The prevalence of antibodies to the human T lymphotropic virus (HTLV) in Ghana, West Africa

Geographic distribution, clinical epidemiology and genetic diversity of the human oncogenic retrovirus HTLV-1 in Africa, the world's largest endemic area

The African continent is considered the largest high endemic area for the oncogenic retrovirus HTLV-1 with an estimated two to five million infected individuals. However, data on epidemiological aspects, in particular prevalence, risk factors and geographical distribution, are still very limited for many regions: on the one hand, few large-scale and representative studies have been performed and, on the other hand, many studies do not include confirmatory tests, resulting in indeterminate serological results, and a likely overestimation of HTLV-1 seroprevalence. For this review, we included the most robust studies published since 1984 on the prevalence of HTLV-1 and the two major diseases associated with this infection in people living in Africa and the Indian Ocean islands: adult T-cell leukemia (ATL) and tropical spastic paraparesis or HTLV-1-associated myelopathy (HAM/TSP). We also considered most of the book chapters and abstracts published at the 20 international conferences on HTLV and related viruses held since 1985, as well as the results of recent meta-analyses regarding the status of HTLV-1 in West and sub-Saharan Africa. Based on this bibliography, it appears that HTLV-1 distribution is very heterogeneous in Africa: The highest prevalences of HTLV-1 are reported in western, central and southern Africa, while eastern and northern Africa show lower prevalences. In highly endemic areas, the HTLV-1 prevalence in the adult population ranges from 0.3 to 3%, increases with age, and is highest among women. In rural areas of Gabon and the Democratic Republic of the Congo (DRC), HTLV-1 prevalence can reach up to 10-25% in elder women. HTLV-1-associated diseases in African patients have rarely been reported in situ on hospital wards, by local physicians. With the exception of the Republic of South Africa, DRC and Senegal, most reports on ATL and HAM/TSP in African patients have been published by European and American clinicians and involve immigrants or medical returnees to Europe (France and the UK) and the United States. There is clearly a huge underreporting of these diseases on the African continent. The genetic diversity of HTLV-1 is greatest in Africa, where six distinct genotypes (a, b, d, e, f, g) have been identified. The most frequent genotype in central Africa is genotype b. The other genotypes found in central Africa (d, e, f and g) are very rare. The vast majority of HTLV-1 strains from West and North Africa belong to genotype a, the so-called 'Cosmopolitan' genotype. These strains form five clades roughly reflecting the geographic origin of the infected individuals. We have recently shown that some of these clades are the result of recombination between a-WA and a-NA strains. Almost all sequences from southern Africa belong to Transcontinental a-genotype subgroup.

Prevalence and Molecular Epidemiology of Human T-Lymphotropic Virus Type 1 among Women Attending Antenatal Clinics in Sub-Saharan Africa: A Systematic Review and Meta-Analysis

Human T-cell lymphotropic virus type 1 (HTLV-1) imposes a substantial disease burden in sub-Saharan Africa (SSA), which is arguably the world's largest endemic area for HTLV-1. Evidence that mother-to-child transmission persists as a major mode of transmission in SSA prompted us to estimate the pooled prevalence of HTLV-1 among pregnant women throughout the region. We systematically reviewed databases including EMBASE, MEDLINE, Web of Science, and the Cochrane Database of Systemic Reviews from their inception to November 2018. We selected studies with data on HTLV-1 prevalence among pregnant women in SSA. A random effect meta-analysis was conducted on all eligible data and heterogeneity was assessed through subgroup analyses. A total of 18 studies, covering 14,079 pregnant women, were selected. The evidence base was high to moderate in quality. The pooled prevalence, per 100 women, of the 18 studies that screened HTLV-1 was 1.67 (95% CI: 1.00-2.50), a figure that masks regional variations. In Western, Central, Southern, and Eastern Africa, the numbers were 2.34 (1.68-3.09), 2.00 (0.75-3.79), 0.30 (0.10-0.57), and 0.00 (0.00-0.21), respectively. The prevalence of HTLV-1 infection among pregnant women in SSA, especially in Western and Central Africa, strengthens the case for action to implement routine screening of pregnant women for HTLV-1. Rigorous studies using confirmatory testing and molecular analysis would characterize more accurately the prevalence of this infection, consolidate the evidence base, and further guide beneficial interventions.

