Comparison of signal-to-cutoff values in first, second, and third generation enzyme immunoassays for the diagnosis of HTLV-1/2 infection in “at-risk” individuals from São Paulo, Brazil

Multi-Epitope Protein as a Tool of Serological Diagnostic Development for HTLV-1 and HTLV-2 Infections

A multi-epitope protein expressed in a prokaryotic system, including epitopes of Env, Gag, and Tax proteins of both HTLV-1 and HTLV-2 was characterized for HTLV-1/2 serological screening. This tool can contribute to support the implementation of public policies to reduce HTLV-1/2 transmission in Brazil, the country with the highest absolute numbers of HTLV-1/2 infected individuals. The chimeric protein was tested in EIA using serum/plasma of HTLV-infected individuals and non-infected ones from four Brazilian states, including the North and Northeast regions (that present high prevalence of HTLV-1/2) and Southeast region (that presents intermediate prevalence rates) depicting different epidemiological context of HTLV-1/2 infection in our country. We enrolled samples from Pará (n = 114), Maranhão (n = 153), Minas Gerais (n = 225) and São Paulo (n = 59) states; they are from blood donors' candidates (Pará and Minas Gerais), pregnant women (Maranhão) and HIV+/high risk for sexually transmitted infection (STI; São Paulo). Among the HTLV-1/2 positive sera, there were co-infections with viral (HTLV-1 + HTLV-2, HIV, HCV, and HBV), bacterial (Treponema pallidum) and parasitic (Trypanosoma cruzi, Schistosma mansoni, Strongyloides stercoralis, Entamoeba coli, E. histolytica, and Endolimax nana) pathogens related to HTLV-1/2 co-morbidities that can contribute to inconclusive diagnostic results. Sera positive for HIV were included among the HTLV-1/2 negative samples. Considering both HTLV-1 and HTLV-2-infected samples from all states and different groups (blood donor candidates, pregnant women, and individuals with high risk for STI), mono or co-infected and HTLV-/HIV+, the test specificity ranged from 90.09 to 95.19% and the sensitivity from 82.41 to 92.36% with high accuracy (ROC AUC = 0.9552). This multi-epitope protein showed great potential to be used in serological screening of HTLV-1 and HTLV-2 in different platforms, even taking into account the great regional variation and different profile of HTLV-1 and HTLV-2 mono or co-infected individuals.

Performance of Commercially Available Serological Screening Tests for Human T-Cell Lymphotropic Virus Infection in Brazil

Serological screening for human T-cell lymphotropic virus type 1 (HTLV-1) is usually performed using enzyme-linked immunosorbent assay (ELISA), particle agglutination, or chemiluminescence assay kits. Due to an antigen matrix improvement entailing the use of new HTLV antigens and changes in the format of HTLV screening tests, as well as newly introduced chemiluminescence assays (CLIAs), a systematic evaluation of the accuracy of currently available commercial tests is warranted. We aimed to assess the performance of commercially available screening tests for HTLV infection diagnosis. A diagnostic accuracy study was conducted on a panel of 397 plasma samples: 200 HTLV-negative plasma samples, 170 HTLV-positive plasma samples, and 27 plasma samples indeterminate by Western blotting (WB). WB-indeterminate samples (i.e., those yielding no specific bands for HTLV-1 and/or HTLV-2) were assessed by PCR, and the results were used to compare agreement among the commercially available ELISA screening tests. For performance analysis, WB-indeterminate samples were excluded, resulting in a final study panel of 370 samples. Three ELISA kits (Murex HTLV-1/2 [Murex], anti-HTLV-1/2 SYM Solution [SYM Solution], and Gold ELISA HTLV-1/2 [Gold ELISA]) and one CLIA kit (Architect rHTLV-1/2) were evaluated. All screening tests demonstrated 100% sensitivity. Concerning the HTLV-negative samples, the SYM Solution and Gold ELISA kits had specificity values of >99.5%, while the Architect rHTLV-1/2 test presented 98.1% specificity, followed by Murex, which had a specificity of 92.0%. Regarding the 27 samples with WB-indeterminate results, after PCR confirmation, all ELISA kits showed 100% sensitivity but low specificity. Accuracy findings were corroborated by the use of Cohen's kappa value, which evidenced slight and fair agreement between PCR analysis and ELISAs for HTLV infection diagnosis. Based on the data, we believe that all evaluated tests can be safely used for HTLV infection screening.

