[Characterisation of a monoclonal antibody against Trypanosoma evansi and its application for detecting circulating antibodies]

Monoclonal antibodies were obtained against Trypanosoma evansi. The 2-4F6 IgM monoclonal antibody (Mab) was chosen for the study because of its ability to detect antigens and its specificity (as it did not recognise T. cruzi, T. equiperdum, Babesia equi or B. caballi). The immunoblot test revealed that the 2-4F6 IgM Mab recognises epitopes in two antigenic bands, one measuring 85 kDa and the other 122 kDa. An immunoassay for antigen detection in serum using polyclonal antibodies for capture, the Mab 2-4F6 as primary antibody and an antimouse IgM as secondary antibody gave positive results in 10 of the 11 equidae infected with T. evansi, whereas 20 controls gave negative results. These research results show that the Mab 2-4F6 and the antigen it recognises are useful in identifying equidae infected with T. evansi.

[Validation of an indirect immunoenzyme assay for the detection of antibodies against Trypanosoma evansi in horses in Argentina]

An indirect enzyme-linked immunosorbent assay (ELISA) to detect antibodies against Trypanosoma evansi was evaluated using 90 different sera, obtained from naturally-infected horses. As negative controls, 218 sera from the T. evansi-free zone of Argentina, and 90 uninfected sera from the enzootic zone were used. The results of the ELISA were expressed in terms of percent positivity (PP) when compared with a positive primary reference serum, obtained from a horse experimentally-infected with T. evansi. The inter-assay coefficient of variation (CV), expressed as PP, was 44.7% for the negative control serum, 8.8% for the mildly positive reference serum, and 9.2% for the secondary positive control serum, while the intra-assay CV for each of the above sera was 6%, 2.8% and 5%, respectively. Positive and negative serological results were differentiated using a histogram of the distribution of the results obtained using sera from infected and uninfected animals from the enzootic zone (expressed in PP). A PP of 50 indicated a sensitivity of 95.5% for a confidence interval (CI) of 91.3% to 99.7%, and a specificity of 98% for a CI between 95% and 100%. Positive and negative predictive values were established for each rate of prevalence between 0.01% and 25%. The use of reference control sera in each assay enabled reproducible results to be obtained. The author recommends that this methodology be used whenever certification of the T. evansi status of horses is required, and particularly when animals are to be moved from an infected to a disease-free area.

Sensitivity of antigen ELISA test for detecting Trypanosoma evansi antigen in horses in the subtropical area of Argentina

The sensitivity of an antigen detection enzyme immunoassay (Ag-ELISA) based on a Trypanosoma brucei group-specific monoclonal antibody was evaluated to detect circulating Trypanosoma evansi antigen in horse sera. Three horses and 2 mules were experimentally infected with T. evansi. Circulating antigens were detected on 7 and 21 days postinfection. Antigen levels increased during the course of the illness and remained high even when parasitemia was low or when parasites could not be detected. Antigens were cleared from serum when drug treatment was effective but persisted when it was not. In 6 outbreaks of "mal de caderas" involving 125 horses, T. evansi was found in 78 horses using standard parasite detection methods and antigenemia was detected in 58 of them (74%). The Ag-ELISA sensitivity rate varied between 63% and 100% for the 6 different outbreaks. A combination of Ag-ELISA and parasitologic methods diagnosed a total of 93 infected animals. These results show that the Ag-ELISA test is useful both to diagnose T. evansi and to assess the efficacy of drug treatment in horses.

[Outbreaks of equine trypanosomiasis caused by Trypanosoma evansi in Formosa Province, Argentina]

Tests on 257 blood samples from 21 herds of horses in Formosa Province of Argentina, using the technique of centrifuging microhaematocrit capillary tubes, revealed Trypanosoma evansi in 90 of 137 animals in eight herds. Application of the direct agglutination test to serum samples from the same animals revealed antibodies to T. evansi in 107 horses. Antibody was also detected in nine horses from two herds where the parasite was not detected. Outbreaks of 'mal de caderas' occurred in the humid (eastern) and sub-humid (central) zones of Formosa. More than 95% of the equine population of the province is found in these zones (57,000 horses). In six strains of T. evansi, maintained by passage in mice, between 3% and 20% of parasites possessed a kinetoplast.

