Detection of Trichinella infection in slaughter horses by ELISA and western blot analysis

Statistical approach to Trichinella infection in horses handled by rural slaughterhouses across five distinctive socioeconomic regions in Mexico

This work aimed to investigate the prevalence of Trichinella infection in horses (Equus ferus caballus) handled by rural slaughterhouses across five distinctive socioeconomic regions in Mexico. Serum samples were obtained by non-probabilistic convenience sampling in the Eastern, Southern Central and Western regions (100 samples of each). Additionally, muscle tissue samples were collected from the East (n=45), Southeastern (n=88), Southern Central (n=39) and Southwestern (n=11) regions. Antibodies were determined by Western blot and the muscle tissue was examined by artificial digestion. A global antibody prevalence of 2% was obtained. Regionally, a prevalence of 5% was observed in the East and 1% in the Southern Central region. No antibodies were detected in the West region and no larvae were found in the muscle tissue samples. These findings support the low presence of Trichinella in Mexican horses, which can positively impact the Mexican horse meat trade.

Trichinella spp. imported with live animals and meat

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

Pathological and parasitological traits in experimentally infected cats with Gnathostoma binucleatum (Spirurida: Gnathostomatidae)

This study aims to describe some of the unknown pathological and parasitological traits of experimental feline gnathostomosis. Thirteen female cats were orally inoculated with 30 advanced third-stage Gnathostoma binucleatum larvae and were euthanized at various post-infection (p.i.) periods. Clinically, the cats presented with nausea, vomiting, abdominal pain and other nonspecific signs. None of the cats shed eggs in their fecal matter. One cat, euthanized at 6 months p.i., developed a fibrous vascular nodule 2-3 cm in diameter within its gastric wall. The nodule contained caverns filled with mucous and bloody fluid as well as a juvenile worm. The histological characteristics of the nodule were observed, and the morphology of the juvenile worm was revealed using scanning electron microscopy. Another cat, euthanized at 10 months p.i., was found to have a larva within its diaphragm. Infected cats developed increased antibody titers against antigens of G. binucleatum adults and larvae beginning in the first month p.i., and these titers were maintained until the end of the experiment, suggesting the presence of undetected migrating larvae. The low number of cats with parasites and poor development of the parasites found suggest that cats have a low susceptibility to infection by G. binucleatum and cast doubt on the importance of domestic cats in maintaining the biological cycle of this parasite in nature.

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.

Rapid detection of Trichinella spiralis larvae in muscles by loop-mediated isothermal amplification

Trichinella spiralis is a tissue-dwelling nematode parasite. A loop-mediated isothermal amplification (LAMP) assay was developed and validated for the sensitive and rapid detection of T. spiralis larvae in muscle samples. Sixteen sets of primers were designed to recognise distinct sequences of a conserved gene, a 1.6kb repetitive element of the Trichinella genome. One set of primers was selected as the most appropriate for rapid detection. The specificity and sensitivity of the primers in LAMP reactions for T. spiralis larvae and muscle samples of mice infected with T. spiralis were determined. Another 10 heterologous parasites were selected for specificity assays. The results showed that target DNA was amplified and visualised by monitoring turbidity and adding calcein detection methods within 70min at an isothermal temperature of 63°C. The sensitivity of LAMP with the detection limit of 362fg/μl was >10 times higher than that for PCR. The designed primers had a good specificity. No cross-reactivity was found with the DNA of any other parasites. The assay was able to detect T. spiralis in all mouse muscle samples infected with 10 T. spiralis larvae on day 20 p.i. We believe this is the first report regarding the application of the LAMP assay for detection of T. spiralis larvae in muscle samples from experimentally infected mice. This method demonstrates a potentially valuable means for the direct detection of T. spiralis larvae in meat inspection.

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.

