected control group revealed 6 differently changed spots at 13 d.p.i. and 2 differently changed spots at 60 d.p.i. Among these 27 spots, 15 were successfully identified. Depending on the Trichinella species triggering the infection and the time point of serum collection, they were IgM heavy-chain constant region, antithrombin III-precursor, immunoglobulin gamma-chain, clusterin, homeobox protein Mohawk, apolipoprotein E precursor, serum amyloid P-component precursor, Ig lambda chains, complement C3 isoform X1, and apolipoprotein A-I. Our results demonstrate that various Trichinella species and different phases of the invasion produce a distinct, characteristic proteomic pattern in the serum of experimentally infected pigs.

The occurrence and muscle distribution of Trichinella britovi in raccoon dogs (Nyctereutes procyonoides) in wildlife in the Głęboki Bród Forest District, Poland

The raccoon dog (Nyctereutes procyonoides) is an introduced, invasive species in Europe. Literature data show that raccoon dogs act as a reservoir of many dangerous parasites, including nematodes of the genus Trichinella. The aims of the study were to determine the prevalence of Trichinella spp. infection in raccoon dogs collected from the Głęboki Bród Forest District between 2013 and 2016, and to evaluate their distribution in the muscle tissue of the host. The larvae of Trichinella spp. were detected in 45 raccoon dogs (39.82%), and all of them were identified as T. britovi. No mixed infection was observed. The intensity of infection ranged from 0.02 to 622.92 larvae per gram (LPG), and the highest mean was observed in the tongue and lower forelimb in both examined sexes. The raccoon dog may play a significant role as a reservoir of T. britovi in the wildlife in the examined area.

International Commission on Trichinellosis: Recommendations on the use of serological tests for the detection of Trichinella infection in animals and humans

Serological methods are widely used for detection of infections in animals and humans. The recommendations provided here take into account the best current methods for the serological detection of Trichinella infection. They are based on current scientific information including unpublished data from laboratories with relevant expertise in this field. These recommendations represent the official position of the International Commission on Trichinellosis (ICT) regarding acceptable methods for the use and interpretation of serology testing for Trichinella infection in animals and humans.

The ICT does not recommend use of serological methods for testing individual carcasses of animals at slaughter for assuring food safety. For detection of human infections, for epidemiological studies in animals and humans, and for monitoring Trichinella infection in swine, the ICT recommends ELISA using excretory/secretory (ES) antigens. These antigens are obtained from the in-vitro maintenance of Trichinella spiralis muscle larvae and are recognized by sera from hosts infected by all Trichinella species and genotypes identified thus far. In most situations, positive results obtained by ELISA should be confirmed by western blot. Serological assays should be properly standardized and validated for their intended purpose. The components of the test that are critical for maintaining suitable performance should be identified and appropriately checked. Users of commercial tests should verify that the test has been adequately evaluated by an independent body. Serology is useful for detecting Trichinella in animals and humans but its limitations need to be taken into account when interpreting the results.

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Trichinella serology is not recommended for testing individual animals to assure food safety.

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Serological assays should be standardized and validated for their intended purpose.

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ELISA using excretory/secretory antigens is the test recommended by the ICT.

Use of ELISA and Western blot for serological detection of antibodies to E-S antigens of Trichinella spiralis muscle larvae in sera of swine experimentally infected with Trichinella spiralis

