Molecular epidemiology of drug resistance markers of Plasmodium falciparum malaria in Thailand.

To determine differences in the distribution of drug resistance mutations in the Plasmodium falciparum chloroquine resistance transporter (pfcrt) and P. falciparum multi-drug resistance 1 (pfmdr1) genes of P. falciparum isolates in Thailand, a study was conducted using polymerase chain reaction-restriction fragment length polymorphism to detect mutations in P. falciparum isolates obtained from three areas with different levels of in vivo mefloquine (MQ) resistance. All isolates carried mutant allele T76 of the pfcrt gene and wild-type allele D1246 of the pfmdr1 gene except for one isolate, which showed the wild-type K76 allele. This isolate was obtained from Chanthaburi Province, an area with high MQ resistance. Relatively low rates of the mutant alleles D1042 and Y86 of the pfmdr1 gene were found among Thai isolates of P. falciparum. However, a statistically significant difference in the distribution was noted. Most of the mutant isolates were found among isolates from areas with moderate or low MQ resistance. Only one isolate with mixed mutant and wild-type N1042 and D1042 and two mutants of Y86 were found among the isolates from areas with high MQ resistance. The findings provide limited support for the hypothesis that mutant alleles of pfmdr1 may be associated with increased sensitivity to MQ.

Determining cost-effectiveness and cost component of three malaria diagnostic models being used in remote non-microscope areas.

This cross-sectional experimental study developed a methodology to analyze the cost-effectiveness of three malaria diagnostic models: microscopy; on-site OptiMAL; and on-site Immunochromatographic Test (on-site ICT), used in remote non-microscope areas in Thailand, from both a public provider and patient perspective. The study covered six areas in two highly malaria-endemic areas of provinces located along the Thai-Myanmar border. The study was conducted between April and October 2000, by purposively recruiting 436 malaria suspected cases attending mobile malaria clinics. Each patient was randomly selected to receive service via the three diagnostic models; their accuracy was 95.17%, 94.48% and 89.04%, respectively. In addition, their true positive rates for all malaria species were 76.19%, 82.61% and 73.83%; for falciparum malaria 85.71%, 80.95% and 80.00%, and for vivax malaria 57.14%, 100% and 50%, respectively, with the parasitemia ranging from 80 to 58,240 microl of blood. Consequently, their costs were determined by dividing into provider and consumer costs, which were consequently classified into internal and external costs. The internal costs were the costs of the public providers, whereas the external costs were those incurred by the patients. The aggregate costs of these three models were 58,500.35, 36,685.91, and 40,714.01 Baht, respectively, or 339.53, 234.39, and 243.93, in terms of unit costs per actual case. In the case of microscopy, if all suspected malaria cases incurred forgone opportunity costs of waiting for treatment, the aggregate cost and unit cost per actual case were up to 188,110.89 and 944.03 Baht, respectively. Accordingly, the cost-effectiveness for all malaria species, using their true positive rates as the effectiveness indicator, was 446.75, 282.40, and 343.56 respectively, whereas for falciparum malaria it was 394.80, 289.37 and 304.91, and for vivax malaria 595.67, 234.39 and 487.86, respectively. This study revealed that the on-site OptiMAL was the most cost-effective. It could be used to supplement or even replace microscopy for this criteria in general. This study would be of benefit to malaria control program policy makers to consider using RDT technology to supplement microscopy in remote non-microscope areas.

Comparison of the OptiMAL rapid test with routine microscopic examination of Giemsa-Stained Thick Blood Film for diagnosis of malaria.

The OptiMAL is a rapid immunodiagnostic test developed by Flow Inc., Portland, Oreg. for diagnosis and differentiation of P. falciparum and non P. falciparum malaria infection. It has been based on detection of circulating parasite lactate dehydrogenase enzyme (pLDH), produced by live Plasmodium parasites. The purpose of this study was to compare the efficacy of the OptiMAL test with routine microscopic examination of Giemsa-Stained Thick Blood Film (routine GS-TBF) for the diagnosis of malaria at a local malaria clinic in a hyperendemic area of Thailand by using a standard GS-TBF (standard GS-TBF) as reference. One hundred and seventy five patients attending the clinic were recruited; 50, 42 and 83 were falciparum malaria, vivax malaria and non-malaria patients, respectively. Compared with the reference, the OptiMAL test had sensitivities of 92 per cent and 97.6 per cent, whereas, the routine GS-TBF had sensitivities of 81.3 per cent and 81 per cent for the detection of P. falciparum and P. vivax, respectively. Both tests showed no false positive resulting in 100 per cent specificities. However, the OptiMAL test was able to detect only 20 per cent of infection with less than 200 parasitaemia/microlitre. It was also shown in our study that the OptiMAL test was advantageous in follow-up of the treatment outcome. No false positive occurred among 40 follow-up cases. The OptiMAL test detected malaria infection more accurately than the routine GS-TBF (p < 0.05) and was simple, easy to perform and rapid. It is an alternative tool for the diagnosis of malaria in a hyperendemic area where experienced microscopists are not available.

