Detection and quantification of HIV type 1 RNA in nasopharyngeal washes from HIV-infected subjects.

Human immunodeficiency virus type 1 (HIV) RNA load was measured in paired samples of peripheral blood plasma and nasopharyngeal (NP) washes from 97 Thai subjects infected with subtype E or B. HIV RNA was quantifiable in 93% of peripheral blood plasma samples tested and was inversely correlated (rho =-0.524; p < 0.001) with CD4 absolute count. HIV RNA was quantifiable in 29% of NP samples tested, and the median value was less than that of plasma viral load. HIV RNA load in NP samples was correlated (rho = 0.388; p < 0.001) with viral load in peripheral blood. HIV RNA was not detected in NP washes from subjects with undetectable plasma viral load. Virus isolation attempts on two NP samples were negative. The results do not support local HIV production in the nasopharynx, but extend current knowledge of HIV shedding to include the NP compartment.

A phase I/II trial of HIV SF2 gp120/MF59 vaccine in seronegative thais.AFRIMS-RIHES Vaccine Evaluation Group. Armed Forces Research Institute of Medical Sciences and the Research Institute for Health Sciences.

Fifty-two human immunodeficiency virus type 1, seronegative Thai adults from the community were enrolled in a double-blind, placebo controlled, phase I/II trial of HIV SF2 gp120/MF59 vaccine to determine the safety and immunogenicity of this recombinant, B clade, HIV envelope protein vaccine. Twenty-six subjects were enrolled at each of two sites in Thailand, Bangkok and Chiang Mai. Twelve subjects received placebo and 40 subjects received vaccine (50 microg). Subjects were immunized according to one of two schedules, 0, 1 and 4 or 0, 1 and 6 months. The frequency of adverse reactions was not different between placebo and vaccine subjects, nor between immunization schedules. Of vaccinees, all developed high-titer binding antibody to the immunogen (rgp120), 39 developed neutralizing antibody (NA) responses against homologous virus (HIV-1(SF2)), and 22 developed NA against heterologous virus (HIV-1(MN)). No subject demonstrated intercurrent HIV infection, however screening EIA reactivity occurred in 27% of recipients. Thus, this candidate HIV vaccine was found to be safe and immunogenic in Thai adults, laying the foundation for development of a subtype E construct in this population.

Nationwide surveillance of HIV-1 prevalence and subtype in young Thai men.

As part of routine surveillance, an HIV-1 serosurvey of 366,074 members of successive cohorts of young Thai men entering service with the Royal Thai Army (RTA) was conducted between November 1989 and November 1995. We analyzed regional and temporal trends in HIV-1 seroprevalence in young men in Thailand and determined the proportion of infections resulting from subtypes E and B in this population in 1992 and 1995. The prevalence in 1992 was compared with that in 1995 by region and demographic group. The HIV-1 subtype was determined in a random sample of HIV-1-positive specimens in 1992 and 1995 using a V3 peptide enzyme immunoassay. From a peak of 3.7% in 1993, overall seroprevalence declined to 3.0% in 1994 and further in 1995 to 2.5%. Between 1992 and 1995, the absolute decrease in seroprevalence was greatest in the upper North (from 12.5% to 5.3%), where the prevalence has been the highest. Overall, 96.9% and 95.9% of typable specimens were determined to be subtype E in 1992 and 1995, respectively. Decline in HIV-1 seroprevalence among young men in Thailand has continued, which suggests that HIV control programs in Thailand may have been successful in decreasing spread of HIV-1. Almost all HIV-1 infections resulted from subtype E.

Lymphocyte immunophenotype reference ranges in healthy Thai adults: implications for management of HIV/AIDS in Thailand.

Lymphocyte immunophenotype reference ranges for T, B, and NK subsets were determined for healthy adult Thais in a multi-center study in Bangkok. Immunophenotyping was by flow cytometry using lysed whole blood. A standard protocol for flow cytometry instrumentation, reagents and quality control was used to minimize site differences and to facilitate comparison of the Thai reference values to those found for Caucasians in previous studies. Major differences were determined for CD3(T), CD4 (T helper/inducer) and CD16+56 (NK) lymphocyte percentages and CD4 lymphocyte absolute counts. Age trends and sex differences were also observed. Compared to Caucasians, Thais, particularly Thai males, had lower CD3 and CD4 T lymphocyte percentages and absolute numbers whereas the percentage of NK lymphocytes was higher. Heterogeneity attributed to biological variation of CD4 T lymphocyte but not other immunophenotype subset distributions was also observed in a well defined geographic population. This study demonstrates the importance of ethnicity, age, sex and possibly environment as factors that influence distribution characteristics of normal lymphocyte immunophenotype reference values. These observations have important implications for the use of lymphocyte subsets-particularly CD3+ CD4+ T lymphocyte measurements as applied to HIV disease staging, AIDS definition and the overall clinical management of HIV/AIDS in Thailand.

