Drug resistant malaria on the Thai-Myanmar and Thai-Cambodian borders.

We describe the changing epidemiology of drug resistant malaria in Thailand over the past decade. Factors determining the characteristic patterns of the development and spread of resistance to anti-malarial drugs on the Thai-Cambodian border and the Thai-Myanmar border are explored, namely, population dynamics, drug usage and malaria control measures. The introduction of artesunate-mefloquine combination in selected areas along the two borders in 1995 is believed to be one of the multiple factors responsible for stabilizing the multidrug resistance problems in Thailand today. Other control measures and inter-governmental co-operation must continue to be strengthened in order to limit the spread of drug resistance malaria in the Southeast Asian region.

Vaccine-preventable disease susceptibility in a young adult Micronesian population.

Current US military recruit vaccination policy presumes that recruits have had a complete childhood immunization series. This assumption may not be appropriate for recruits from Micronesia, who may have had limited access to modern health care, including immunization programs. During 1988 and 1990, a cross-sectional serosurvey was conducted among 66 US military recruits, 56 from the Federated States of Micronesia and 10 from the Republic of the Marshall Islands, collectively referred to as Micronesia. Antibody seronegativity levels for 12 vaccine-preventable (or potentially so) diseases were: measles (52%), mumps (14%), rubella (21%), varicella (38%), diphtheria (39%) tetanus (0%), polio type 1 (4%), polio type 2 (0%), polio type 3 (14%), hepatitis A (9%), hepatitis B (17%), and hepatitis C (98%). Compared with Army recruits in general, Micronesian recruits were significantly more likely to be seronegative for measles and varicella and seropositive for hepatitis types A and B. Personal histories of disease were felt to be inadequate in predicting antibody status.

Comparison of mefloquine, chloroquine plus pyrimethamine-sulfadoxine (Fansidar), and chloroquine as malarial prophylaxis in eastern Thailand.

From July 1983 to March 1984 a randomized double blind prophylactic trial in Thai gem miners working across the border in Cambodia was conducted to determine the prophylactic efficacy of 3 drug regimens against P. falciparum and P. vivax malaria along the Thai-Cambodian border. Gem miners have a high incidence of malaria. Maximum duration of individual participation was 14 weeks. Of 334 participants in this study who were seen every 2 weeks, 145 received mefloquine 500 mg fortnightly, 112 received chloroquine 300 mg base weekly plus Fansidar (1000 mg sulfadoxine and 50 mg pyrimethamine) fortnightly and 77 received chloroquine as 300 mg base weekly. The significant reduction of vivax malaria in study subjects (compared to background incidence) implied good compliance with self administration of chloroquine in the intervening weeks between scheduled appointments. The attack rate in each prophylactic regimen was 2188 cases/1000/year with mefloquine, 8338 cases/1000/year with chloroquine-Fansidar and 10,207 cases/1000/year receiving chloroquine alone. There was a 79% prophylactic efficacy for mefloquine and 18% efficacy for the chloroquine plus Fansidar regimen compared to chloroquine. Using life table analysis, 56% of the mefloquine group, 6% of the chloroquine-Fansidar group and 4% of the chloroquine group were malaria free at the end of the 14 weeks study. The chloroquine plus sulfadoxine-pyrimethamine regimen prescribed for prophylaxis is no longer effective for multidrug resistant strains of P. falciparum in the study area. This study also seriously questions the efficacy of mefloquine prophylaxis.

In vitro mefloquine resistance of Plasmodium falciparum isolated from the Burmese border region of Thailand.

The in vitro susceptibility of twenty isolates of Plasmodium falciparum from Tha Song Yang, Tak province, Thailand were determined. The isolates were resistant to chloroquine (IC50 = 220 nM; MIC = 762 nM), quinine (IC50 = 252 nM; MIC = 1010 nM), and pyrimethamine (IC50 = 16400 nM; MIC = 43100 nM) but generally sensitive to mefloquine (IC50 = 6.90 nM; MIC = 20.9 nM) and halofantrine (IC50 = 8.73 nM; MIC = 2.71 nM). Two isolates were identified which appeared resistant to mefloquine (IC50 = 23.1 nM; MIC = 56.6 nM). These isolates may represent an extension of a population of parasites from eastern Thailand.