THE DIRECT AGGLUTINATION-TEST FOR DIAGNOSIS OF VISCERAL LEISHMANIASISUNDER FIELD CONDITIONS IN SUDAN - COMPARISON OF AQUEOUS AND FREEZE-DRIED ANTIGENS

The performance of the direct agglutination test (DAT) was evaluated u nder field conditions in an endemic area of visceral leishmaniasis in eastern Sudan, using aqueous (Aq) antigen which has to be kept refrige rated and a newly developed freeze-dried (FD) antigen which is stable at ambient temperature. Both antigens compared well, with 92-98% of re adings being identical or only with one dilution difference in titre. FD antigen gave titres that were identical with Aq antigen in 73% of s amples, higher in 19%, and lower in 8%. Owing to high ambient temperat ures and low humidity, microtitre plate wells dried out during the sta ndard procedures for elution and incubation. However, shortening the e lution time from 12 to 4 h proved possible for both antigens; incubati on could be reduced from 24 to 10 h for Aq antigen, after which the pl ates could still be read. Incubation with FD antigen required 18 h and the plates needed to be kept cool because of evaporation. Despite the longer procedure with the FD antigen, the DAT can be completed in 24 h and the use of this stable antigen, that does not require refrigerat ion, is a major improvement in performing the DAT under unfavourable f ield conditions.