Short Communication: Failures in Detecting HTLV-1 and HTLV-2 in Patients Infected with HIV-1

Changes in retrovirus acquisition/transmission behaviors have been reported in Brazil, with a concerning increase in HIV-1-infected individuals aged 15-39 years. In São Paulo, HIV-1/HTLV-1 and HIV-1/HTLV-2 coinfections have been associated with intravenous drug use and failure to detect HTLV-1/2 (human T cell lymphotropic virus types 1 and 2) with immunosuppression and the use of highly active antiretroviral therapy (HAART). Negative results for HTLV serologic [western blotting (WB)] and molecular [real-time PCR pol (qPCR)] confirmatory assays have been reported, whereas the best sensitivity has been found for INNO-LIA (LIA). In this study, we expand our previous data by analyzing a group of young patients (n = 1,383; median age 35.6 years) who recently acquired HIV by sexual contact, the majority of whom were HAART naïve, and comparing the performances of four HTLV confirmatory assays: LIA, WB, qPCR, and PCR-RFLP (tax). We confirmed HTLV infection in 58 (4.2%) blood samples: 29 HTLV-1, 24 HTLV-2, 1 HTLV-1+HTLV-2, and 4 HTLV. LIA, WB, qPCR, and PCR-RFLP sensitivities were 94.8%, 82.8%, 79.2%, and 74.5%, respectively. Associations of HTLV infection with female gender (OR = 2.28, 1.31-4.00) and age >40 years (p < .0001) were detected. The results confirm the low sensitivities of molecular assays and the best performance of LIA in detecting HTLV-1/2 in such patients. We hypothesize that the negative PCR results are due to the presence of defective provirus and/or low proviral load circulating in such patients, with inconclusive WB coinciding with the seroconversion period. Corroborating the associations obtained, repeated exposure is required for HTLV sexual transmission/acquisition, which is more efficient from male to female.

Comparative performances of serologic and molecular assays for detecting human T lymphotropic virus type 1 and type 2 (HTLV-1 and HTLV-2) in patients infected with human immunodeficiency virus type 1 (HIV-1)

The present study evaluated several techniques currently available (commercial kits and in-house assays) for diagnosing human T lymphotropic viruses types 1 and 2 in two groups of patients enrolled at HIV/AIDS specialized care services in São Paulo: Group 1 (G1), n = 1608, 1237 male/371 female, median age 44.3 years old, majority using highly active antiretroviral therapy (HAART); G2, n = 1383, 930 male/453 female, median age of 35.6 years old, majority HAART naïve. Enzyme immunoassays [(EIA) Murex and Gold ELISA] were employed for human T lymphotropic viruses types 1 and 2 screening; Western blotting (WB), INNO-LIA (LIA), real-time PCR pol (qPCR), and nested-PCR-RFLP (tax) were used to confirm infection. Samples were considered human T lymphotropic viruses types 1 and 2 positive when there was reactivity using at least one of the four confirmatory assays. By serological screening, 127/2991 samples were positive or borderline, and human T lymphotropic virus infection was confirmed in 108 samples (three EIA-borderline): 56 human T lymphotropic virus type 1 [G1 (27) + G2 (29)]; 45 human T lymphotropic virus type 2 [G1 (21) + G2 (24)]; one human T lymphotropic virus type 1 + human T lymphotropic virus type 2 (G2); six human T lymphotropic virus [G1 (2) + G2 (4)]. Although there were differences in group characteristics, human T lymphotropic viruses types 1 and 2 prevalence was similar [3.1% (G1) and 4.2% (G2), p = 0.113]. The overall sensitivities of LIA, WB, qPCR, and PCR-RFLP were 97.2%, 82.4%, 68.9%, and 68.4%, respectively, with some differences among groups, likely due to the stage of human T lymphotropic virus infection and/or HAART duration. Indeterminate immunoblotting results were detected in G2, possibly due to the seroconversion period. Negative results in molecular assays could be explained by the use of HAART, the occurrence of defective provirus and/or the low circulating proviral load. In conclusion, when determining the human T lymphotropic virus infection, the findings highlight that there is a need to consider the blood samples with borderline results in screening assays. Of all the tested assays, LIA was the assay of choice for detecting human T lymphotropic virus type 1 and human T lymphotropic virus type 2 in human immunodeficiency virus type 1-infected patients.

The best algorithm to confirm the diagnosis of HTLV-1 and HTLV-2 in at-risk individuals from São Paulo, Brazil

The ability to confirm the diagnosis of human T-lymphotropic virus types 1 and 2 (HTLV-1 and HTLV-2) in at-risk individuals in São Paulo, Brazil by Western blotting (WB), conventional polymerase chain reaction (tax and pol PCR) and real-time PCR (pol) is compared. Seventy-three blood samples that were reactive in HTLV-1/2 serological screening enzyme immunoassays (EIAs) were evaluated. HTLV-1/2 was confirmed in 53 blood samples: 48 were positive by WB, 41 were positive by PCR and 42 scored positive by real-time PCR assays (37 of 48 WB-positive samples plus five WB-indeterminate samples that were further confirmed by sequencing). Although WB was able to detect more cases of HTLV-1/2 infection, the real-time PCR assay was able to discriminate between these two viruses and confirm an individual HTLV-1/HTLV-2 diagnosis in two HTLV WB-untyped samples and five WB-indeterminate samples. Because of the large number of WB-indeterminate samples and the cost of the WB assay in Brazil, it is proposed an algorithm that employs two EIAs for screening and then real-time PCR to confirm the infection, followed by testing any PCR-negative samples with the WB assay. This strategy reduces costs and improves the accuracy of the diagnosis of HTLV-1/2.