Early diagnosis of human Lassa fever by ELISA detection of antigen and antibody.

Sequential serum samples, beginning on the day of hospital admission, from three patients with Lassa fever were tested for the presence of Lassa-virus antigens and antibodies by means of an enzyme-linked immunosorbent assay. Lassa-virus antigens were detected in the first serum sample from each patient, thus providing an early definitive diagnosis. In contrast, seroconversion was not detectable by ELISA or indirect fluorescent antibody techniques until 3 days or more after admission. The antigen-detection ELISA has important advantages over conventional infectivity titrations; it takes only hours to carry out and can be accomplished safely, with beta-propiolactone-inactivated samples. Development of antibodies coincided with a decline in antigenaemia. All acute-phase Lassa-fever sera contained either antigen or IgM antibody, and most contained both, thus allowing early diagnosis with single serum samples. More extensive testing of these ELISA techniques is recommended in field hospitals where Lassa fever is endemic and rapid diagnostic tools are needed.