Standardization of ELISA for detection of antibodies to orthopoxviruses

The experience with ELISA technique utilized at serological screening for orthopoxviruses in the Republic of Ivory Coast revealed factors reducing the sensitivity and the specificity of the test. It was found out that routine controls such as "positive" and "negative" sera as well as the accepted reading of the results by two-fold or higher increase of OD values as compared to the "negative" control may be not sufficient. A significantly enhanced sensitivity and specificity of reaction was achieved by simultaneous examination of each serum under study with a control antigen. Selection of optimal dilutions of each test component followed by spectrophotometric assay and calculation of results according to the given formula contributed to the same aim. As a result of these improvements the rate of antibody detection among revaccinees was enhanced from 19 to 78.8% and the titres of ELISA and virus neutralization tests correlated in 88% of cases.