The prevalence of human T-lymphotropic virus type 1 & 2 (HTLV-1/2) in South African blood donors

BACKGROUND AND OBJECTIVES

Donated blood is not currently screened for human T-cell lymphotropic virus (HTLV) in South Africa. Several small studies have detected HTLV-1 in South Africa, but prevalence by geographic region or population group is unavailable.

MATERIALS AND METHODS

We performed a large seroprevalence study of South African blood donors during 3 months in 2013. All geographic regions except the Western Cape were included, and Black and Coloured (local term for mixed race) donors were oversampled. Identity-unlinked plasma samples were screened with the Abbott Prism HTLV-1/2 assay, and repeatedly reactive samples were tested by the Inno-LIA HTLV-1/2 Score confirmatory assay. Odds ratios were calculated with multivariable logistic regression.

RESULTS

Of 46 752 donors tested, 133 (0·28%) were initially reactive, 111 (0·24%) repeatedly reactive and 57 (0·12%) confirmed positive for HTLV-1; none were HTLV-2 positive. Prevalence was 0·062% weighted to annual blood donations but highly concentrated in the Black population group (OR = 20·24 CI: 2·77-147·88); higher in females than males (OR = 1·81 CI: 1·06-3·08); and in donors aged >50 years compared to ages 16-19 (OR = 6·4 CI: 2·95-13·86). After controlling for age, sex and population group, there was no difference in prevalence between new and repeat blood donors or among geographic regions within South Africa.

CONCLUSIONS

We conclude that HTLV-1 infection is widespread among the Black population of South Africa and its epidemiology is similar to other endemic areas. Because South Africa is increasing its recruitment of Black blood donors, the implications for blood screening require further consideration.

Re-emergence of human T-lymphotropic viruses in West Africa

Human T-lymphotropic viruses (HTLV) are Deltaretroviruses that infect millions of individuals worldwide via the same transmission routes as HIV. With the aim of exposing the possible re-emergence of HTLV in West Africa since discovery, a systematic review was carried out, focusing on the distribution of the virus types and significance of frequent indeterminate reports, while highlighting the need for mandatory routine blood screening. Capturing relevant data from discovery till date, sources searched were Google Scholar, CrossRef, NCBI (PubMed), MEDLINE, Research Gate, Mendeley, abstracts of Conferences and Proceedings, organization websites and reference lists of selected papers. A total of 2626 references were initially retrieved using search terms: Worldwide prevalence of HTLV, HTLV in Africa, HTLV in West Africa, HTLV subtypes, HTLV 3 and 4 in Africa, HTLV of African origin, HTLV seroindeterminate results, Spread of HTLV. These references were rigorously trimmed down to 76. Although evidence shows that HTLV is still endemic in the region, West Africa lacks recent epidemiological prevalence data. Thorough investigations are needed to ascertain the true cause of indeterminate Western Blot results. It is imperative that routine screening for HTLVs be mandated in West African health care facilities.

Seroprevalence of HTLV-1 and HTLV-2 amongst mothers and children in Malawi within the context of a systematic review and meta-analysis of HTLV seroprevalence in Africa

OBJECTIVES

Human T-lymphotropic virus (HTLV)-1 causes T-cell leukaemia and myelopathy. Together with HTLV-2, it is endemic in some African nations. Seroprevalence data from Malawi are scarce, with no reports on associated disease incidence. HTLV seroprevalence and type were tested in 418 healthy mothers from Malawi. In addition, we tested the sera of 534 children to investigate mother-to-child transmission. To provide context, we conducted a systematic review and meta-analysis of HTLV seroprevalence in African women and children.

