Preparation and evaluation of a glycerol-preserved direct agglutination antigen for long-term preservation: a comparative study of the detection of anti-Leishmania infantum antibodies in human and dog.

OBJECTIVE To prepare and evaluate a glycerol-preserved antigen from an Iranian strain of Leishmania infantum (L. infantum) for use in glycerol-preserved direct agglutination tests (GP-DAT) as an alternative to freeze dried direct agglutination tests (FD-DAT) that use freeze-dried antigen. METHODS Glycerol-preserved DAT antigen was prepared and stored at different temperatures. We tested antigen stored at 4 °C, 22-37 °C and 50 °C over a period of 365 days. Seven hundred twenty-nine serum samples were collected from different geographical zones of Iran from 2007-2009, and 80 of these samples were pooled to produce sera. Each pooled serum contained 10 sera. All positive and negative pooled sera were separately tested for anti-L. infantum antibodies with GP-DAT, FD-DAT and formaldehyde-fixed direct agglutination test (FF-DAT) antigens; tests were performed on both human and dog sera over a period of 12 months. RESULTS There was strong agreement between the results obtained using GP-DAT and FD-DAT antigens stored at 22-37 °C for 12 months for both human (100%) and dog (100%) pooled sera. The direct agglutination test results were highly reproducible (weighted kappa: GP=0.833, FD=0.979 and FF=0.917). CONCLUSIONS Because GP-DAT antigen is highly stable over a range of temperatures and is easy to transport in the field, this type of antigen may be particularly useful in areas with endemic visceral leishmaniasis.