Human T-cell Lymphotropic Virus Type I Seroprevalence Research Articles

Human T-cell lymphotropic virus type I (HTLV-I) confirmed by PCR-Southern blot and sequencing analysis in a woman with tropical spastic paraparesis

Human T-cell lymphotropic virus type I (HTLV-I) is a human retrovirus and the aetiological agent of a progressive neurological disease called tropical spastic paraparesis/HTLV-I-associated myelopathy (TSP/HAM), as confirmed by evidence accumulated in HTLV-I seroprevalence studies. TSP/HAM is rarely diagnosed in Italy, given the low prevalence of HTLV-I in the population. TSP/HAM begins insidiously in the fourth decade, mainly with spastic paraparesis of the lower extremities and positive Babinski reflex, as well as interfering with bowel and bladder functions. In this study we report the clinical, virological and haemato chemical data of a 54-year-old woman, born in the Ivory Cost, with symptoms suggestive of TSP. The presence of HTLV-I infection was demonstrated by the detection of antibodies in serum and in cerebrospinal fluid by immunoenzymatic assay and Western blot analysis. In addition, viral isolation was carried out in peripheral blood cells, and the presence of HTLV-I proviral DNA was confirmed by polymerase chain reaction/Southern blot and sequencing analysis. According to our results, HTLV-I testing might be useful when TSP/HAM is suspected.

Soroprevalência do vírus linfotrópico-T humano tipo I entre gestantes em Goiânia, GO, Brasil

OBJETIVO: avaliar a soroprevalência do vírus linfotrópico de células-T humano tipo I (HTLV-I) entre as gestantes atendidas na rede pública municipal de saúde de Goiânia, estado de Goiás, na região Centro-Ceste do Brasil, e algumas características epidemiológicas do grupo estudado. MÉTODOS: durante o período de setembro de 2003 a dezembro de 2004, 15.485 grávidas foram rastreadas para o HTLV-I utilizando o ensaio imunoenzimático, a partir de sangue seco em papel de filtro, e para a confirmação da infecção realizou-se a reação em cadeia de polimerase, a partir do sangue total. Foram avaliados os parâmetros epidemiológicos: idade média, idade de 30 anos ou mais, grau de instrução menor que nove anos, estado civil e número de gestações. Os parâmetros idade média, idade de 30 anos ou mais e grau de instrução menor que nove anos foram comparados entre os grupos de gestantes infectadas e não infectadas. O teste t de Student e o teste exato de Fisher foram utilizados para os cálculos estatísticos. RESULTADOS: a prevalência encontrada foi 0,1%. Entre as gestantes infectadas a média de idade foi 26,4 anos, 43,7% delas apresentavam idade de 30 anos ou mais e 62,5% estudaram menos que nove anos. No grupo de gestantes não infectadas a média de idade foi 24,4 anos, 15,4% delas apresentavam idade de 30 anos ou mais e apenas 41,5% estudaram menos que nove anos. Só ocorreu diferença com significância estatística para os parâmetros idade de 30 anos ou mais e grau de instrução menor que nove anos. CONCLUSÃO: esse estudo demonstra que a soroprevalência do HTLV-I entre gestantes em Goiânia no período estudado foi 0,1%. Ela foi maior em gestantes com idade de 30 anos ou mais e naquelas com grau de instrução menor que nove anos

Seroprevalence of human T-cell lymphotropic virus type I among pregnant women in Accra, Ghana

Infection with human T-cell lymphotropic virus type I (HTLV-I) occurs mainly in Japan, Central and West Africa and the Caribbean Basin. Although antibody to HTLV-I has been reported among pregnant women in several endemic countries, there is no information regarding the seroprevalence in pregnant Ghanaian women. The reported seroprevalence of HTLV-I among healthy Ghanaian blood donors is between 0.5 and 4.2 %. Therefore, this study was conducted to determine the seroprevalence of HTLV-I among pregnant women attending the antenatal clinic at the 37 Military Hospital, Accra, Ghana, between the months of January and December 2003. The presence of antibodies specific for HTLV-I/II was tested using a particle agglutination test (PAT) kit and confirmed by Western blotting (WB). Of the 960 sera tested, HTLV-I/II antibodies were detected in 24 samples using the PAT kit. WB results indicated that, of the 24 positive PAT specimens, 20 specimens (83.3 %) were HTLV-I positive, one (4.2 %) was HTLV-II positive, two (8.3 %) were HTLV positive and one (4.2 %) was indeterminate. Therefore, the overall seroprevalence of HTLV-I was 2.1 %. Seroprevalence increased with age, suggesting sexual contact as the primary mode of transmission among women of childbearing age, rather than breastfeeding during infancy. The seroprevalence of 2.1 % reported here for HTLV-I in pregnant women in Accra is comparable to that of human immunodeficiency virus among the same population. In conclusion, the results indicate that HTLV-I is prevalent among asymptomatic Ghanaian pregnant women and thus there is a need to consider introducing antenatal screening for HTLV-I in Ghana.