METHODS

Stored samples from a previous childhood cancer and BBV study were analysed. ELISA was used for HTLV screening followed by immunoblot for confirmation and typing. Standard methods were used for the systematic review.

RESULTS

HTLV seroprevalence was 2.6% (11/418) in mothers and 2.2% (12/534) in children. Three mothers carried HTLV-1 alone, seven had HTLV-2 and one was dually infected. Three children carried HTLV-1 alone, seven had HTLV-2 and two were dually infected. Only two corresponding mothers of the 12 HTLV-positive children were HTLV positive. The systematic review included 66 studies of women and 13 of children conducted in 25 African countries. Seroprevalence of HTLV-1 varied from 0 to 17% and of HTLV-2 from 0 to 4%.

CONCLUSIONS

In contrast to findings from other studies in Africa, the seroprevalence of HTLV-2 was higher than that of HTLV-1 in Malawi and one of the highest for the African region. The lack of mother-child concordance suggests alternative sources of infection among children. Our data and analyses contribute to HTLV prevalence mapping in Africa.

Epidemiological Aspects and World Distribution of HTLV-1 Infection

The human T-cell leukemia virus type 1 (HTLV-1), identified as the first human oncogenic retrovirus 30 years ago, is not an ubiquitous virus. HTLV-1 is present throughout the world, with clusters of high endemicity located often nearby areas where the virus is nearly absent. The main HTLV-1 highly endemic regions are the Southwestern part of Japan, sub-Saharan Africa and South America, the Caribbean area, and foci in Middle East and Australo-Melanesia. The origin of this puzzling geographical or rather ethnic repartition is probably linked to a founder effect in some groups with the persistence of a high viral transmission rate. Despite different socio-economic and cultural environments, the HTLV-1 prevalence increases gradually with age, especially among women in all highly endemic areas. The three modes of HTLV-1 transmission are mother to child, sexual transmission, and transmission with contaminated blood products. Twenty years ago, de Thé and Bomford estimated the total number of HTLV-1 carriers to be 10-20 millions people. At that time, large regions had not been investigated, few population-based studies were available and the assays used for HTLV-1 serology were not enough specific. Despite the fact that there is still a lot of data lacking in large areas of the world and that most of the HTLV-1 studies concern only blood donors, pregnant women, or different selected patients or high-risk groups, we shall try based on the most recent data, to revisit the world distribution and the estimates of the number of HTLV-1 infected persons. Our best estimates range from 5-10 millions HTLV-1 infected individuals. However, these results were based on only approximately 1.5 billion of individuals originating from known HTLV-1 endemic areas with reliable available epidemiological data. Correct estimates in other highly populated regions, such as China, India, the Maghreb, and East Africa, is currently not possible, thus, the current number of HTLV-1 carriers is very probably much higher.

Seroprevalence of six different viruses among pregnant women and blood donors in rural and urban Burkina Faso: A comparative analysis

A seroprevalence study was carried out of six different human pathogenic viruses, namely human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), human T-cell leukemia virus (HTLV), human herpesvirus type 8 (HHV-8), and dengue virus among pregnant women and blood donors from rural (Nouna) and urban (Ouagadougou) Burkina Faso, West Africa. A total of 683 samples from blood donors (n = 191) and pregnant women (n = 492) were collected from both sites and screened for the different virus infection markers resulting in the following prevalence values for Nouna or Ouagadougou, respectively: HIV 3.6/4.6, anti-HBV core (anti-HBc) 69.6/76.4, HBV surface antigen (HBsAg)14.3/17.3, HCV 2.2/1.5, HTLV 1.4/0.5, HHV-8 11.5/13.5, dengue virus 26.3/36.5. Individuals aged > or =25 years were more likely to be infected with HIV than those below 24 years (P < 0.05). Infection with HIV increased the likelihood of co-infection with other viruses, such as HHV-8, HBV and HTLV. Co-infection studies involving five viruses (HBV-HBsAg, HHV-8, HIV, HCV, and HTLV) showed that 4.8% (33/683) of the studied population were dually infected, with HBsAg+ HHV-8 (13/33), HBsAg+HIV (8/33) and HIV+HHV-8 (8/33) being the most common co-infections. Of the population studied 0.6% (4/683) was triply infected, the most common infection being with HBV+HIV+HHV-8 (3/4). There was no difference in the prevalence of HIV, anti-HBc, HBsAg, HCV, HTLV, and HHV-8 either among blood donors or pregnant women in urban or rural setting, while dengue virus prevalence was relatively lower in rural (26.3%) than in urban (36.5%) Burkina Faso.

