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Characteristics and interpretation of the indirect-ELISA for Trypanosoma vivax; proposal for the standardisation of the results

Desquesnes M., Tresse L.. 1999. In : Vokaty S. (ed.), Desquesnes M. (ed.). Proceedings of first symposium on new world trypanosomes = [Actes du 1er symposium sur les trypanosomes d'Amérique]. Bridgetown : IICA, p. 95-104. Symposium on New World Trypanosomes. 1, 1996-11-20/1996-11-22, Georgetown (Guyana).

Indirect-ELISA for T. vivax is the most sensitive technique for antibody detection of T. vivax infections. A group of expert has given recommendations for standardisation of the indirect-ELISA. Based on these recommendations we have added some proposals for standardisation and presentation of the results; the example of the indirect-ELISA for T. vivax in cattle is presented. Characteristics of the indirect-ELISA have been studied in experimental conditions in sheep, and in natural infections, in cattle in French Guyana. It is proposed to present the results in relative percentage of positivity " RPP ": percentage of positivity relative to negative and positive reference samples to avoid any variation from plate to plate, or dependant of the activity of the reagants. Reference samples are chosen to be representative of the infected and non infected populations. 300 samples from each population are tested, mean response to the test is recorded and the reference samples selected for a similar response. Such presentation of the results allow to determine sensitivity and specificity of the test when fixing the cut off line either on a graph of the distribution of the responses in infected and non infected populations or, directly with the Gaussian distributions. Characteristics of the test in 13 sheep experimentally infected with T. vivax indicated that the RPP of the samples is below 5% before infection, reaches 50% in 12-30 days post infection (p.I.), remains above 30% throughout the infection, and decreases below 30% within 2-3 months after a sterilizing treatment. It is suggested to use RPP for the presentation of the results in ELISA tests, for better standardisation and comparison of the results between laboratories

Mots-clés : trypanosoma vivax; test elisa; méthode; analyse de données; bovin; ovin; expérimentation; guyane française; france

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