H.R. Gamble

Diagnosis of swine trichinosis by enzyme-linked immunosorbent assay (ELISA) using an excretory- secretory antigen

An excretory--secretory (ES) antigen was used in a serodiagnostic enzyme-linke immunosorbent assay (ELISA) for swine trichinosis. ELISA procedures included a double-antibody test, using either an anti-swine IgG or a protein A enzyme conjugate, and a triple-antibody test using a pig IgG heavy-chain specific second antibody with a conjugated third antibody. The ES antigen was effective in eliminating all false-positive reactivity in sera from farm-raised hogs. The triple-antibody procedure was more sensitive and demonstrated a greater efficiency in detecting positive animals and early seroconversions. Naturally-infected pigs with worm burdens as low as 0.01 larvae per gram (LPG) of diaphragm were seropositive using these procedures. Seroconversion in experimentally-infected animals receiving low doses of muscle larvae (500) occurred considerably later than in animals receiving high doses (10000). This might account for false-negative reactions in naturally-infected animals with very low (less than 0.1 LPG) worm burdens.

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.

Prevalence of Toxoplasma gondii infection in domestic pigs in the New England states

To determine regional prevalence of infection with Toxoplasma gondii, 1897 pigs from 85 farms in five New England states were tested using a modified direct agglutination test. Sera were diluted 1:25 and a titer at this dilution was indicative of T. gondii infection. Farm management questionnaires were completed at the time of blood collection and were used to develop descriptive statistics on farms tested and to determine measures of association for risk factors for the presence of T. gondii-seropositive pigs. A total of 900 seropositive pigs were identified for a prevalence rate of 47.4%. Of 85 herds tested, 77 had at least one positive pig for a herd prevalence rate of 90.6%. Within herd prevalence ranged from 4% to 100% (mean = 48.4%). All farms studied had one or more risk factors for exposure to T. gondii. However, statistical associations with individual risks could not be made, most likely due to the extremely high prevalence. The results obtained here suggest that education on farm management practices to reduce exposure to T. gondii should be targeted to include small producers.

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.

SEROLOGIC PREVALENCE OF TOXOPLASMA GONDII IN HORSES SLAUGHTERED FOR FOOD IN NORTH AMERICA

Serum samples from 1788 horses slaughtered for food in North America were tested for antibodies to Toxoplasma gondii using the modified direct agglutination test (MAT). Antibodies to T. gondii were found by the MAT in 124 (6.9%) of 1788 sera; the titers were 1:20 (69 horses), 1:40 (37 horses), 1:80 (9 horses), and > or =1:160 (9 horses). A total of 339 selected horses were also tested by the Sabin-Feldman dye test (DT). Dye test antibodies were found in 54 horses with titers of 1:10 (29 horses) 1:20 (12 horses), 1:40 (4 horses) and 1:80 (9 horses). There was no correlation between the DT and the MAT.

Prevalence and risk association for Trichinella infection in domestic pigs in the northeastern United States.

To determine Trichinella infection in a selected group of farm raised pigs, 4078 pigs from 156 farms in New England and New Jersey, employing various management styles, were selected based on feed type (grain, regulated waste, non-regulated waste). The number of pigs bled from each farm were based on detecting infection assuming a 0.05 prevalence rate. Serum was tested by enzyme-linked immunoassay for antibodies to Trichinella spiralis. Seropositive pigs were tested by digestion at slaughter (when possible) for the presence of Trichinella larvae. Questionnaires completed at the time of serum collection were used to develop descriptive statistics on farms tested and to determine measures of association for risk factors for the presence of Trichinella-seropositive pigs. A total of 15 seropositive pigs on 10 farms were identified, representing a prevalence rate of 0.37% and a herd prevalence rate of 6.4%. A total of nine seropositive pigs and one suspect pig from six farms were tested by digestion; four pigs (representing three farms) harbored Trichinella larvae at densities of 0.003-0.021 larvae per gram (LPG) of tissue; no larvae were found in six pigs. Risk factors which were significantly associated with seropositivity included access of pigs to live wildlife and wildlife carcasses on the farm; waste feeding had no statistically significant association with seropositivity for Trichinella infection in pigs. The presence of Trichinella infection in pigs in New England and New Jersey has declined during the past 12 years when compared with previous prevalence studies.

Historical perspectives and current global challenges of Trichinella and trichinellosis

Trichinella spiralis and related species of Trichinella have had a long history of causing human disease, and as a foodborne pathogen have had a major impact on international commerce of pork and other meat animal species which are known to transmit the parasite. Our knowledge of Trichinella has increased substantially over the past few years particularly in the areas of phylogeny, host diversity, epidemiology and control. In this paper, we provide a brief overview of our understanding of Trichinella from its discovery to present time. Past and current challenges of the control of Trichinella and trichinellosis are summarized. As editors of this special issue of Veterinary Parasitology, we introduce a series of invited review articles prepared by experts from around the world, summarizing recent knowledge in Trichinella and trichinellosis.

Seroprevalence of Trichinella infection in domestic swine based on the National Animal Health Monitoring System's 1990 and 1995 swine surveys

Swine sera collected by the US Department of Agricultures Center for Animal Health Monitoring during 1990 and 1995 was tested for antibodies to Trichinella spiralis using an enzyme immunoassay. From a total of 3048 sera collected from lactating sows in 1990, five sera tested positive for a prevalence of 0.16%. From a total of 7987 sera collected from both finishing pigs and gestating sows in 1995, one serum was positive for a prevalence of 0.013%. Responses to questionnaires administered at the time of serum collection showed that seropositive farms had management variables consistent with known risk factors for exposure to trichinae.

Application of hybridoma technology to the diagnosis of parasitic disease.

Recent applications of hybridoma-derived monoclonal antibodies to the diagnosis of parasitic disease are reviewed. Diagnostic tests, utilizing monoclonal antibodies, have included radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA) techniques to detect parasite antigen in host tissues and body fluids and circulating host antiparasite antibody. In general, the use of monoclonal-derived reagents has greatly increased the specificity of diagnosis by eliminating cross-reactions between closely related parasite species, without suffering a significant loss of sensitivity.