Seroepidemilogy of human T‐lymphotropic retrovirus type I (HTLV‐I) in residents of niigata prefecture, Japan. Comparative studies by indirect immunofluorescence microscopy and enzyme‐linked immunosorbent assay

A large sample of carriers of human T‐lymphotropic retrovirus type 1 (HTLV‐I) in Niigata Prefecture was examined for the detection of natural antibodies to HTLV‐I‐related antigens in sera using both indirect immunofluorescence microscopy (IFM) and enzyme linked immunosorbent assay (ELISA). The present findings are based on multiple surveys, using each assay technique at least twice. Although Niigata Prefecture has been considered a non‐endemic region for HTLV‐I, Sado Island has been proven by this study to be a relatively endemic pocket within this non‐endemic area. Seropositivity was highest in residents of Sado Island; 97/1, 117 (8.7%) by IFM and 33/1, 061 (3.1 %) by ELISA; followed by Niigata City, 18/650 (2.8%) by IFM and 16/638 (2.5%) by ELISA; and lowest in the remaining areas, 57/2, 631 (2.2%) by IFM and 20/2, 551 (0.8%) by ELISA. Seropositivity was demonstrated in 172/4, 398 (3.9%) by IFM and 69/4, 250 (1.6%) by ELISA in Niigata Prefecture taken as a whole. In general, the incidence of seropositive residents increased gradually with age. The sex difference was not significant. The serum samples tested were categorized into 4 groups; (1) IFM and ELISA both positive, (2) IFM positive but ELISA negative, (3) IFM negative but ELISA positive, and (4) IFM and ELISA both negative. By absorption tests, IFM and ELISA seemed to recognize different specific antibodies in sera; IFM recognized antibodies to HTLV‐I‐related cellular antigens in addition to HTLV‐I‐viral antigens, but ELISA recognized antibodies to HTLV‐I viral antigens alone. Thus, IFM detected a broader spectrum of antigens, resulting in recognition of more positive sera than those detected by ELISA.