Trichinella diagnostics and control: mandatory and best practices for ensuring food safety

Because of its role in human disease, there are increasing global requirements for reliable diagnostic and control methods for Trichinella in food animals to ensure meat safety and to facilitate trade. Consequently, there is a need for standardization of methods, programs, and best practices used in the control of Trichinella and trichinellosis. This review article describes the biology and epidemiology of Trichinella, and describes recommended test methods as well as modified and optimized procedures that are used in meat inspection programs. The use of ELISA for monitoring animals for infection in various porcine and equine pre- and post-slaughter programs, including farm or herd certification programs is also discussed. A brief review of the effectiveness of meat processing methods, such as freezing, cooking and preserving is provided. The importance of proper quality assurance and its application in all aspects of a Trichinella diagnostic system is emphasized. It includes the use of international quality standards, test validation and standardization, critical control points, laboratory accreditation, certification of analysts and proficiency testing. Also described, are the roles and locations of international and regional reference laboratories for trichinellosis where expert advice and support on research and diagnostics are available.

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

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

TSL-1 antigens of Trichinella: An overview of their potential role in parasite invasion, survival and serodiagnosis of trichinellosis

The majority of studies on the immunobiology of Trichinella species have centred on the larval muscular phase (L1) with a view to identifying immunodominant antigens located on the surface of the cuticle and in the larval secretions; the nucleus of the parasite-host interaction. These antigens have been classified as eight groups (TSL-1-TSL-8), of which those belonging to the group TSL-1 have been most intensely studied. The principal constituents are glycoproteins, glycan carriers that contain a unusual sugar, the tyvelose (3,6-dideoxy-d-arabinohexose). Studies aimed at improving serodiagnostic techniques to detect trichinellosis indicate that these antigens are ideal candidates. They are capable of inducing a strong humoral response involving the generation of specific antibodies against beta-tyvelose, a sugar that seems to be exclusive to the Trichuroidea. Furthermore, these glycoproteins appear to fulfil an important function in the development and maintenance of the parasite in the muscular niche, and they appear to be fundamental for the invasion of the intestinal epithelium. It has also been demonstrated that specific monoclonal antibodies against tyvelose can mediate a degree of immunoprotection in the rat through the phenomenon known as rapid expulsion.

Distribution of muscle larvae and antibody dynamics in goats experimentally infected with Trichinella spiralis

Herbivorous animals can play a very important role in spreading trichinellosis. In the study presented here, the susceptibility and distribution of Trichinella spiralis infection was examined in 16 goat kids. The goats were inoculated with 10,000 T. spiralis larvae isolated by artificial digestion methods. The animals were necropsied per two animals in weekly intervals, and the larval burdens in different muscle tissue and anti-Trichinella antibodies measured with the indirect enzyme-linked immunosorbent assay (ELISA) serological method using excretory-secretory (E/S) antigen for detecting anti-Trichinella antibodies were assessed during the experiment. T. spiralis larval burden was maximal at 6 weeks postinoculation (480-5,057 larvae/g according to locality), and the larvae were also found in the myocardium (0.77 larvae/g). In this paper, our next step was to compare the specificity and the time of seroconversion by means of ELISA based on E/S antigen prepared from T. spiralis. Antibody response was detected in all 16 goats. The ELISA test carried out showed the first increments in optical density 2 weeks postinfection (p.i.), reached their peak 4 weeks p.i., and remained elevated from that day until the end of the experiment (10 weeks p.i.). These results indicated that specific anti-Trichinella antibodies in goats persist for a relatively long time.

Influence of methods for Trichinella detection in pigs from endemic and non-endemic European region

A total of 1401 German and 226 Croatian pigs raised either indoors or outdoors were tested for Trichinella infection by direct and indirect detection methods. A 10 g sample of diaphragm were examined for muscle larvae by the artificial digestion method; the species was determined by multiplex polymerase chain reaction (PCR). For detection of anti-Trichinella IgG, serum samples diluted 1:100, and meat juice samples diluted 1:10, were tested by enzyme-linked immunosorbent assay. All German pigs and those Croatian pigs raised indoors proved to be Trichinella-negative by all methods. Muscle larvae were detected in a total of eleven of the Croatian pigs, which were raised on small outdoor farms. For eight isolates, PCR results demonstrated that recovered larvae were Trichinella spiralis. Anti-Trichinella-IgG was detected in serum and meat juice of digestion positive animals when the worm burdens exceeded 0.38 larvae per gram of muscle. Positive results in Croatian pigs indicate a higher risk of infection for outdoor farming in areas where Trichinella is endemic. Results of direct and indirect detection were compared and are discussed with special regard to specificity and sensitivity of methods.

