HTLV‐I/II infection in a high viral endemic area of Zaire, Central Africa: Comparative evaluation of serology, PCR, and significance of indeterminate Western blot pattern

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Abstract
The frequency of indeterminate Western blot (WB) seroreactivities against HTLV‐I “gag encoded proteins” only, and the use of low specific diagnostic WB criteria led to the overestimation of HTLV‐I seroprevalence in initial studies in intertropical Africa and Papua New Guinea. In order to clarify the meaning of such seroreactivity, 98 blood samples of individuals from a high HTLV‐I endemic area in Zaire, Central Africa were studied by a WB assay containing HTLV‐I disrupted virions enriched with a gp 21 recombinant protein and a synthetic peptide from the gp 46 region (MTA‐1), and by the polymerase chain reaction (PCR) with 3 primers pairs and 4 different HTLV‐I and or HTLV‐II‐specific probes. These 98 samples were taken mainly from patients with neurological diseases and from their relatives. Using stringent WB criteria, 28 sera (29%) were considered as HTLV‐I‐positive, 3 as negative and 67 (68%) as indeterminate. A large proportion of these indeterminate sera would have been considered as HTLV‐I‐positive samples according to previous low specific WB diagnostic criteria. After PCR, 35 samples (36%) were considered as positive for the presence of HTLV‐I proviral DNA. Out of the 67 WB seroindeterminate, 10 (15%) were found HTLV‐I‐positive by PCR. These 10 individuals exhibited in WB multiple band reactivity with p19 and/or p24 (7 cases of both) associated in 6 cases with rgp 21, but never with MTA‐1. No samples were found PCR‐positive for HTLV‐II despite the findings of 11 sera suggestive of HTLV‐II by WB. These findings demonstrate that even in a high HTLV‐I endemic area, only a minority (about 15%) of the WB‐seroinde‐terminate individuals could be considered as infected by HTLV‐I, and that very stringent WB criteria could lead to overlooking some infected individuals.

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