Comparison of three methods for detection of prolonged experimental trichinellosis in pigs

Survey on porcine trichinellosis in Ecuador

A survey on porcine trichinellosis was organised in Ecuador between 2000 and 2003. Blood samples were taken in slaughterhouses (study 1, n=2000; study 2, n=331) and in a remote village where pigs are free roaming (study 3, n=646) and examined by ELISA using excretory/secretory (E/S) antigens. Seven samples (0.35%) in study 1 and none of the samples of study 2 were serologically positive. Thirty-seven (5.72%) village pigs tested positive by E/S ELISA in study 3. Sero-positive results by the E/S ELISA in study 1 were confirmed by ELISA using beta-tyvelose antigen, and by immunoblot. Muscle samples taken from pigs slaughtered in the abattoir (study 2) and from animals that showed a positive serology in study 3 were examined by trichinoscopy and artificial digestion. These techniques failed to demonstrate the presence of muscle larvae. The results of this survey need confirmation, but suggest that Trichinella is present in Ecuador; however, prevalence and parasite burdens are likely to be very low. The likelihood of detecting trichinellosis are higher in traditional settings than in pigs raised on improved farms.

Trichinella strain, pig race and other parasitic infections as factors in the reliability of ELISA for the detection of swine trichinellosis

An enzyme-linked immunosorbent assay (ELISA) using crude worm extracts (CWE) and mixtures of these as antigens of five Spanish isolates (P, C, B1, B2 and W) was developed for detecting homologous and heterologous experimental infections with these isolates between-14 and 82 days post-infection (p.i.) in white and Iberian pigs. A total of 243 pigs (Iberian or cross-bred with this race) with numerous parasitic infections were also screened for the presence of antibodies to a mixture of CWE of C, B1 and B2 isolate. The test showed a specificity of 93.1-98.9% depending on the cut-off values and a maximum sensitivity of 92.8-100% between days 34 and 82 p.i. A low grade of infectivity was shown in the T3 isolates compared to the T1 isolates (P, C, B1 and B2) but high cross-reactions were observed between all the isolates with minor differences between P and W isolates. The highest antibody response was found in P infections and the lowest in pigs infected with the W isolate. A clear association between the presence of several parasitic infections and false positive reactions was not found, but an important relation was shown between high background levels and the Iberian race in experimentally and conventionally raised pigs.

Diagnostic tests for Trichinella spiralis infection in pigs. A comparative study of ELISA for specific antibody and histamine release from blood cells in experimental infections

A study on the histamine release test (HR) for the demonstration of infections with Trichinella spiralis in pigs was carried out on 18 pigs, six infected with 200 larvae, six infected with 5000 larvae and six non-infected (control group). The results obtained by HR during a 7 week infection were compared with those of the enzyme-linked immunosorbent assay (ELISA). All inoculated pigs were found to be positive on Day 40 post-inoculation (p.i.) by necropsy examination of selected muscle groups, with mean recoveries of 7.9 and 225 larvae g-1 of tissue in the low- and high-dose group, respectively. At this time, all animals of the high-dose group and five out of six animals of the low-dose group were antibody positive in ELISA with any of three coating antigens employed (a crude muscle larva extract, an excretory/secretory (ES) antigen and a purified 45 kDa antigen). HR performed on whole blood was positive in four out of six pigs of the high-dose group and one out of six pigs of the low-dose group. The earliest ELISA seroconversions took place at Day 15 p.i. with crude and ES antigens. The earliest measurable reaction in HR performed on whole blood was found on Day 19 p.i. There was considerable individual variation regarding which test was the most sensitive for the early detection of infection. Washing of the blood cells prior to antigen provocation led to a markedly improved sensitivity of HR, all animals of the high-dose and three out of six animals of the low-dose group being positive by Day 40 p.i. The time course of the development of ELISA titres and HR reactivity indicated that this effect is due to the removal of blocking antibodies.

Experimental trichinellosis in horses: biological and parasitological evaluation

Three groups of three horses each were, respectively, infected with 5000, 20,000 and 50,000 larvae of Trichinella spiralis. The strain used was isolated from a human biopsy during horsemeat-related outbreaks of trichinellosis in France. Transient muscular disorders were only observed in two of the horses infected with 50,000 larvae but none of the horses had fever. A significant increase in blood eosinophils was noticed in 5 horses. Serum LDH, aldolase and CPK peaked at the fifth week post-infection. Specific IgG assayed by indirect immunofluorescence and ELISA, appeared 2-5 weeks post-infection and disappeared between 16 and 40 weeks. The distribution of T. spiralis larvae was maximal in the tongue, masseters and diaphragm, but a large decrease in the number of larvae recovered from the muscles was noticed among the horses slaughtered at the beginning and end of the experiment. In muscular histological sections, larvae were observed in an intramyofibrillar position and were surrounded by a mild to severe inflammatory reaction.

Evaluation of excretory-secretory antigens for the serodiagnosis of swine trichinellosis

Groups of hog sera from endemic and non-endemic areas for swine trichinellosis in Yugoslavia were tested by ELISA using excretory-secretory (ES) antigens collected from T. spiralis muscle larvae maintained in vitro for 24, 48 or 72 h. The 24-h ES had the highest level of specificity for T. spiralis infection. Antigen preparations recovered after 48 or 72 h yielded an increasing rate of false-positive reactions. Additional antigens occurred in the 48- and 72-h ES preparations as determined by gel electrophoresis and monoclonal antibody binding. The occurrence of false-negative reactions was directly correlated with T. spiralis worm burdens. Hogs with muscle larvae densities greater than 10 larvae per gram were all positive by ELISA. Among 17 hogs with less than 10 larvae per gram, only one hog was negative by ELISA with 24-h ES antigen; the false-negative rate was higher with 48- and 72-h ES. These results show that ES antigen produced during the first 24 h of in vitro cultivation is highly specific for the immunodiagnosis of swine trichinellosis.