Challenges in diagnosing the Human T-Cell Lymphotropic Virus type 1 and type 2 (HTLV-1 and HTLV-2) in patients infected with HIV-1

Abstract

Since the 90 decade, the Instituto Adolfo Lutz (IAL) has performed the diagnosis of Human T-cell
Lymphotropic Virus type 1 and type 2 (HTLV-1and HTLV-2), and thenceforth the difficulties in
diagnosing HTLV-2 have been reported, mostly in HIV-infected patients. The present study aimed
at evaluating the several diagnostic techniques currently available (commercial kits and in-house
assays), and to establish the best algorithm to be employed for diagnosing HTLV-1/-2 in patients
infected with HIV-1. The study population was composed by two patient groups attended at HIV/
AIDS specialized services care in São Paulo: the pioneer one [Group 1 (G1), n=1,608], and the
other with the most recent historical health setting [Group 2 (G2), n=1,383. The majority of the
both groups were composed by male patients [G1 (76.9%) and G2 (67.2%)], with average ages
of 44.3 (G1) and 35.6 (G2) years old. The assays employed for HTLV-1/-2 screening in 2,991
blood samples were the 3rd generation enzyme immunoassays (Murex and Gold ELISA); and those
reagent samples were subsequently confirmed by Western Blot (WB) and INNO-Lia (LIA), and
by means of two molecular methodologies, real-time PCR (qPCR – pol) and nested-PCR-RFLP
(tax). Samples were considered HTLV-1/-2 positive when they showed specific reactivity, at least
in one of the four confirmatory assays used in this study. HTLV-1/-2 prevalence of 3.1% (G1) and
4.2% (G2) were detected. Differences in sex (G2) and average age among the HIV-mono-infected
individuals and the HIV/HTLV-co-infected patients were found. Among the co-infected patients,
47.0% (G1) and 51.7% (G2) were female, and the average age was higher in G1 (49.5 vs. 43.5 years
old). By serological screening, 127 sera samples were reagent, and the truly HTLV infection was
confirmed in 108 samples, being 56 HTLV-1 [G1 (27) + G2 (29)], 45 HTLV-2 [G1 (21) + G2 (24)],
one HTLV-1 + HTLV-2 double infection (G2) and six HTLV [G1 (2) + G2 (4)]. Of 19 reactive blood
samples at screening assay, nine remained indeterminate (G2), and ten were considered negative
[G1 (1) + G2 (9)]. The confirmatory assays employed for analyzing the blood samples from the
patients included in the present study with better sensitivity values was LIA (97.2%). The obtained
results confirmed that none of the confirmatory tests showed 100% sensitivity in detecting HTLV1/-2 in samples from HIV-infected patients; thus, the use of combined tests should be crucial.
Accordingly, the best cost-effective algorithm to be applied for testing these patients should be by
employing qPCR as the first choice, and followed by LIA to analyze the negative samples.