Increased prevalence of HTLV-1 among HIV-2-infected women but not HIV-2-infected men in rural Guinea-Bissau

OBJECTIVE

To assess the prevalence of HTLV infection and its association with HIV and other potential risk factors.

DESIGN AND SETTING

A cross-sectional survey and a case-control study in a rural community in Guinea-Bissau.

METHODS

A total of 2770 people were included in an HIV and HTLV seroepidemiologic survey. Three hundred of these participants were selected for a case-control study on HIV-2. Sera from both studies were tested for HTLV.

RESULTS

In all, 2501 and 298 subjects in the survey and case-control study, respectively, were tested for HTLV. Overall HTLV-1 prevalence was 5.2% and it was higher in women (odds ratio [OR], 1.36; confidence interval [CI], 0.92-2.02). Apart from an infected spouse, no significant risk factors could be identified for men. In women, HIV-2 infection (adjusted OR, 5.58; CI, 3.09-10.1), having an infected spouse, and area of residence were significantly associated with HTLV-1 infection. The association between HTLV-1 and HIV-2 was significantly different for men and women (test of interaction, p =.002).

CONCLUSIONS

In women, the most important determinant of HTLV-1 seropositivity was HIV-2 infection. Because the pattern was significantly different for men and women, common sexual risk factors may not be sufficient to explain the co-occurrence of HIV-2 and HTLV-1 in women. These observations may have implications in geographic areas where both types of retroviruses are prevalent.

Human T-cell lymphotropic virus type 1 gag indeterminate western blot patterns in Central Africa: relationship to Plasmodium falciparum infection

To gain insight on the significance of human T-cell lymphotropic virus type 1 (HTLV-1) indeterminate serological reactivities, we studied villagers of South Cameroon, focusing on a frequent and specific HTLV-1 Gag indeterminate profile (HGIP) pattern (gag p19, p26, p28, and p30 without p24 or Env gp21 and gp46). Among the 102 sera studied, 29 from all age groups had a stable HGIP pattern over a period of 4 years. There was no epidemiological evidence for sexual or vertical transmission of HGIP. Seventy-five percent of HGIP sera reacted positively on MT2 HTLV-1-infected cells by immunofluorescence assay. However, we could not isolate any HTLV-1 virus or detect the presence of p19 Gag protein in cultures of peripheral blood mononuclear cells obtained from individuals with strong HGIP reactivity. PCR experiments conducted with primers for HTLV-1 and HTLV-2 (HTLV-1/2 primers) encompassing different regions of the virus did not yield HTLV-1/2 proviral sequences from individuals with HGIP. Using 11 peptides corresponding to HTLV-1 or HTLV-2 immunodominant B epitopes in an enzyme-linked immunosorbent assay, one epitope corresponding to the Gag p19 carboxyl terminus was identified in 75% of HGIP sera, while it was recognized by only 41% of confirmed HTLV-1-positive sera. A positive correlation between HTLV-1 optical density values and titers of antibody to Plasmodium falciparum was also demonstrated. Finally, passage of sera through a P. falciparum-infected erythrocyte-coupled column was shown to specifically abrogate HGIP reactivity but not the HTLV-1 pattern, suggesting the existence of cross-reactivity between HTLV-1 Gag proteins and malaria-derived antigens. These data suggest that in Central Africa, this frequent and specific Western blot is not caused by HTLV-1 infection but could instead be associated with P. falciparum infection.