[Determination of the survival of Trypanosoma evansi in equine blood, using the microhematocrit method]

The microhaematocrit (MH) technique was used to study the survival of Trypanosoma evansi in blood from two herds of naturally-infected horses. A comparison was made between samples treated with ethylenediaminetetraacetic acid and sodium citrate (alone or with 1% glucose), and sent to the laboratory packed in ice. In general, the number of samples yielding positive results by the MH technique showed the least variation during the first 24-36 h after sample collection. Survival varied with the anticoagulant used, but it declined rapidly from 48 h after collection, although live parasites were still observed in up to 10% of samples until the seventh day. On the basis of the results obtained, the authors recommend the use of sodium citrate in treating equine blood samples for the parasitological diagnosis of T. evansi.

[Eumycotic mycetomas in horses caused by Curvularia verruculosa]

The fungus Curvularia verruculosa, which produces eumycotic mycetomas, was isolated from skin of horses with granulomatous lesions on the legs. The isolation was made in Sabouraud dextrose agar medium. The horses came from Comandante Fontana suburb, Formosa-Argentina. This finding would be the first report of Curvularia in horses in Argentina.

Serological diagnosis of Trypanosoma evansi (Steel, 1885) in horses using a direct agglutination test

A direct agglutination test is described to diagnose 'Mal de Caderas' caused by Trypanosoma evansi. The antigen used was a suspension of trypsin-treated parasites stabilized with formalin. The test was evaluated in horses with both natural and experimental infections. Test sensitivity and specificity were 94 and 97%, respectively. Treatment of serum with 2-mercaptoethanol before testing permitted the differentiation of IgM and IgG antibodies, and possible differentiation of current infection from past exposure to the parasite. The antigen was stable over a 6-month evaluation period and also showed good reproducibility between different batches. The direct agglutination test is proposed as another tool for diagnosis of T. evansi in horses, both for detecting clinical cases and for seroepidemiological studies.

Serum proteins in guinea-pigs and horses infected with Trypanosoma evansi (Steel, 1885)

The serum protein pattern in guinea-pigs infected with T. evansi was analysed and compared with those found in horses with either a natural or experimental infection. In both species, a highly significant decrease in albumin levels and an increase in gamma-globulins were seen, leading to a very low albumin/globulin ratio. No significant differences in total protein levels between healthy and infected animals were registered. Likewise, alpha-globulins were not significantly affected. A decrease in beta-globulins was observed in one horse and in guinea-pigs with experimental infection, while in horses with natural infections this decrease was not constant. The serum protein patterns in guinea-pigs infected with T. evansi appeared similar to those occurring in horses infected with this parasite. Guinea-pigs, therefore may be useful laboratory models for the study of equine trypanosomosis caused by T. evansi.

Comparison between six parasitological methods for diagnosis of Trypanosoma evansi in the subtropical area of Argentina

In a total of 165 blood samples from horses in the Province of Formosa (Argentina), the diagnosis for equine trypanosomiasis (T. evansi) was made using Giemsa-stained smears (GSS), wet blood films (WBF), Strout's concentration method (SCM), haematocrit centrifuge technique (HCT), buffy coat method (BCM) and mouse inoculation of blood (MBI). Trypanosoma evansi was demonstrated in 52 samples. Mouse inoculation gave a sensitivity of 88.2%; HCT 71.1%; BCM 63.4%; WBF 53.8%; SCM 46.1% and GSS 45.6%. No single method alone was totally effective. The haematocrit centrifuge technique, mouse inoculation of blood and Giemsa-stained smears were proposed as the most effective diagnostic combination.

Application of antigens from Taenia hydatigena cyst fluid for the immunodiagnosis of human hydatidosis

Fluid was collected from cysts of Taenia hydatigena in 60 adult sheep and fluid from each animal pooled separately. By double diffusion antigen 5 was demonstrated in all pools but one. The criteria are described for selection and standardization of these preparations for use as antigens for the immunodiagnosis of human hydatid disease. Sera from 50 persons harbouring hydatid cysts and from 50 patients with other disease conditions were examined by the arc-5 double-diffusion test, using two antigens prepared from Echinococcus granulosus and T. hydatigena cyst fluids, respectively. The results showed that a higher diagnostic sensitivity was obtained with the hydatid antigen. The significance of the findings is discussed in terms of their application to human immunodiagnosis in areas where hydatidosis, but not cysticercosis, is rare in livestock.