COMPARATIVE TRENDS OF SEROPREVALENCE AND SEROINCIDENCE RATES OF HUMAN T CELL LYMPHOTROPIC VIRUS TYPE I AND HUMAN IMMUNODEFICIENCY VIRUS 1 IN PREGNANT WOMEN OF VARIOUS ETHNIC GROUPS SHARING THE SAME ENVIRONMENT IN FRENCH GUIANA

The objectives of this study were to compare the seroprevalence and seroincidence rates of human T cell lymphotropic virus type I (HTLV-I) and human immunodeficiency virus 1 (HIV-1) in pregnant women in several ethnic groups in French Guiana between July 1, 1991 and June 30, 2001. This study was conducted in the obstetrics unit of the hospital in Saint Laurent du Maroni in a dynamic cohort of 6,921 pregnant women with 11,679 deliveries, with new entrants each year. The overall seroprevalence of HTLV for all women differed between ethnic groups and was restricted mainly to the descendents of fugitive slaves of African origin known as Noir-Marron (181 of 4,266, 4.24%) and to Haitian women (12 of 287, 4.18%). A decrease in the biennial seroprevalence of HTLV-I was observed over time among deliveries of the Haitian women (P = 0.037), but it remained stable among Noir-Marron (P = 0.22). Fifteen of the 17 HTLV-I seroconversions occurred in the Noir-Marron, giving an incidence of 0.18 per 100 person-years. The overall seroprevalence of HIV-1 was higher in the Haitian women (10 of 293, 3.41%) than in the Noir-Marron (34 of 4,310, 0.79%) and Amerindians (4 of 552, 0.72%). A highly significant increase in the biennial seroprevalence of HIV-1 was observed among the deliveries of the Noir-Marron (P = 0.0003), but it remained stable among Haitian women (P = 0.44). Ten of the 13 HIV-1 seroconversions were observed in Noir-Marron, giving an incidence rate of 0.12 per 100 person-years. These data demonstrate the differential spreading of these two human retroviruses among pregnant women in different ethnic groups living in the same environment. While HTLV-I, which is highly endemic in groups of African origin, showed a slight decrease over time in a suspected cohort effect, HIV-1 spread rapidly in an epidemic mode, especially in the groups of the lowest socioeconomic levels.

A cluster of human T-cell lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis in Jujuy, Argentina.

Compared with other regions in Argentina, greater human T-cell lymphotropic virus type I (HTLV-I) seroprevalence has been reported in Jujuy Province, where it reaches 2.32% in the general population, so that a search for HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) cases deserved to be carried out. Accordingly, a clinically diagnosed and serologically confirmed cluster of cases in 1 man and 10 women, including 2 sisters, is described here. Most patients (9/11) were born in Cochinoca Department, located in an Andes highland area called Puna Jujeña, situated at more that 3400 m above sea level. No history of risk factors was disclosed, except for a single transfusion in 1 patient. In contrast to the Andean region of Bolivia, where high HTLV-I seroprevalence is in part attributable to Japanese immigrants, the Jujuy population mainly consists of aborigines, mestizos, and European descendants. Therefore, the long-term presence of virus in Jujuy natives may be taken for granted. Considering the HAM/TSP cluster described here plus previously reported isolated cases in neighboring Salta Province, we speculate that the Puna Jujeña region and regions in that vicinity would be a microepidemic focus of disease. To determine the role of possible pathogenic cofactors such as geographic, ethnic, genetic, and cultural features, further pertinent surveys are required in subtropical northwestern Argentina.

Seroprevalence and demographic characteristics of HTLV-I among blood donors in Taiwan: 1996-1999.

