Hemagglutination inhibition antibodies against Sindbis virus in human and bovine sera in Eastern Sicily

Previously the authors reported on the isolation of a Sindbis-related virus (SRV) from Hyalomma marginatum ticks in Eastern Sicily. To obtain information about the virus circulation, they carried out a serological survey in 5 areas up to 80 km distant from the original locality. The human sera were collected from May to September 1978, from 331 male and female inhabitants of small towns, aged from 2 to 81 yr. Bovine sera were collected at the same time from 288 animals grazing in little farms. The sera were stored at -20°C until tested. After acetone treatment and goose red cell adsorption, all sera were tested for haemagglutination inhibition (HI) against 8 units of both Sindbis prototype virus and SRV at pH 6.2 and at 37°C. The total incidence of positive human sera was 2.11% against SRV and 1.51% against Sindbis prototype. Only 3 sera reacted against both antigens. The HI titres varied from 20 to 160. The sera reacting with both antigens showed the highest titres against SRV. The total incidence of positive bovine sera was 29.16% against SRV and 13.88% against Sindbis prototype. The HI titres varied from 20 to 320; 27 sera reacted against both antigens and showed the highest titres against SRV. These data seem to demonstrate a quite active circulation of SRV, in particular in the area in which this virus had been isolated from the infected ticks. The higher proportion of positive reactions with SRV may be due to avidity of freshly isolated strains and/or to antigenic differences between Sindbis prototype and SRV.