Prevalences of HTLV-1 infection and associated risk determinants in an urban population in Guinea-Bissau, West Africa

OBJECTIVE

To assess the prevalence and modes of transmission of HTLV-1 infection in an adult population in Bissau, and to evaluate possible interactions between the pattern of spread of HTLV-1 and HIV-1/HIV-2.

DESIGN AND METHODS

Univariate and multivariate analyses were used to evaluate gender-and age-specific HTLV-1 prevalences as well as associated risk determinants in an adult population based on a serosurvey comprising 2127 individuals from 304 randomly selected houses in Bissau.

RESULTS

Using stringent Western blot criteria, the overall seroprevalence of HTLV-1 was 3.6%, 2.2% among men and 4.7% among women, respectively. One individual was seropositive to HTLV-2. The prevalence of HTLV-1, which increased with age in both genders, however more markedly among women, was >4 times higher (9.4%) among older individuals (>44 years of age) than among younger individuals (2.4%). Blood transfusion and HIV-2 seropositivity were independently associated with HTLV-1 seropositivity in men. Among women, both HIV-2 seropositivity and HIV-1 seropositivity were significant risk determinants. Having had sexual partners was associated with a fivefold increased risk among women but did not reach significance.

CONCLUSION

The adult population of Guinea-Bissau has a higher prevalence of HTLV-1 than reported from most other countries in West Africa. The gender-and age-specific pattern of spread of HTLV-1 closely resembles that observed for HIV-2, another retrovirus prevalent to the region. The close correlation between HTLV-1 and HIV-2 most likely reflects the shared risk factors related to sexual behavior. The implication of the high percentage of double infections in this population needs to be determined.

HTLV-1 infection in a population-based cohort of older persons in Guinea-Bissau, West Africa: risk factors and impact on survival

In 1989, a population-based cohort of persons aged > or = 50 years was established in an urban area of Guinea-Bissau, West Africa. Overall, 346 persons were interviewed in detail about risk behaviors and had capillary blood drawn. Among women, 12.4% were HTLV-1 seropositive, compared with 4.6% in men. No HTLV-2 was found. Seropositivity varied considerably according to place of birth and ethnic group. In women, but not in men, HTLV-1 seropositivity was strongly associated with early sexual debut (10-14 yrs, 33.3%; 15-17 yrs, 26.0%; 18-20 yrs, 6.5%; 21+ yrs, 0%; ptrend = 0.001), lifetime number of male partners (ptrend = 0.006), and the male partner's number of co-wives (ptrend = 0.006). There was also a 3.1-fold increased risk of being HTLV-1 seropositive if the woman was also HIV-2 seropositive. In a multivariate-risk-factor analysis, the strongest association with HTLV-1 was a history of having been bitten by a monkey (n = 11; combined OR adjusted = 10.1; 95% CI 2.3-44.4). Ornamental scarification was associated with a 3.3-fold increased risk. Ethnic affiliation also significantly influenced the risk of being HTLV-1 seropositive. Follow-up performed in January 1996 revealed no difference in survival between HTLV-1-seropositive and -seronegative individuals over 6 years (rate ratio = 1.4, 95% CI 0.7-2.8). In conclusion, this population, which has very high HIV-2 seroprevalence, is also highly endemic for HTLV-1. Whereas sexual behaviors are clearly important for HTLV-1 spread in women, non-sexual risk factors were the only ones of potential importance in men. HTLV-1 had no impact on survival in this older population.