Screening for the human T-cell lymphotropic virus type I (HTLV-I) and-II in blood donors was implemented in Taiwan beginning in February 1996. The purpose of the present study was to investigate the changes in HTLV-I seroprevalence in all unpaid blood donors in Taiwan during the period from February 1996 to December 1999 and to determine the influence of age and sex on the HTLV-I seropositivity of donors. HTLV-I and HTLV-II screening was performed using combined HTLV-I/II immunoassay. Repeated reactive samples were confirmed by Western blot analysis. Of a total of 3,701,087 donors in all 6 blood centers in Taiwan, 2,311 (0.058%) were seropositive for HTLV-I. The HTLV-I seropositivity was 0.130%, 0.063%, 0.044%, and 0.032% in the years 1996, 1997,1998, and 1999, respectively. There was a linear increase of HTLV-I seropositivity with advancing age. The HTLV-I carrier rate for female donors was twice that for the male donors. Ninty-seven percent of HTLV-I seropositive results came from first-time donors. Our findings suggest that Taiwan is a low-prevalence nonendemic area for HTLV-I infection. The large-scale HTLV-I screening program has decreased HTLV-I seropositivity among blood donors and is useful for preventing HTLV-I transmission via blood transfusion.

Evaluation of adult T-cell leukemia/lymphoma incidence and its impact on non-Hodgkin lymphoma incidence in southwestern Japan.

The incidence of adult T-cell leukemia/lymphoma (ATL) and its impact on that of total non-Hodgkin lymphoma (NHL) were evaluated in Nagasaki, an area in southwestern Japan where human T-cell lymphotropic virus type I (HTLV-I) is endemic. The first study area comprised 4 towns located on the K Islands, which had a population of 26,870 in 1990. The overall HTLV-I seroprevalence estimated from the serologic survey of 18,485 subjects was 16.2%. By using the data from the Nagasaki Prefectural Cancer Registry (NPCR) and reviewing clinical and laboratory information, we identified 40 cases of ATL and 35 cases of other NHL diagnosed between 1985 and 1995. The crude annual incidence of ATL among 100,000 HTLV-I carriers aged 30 or older was estimated at 137.7 for men and 57.4 for women, with a significant sex difference after adjustment for age (rate ratio = 2.50, 95% confidence interval 1.32-4.73). The cumulative risk from 30 to 79 years of age was estimated at approximately 6.6% for men and 2.1% for women. Among the entire population, ATL accounted for 51 to 59% of the total NHL incidence, showing the strong impact of HTLV-I infection. The second study area comprised the whole of Nagasaki Prefecture (total population in 1990 = 1.56 million). Between 1985 and 1995, 989 cases of ATL and 1,745 cases of other NHL were registered in the NPCR. The world age-standardized annual incidence rate of ATL per 100,000 persons aged 30 or older was estimated at 10.5 for men and 6.0 for women, which accounted for approximately 37 to 41% of the total NHL incidence.

Decrease of human T-cell lymphotropic virus type I prevalence and low incidence among pregnant women from a high endemic ethnic group in French Guiana

To assess the prevalence and incidence of human T-cell lymphotropic virus type I (HTLV-I), 4,234 pregnant women of different ethnic origins were tested before each delivery between 1991 and 1997 in a high HTLV-I endemic area of French Guiana. HTLV-I was significantly more prevalent among ethnic groups of African descent as the Noir-Marrons (4.8%, 95% confidence interval [CI]: 4.0-5.6) and Haitians (5%, 95% CI 1.6-8.4). An age dependence of HTLV-I seroprevalence was observed. The mean age of Noir-Marron HTLV-I seronegative women was lower than for HTLV-I seropositive women (24. 7 vs. 28.6, p < 0.001). A decline in HTLV-I seroprevalence was observed, particularly in the Noir-Marron younger than 21 years old (p = 0.04). For five HTLV-I seroconversions observed, the incidence per 100 women-years in the Noir-Marron group was 0.19 (95% CI 0.02-0. 35) for all women, 0.32 in those 25 years old or younger (95% CI 0-0. 64), and 0.07 in those older than 25 years (95% CI 0-0.2). This observation was inconsistent with HTLV-I seroprevalence observed for those 25 years old or younger (2.8%) and those older than 25 (8.3%). These data demonstrate, for the first time outside Japan, a birth cohort effect for HTLV-I in a highly endemic ethnic group.

