Human T-lymphotropic virus type II in Japan

Detection of early phase human T-cell leukemia virus type 1 and 2 infection with an improved confirmatory test

BACKGROUND

Human T-cell leukemia virus type 1 (HTLV-1) is a blood-borne virus, and mandatory testing of donated blood for HTLV-1 antibodies has been adopted by Japanese Red Cross blood centers since 1986. A confirmatory line immunoassay was initiated in 2019 for individuals who were seroreactive in the screening test. This decreased the incidence of indeterminate individuals, however, donors with indeterminate results are not informed of their HTLV-1 seroreactivity and they can continue to donate blood.

OBJECTIVES

To clarify the characteristics of indeterminate line immunoassay results among Japanese blood donors.

STUDY DESIGN

Of 759,259 blood donors in the Kyushu district of Japan, an area endemic for HTLV-1, 101 cases were classified as indeterminate by line immunoassay testing. We examined these cases using alternative secondary antibodies, anti-human-Ig (IgG/IgM/IgA) and -IgM antibodies, to detect the early phase of HTLV infection.

RESULTS

Using anti-human-Ig and -IgM antibodies, HTLV infection status was confirmed in 37 individuals (HTLV-1-positive, 2; HTLV-positive, 27; HTLV-negative, 8). Among the remaining 64 indeterminate individuals, we identified one HTLV-2-infected 18-year-old female. A previous blood donation from this individual showed a negative anti-HTLV screening test result (signal-to-cutoff ratio = 0.1). Therefore, this case was considered to be an HTLV-2 seroconversion case.

CONCLUSIONS

These results indicate that the procedure for diagnosing HTLV infection should be reconsidered and that an accurate detection system for the early phase of HTLV infection is urgently needed for public health in Japan. Moreover, the issue of HTLV-2 infection needs a higher profile in Japan.

First case of molecularly identified and genetically characterized human T-cell leukemia virus type 2 infection in a pregnant woman in non-endemic Japan

Human T-cell leukemia virus type 2 (HTLV-2) is non-endemic in Japan unlike the related HTLV type 1. Previously, although HTLV-2-seropositivity was identified via western blotting in one male blood donor in Japan, there have been no reports of HTLV-2 provirus detection by nucleic acid testing. In this report, one Japanese pregnant woman was clinically diagnosed as being HTLV-2-infected with a line immunoassay for specific antibodies after primary testing through prenatal screening in Japan. In genomic DNA of her peripheral blood mononuclear cells, HTLV-2 proviral genome was detected by nucleic acid testing (three methods) with quantitative polymerase chain reaction. The full-genome sequence of this strain was successfully determined. The identified virus was interestingly characterized as a presumed progenitor of subtypes a and c by recombination region and phylogenetic tree analyses. In conclusion, the present infection is, to our knowledge, the first case of molecularly identified and genetically characterized HTLV-2 infection found via prenatal screening in non-endemic Japan.

Nucleotide sequence variation of human T-lymphotropic virus type II in Vietnam

A high rate of human T-lymphotropic virus type II (HTLV-II) infection has been documented in intravenous drug abusers (IVDAs) in South Vietnam. We have investigated the molecular characteristics of the virus and have shown that one HTLV-II subtype is predominant in Ho Chi Minh City. This molecular subtype, HTLV-IIb, was identified in a number of South Vietnamese by nucleotide sequence analysis of the long terminal repeat (LTR) region. HTLV-IIa was not found. These findings suggest that HTLV-IIb is endemic in IVDAs in South Vietnam, although IVDAs in urban areas in North America are predominantly infected with HTLV-IIa.