Anti-Trichinella antibodies detected in chronically infected horses by IFA and Western blot, but not by ELISA

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 They are based on current scientific information including unpublished data from laboratories with relevant expertise in this field.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.

A competitive enzyme-linked immunosorbent assay for rapid detection of antibodies against Trichinella spiralis and T. britovi - one test for humans and swine

Infection with parasites from the Trichinella genus occurs in many vertebrates but disease only occurs in humans (trichinellosis). Humans are infected after the consumption of raw or undercooked meat from infected wild or domestic animals (usually swine or horses). Using the monoclonal antibody (mAb) 7C2C5, specific for an epitope unique to the muscle larvae of the genus Trichinella, we have developed a competitive enzyme-linked immunosorbent assay (c-ELISA) that enables the rapid detection of Trichinella-specific antibodies in sera originating from two different host species (human, swine) infected with either Trichinella spiralis or Trichinella britovi. This novel c-ELISA exhibited 100% specificity and sensitivity, as confirmed by a Western blot test. The assay is easy to use (one incubation step), and the time required for the procedure (45 min) is shorter than in any other ELISA format. This test could be useful for both the detection and surveillance of Trichinella infections.

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.

Species-specific antibody responses to the recombinant 53-kilodalton excretory and secretory proteins in mice infected with Trichinella spp

The 53-kDa proteins in larval excretory and secretory (E-S) products were expressed from five Trichinella species (T. spiralis, T. britovi, T. nativa, T. pseudospiralis, and T. papuae), using the Escherichia coli expression system, and the antibody responses to the 53-kDa recombinant proteins in mice infected with Trichinella spp. were analyzed by Western blotting. The 53-kDa protein is conserved among the five Trichinella species, with >60% similarity in amino acid sequences. The 53-kDa recombinant proteins of T. spiralis and T. pseudospiralis reacted to sera from mice infected with T. spiralis and T. pseudospiralis at 8 days postinfection (p.i.), respectively. An antibody against the 53-kDa recombinant protein of T. spiralis recognized the 53-kDa protein in the crude extracts from adult worms and 30-day p.i. muscle larvae and E-S products from muscle larvae of T. spiralis but did not recognize any proteins from T. pseudospiralis. The sera from the mice infected with T. spiralis strongly reacted with the 53-kDa recombinant protein of T. spiralis but did not react with the 53-kDa recombinant proteins of T. britovi, T. nativa, T. pseudospiralis, and T. papuae. Similarly, the sera from mice infected with T. britovi, T. nativa, T. pseudospiralis, or T. papuae strongly reacted with the 53-kDa recombinant proteins of T. britovi, T. nativa, T. pseudospiralis, or T. papuae, respectively. These results showed that the 53-kDa recombinant proteins provide early and species-specific antibody responses in mice infected with Trichinella spp.

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.

Usefulness of Toxoplasma gondii recombinant antigens (GRA1, GRA7 and SAG1) in an immunoglobulin G avidity test for the serodiagnosis of toxoplasmosis

The precise diagnosis of an acute and recent Toxoplasma infection in pregnant women and the newborn child is important before treatment. This study describes a new Toxoplasma gondii IgG avidity test based on a combination of recombinant GRA1, GRA7 and SAG1 antigens and shows that this test is useful for diagnostic purposes and may replace the lysed, whole-cell antigens. Although more sera need to be tested, the results obtained here suggest that the IgG avidity test performed with rec-antigens correlated more with the stage of a T. gondii infection than the IgG avidity results obtained with the lysed, whole-cell antigen test, the VIDAS Toxo IgG avidity (bioMérieux).