Use of glycerol as an alternative to freeze-drying for long-term preservation of antigen for the direct agglutination test

Use of glycerol as an alternative to freeze-drying for long-term preservation of antigen for the direct agglutination test
November 2003
Abdallah el Harith1,2, Mohamed el Mutasim2, Durria Mansour2, el Fadil Mustafa2 and Harold Arvidson2
Tropical Medicine & International Health
Volume 8 Issue 11 Page 1025
Blackwell Synergy
1 Dutch Ministry of Foreign Affairs, Ahfad Mission, Omdurman, Sudan
2 Ahfad University for Women, Omdurman, Sudan
Summary
The potential of glycerol for long-term preservation of the direct agglutination test (DAT) antigen was evaluated at a fluctuating laboratory temperature of 2537 ?C and at constant temperatures of 37 and 45 ?C for a period of 222 days. DAT titres recorded for the three antigen aliquots preserved in 50% (v/v) glycerol and stored at 2537, 37 or 45 ?C at 11 time intervals were within the same range of the control antigen kept at 4 ?C. Performance of the glycerol-preserved antigen stored at 45 ?C was compared with that of a freeze-dried version on 24 visceral leishmaniasis (VL) and 54 non-VL patients. For all non-VL patients, a maximum DAT titre of 1/800 was recorded for either of the two antigens. For all VL patients, in comparison with the freeze-dried, the glycerol-preserved antigen always had equal or higher titre; in 16 of the 24 VL sera tested, the latter antigen scored three- to sixfold higher titres. As this glycerol preservation method is economical and easy to perform, it has better potential for wider-scale application than freeze-drying.
Introduction Go to: ChooseTop of pageIntroduction <<Material and methodsResultsDiscussionConclusionAcknowledgementsReferences
Diagnosis of visceral leishmaniasis (VL) in the human and canine reservoir has significantly been enhanced by the introduction of the direct agglutination test (DAT) (Harith et al. 1986,1989). The high ambient temperatures and the lack of reliable cold chain facilities in most of the VL endemic areas have limited application of the test to central and district laboratories. Several improvements were introduced to DAT antigen processing in order to maintain stability under rural conditions (Harith et al. 1989,1995). A freeze-dried antigen was field evaluated and found to be adequately stable for considerable periods at temperature levels up to 45 ?C (Meredith et al. 1995; Zijlstra et al. 1997). The major shortcomings of this approach are that preservation by freeze-drying requires sophisticated equipment, a continuous electrical supply and a high level of skill. Procuring the freeze-dried reagent is also rather costly and therefore unaffordable for most VL cases. The need for highly equipped laboratories for producing such preserved DAT antigen greatly limits application of this important diagnostic tool to economically privileged VL endemic areas. We describe a simple but equally efficient method for antigen preservation that can easily be executed at almost all laboratories in VL endemic areas.
Please visit the Web site to view the report in its entirety.