The aim of the present study was to evaluate the detection of trichinellosis using ELISA, and to determine the degree of variation of IgG antibodies against excretory-secretory (E-S) antigens of T. spiralis muscle larvae. Ten young Polish Large White native breed pigs were experimentally inoculated with a low dose of 300 invasive Trichinella spiralis (T. spiralis) muscle larvae (ML). Pig sera were collected at 7 and 9 days prior to the experimental infection with T. spiralis and at 9, 14, 20, 23, 25, 27, 30, 33, 37, 41 and 46 days post-infection (d.p.i.). Western blotting was used as a follow-up test to detect anti-T. spiralis IgG and confirm the results provided by ELISA. The molecular weight of the E-S antigenic proteins of T. spiralis muscle larvae reacting with the sera from the infected pigs was determined. Finally, the intensity of T. spiralis infection (lpg) was determined as an average value of 16 muscles taken from each pig. The E-S antigen of T. spiralis muscle larvae in the in-house ELISA and immunoblotting assays did not demonstrate any cross-reaction with non-infected pig sera and sera from pigs naturally infected with Oesophagostomum spp. The ELISA assay did not recognize trichinellosis in pigs until 27 days after the T. spiralis infection. The anti-Trichinella IgG antibodies were first detected on day 30 post-infection. The immunoblotting technique confirmed the presence of anti-Trichinella IgG antibodies in all serum samples evaluated as ELISA-positive. The Western blot detected anti-Trichinella IgG antibodies on the same day they were detected for the first time by ELISA in five pigs, whereas the immunoblot assay detected seroconversion 2, 3 or 4 days earlier than ELISA in the remaining three pigs. The swine sera reacted with a broad range of T. spiralis ML E-S antigens with molecular weights ranging from 30 to 88 kDa and the most frequently recognized proteins were 45, 49 and 60 kDa.

Seroprevalence of Trichinella infections in domestic dogs from Slovakia

Trichinellosis is constantly present in the sylvatic cycle in Slovakia, with several sporadic human outbreaks registered since the 1960s. The largest outbreak of trichinellosis occurred in 1998 and was related to the consumption of dog meat that had been added to smoked pork sausages. The aim of this study was to estimate the seroprevalence of Trichinella infection in domestic dogs in various regions of Slovakia. Out of 439 dogs tested, 56 (12.8%) were classified as a seropositive based on the enzyme-linked immunosorbent assay (ELISA), with confirmation by Western blotting. The highest seropositivity was recorded among dogs from the eastern part of Slovakia, in the Prešov (22.9%) and Košice (17.1%) regions, long considered to be highly endemic for Trichinella occurrence and where the prevalence of infection in the vulpine population is also the highest in Slovakia. Trichinella-seropositive animals were detected significantly more often in dogs kept in rural areas (21.1%) when compared with animals living in towns or suburban localities (7.7%). On the other hand, neither age, nor gender and size of the dogs were shown to be a significant factor for Trichinella infection (P > 0.05). The present results indicate that the dog population in Slovakia is at high risk of exposure to Trichinella parasites and could potentially represent a suitable host group for serological monitoring of Trichinella infection as convenient sentinel animals.

Cross-Sectional Study of Anti-Trichinella Antibody Prevalence in Domestic Pigs and Hunted Wild Boars in Estonia

Trichinella spp. are relevant zoonotic pathogens in Estonia. The aim of this nationwide cross-sectional study was to estimate the seroprevalence of Trichinella spp. in domestic pigs (Sus scrofa domestica) and hunted wild boars (Sus scrofa). Serum samples from 374 pigs, originating from 14 farms, and meat juice samples from 470 wild boars were tested for immunoglobulin G antibodies against Trichinella excretory/secretory antigens using a commercial enzyme-linked immunosorbent assay (ELISA). Antibodies against Trichinella were not detected in the domestic pigs, indicating effective parasite control strategies in the farms. By contrast, 42.1% of the wild boars tested positive, indicating substantial infection pressure in the sylvatic cycle. Further analysis of a subset of the wild boar samples, using another ELISA and Western blot, yielded a confirmed seroprevalence estimate of 17.4%. A substantial proportion of wild boars in Estonia had evidence of exposure to Trichinella spp. and may have carried infective larvae. Undercooked Estonian wild boar meat is a potential source of Trichinella spp. infections to humans and other hosts.

Quantitative Risk Assessment of Human Trichinellosis Caused by Consumption of Pork Meat Sausages in Argentina

In Argentina, there are three known species of genus Trichinella; however, Trichinella spiralis is most commonly associated with domestic pigs and it is recognized as the main cause of human trichinellosis by the consumption of products made with raw or insufficiently cooked pork meat. In some areas of Argentina, this disease is endemic and it is thus necessary to develop a more effective programme of prevention and control. Here, we developed a quantitative risk assessment of human trichinellosis following pork meat sausage consumption, which may be used to identify the stages with greater impact on the probability of acquiring the disease. The quantitative model was designed to describe the conditions in which the meat is produced, processed, transported, stored, sold and consumed in Argentina. The model predicted a risk of human trichinellosis of 4.88 × 10(-6) and an estimated annual number of trichinellosis cases of 109. The risk of human trichinellosis was sensitive to the number of Trichinella larvae that effectively survived the storage period (r = 0.89), the average probability of infection (PPinf ) (r = 0.44) and the storage time (Storage) (r = 0.08). This model allowed assessing the impact of different factors influencing the risk of acquiring trichinellosis. The model may thus help to select possible strategies to reduce the risk in the chain of by-products of pork production.