Trichinella nativa and T. spiralis induce distinguishable histopathologic and humoral responses in the raccoon dog (Nyctereutes procyonoides)

Three experimental groups of six male raccoon dogs (Nyctereutes procyonoides) each were formed by placing one of three littermates from six litters into each group. One group was inoculated with pig-origin Trichinella spiralis, the second was inoculated with raccoon dog-origin T. nativa, and the third served as a control group. The infective dose was 1,000 larvae/kg of body weight. Every third week, biopsies from M. triceps brachii were taken, and serum samples were collected for up to 12 weeks postinfection. In the early phase of the infection, cysts of both parasites were elongated cylinders that later became more spherical. However, at the end of the experiment, the cysts of T. nativa were more rounded than those of T. spiralis (mean length/width = 2.5 versus 1.5 in T. spiralis versus T. nativa, respectively). Both species accumulated a collagen-rich capsule around the nurse cell, but the capsule was thicker in T. nativa. In both parasites, the total surface area of the sagittal section of the cyst was equal. Inflammation was more intense around T. nativa cysts. Specific antibodies were recognizable 2 weeks after infection by both enzyme-linked immunosorbent assay (ELISA) and western blot. In western blots, serum from both T. nativa- and T. spiralis-infected animals recognized the same components, but reaction with the homologous antigen was stronger. The same pattern was also seen in the ELISA. Immunoreactive epitopes were localized only in internal organs and cuticula of larvae in muscle.

Trichinella in horses: a low frequency infection with high human risk

After the initial report in 1976 of a trichinellosis epidemic caused by the consumption of infected horsemeat, 12 other outbreaks have been described in Europe. Since the first serious human outbreak several experiments have confirmed the susceptibility of horses to Trichinella species and the rapid disappearance of specific antibodies in this host that prevents the use of serological methods for routine screening. A review of the distribution of parasite burdens in muscles of naturally or experimentally infected horses indicates that the tongue is the most likely sample to contain detectable numbers of Trichinella larvae in low level infections. Requirements for testing of horsemeat are specified in legislation of the European Union, and other recommendations are published elsewhere. The EEC directives have evolved into very specific requirements which specify the testing of at least 5g of tongue, masseter or diaphragm per horse using a pooled digestion assay. More recently, France has revised the requirement for sample size to 10g for horsemeat originating from countries with high prevalence of Trichinella. To address the continuing outbreaks of human trichinellosis due to infected horsemeat, the development and implementation of a quality assurance system for testing is being considered.

Immunoelectrotransfer blot assay in acute and chronic human trichinellosis

An immunoelectrotransfer blot assay (IETB) using excretory secretory products of muscle larvae of Trichinella spiralis (ML-ESP) and the avidin biotin system was developed in order to characterize reactivity against ML-ESP in sera from patients with acute and chronic trichinellosis. A complete pattern of up to 13 bands was developed by sera from individuals with trichinellosis where doublets, triplets, or single bands were shown to have molecular weights of roughly 66, 55, 45, 36, 29, 24, and 14 kDa. The bands at approximately 55, 36, 29, and 14 kDa proved specific for T. spiralis. The band at approximately 55 kDa was present in all trichinellosis sera, whereas the approximately 14-kDa band was present in only a small percentage of sera. The development of approximately 36- and 29-kDa bands suggests a modulation of the reactivity against ML-ESP over time. IETB proved more sensitive for the population of chronic trichinellosis under study than a conventional diagnostic enzyme-linked immunosorbent assay, allowing negative or borderline serum samples to be determined. Thus, this technique, when applied for human trichinellosis surveillance, should provide a useful tool in endemic areas.