Assessment of a new immunoassay for serological confirmation and discrimination of human T-cell lymphotropic virus infections

The present study evaluated a new confirmatory assay for antibodies to human T-cell lymphotropic virus type 1 and 2 (HTLV-1 and HTLV-2) proteins performed with serum samples from various commercial sources. The new test is a line immunoassay (LIA) with a nylon membrane sensitized with the most relevant antigens of HTLVs: the envelope gp46 and gp21 as well as the gag p24 and p19 antigens, represented by either recombinant proteins or synthetic peptides. A total of 176 serum or plasma samples were tested, of which 66 were HTLV-1 positive, 72 were HTLV-2 positive, and 38 were HTLV negative; of the 38 HTLV-negative samples 23 were indeterminate by Western blotting (WB). Serially diluted samples (n = 33) from HTLV-1- and HTLV-2-infected patients were also analyzed to determine the sensitivity of the new assay. The new confirmatory assay (INNO-LIA HTLV) performed markedly better than WB assays for those samples reactive by screening. Accurate confirmation of the presence of HTLV-1 and HTLV-2 antibodies and accurate discrimination of HTLV-1 and HTLV-2 antibodies were obtained for all the HTLV-seropositive samples. Due to its enhanced specificity and sensitivity, the new assay not only improves the ability to confirm and discriminate HTLV infections but also eliminates the vast majority of WB-indeterminate and false-positive specimens.

Comparison of HHV-6 antibody titers in West Africa and the Caribbean

Human herpesvirus-6 (HHV-6) infection seems to be ubiquitous early in life, but antibody responses vary by geographic area. We compared HHV-6 antibody titer in 123 West African and 122 Caribbean serum samples. A quantitative immunofluorescence assay (IFA) using antigens derived from an HSB-2 cell line was used to test for IgG HHV-6 (GS strain) antibodies. The prevalence of HHV-6 antibodies was high (98%) in both sites. African samples had a significantly higher geometric mean titer (GMT: 697) than did Caribbean samples (GMT: 99). There was no difference between males (GMT: 260) and females (GMT: 270) overall. Children up to and including 9 years old had significantly higher titers (GMT: 483) than did all others (GMT: 237), and female children tended to have higher titers than did male children. In both areas there was a trend towards highest titer at younger age, followed by a decrease in titer during adulthood and middle age, and a secondary rise in titer in the oldest age group. Environmental and host factors may explain these geographic differences in antibody responses between two groups of African origin.

Presence of human T lymphotropic virus types I and II in Ghana, west Africa

Until recently, HTLV-I was considered to be an Old World virus and HTLV-II was thought to be endemic in the Americas. However, the presence of HTLV-II among Pygmies and other populations of Africa has raised doubts as to whether HTLV-II is primarily a New World virus. The large serosurveys conducted in the urban and rural areas of southern Ghana have identified a 1-2% prevalence for HTLV-I/II. To define the HTLV type, we have used a Western blot assay (HTLV-2.3 blot) that allows simultaneous confirmation and differentiation between HTLVs. Samples (n = 139) were chosen on the basis of previous reactivity with either an enzyme immune assay or r21e-spiked WB results. The WB 2.3 analysis of these specimens identified 55 (40%) to be HTLV positive, 70 (50%) to be HTLV indeterminant, and 14 (10%) to be HTLV negative for HTLV. HTLV seroindeterminant patterns ranged from both gag and env (14 were r21+, p24+, and/or p19+ [all were RIPA negative]) to gag only (21 were p24+/p19+, 16 were p19+, and 7 were p24+), and env only (8 were r21+ and 4 were rgp46+) reactivities. Of the 55 HTLV-positive specimens, 41 were typed as HTLV-I, 9 were HTLV-II, and 5 could not be typed (HTLV-I/II). Of the nine HTLV-II-positive specimens, three were from patients with Burkitt's lymphoma and six were from healthy individuals (two pregnant women) with no obvious risk factors for HTLV-II.(ABSTRACT TRUNCATED AT 250 WORDS)