Diagnostic accuracy of porcine acute phase proteins in meat juice for detecting disease at abattoir

The aim of this work was to evaluate whether acute phase protein (APP) determinations could assist Official Veterinarians carrying out work in slaughterhouses. To test this hypothesis, the diagnostic accuracy of APP determinations in meat juice of pigs was analysed to differentiate between healthy and diseased pigs. One hundred and one pigs of two different origins were classified into two groups according to their health status (healthy and diseased pigs), which was determined by a veterinary clinical examination on the farm. To assess the pigs' immune status, against the main porcine diseases, serological analyses were monitored. A general idea of the degree of disease coverage was analysed by examining organ lesions postmortem. Haptoglobin (Hp) and C reactive protein (CRP) were measured in meat juice samples. 72.13 per cent of pigs appeared to be seropositive for the porcine respiratory and reproductive syndrome virus, and almost 86.2 per cent of them had concomitant infections with other pathogens, such as Porcine circovirus type 2 or Swine influenza virus. Median Hp and CRP concentrations were significantly higher in diseased animals at different stages of the production chain, when compared with levels found in healthy finishing pigs (P<0.0001). Receiver operating characteristic analysis showed the highest sensitivity-specificity pairs, nearly 80-90 per cent, at cut-off levels of 83 and 10 µg/ml for Hp and CRP determinations, respectively, with high AUCs 0.9. This cut-off could be useful for veterinary inspections at the time of slaughter, to differentiate between the carcase of a healthy animal and the carcase of an animal suffering from a systemic disease, which should be completely condemned.

Effect of temperature on the survival of Alaria alata mesocercariae

Recent findings of Alaria alata mesocercariae in wild boars and other animals in Europe reinforced the concern about the public health risk posed by this parasite especially if the game meat is insufficiently heated during preparation. Cooking and freezing are effective methods for the inactivation of parasites in meat whereas refrigeration is considered as an essential part of the Good Hygiene Practice. Additionally, microwave dielectric heating may represent an equally effective tool for parasite inactivation. Therefore, isolated vital mesocercariae were examined with respect to their resilience against heating, refrigeration, freezing, and microwave heating. A. alata mesocercariae stored in Ringer's solution do not survive heating temperatures that exceed 60.0 °C. Similarly, exposure to microwave heating ensured an inactivation of all parasite developmental stages after 90 s of treatment. In contrast, the parasites' tolerance towards cold is far higher as the mesocercariae survived refrigeration temperatures (4.0 ± 2 °C) in Ringer's solution for up to 13 days. An effective inactivation by cold is therefore only guaranteed if the infested game meat is frozen to a core temperature of -13.7 °C for a minimum of 2 h at least. Game meat should be handled with the same or even higher caution than meat of husbandry animals since wild animals may be infected with parasites or other zoonotic agents that are not common in livestock. It is therefore of crucial importance that appropriate temperature time protocols are used for the reliable inactivation of these zoonotic agents.

Recognition of antigens of three different stages of the Trichinella spiralis by antibodies from pigs infected with T. spiralis

Infective muscle larvae (ML), adults (Ad) and new born larvae (NBL) of Trichinella spiralis express many immunogenic proteins which can elicit a host protective response, and may be useful in the diagnosis of Trichinella infected humans and animals. The present study was carried out to identify T. spiralis antigens recognized by antibodies from pigs infected with T. spiralis. To that end, the crude extracts of ML, Ad, NBL and ML excretory-secretory (E-S) and Ad E-S proteins were analyzed by sodium dodecyl sulfate polycrystalline gel electrophoresis (SDS-PAGE). To identify antigens of T. spiralis that are recognized by host antibodies, crude extracts and E-S proteins were subjected to immunoblot with antisera derived from pigs experimentally infected with 200 or 20,000 T. spiralis ML. Searching for T. spiralis antigens with diagnostic potential, immunoblots showed that all T. spiralis antisera, regardless of the infective dose, recognized common proteins in each examined life stage with molecular weights around 20-27 kDa, 41 kDa and 197-105 kDa. Interestingly, all the common proteins were detected by T. spiralis sera throughout the infection, from 5 days post infection (dpi) to 60 dpi. These results extend our knowledge of specific antigenic components of T. spiralis. The finding of common components among all T. spiralis life stages may be useful in the preparation of parasite antigens for diagnostic use, as these antigens are relevant regardless of infection phase.

