A total of 166 sera from adult residents in a northern Italian area (Gorizia province) was examined by the hemagglutination-inhibition test for antibodies against 10 arthropod-borne viruses : two from group A, five from group B, and Bunyamwera and Phlebotomus fever (Sicilian and Napolitan strains).
Fifty-eight sera (35%) reacted with one or more antigen. No evidence was found of immunity to viruses of group A or to Bunyamwera virus. Twenty sera (12%) reacted with group B viruses, two monotypically with TBE, eight monotypically with WN, and three with a titer with WN greater than with other group B antigens. One serum reacted at very high dilution (1 :81,820) with dengue 1 ; this donor had lived in Egypt until 1962.
Some of the HI-positive sera were further tested with TBE and WN viruses by the mouse- neutralization test. The presence of antibodies was confirmed in the two sera reacting monotypically with TBE. WN-neutralizing antibodies were not evidenced, except in one serum, indicating perhaps the presence of a closely related virus.
Forty five sera (27 %) reacted with Phlebotomus-fever antigens (Sicilian and Napolitan strains) in the HI test. NT antibodies to the Sicilian strain were detected only in two sera among the HI positive tested.