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

Application of a recombinant novel trypsin from Trichinella spiralis for serodiagnosis of trichinellosis

BACKGROUND

The excretory/secretory (ES) antigen of Trichinella spiralis muscle larvae (ML) is currently the most widely used diagnostic antigen to detect T. spiralis infection. However, this antigen has certain drawbacks, such as a complicated ES antigen preparation process and lower sensitivity during the early phase of infection. The aim of this study was to investigate the features of a novel T. spiralis trypsin (TsTryp) and evaluate its potential diagnostic value for trichinellosis.

METHODS

The TsTryp gene was cloned and recombinant TsTryp (rTsTryp) expressed. Western blotting and an enzyme-linked immunosorbent assay (ELISA) were performed to confirm the antigenicity of rTsTryp. The expression pattern and distribution signature of TsTryp at various life-cycle stages of T. spiralis were analyzed by quantitative PCR, western blotting and the immunofluorescence test. An ELISA with rTsTryp and ML ES antigens was used to detect immunoglobulins G and M (IgG, IgM) in serum samples of infected mice, swine and humans. The seropositive results were further confirmed by western blot with rTsTryp and ML ES antigens.

RESULTS

TsTryp expression was observed in diverse T. spiralis life-cycle phases, with particularly high expression in the early developmental phase (intestinal infectious larvae and adults), with distribution observed mainly at the nematode outer cuticle and stichosome. rTsTryp was identified by T. spiralis-infected mouse sera and anti-rTsTryp sera. Natural TsTryp protease was detected in somatic soluble and ES antigens of the nematode. In mice infected with 200 T. spiralis ML, serum-specific IgG was first detected by rTsTryp-ELISA at 8 days post-infection (dpi), reaching 100% positivity at 12 dpi, and first detected by ES-ELISA at 10 dpi, reaching 100% positivity at 14 dpi. Specific IgG was detected by rTsTryp 2 days earlier than by ES antigens. When specific IgG was determined in serum samples from trichinellosis patients, the sensitivity of rTsTryp-ELISA and ES antigens-ELISA was 98.1% (51/52 samples) and 94.2% (49/52 samples), respectively (P = 0.308), but the specificity of rTsTryp was significantly higher than that of ES antigens (98.7% vs. 95.4%; P = 0.030). Additionally, rTsTryp conferred a lower cross-reaction, with only three serum samples in total testing positive from 11 clonorchiasis, 20 cysticercosis and 24 echinococcosis patients (1 sample from each patient group).

CONCLUSIONS

TsTryp was shown to be an early and highly expressed antigen at intestinal T. spiralis stages, indicating that rTsTryp represents a valuable diagnostic antigen for the serodiagnosis of early Trichinella infection.

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.

Immunoproteomic Analysis of Trichinella britovi Proteins Recognized by IgG Antibodies from Meat Juice of Carnivores Naturally Infected with T. britovi

Infection with Trichinella nematodes elicits non-specific and specific immune responses; these depend on the dose of infection, the nematode, and the host species. Few studies have examined the presence of specific antibodies against Trichinella spp. in the meat juice of wild animals. The aims of the study were to determine the prevalence of antibodies against Trichinella spp. in meat juice and to identify the specific proteins reacting with the meat juice from free-living carnivores naturally infected with the parasite. Meat juice samples were taken from foxes, badgers, raccoon dogs, and martens and tested with indirect ELISA. Antibodies against Trichinella spp. were detected in 10% of foxes and 46% of raccoon dogs. The ELISA results were confirmed by immunoblot, which revealed different protein patterns in meat juice from red foxes, raccoon dogs, and badgers. The most frequently observed bands were sent for further analysis by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) for the detection of Trichinella britovi immunogenic proteins. The results confirm the presence of proteins such as serine protease and heat shock proteins associated with Trichinella infection. These findings provide that meat juice is a useful matrix for proteomic analysis.