Farmed wild boars exposed to Toxoplasma gondii and Trichinella spp

The meat of wild boar (Sus scrofa L.) can be a source of human infections with zoonotic parasites Toxoplasma gondii and Trichinella spp. We screened 197 wild boar sera collected at slaughter from 25 Finnish farms in 2007-2008 for serological evidence of infections with these parasites. Using a commercial direct agglutination test at a serum dilution of 1:40, T. gondii-specific IgG antibodies were detected in 65 (33.0%) samples, on 14 (56.0%) farms. Females, animals older than 24 months, animals of small herds, and animals originating from south-western parts of Finland were more often T. gondii-seropositive than were males, younger animals, animals of larger herds, and animals originating from the north and east, respectively. Four (2.0%) of the sera, originating from three (12.0%) farms, tested Trichinella-seropositive with an in-house ELISA and a conservative cut-off for seropositivity. One farm had both T. gondii- and Trichinella-seropositive animals. Taken together, an infection source had been present on 16 (64.0%) farms, and 69 (35.0%) of the 197 farmed wild boars intended for human consumption had specific serological evidence of exposure to a zoonotic parasite.

Specific serum antibody responses following a Toxoplasma gondii and Trichinella spiralis co-infection in swine

The aim of this study was to examine the dynamics of parasite specific antibody development in Trichinella spiralis and Toxoplasma gondii co-infections in pigs and to compare these with antibody dynamics in T. spiralis and T. gondii single infections. In this experiment, fifty-four pigs were divided into five inoculated groups of ten animals, and one control group of four animals. Two groups were inoculated with a single dose of either T. gondii tissue cysts or T. spiralis muscle larvae, one group was inoculated simultaneously with both parasites and two groups were successively inoculated at an interval of four weeks. Specific IgG responses to the parasites were measured by ELISA. T. gondii burden was determined by MC-PCR carried out on heart muscle and T. spiralis burden by artificial digestion of diaphragm samples. Specific IgG responses to T. gondii and T. spiralis in single and simultaneously inoculated animals showed a respective T. gondii and T. spiralis inoculation effect but no significant interaction of these parasites to the development of specific antibodies with the serum dilutions used. Moreover, our data showed that the specific IgG response levels in groups of animals successively or simultaneously co-infected were independent of a respective previous or simultaneous infection with the other parasite. Additionally, no differences in parasite burden were found within groups inoculated with T. gondii and within groups inoculated with T. spiralis. Conclusively, for the infection doses tested in this experiment, the dynamics of specific antibody development does not differ between single and simultaneous or successive infection with T. gondii and T. spiralis. However, lower parasitic doses and other ratios of doses, like low-low, low-high and high-low of T. gondii and T. spiralis in co-infection, in combination with other time intervals between successive infections may have different outcomes and should therefore be studied in further detail.

Quality control of Toxoplasma gondii in meat packages: standardization of an ELISA test and its use for detection in rabbit meat cuts

Toxoplasma gondii causes severe disease both to man and livestock and its detection in meat after slaughtering requires PCR or biological tests. Meat packages contain retained exudate that could be used for serology due to its blood content. Similar studies reported false negative assays in those tests. We standardized an anti-T. gondii IgG ELISA in muscle juices from experimentally infected rabbits, with blood content determination by cyanhemoglobin spectrophotometry. IgG titers and immunoblotting profiles were similar in blood, serum or meat juice, after blood content correction. These assays were adequate regardless of the storage time up to 120 days or freeze-thaw cycles, without false negative results. We also found 1.35% (1/74) positive sample in commercial Brazilian rabbit meat cuts, by this assay. The blood content determination shows ELISA of meat juice may be useful for quality control for toxoplasmosis monitoring.