Intrafamilial transmission of HTLV-I and its association with anti-Tax antibody in an endemic population in Japan.

To assess the relationship of anti-Tax antibody to human T-cell lymphotropic virus type-I (HTLV-I) transmission, the sero-prevalence of HTLV-I was analyzed among married couples and among mother/child (both adults) pairs. HTLV-I seroprevalence was significantly higher among wives with anti-Tax+ than those with anti-Tax- HTLV-I carrier husbands (82.4% vs. 59.5%). However, in the group of wives aged 60 years or older, there was no statistical difference in HTLV-I seropositivity based on the husbands' anti-Tax sero-status. In the group whose wives were less than 60 years old, more anti-Tax sero-positive than sero-negative husbands had high DNA levels (57.1% and 20.0%), whereas in the group of husbands whose wives were aged 60 years or older, the number of anti-Tax sero-positive and sero-negative individuals with high DNA levels was similar. HTLV-I sero-prevalence was significantly higher among the adult men with anti-Tax+ carrier mothers than those with anti-Tax- carrier mothers (52.0% vs. 14.3%). For women, HTLV-I sero-prevalence did not differ significantly according to their mothers' anti-Tax sero-status. Our results suggest that the presence of anti-Tax antibody in HTLV-I carriers is an age-dependent risk factor for male-to-female HTLV-I transmission. Furthermore, the effect of the mother's anti-Tax antibody as a risk factor for vertical HTLV-I transmission could be observed in men even after becoming adults.

Human T-cell lymphotropic virus type I-associated facial nerve palsy in Trinidad and Tobago.

To assess the association of the human T-cell lymphotropic virus type I (HTLV-I) and idiopathic facial nerve palsy of the lower motor neuron type, we studied 78 patients consecutively admitted to the Port of Spain General Hospital in Trinidad, the West Indies, with a confirmed diagnosis of idiopathic facial nerve palsy. Patients were compared with two control groups: a population-based group of persons 20 years and older and a hospital-based group of patients 15 to 84 years old admitted to the medical wards. Sixty-two patients were Trinidadians of African origin and 16 were Trinidadians of East Indian origin. None of the East Indian patients was HTLV-I antibody positive. Three Afro-Trinidadians were infected with human immunodeficiency virus type 1 and 1 was coinfected with this virus and HTLV-I. Of the remaining 58 Afro-Trinidadians, 12 (20.7%) were HTLV-I positive only. This rate was statistically higher than the HTLV-I seroprevalence in the Afro-Trinidadian general population (3.5%) and the hospital control group (5.6%). After age standardization, the HTLV-I prevalence for patients with facial nerve palsy remained significantly elevated. HTLV-I antibody assays should be performed on all patients with idiopathic facial nerve palsy of the lower motor neuron type who live in HTLV-I endemic areas or are migrants from these areas.

HTLV-I uveitis.

Human T-cell lymphotropic virus type I (HTLV-I) is known to cause adult T-cell leukemia/T-cell lymphoma and tropical spastic paraparesis/HTLV-I-associated myelopathy. Recent seroepidemiologic, clinical, and virologic studies indicate that the virus is also related to a certain type of uveitis, which has been classified as uveitis without defined etiologies or idiopathic uveitis. According to the seroepidemiologic survey, the seroprevalence of HTLV-I in patients with idiopathic uveitis was significantly higher than that of two control groups, that is, patients with uveitis with defined etiologies and patients with nonuveitic ocular diseases. Clinically, the uveitis seen in HTLV-I carriers is characterized by moderate to severe cellular infiltration in the eye and by moderate retinal vasculitis, and the intraocular inflammation responds well to corticosteroid therapy. Interestingly, 25% of female patients with the disease had a previous history of Graves disease with hyperthyroidisms. The following virologic, molecular biologic findings suggest that cytokines produced by HTLV-I-infected T cells in the eye play the central role in the pathogenic mechanisms of the uveitis: (a) the virus load in the peripheral blood monocytes analyzed by the quantitative polymerase chain reaction methods was significantly greater in patients with the uveitis than in asymptomatic carriers, (b) the proviral DNA of HTLV-I and the gene expression of the virus at the mRNA level was detected in the infiltrating cells from the eyes of the patients, (c) the virus particles were detected by electron-microscopic examination in the T-cell clones established from the intraocular fluid of the patients, and (d) the HTLV-I-infected T cells produced a variety of cytokines without any stimuli, such as interleukin (IL)-1 alpha, IL-2, IL-3, IL-6, IL-8, IL-10, tumor necrosis factor alpha, interferon-gamma, and granulocyte-macrophage colony-stimulating factor. Based on the seroepidemiologic, clinical, and virologic data, the uveitis seen in HTLV-I carriers is considered to be a distinct clinical entity related to HTLV-I infection, and the disease is designated as HTLV-I uveitis.