Correlates of HIV-1 seropositivity among young men in Thailand.

Geographic and demographic correlates of risk for HIV-1 seropositivity were studied in 120,216 young men selected by lottery for service in the Royal Thai Army (RTA). The study population consisted of men selected between November 1991 and May 1993. Venous blood was collected at induction, and a brief demographic questionnaire was administered. HIV-1 seropositivity was established by Western blot confirmation of duplicate reactive ELISAs. Geographic variable provided the strongest correlate of risk, clearly distinguishing residents of the upper north, Bangkok, and the central region from the northeast. Overall 12.2% of men from the upper north were HIV-positive. Men who had lived in rural areas were at less risk in most regions of the country, but had equal risk in the upper north. Unmarried men and those with less education were at higher risk throughout the country. These data provide valuable information on the prevalence of HIV infection in one segment of the general population. Continued surveillance of this group will facilitate evaluation of Thailand's response to the epidemic.

PIP: During November 1991 to May 1993, interviews were conducted with and blood samples drawn from 120,216 male military recruits aged 21-29 of the Royal Thai Army (RTA) from every geographic region and social stratum of Thailand. 93.5% were 21 years old. These men are somewhat more representative of the general population than the traditional high risk groups since selection for military service is by lottery and includes all regions of Thailand. The overall HIV seroprevalence was 3.5%. Men from the Upper North region had the highest HIV seroprevalence rate (12.2% vs. 2-4%). This region encompassed the following provinces: Phayao, Chiang Rai, Chiang Mai, Lamphun, Lampang, Phrae, Nan, and Mae Hong Sun. The multivariate analysis of the 97,848 men with a complete set of demographic data and confirmed serostatus (83% of all men inducted) revealed that region of residence was a significant predictor of HIV infection. The odds ratio (OR) of HIV infection among men in the Upper North region was 7.83 (p 0.01). In every region of the country except Upper North, the risk of HIV infection was higher for men from urban areas than those from rural areas (OR = 1.37). In the Upper North region, rural residents were more likely to have HIV infection than urban residents. The higher the man's educational status, the less likely he was to have HIV infection (OR = 0.31 for 13-16 years of education; p 0.01). Risk of HIV infection attributable to age was only significant in unmarried men (OR = 1.76; p 0.01). Thailand has already introduced extensive AIDS education and prevention efforts; they should continue.

Incidence of HIV-1 infection among young men in Thailand.

Royal Thai Army (RTA) enlistees were tested for HIV-1 seropositivity prospectively in order to explore their feasibility as a cohort in an HIV-1 preventive vaccine efficacy trial. The 17,615 seronegative enlistees, virtually all 21-year-old men, contributed 10,409 person-years (p-y) of follow-up. Cohorts were enlisted in November 1991 and May 1992 from northern Thailand and Bangkok. The follow-up rate was 50%, with loss to follow-up significantly associated with location of the base, marital status, and educational level. Seroincidence was 0.5/100 p-y for recruits stationed in Bangkok, 1.0/100 p-y in the lower north, and 3.2/100 p-y in the upper north. In a multiple regression model, the young man's birthplace was strongly associated with risk of infection, suggesting that transmission occurred during leave as well as during duty. Incidence rates were significantly lower in those who were married at the time of enlistment and in those with > or = 10 years of education. The seroincidence rates among recruits stationed in the upper north support vaccine trial feasibility, but follow-up rates need to be improved.

Occupational malaria in Thai Rangers: epidemiological, clinical and immunological features.

Malaria continues to be a serious disease threat to soldiers deployed in tropical environments. Distinct features of the disease and the host immune response require that malaria occurring in occupational groups be investigated separately from the infection as found in endemic populations. For the first time since the Vietnam War, malaria has been systematically studied in soldiers under combat conditions. In this report we describe characteristics of malaria as experienced by Thai Rangers operating on the Lao-Cambodian border.

Characterization of antibodies to sporozoites in Plasmodium falciparum malaria and correlation with protection.

The antibody response to sporozoites of Plasmodium falciparum and the role of these antibodies in protection against malaria have not been systematically investigated. An understanding of antisporozoite antibodies in natural infection is, however, important to the development of a human malaria vaccine. In a prospective study in Thailand, an antibody response to sporozoites was observed only in individuals who developed parasitemia. Antibodies were detected against an epitope in the repeat region of the circumsporozoite (CS) protein. Current candidate sporozoite vaccines are based on CS repeat antigens. The CS antibody response was of low magnitude, peaked after detection of parasitemia, and had a serum half-life of less than 1 month. CS antibody boosting occurred in only 6% of reinfected individuals. These observations suggest that antisporozoite antibody is poorly developed under natural conditions and appears not to protect against development of malaria.