Evaluation of a Western Blot and ELISA for the detection of anti-Trichinella-IgG in pig sera

Human trichinellosis is a foodborne disease caused by ingestion of infective Trichinella muscle larvae via pork or meat of other food animals which are susceptible to this zoonotic parasite. There are new approaches for a risk-oriented meat inspection for Trichinella in pigs which are accompanied by monitoring programmes on herd level to control freedom from this parasite. For this purpose, testing schemes utilizing serological tests with a high sensitivity and specificity are required. This study aimed at the evaluation of an ELISA and a Western Blot (WB) for the detection of anti-Trichinella-IgG in terms of sensitivity and specificity taking results of artificial digestion as gold standard. For this purpose, 144 field sera from pigs confirmed as Trichinella-free as well as 159 sera from pigs experimentally infected with T. spiralis (123), T. britovi (19) or T. pseudospiralis (17) were examined by ELISA (excretory-secretory antigen) and WB (crude worm extract). Sera from pigs experimentally infected with four other nematode species were included to investigate the cross-reactivity of the antigen used in the WB. For all Trichinella-positive pig sera, band pattern profiles were identified in the WB and results were analysed in relation to ELISA OD% values. Testing of pig sera revealed a sensitivity of 96.8% for the ELISA and 98.1% for the WB whereas the methods showed a specificity of 97.9 and 100%, respectively. WB analysis of Trichinella-positive pig sera revealed five specific band patterns of 43, 47, 61, 66, and 102 kDa of which the 43 kDa protein was identified as the predominant antigen. The frequency of the band pattern profile was irrespective of the dose and the period of infection as well as the Trichinella species investigated. In conclusion, monitoring in swine farms for Trichinella antibodies should be based on screening pig sera by means of ELISA followed by confirmatory testing through WB analysis.

Validation of a Western Blot for the detection of anti-Trichinella spp. antibodies in domestic pigs

Trichinellosis is a zoonotic disease in humans caused by Trichinella spp. According to international regulations and guidelines, serological surveillance can be used to demonstrate the absence of Trichinella spp. in a defined domestic pig population. Most enzyme-linked immunosorbent assay (ELISA) tests presently available do not yield 100% specificity, and therefore, a complementary test is needed to confirm the diagnosis of any initial ELISA seropositivity. The goal of the present study was to evaluate the sensitivity and specificity of a Western Blot assay based on somatic Trichinella spiralis muscle stage (L1) antigen using Bayesian modeling techniques. A total of 295 meat juice and serum samples from pigs negative for Trichinella larvae by artificial digestion, including 74 potentially cross-reactive sera of pigs with other nematode infections, and 93 meat juice samples from pigs infected with Trichinella larvae were included in the study. The diagnostic sensitivity and specificity of the Western Blot were ranged from 95.8% to 96.0% and from 99.5% to 99.6%, respectively. A sensitivity analysis showed that the model outcomes were hardly influenced by changes in the prior distributions, providing a high confidence in the outcomes of the models. This validation study demonstrated that the Western Blot is a suitable method to confirm samples that reacted positively in an initial ELISA.

Epidemiology, diagnosis, treatment, and control of trichinellosis

SUMMARY

Throughout much of the world, Trichinella spp. are found to be the causative agents of human trichinellosis, a disease that not only is a public health hazard by affecting human patients but also represents an economic problem in porcine animal production and food safety. Due to the predominantly zoonotic importance of infection, the main efforts in many countries have focused on the control of Trichinella or the elimination of Trichinella from the food chain. The most important source of human infection worldwide is the domestic pig, but, e.g., in Europe, meats of horses and wild boars have played a significant role during outbreaks within the past 3 decades. Infection of humans occurs with the ingestion of Trichinella larvae that are encysted in muscle tissue of domestic or wild animal meat. Early clinical diagnosis of trichinellosis is rather difficult because pathognomonic signs or symptoms are lacking. Subsequent chronic forms of the disease are not easy to diagnose, irrespective of parameters including clinical findings, laboratory findings (nonspecific laboratory parameters such as eosinophilia, muscle enzymes, and serology), and epidemiological investigations. New regulations laying down rules for official controls for Trichinella in meat in order to improve food safety for consumers have recently been released in Europe. The evidence that the disease can be monitored and to some extent controlled with a rigorous reporting and testing system in place should be motivation to expand appropriate programs worldwide.