Lateral flow immunoassay strips based on europium(III) chelate microparticle for the rapid and sensitive detection of Trichinella spiralis infection in whole blood samples of pigs

Trichinellosis is a major food-borne parasitosis caused by ingesting raw or semi-raw meat products from pigs infected with Trichinella spiralis (T. spiralis). Although China is the largest consumer of pork in the world, the current diagnostic method of T. spiralis is exclusively performed in a laboratory setting, due to its complexity and laborious procedure. Here, in order to solve the detection problems in the pig breeding industry, a rapid, sensitive, and on-site serological diagnosis method was developed. The novel lateral flow immunoassay strip (ICS) is based on europium(III) chelate microparticle (ECM) to detect T. spiralis-specific IgG antibody in the serum and whole blood samples from pigs. The structure of the blood-filtering pad and the conjugate pad was added to the ICS, allowing for whole blood samples to be detected and enabling on-site deployment. By comparing the detection results of the serum samples and the whole blood samples, the detection limit of this method was evaluated. Thereafter, this method was used to investigate Trichinella infection in Chongqing, Sichuan, Inner Mongolia, Guangxi, and Liaoning provinces of China, and the results were almost consistent with the standard method of artificial digestion. Taking advantage of its user-friendly procedure, short detection time (3 min), and sensitivity, the ECM-ICS could be employed for monitoring the epidemic of Trichinella infection and ensuring meat safety.

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.

Upconverting phosphor technology-based lateral flow assay for the rapid and sensitive detection of anti-Trichinella spiralis IgG antibodies in pig serum

Background

Trichinella spiralis is a zoonotic food-borne parasite. A disease caused by infection with T. spiralis is called trichinellosis in humans. It is important to investigate the epidemic situation and the surveillance of herds and then prevent infection in humans. Therefore, this study is to develop a rapid and sensitive diagnostic method for on-site test in domestic and wild animals.

Methods

Upconverting phosphor nanoparticles (UCNPs), an excellent optical label, were conjugated with the excretory-secretory (ES) antigens from T. spiralis muscle larvae (ML) or goat anti-rabbit IgG, and a lateral flow (LF) assay based on these probes (UCNPs-ES/goat anti-rabbit IgG) was developed for the rapid and sensitive detection of anti-T. spiralis IgG antibodies in pig serum. The assay is named the UPT-LF-ES assay. In addition, the probes were characterized, and the assay was optimized. A cut-off threshold of the assay was also identified by using 169 known negative pig samples. Performance of the assay to T. spiralis with different infective numbers, cross-reactivity with other parasitic infections, the single-blinded experiment, and coincidence were evaluated with the assay.

Results

The UPT-LF-ES assay was successfully constructed and optimized based on the probes of UCNPs-ES/goat anti-rabbit IgG. In the pigs infected with 100, 1000, and 10,000 ML, positive results were first presented at 35 days post-infection (dpi), 30 dpi, and 25 dpi, respectively. The assay had no cross-reaction with other parasitic infections. A single-blinded experiment indicated that the sensitivity and specificity of the UPT-LF-ES assay were 100% and 100%, respectively, the area under the receiver operating characteristic (ROC) curve was 1.000. In addition, the value detected by the UPT-LF-ES assay was significantly different between positive and negative samples. Moreover, compared with the “gold standard” magnetic stirrer method, the coincidence rate of the UPT-LF-ES assay was 87.27%, and the kappa (K) coefficient was 0.7454, showing a substantial agreement.

Conclusions

The UPT-LF-ES assay is a useful point-of-care test (POCT) with T. spiralis in the detection of pig, which contributes to preventing human trichinellosis.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04949-2.

Recombinant cystatin-like protein-based competition ELISA for Trichinella spiralis antibody test in multihost sera

Objectives

Trichinella spiralis is a zoonotic parasite with a complex parasitic life cycle and exposed to animals or humans by infectious meat. To control transmissions of T. spiralis through the food chain to humans, sensitive and selective multihost sera-diagnosis is urgent needed for monitoring T. spiralis exposure.

Methods

A competition enzyme-linked immunosorbent assay (cELISA) for T. spiralis infection diagnosis in multihost sera was developed based on recombinant cystatin-like protein (rCLP-cELISA) as well as monoclonal antibodies. The sensitivity and accuracy of the rCLP-cELISA were quantified using swine (n = 1316), mice (n = 189) and human (n = 157) serum samples. T. spiralis-antibody targeting test ability of the rCLP-cELISA in swine (n = 22) and human (n = 36), instead of other parasites or viruses antibodies, was evaluated.

Results

The rCLP-cELISA showed high agreement with commercial ELISA kits in field swine sera assessed by Cohen’s kappa value (κ = 0.7963). And it showed 100% specificity in human trichinellosis detection with sensitivity of 96.49%, no cross-reaction with other parasite or virus infections, and high positive detection rate of 87.5% in low-dose infected swine. Besides, the rCLP-cELISA exhibited potential in the detection of T. spiralis, T. nelsoni and Trichinella T8 infections.

Conclusions

The rCLP-cELISA can be used for T. spiralis-associated antibody test in multihost sera.