Tropical spastic paraparesis/HTLV-I-associated myelopathy in Europe and in Africa: clinical and epidemiologic aspects.

We review here the epidemiologic and clinical aspects of tropical spastic paraparesis, human T-cell lymphotropic virus type I (HTLV-I)-associated myelopathy (TSP/HAM) as observed in Europe and in Africa. Europe is not an endemic region for HTLV-I (seroprevalence in blood donors, < 0.03%), and TSP/HAM is thus rarely observed in European countries. Most of the few patients suffering from TSP/HAM are first- or second-generation immigrants from HTLV-I endemic areas (mostly the West Indies), and the clinicoepidemiologic aspects of these patients are similar to those seen in endemic areas. However, rare cases occur in European-born subjects with or without risk factors for HTLV-I infection, which raises the possibility of limited foci areas in Europe. Although Africa is considered as a primary HTLV-I endemic area, with at least a few million infected inhabitants, epidemiologic data on the situation of TSP/HAM in Africa remain scarce. Relatively few cases of patients with TSP/HAM have been reported in Africa, including some clusters in Zaire (prevalence, 50/100,000) and in South Africa and sporadically in the main cities of some Western, Central, and Eastern African countries. The paucity of clinical and epidemiologic data on TSP/HAM may be linked to several factors, including the paucity of neurologists, the lack of laboratory and radiologic facilities, and the chronicity of the disease, along with the limited number of field epidemiologic studies performed on this topic and the wide diversity of causes (toxic, nutritional, and infectious) of chronic myelopathies as seen on the African continent.

Risk Factors for Maternal HTLV-I Infection in French Guiana

The aim of this study was to compare rates of human T-cell lymphotropic virus type I (HTLV-I) seroprevalence in pregnant women belonging to different ethnic groups in French Guiana and to determine the risk factors associated with HTLV-I seropositivity. All 1,873 deliveries between 1 July 1991 and 30 June 1993 in the only gynecologic and obstetric unit at Saint Laurent du Maroni were enrolled. Serologic status could be established for 1,727 women, with 75 (4.3%) being HTLV-I seropositive. The HTLV-I seroprevalence rate differed significantly between ethnic groups: 5.7% for Noir-Marron (70/1,302), 6.3% for Haitian (3/50), and 0% for Creole (126), Amerindians (166), and Hmong (64). In Noir-Marron pregnant women, HTLV-I seropositivity was associated with a maternal age of > 35 years [odds ratio (OR), 3.3; 95% confidence interval (CI), 1.4-7.6], prior miscarriage (OR, 1.7; CI, 1-2.8), prior cesarean section (OR, 2.1; CI, 1.1-4.0), a parity > 4 (OR, 4.0; CI, 1.8-8.8), a gravidity > 6 (OR, 4.2; CI, 2.0-7.2), and a negative Rhesus factor (OR, 2.2; CI, 1.1-4.5). Two separate stepwise logistic regressions were done because gravidity and parity were highly correlated. HTLV-I seropositivity remained associated with a gravidity > 6 (OR, 3.9; CI, 2.1-7.4) and a negative Rhesus factor (OR, 2.6; CI, 1.2-5.3) for the first model and with a parity > 4 (OR, 4.1; CI, 1.9-9.0) and a negative Rhesus factor (OR, 2.5; CI, 1.2-5.1) for the second model.(ABSTRACT TRUNCATED AT 250 WORDS)

Seroprevalence of HTLV-I and HTLV-II among Intravenous Drug Users and Persons in Clinics for Sexually Transmitted Diseases