Complement membrane attack complex formation and infectivity of Trichinella spiralis and T. nativa in rats

Rats readily become infected with Trichinella spiralis but are more resistant to T. nativa. We infected complement factor C6-deficient (C6-) rats and control (C6+) rats with T. spiralis and T. nativa to compare the effects of membrane attack complex on these parasites in vivo. The 2000 larvae infection dose per rat yielded 652 lpg (larvae per gram) in the C6- group and 608 lpg in the C6+ group with T. spiralis, whereas with T. nativa the corresponding figures were only 1.05 and 1.87 lpg. The difference between the Trichinella species was evident, but the infection intensity was unaffected by the C6 deficiency. When newborn larvae were incubated in C6-deficient and control rat sera for 24h in vitro, no changes in viability were observed. Immunohistochemistry revealed that the musculature of cross-sectioned adults and certain stichocytes bound human complement factors C3, C8 and C9, but not C1q. Interestingly, the outermost layer of the cuticle and the newborn larvae did not show any binding activity. Similar findings were obtained with immunofluorescence microscopy of intact newborn larvae. These results indicate that both T. spiralis and T. nativa have efficient mechanisms to protect themselves against complement attack. The difference in infectivity for rats between the two species, however, is not due to a differential resistance to complement membrane attack complex.

Serological detection of Trichinella spiralis in swine by ELISA (enzyme-linked immunosorbent assay) using an excretory-secretory (E/S) antigen

The enzyme-linked immunosorbent assay (ELISA) method is recommended for farm surveillance programs and may be useful for epidemiological studies in wildlife or for establishing Trichinella-free areas. In this study, our interest was to compare the specificity and the time of seroconversion of excretory-secretory (E/S) antigens prepared from Trichinella spiralis. A group of eight pigs was inoculated with 500 T. spiralis larvae per animal, and blood sampling was performed at 3 and 4-day intervals during all experiments. The numbers of muscle larvae were determined in four different muscles groups. The larvae per gram burden shows that the most heavily parasitized muscles were the diaphragm [mean = 43.7 larvae per gram (lpg)] and the tongue (mean = 16.9 lpg). Antibody responses were detected by any of eight infected pigs of T. spiralis. Using the ELISA method with E/S antigen, antibodies to T. spiralis were first found on the day 21st p.i. The initial detection of antibodies varied from 21st to 31st day p.i., and the peak was reported 42nd day p.i. Dynamic of antibodies was stable or increased slightly throughout the experimental period (60 days post-inoculation). Our results represent important data for validation of a serological test, especially if blood samples are taken during early stages of infection.

Concurrent infection with Trichinella spiralis and other helminths in pigs

The aim of this study was to investigate possible influence of different helmintosis in the development of Trichinella spiralis in experimental infected pigs. Forty-two Iberian pigs were allocated to six groups. Three groups were single inoculated with Ascaris suum, Metastrongylus apri or T. spiralis, respectively. Two groups were co-infected with T. spiralis and A. suum or T. spiralis and M. apri, respectively, while the last group included uninfected control pigs. Clinical signs were only observed in pigs with single or concurrent M. apri infections, with more severe respiratory symptoms in pigs with mixed M. apri infection. The number of A. suum and M. apri lung larvae, intestinal larvae of A. suum and adult M. apri were reduced in pigs with mixed Trichinella infections compared to pigs with single infections. In contrast, the number of liver white spots was higher in pigs with mixed infections. While T. spiralis muscular larval burdens were increased in pigs concomitantly infected with M. apri, they were reduced in pigs concomitantly infected with A. suum, compared to pigs receiving single infections with either of these helminths. Pigs with single or mixed A. suum infections showed higher eosinophil levels compared to the remaining groups. IgGt, IgG1, IgG2 and IgM against T. spiralis antigen could not be detected in pigs with single Ascaris or Metastrongylus infections, indicating that no cross-antibodies were produced. IgGt, IgG1 and IgM antibodies were detected earlier and generally at higher levels in mixed T. spiralis infections compared to single T. spiralis infections. The results suggest that T. spiralis had a low synergistic interaction with M. apri in concomitantly infected pigs, and an antagonistic interaction in concurrent infection with A. suum.

