ELISA for detection of IgM and IgG antibodies to sandfly fever Sicilian virus.

An enzyme-linked immunosorbent assay (ELISA) was developed to detect specific human immunoglobulin G and M antibodies to sandfly fever Sicilian (SFS) virus. Acute and early convalescent serum pairs with greater than or equal to 7 days between the 2 specimens were available from 20 patients and all showed significant optical density (OD) increase and significant titre rise (greater than or equal to 4-fold) by IgG ELISA. However, negative or borderline-positive sera were found as late as 11 days after onset of symptoms when tested by IgG ELISA. Specific IgM antibodies were detected during the first week of symptoms, and maximum OD values were obtained during the first 4 weeks after onset of disease. The IgM OD values declined over the following 3-9 months. All sera collected later than 14 months post-onset were negative by IgM ELISA. The combination of early antibody response and the need to test only one serum specimen gives IgM ELISA an advantage over IgG ELISA in patients diagnosis. The IgG ELISA was also evaluated as a seroepidemiological tool and compared to a plaque reduction neutralization test (PRNT) using sera from a normal Cypriot population. Of 183 sera tested, 34 (19%) were positive in plaque reduction neutralization tests (PRNT) and 113 (62%) by IgG ELISA. A number of PRNT-negative sera were strongly positive by IgG ELISA and also by indirect immunofluorescence test, which may suggest the presence of a virus related to SFS in Cyprus which has not yet been isolated.