Background. The human T-cell lymphotropic virus Type I (HTLV-I) is associated with adult T-cell leukemia and myelopathy, whereas HTLV-II infection has uncertain clinical consequences. We assessed the seroprevalence of these retroviruses among intravenous drug users and among patients seen at clinics for sexually transmitted diseases (STD clinics). We used serum samples that were collected in eight cities in 1988 and 1989 during surveys of human immunodeficiency virus infection among intravenous drug users entering treatment and persons seen in STD clinics. The serum samples were tested for antibodies to HTLV, and positive specimens were tested further by a synthetic peptide-based enzyme-linked immunosorbent assay to differentiate between HTLV-I and HTLV-II. Among 3217 intravenous drug users in 29-drug-treatment centers, the median seroprevalence rates of HTLV varied widely according to city (range, 0.4 percent in Atlanta to 17.6 percent in Los Angeles). Seroprevalence increased sharply with age, to 32 percent in persons over 44 years of age. HTLV infection was more common among blacks (15.5 percent) and Hispanics (10.7 percent) than among whites (4.1 percent), and it was strongly associated with a history of heroin injection (P less than or equal to 0.001). Among 5264 patients in 24 STD clinics, the median rates of HTLV infection were much lower (range, 0.1 percent in Atlanta and Newark to 2.0 percent in Los Angeles). Again, this infection was more common among intravenous drug users (7.6 percent) than among non-drug users (0.7 percent). Eighty-four percent of the seropositive samples from drug-treatment centers and 69 percent of those from STD clinics were due to HTLV-II infection (P = 0.03). HTLV infections are common among intravenous drug users and are primarily caused by HTLV-II. Among patients seen at STD clinics, HTLV is strongly associated with intravenous drug use, but the retrovirus is also prevalent among non-drug users.

Declining Seroprevalence and Transmission of HTLV-I in Japanese Families Who Immigrated to Hawaii

This study examined the seroprevalence and transmission of human T cell lymphotropic virus type I (HTLV-I) in Japanese families who originated in Okinawa, an area in which HTLV-I is endemic, and who were currently residing in Hawaii, a nonendemic area. Among a cohort of Japanese men whose sera were collected in Hawaii in 1967-1975, those of Okinawan ancestry had an HTLV-I seroprevalence of 11.4%. This study, conducted in 1987-1988, sampled 142 index subjects from this male cohort and tested them along with their wives, children, and spouses of the children for HTLV-I antibodies. Seropositivity in their wives was 11.4% and 41.2% among the seronegative and seropositive index subjects, respectively; seropositivity also increased from 29.4% to 35.3% to 58.8% with the husbands' increasing antibody levels by tertiles. Elevated antibody levels may be a marker for infectivity, which is associated with more efficient sexual transmission of HTLV-I. The age-adjusted odds ratio for the association of seropositivity between husband and wife, however, was four times lower than that reported among native Okinawans. In addition, a substantially low seroprevalence (1.3%) was found among their offspring. The decline in HTLV-I transmission in this migrant population may be due to low infectivity in the parent generation who live in a nonendemic environment, increasing numbers of offspring marrying outside of the Okinawan community, and improved living circumstances.

Human T-Lymphotropic Virus Type I (HTLV-I) Seroprevalence in Jamaica

An island-wide cohort of 13,260 Jamaicans who applied for food-handling licenses during 1985 and 1986 were tested for antibodies to human T-cell lymphotropic virus type I (HTLV-I). Demographic and residence history data were linked to geographic and ecologic measures of elevation, rainfall, crop-growing areas, population density, and additional measures of urbanization and correlated with HTLV-I antibody status. By logistic regression analysis (performed separately for men and women), men and women who currently resided at low elevation (less than or equal to 1,000 ft (305 m)) were more likely to be HTLV-I infected than were those residing at high elevation. Men, but not women, who were born in citrus-growing areas were more likely to be HTLV-I infected than were men who were born in other areas. By univariate analysis, there was a significant positive trend of increasing HTLV-I seroprevalence with increasing amount of annual rainfall associated with birthplace and primary residence areas. However, these associations did not remain significant after adjusting for age and sex. These environmental associations raise the possibility of new modes of viral transmission or host response to infection, although they may simply be surrogates for socioeconomic status, breastfeeding habits, or sexual behavior, which are known determinants of HTLV-I zero prevalence.