Trichinella nativa in sylvatic wild boars

Of 17 Trichinella isolates from domestic pigs and wild boars (Sus scrofa) in regions where Trichinella nativa is widespread among sylvatic animals, two wild boars from Estonia were found to be naturally infected with this Trichinella species. The other 15 animals were infected with Trichinella spiralis. Trichinella nativa is tolerant to freezing when in the muscles of carnivores. The biological characteristics and temperature tolerance of this species in swine need to be further investigated if pork is certified for consumption following freezing.

Influence of infection intensity on predilection sites in swine trichinellosis

The muscular distribution of Trichinella spiralis or T. britovi was studied by digestion in 59 experimentally infected pigs and seven wild boars. Crus muscle was the predilection site in 89.3% of 28 heavily infected swine with 146–3634 larvae per gram (lpg), but in 51.6% of middle to light infections (0.005–59 lpg) the basis of the tongue showed higher larval densities than the crus muscle. The basis of the tongue was also the predilection site in 71.4% of wild boars. Highest counts in other muscles were found only in lightly infected pigs. The influence of intensity of infection, host species, and Trichinella species on muscle distribution is discussed.

Swine infection with Trichinella spiralis: Comparative analysis of the mucosal intestinal and systemic immune responses

The immune protective response developed by swine against Trichinella spiralis is not yet fully understood, particularly at the mucosal level. This study aimed to characterise intestinal immunity to T. spiralis by comparison with the systemic response in specifically pathogen-free pigs. For this purpose, the kinetics of cytokine and antibody production were assessed in the intestinal mucosa and serum of swine infected with T. spiralis for up to 60 days post-infection (dpi). An ex vivo model of jejunum mucosa culture was used to collect the supernatant as a source of antibodies (Abs). Mucosal antibodies were observed by Western blot from 15 dpi, while serum antibodies were expressed from 20 dpi. Both sources of antibodies initially recognized a 110 kDa protein, followed by the identification of 35, 43/46 and 55/59 kDa proteins. IgG1 and IgA antibodies were strongly expressed within the mucosa. The expression levels of Type 1 (IFN-gamma, IL-12), Type 2 (IL-4, IL-6), pro-inflammatory (TNF-alpha) and regulatory (IL-10, TGF-beta) cytokines were assessed by RT-PCR in the intestinal mucosa and spleen. Both IL-10 and IFN-gamma mRNA levels were increased in mucosa, whereas IL-6 and IL-12 mRNA were expressed in spleen. Taken together, these results demonstrated a mixed Type 1/Type 2 profile, the Type 2 profile being dominant in the mucosa.

Experimental studies in pigs on Trichinella detection in different diagnostic matrices

A total of 72 specific pathogen-free (SPF) and Iberian pigs (three animals per group) were inoculated with 200, 1000 or 20,000 muscle larvae of T. spiralis, T. nativa, T. britovi and T. pseudospiralis. For each animal, the muscle larva burden was evaluated in nine muscle samples by digestion. The anti-Trichinella IgG kinetics in blood samples, taken twice prior and at days 5, 10, 15, 20, 25, 30, 40, 50 and 60 post-inoculation, and in muscle juice, obtained at necropsy, was evaluated by an ELISA using an excretory/secretory antigen. The mean larval recovery rate in SPF/Iberian pigs corresponded with the level of inoculum dose, and tongue, diaphragm and masseter were identified as predilection muscles. In SPF and Iberian pigs receiving 20,000 larvae of T. spiralis, an earlier seroconversion was detected from day 25 post-inoculation. At a 10-fold dilution, the muscle juice showed a good test agreement with blood serum.

Comparison of two antigens for demonstration of Trichinella spp. antibodies in blood and muscle fluid of foxes, pigs and wild boars

For the surveillance of trichinellosis, the digestion method is reliable but also labour intensive. The serological methods for the detection of Trichinella-specific antibodies using ELISA offer a sensitive and relatively specific alternative. For serological studies, sera or plasma from blood samples are the most common source of antibodies, but although the concentration of antibodies is approximately 10-fold lower, muscle fluid can be a good alternative particularly for testing of wildlife samples. In the present study, an indirect ELISA technique was evaluated on both sera and muscle fluids from experimentally infected foxes, pigs, and wild boars using both excretory/secretory (E/S) antigens and a synthetic glycan antigen, beta-tyvelose. Although the synthetic antigen appears to be less sensitive than the E/S antigens, Trichinella-specific IgG antibodies were detected in both serum samples and muscle fluid samples from pigs, wild boars and foxes infected at levels which would be important for food safety or represent a significant reservoir for further transmission.