Infections with T. spiralis that lives in host muscles for long periods of time are commonly difficult to diagnosis without causing a strong immune response or symptoms. The habit of eating raw/undercooked pork meat accidentally introduces humans into the exposure of T. spiralis that circulates between herds and rodents. There is an urgent need for serological antibody test of T. spiralis to monitor the infection of humans as well as hosts in the food chain, which is restricted by the mixture type of current used antigens and species-specific secondary antibodies for different hosts. We developed a novel recombinant cystatin-like protein-based competition enzyme-linked immunosorbent assay (rCLP-cELISA) employing monoclonal antibody. The proposed method showed considerable sensitivity and specificity in filed swine sera and human serum samples with good versatility in mice. Taking advantage of its controllable quality stability, the rCLP-cELISA had potential applications for screening of T. spiralis infections for multihost sera in one test. With the development of monoclonal antibody modification strategies and the discovery of antigenic proteins from parasitic pathogens, the proposed competition ELISA also provides useful reference for the improvement of serological assay for monitoring the exposure of zoonotic parasites.

Development of a rapid and sensitive immunochromatographic strip based on EuNPs-ES fluorescent probe for the detection of early Trichinella spiralis-specific IgG antibody in pigs

Trichinellosis, which is caused by nematodes of the genus Trichinella, is one of the most important zoonotic parasite diseases in the world. A rapid and sensitive immunochromatographic strip (ICS) based on Eu (III) nanoparticles (EuNPs) was developed for the detection of Trichinella spiralis (T. spiralis) infection in pigs. T. spiralis muscle larvae excretory secretory or preadult worm excretory secretory (ML-ES or PAW-ES) antigens were conjugated with EuNPs probes to capture T. spiralis-specific antibodies in pig sera, after which the complex bound to mouse anti-pig IgG deposited on the test line (T-line), producing a fluorescent signal. In the pigs infected with 100, 1000 and 10 000 ML, seroconversion was first detectable for the EuNPs-ML-ES ICS at 30, 25 and 21 days post-infection (dpi) and for the EuNPs-PAW-ES ICS at 25, 21 and 17 dpi. These results show that EuNPs-PAW-ES ICS detects anti-Trichinella IgG in pigs 4–5 days earlier that test using ML-ES antigens. Our ICS have no cross reaction with other parasite infection sera. Furthermore, the detection process could be completed in 10 min. This study indicated that our ICS can be used for the detection of the circulating antibodies in early T. spiralis infection and provide a novel method for on-site detection of T. spiralis infection in pigs.

Immunoproteomic analysis of Trichinella spiralis and Trichinella britovi excretory-secretory muscle larvae proteins recognized by sera from humans infected with Trichinella

The present study compares the immunogenic patterns of muscle larvae excretory-secretory proteins (ML E-S) from T. spiralis and T. britovi recognized by Trichinella-infected human sera. Samples were analyzed using two-dimensional electrophoresis (2-DE) coupled with 2D-immunoblot and liquid chromatography-tandem mass spectrometry LC-MS/MS analysis, two ELISA procedures and a confirmatory 1D-immunoblot test. Sera were obtained from nine patients with a history of ingestion of raw or undercooked meat who presented typical clinical manifestations of trichinellosis and from eleven healthy people. Specific anti-Trichinella IgG antibodies were detected in all samples tested with the Home-ELISA kits, but in only four samples for the commercially-available kit. The 1D-immunoblot results indicated that all nine serum samples were positive for T. spiralis ML E-S antigens, expressed as the presence of specific bands. In contrast, eight of the serum samples with T. britovi E-S ML antigens were positive, with one serum sample taken from a patient at 33dpi (days post infection) being negative. To identify immunoreactive proteins that are specifically recognized by host antibodies, both species of ML E-S proteins were subjected to 2D-immunoblotting with human serum taken at 49 dpi. The sera recognized 22 protein spots for T. spiralis and 18 for T. britovi in 2D-immunoblot analysis. Their molecular weights (MW) ranged from 50 to 60 kDa. LC-MS/MS analysis identified both common and specifically-recognized immunoreactive proteins: transmembrane serine protease 9, serine protease, antigen targeted by protective antibodies and Actin-1 partial were shared for both Trichinella species; hypothetical protein T01_7775 and P49 antigen, partial those specific to T. spiralis; deoxyribonuclease-2-alpha and hypothetical protein T03_17187/T12_7360 were specific to T. britovi. Our results demonstrate the value of 2-DE and 2D-immunblot as versatile tools for pinpointing factors contributing to the parasite-host relationship by comparing the secretomes of different Trichinella species.

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.

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.