Muscle distribution of sylvatic and domestic Trichinella larvae in production animals and wildlife

Only a few studies have compared the muscle distribution of the different Trichinella genotypes. In this study, data were obtained from a series of experimental infections in pigs, wild boars, foxes and horses, with the aim of evaluating the predilection sites of nine well-defined genotypes of Trichinella. Necropsy was performed at 5, 10, 20 and 40 weeks post inoculation. From all host species, corresponding muscles/muscle groups were examined by artificial digestion. In foxes where all Trichinella species established in high numbers, the encapsulating species were found primarily in the tongue, extremities and diaphragm, whereas the non-encapsulating species were found primarily in the diaphragm. In pigs and wild boars, only Trichinella spiralis, Trichinella pseudospiralis and Trichinella nelsoni showed extended persistency of muscle larvae (ML), but for all genotypes the tongue and the diaphragm were found to be predilection sites. This tendency was most obvious in light infections. In the horses, T. spiralis, Trichinella britovi, and T. pseudospiralis all established at high levels with predilection sites in the tongue, the masseter and the diaphragm. For all host species, high ML burdens appeared to be more evenly distributed with less obvious predilection than in light infections; predilection site muscles harbored a relatively higher percent of the larval burden in light infections than in heavy infections. This probably reflects increasing occupation of available muscle fibers as larger numbers of worms accumulate. Predilection sites appear to be influenced primarily by host species and secondarily by the age and level of infection.

Trichinella nativa in a black bear from Plymouth, New Hampshire

A suspected case of trichinellosis was identified in a single patient by the New Hampshire Public Health Laboratories in Concord, NH. The patient was thought to have become infected by consumption of muscle larvae (ML) in undercooked meat from a black bear killed in Plymouth, NH in October 2003 and stored frozen at -20 degrees C fro 4 months. In January 2004, a 600 g sample of the meat was thawed at 4 degrees C, digested in hydrochloric acid and pepsin, and larvae were collected by sedimentation. Intact, coiled, and motile ML were recovered (366 larvae per gram (l pg) of tissue), which were passed into mice and pigs. Multiplex PCR revealed a single 127 bp amplicon, indicative of Trichinella nativa. The Reproductive Capacity Index (RCI) for the T. nativa-Plymouth isolate in mice was 24.3. Worm burdens in the diaphragms of two 3-month-old pigs given 2,500 ML were 0.05 and 0.2l pg by 35 days post-inoculation, while 2.2 and 0.75 l pg were recovered from two 3-month-old pigs given 10,000 ML; no larvae were recovered from four 1-year-old pigs given 2,500 ML (n=2) or 10,000 ML (n=2). Viable larvae were also recovered from frozen black bear meat harvested at two additional locations, one in southern Ontario, Canada, and one in upstate New York, USA. Multiplex PCR using genomic DNA from these parasite samples demonstrated that both isolates were T. nativa. This is the first report of the freeze-resistant species, T. nativa, within the continental United States.

Evaluation of ELISA for detection of Trichinella antibodies in muscle juice samples of naturally infected pigs

The performance characteristics of an ELISA test for trichinellosis in pigs applied to muscle juice was assessed using 314 samples collected from pigs located in endemic areas of Croatia. Peptic digestion was used as the reference method. The diagnostic accuracy of the two compared dilutions (1:10 and 1:100) was considered to be high because the area under the curve (AUC) index was 0.922 and 0.920 for each dilution, respectively. In this study the two graph-receiver operating characteristic (TG-ROC) analysis was used as a tool for selecting cut-off points. Sensitivity, specificity, likelihood ratios, efficiency and Youden's index were used as indices of test accuracy. The cut-off values that minimize overall misclassification cost under an assumption of 3% prevalence were calculated. Our results indicate that the ELISA applied to muscle juice is a highly accurate test and can be adapted to process a large number of samples.