Molecular markers for chloroquine-resistant Plasmodium falciparum malaria in Thailand and Laos.

Chloroquine-resistant Plasmodium falciparum is well documented in Thailand. Laos, however, continues to use chloroquine (CQ) as the first-line therapy for the treatment of P. falciparum malaria. The objective of the present study was to determine the prevalence, in these two areas, of the cg2, pfmdr1 and pfcrt allelic types that have previously been associated with CQ resistance. Isolates of P. falciparum were collected from participants in ongoing treatment studies conducted in Thailand (near the Thai-Cambodian border) and in Laos (Vang Vieng district). The pfmdr1 and pfcrt alleles were characterized by PCR-RFLP and mutations in cg2 were characterized by PCR and single-stranded-conformation-polymorphism (SSCP) electrophoresis. Eight (32%) of the 25 Laotian isolates but only one (4%) of the 25 Thai isolates were found to contain the pfmdr1 mutation N86Y (P = 0.02). In contrast, the cg2 polymorphisms previously associated with CQ resistance were present in only 10 of the isolates from Laos but 24 of those from Thailand (40% v. 96%; P < 0.001). All the samples from both countries contained the pfcrt K76T mutant allele reported to confer resistance to CQ. The results may indicate that drug pressure for the maintenance of the pfmdr1 and cg2 alleles varies in intensity in the Thai and Laotian study areas, probably reflecting differences in the national malaria-treatment policies of Thailand and Laos.

Comparison between microscopic examination, ELISA and quantitative buffy coat analysis in the diagnosis of falciparum malaria in an endemic population.

Monoclonal antibody-based ELISA and QBC (quantitative buffy coat analysis) were tested in two endemic areas with low and high incidence of malaria in Kanchanaburi Province, West Thailand with annual parasite incidence in 1992 of 119 and 5 per 1,000 population, respectively. The numbers of individuals positive by thick blood film examination (TBF) for P. falciparum with or without P. vivax, and P. vivax only were 82 and 69, respectively. The detection limit of ELISA was 10 parasites/10(6) red blood cells (RBC) (0.001% parasitemia). Of 1,095 individuals involved in the study at the beginning of the study, ELISA showed sensitivity, specificity, positive predictive value and negative predictive value of 78.1%, 94.9%, 72% and 98.1%, respectively. Nine of 18 (50%) TBF-positive but ELISA-positive individuals had parasitemia of less than 10 parasites/10(6) RBC. High and low incidence areas did not affect the validity of our result. Regression analysis showed good correlation between log parasitemia and ELISA percent OD increase (Y = 0 + 64.9*logX, r = 0.65), and agreement between TBF and ELISA results was 95.9%. In a fortnightly follow-up, in 82 TBF-positive individuals, both ELISA and TBF positive rates correlatively declined with agreement of 96.3%. With samples taken on the first day of the study, the TBF and QBC results were also correlated with agreement of 95.8% for P. falciparum, 95.6% for P. vivax. During 8 week follow-up involving altogether 191 samples, agreement between TBF and QBC results were 87.4% for P. falciparum. QBC detected more cases with P. falciparum infections but detected smaller number of cases with P. vivax infections.

Competitive antibody binding inhibition ELISA for the detection of Plasmodium falciparum antigen.

A competitive antibody binding inhibition ELISA to detect Plasmodium falciparum-infected cells in clinical specimens was developed. Optimum conditions developed included: 12.5 micrograms/ml of P. falciparum antigen for plate coating, 25 micrograms/ml of polyclonal rabbit anti-P. falciparum IgG, 30 minute incubation of a mixture of infected red blood cell extract with anti-P. falciparum IgG, dilution of 1:500 of alkaline phosphatase-conjugated anti-rabbit IgG, and reading of the absorbance values 60 min after adding the p-nitrophenyl phosphate substrate. Reproducibility of the assay against cultured P. falciparum-infected red blood cells varied according to parasitemia, the higher the parasitemia, the better the reproducibility. The sensitivity of the assay was approximately 110 parasites/10(6) red blood cells. The assay was applied to field conditions involving 103 cases with falciparum malaria, 38 cases with vivax malaria and 30 healthy controls. With the 10% antibody binding inhibition as a cutoff, 87.4% of falciparum cases and 26.3% of vivax cases were positive. After treatment, the majority of cases became parasitologically negative with the corresponding negative assay. Regression analysis showed only weak but statistically significant correlation between the percent inhibition with parasitemia (r = 0.38, p less than 0.001), and this was more clearly shown in patients with high parasitemia.

Malaria clinics in Mae Sot, Thailand: factors affecting clinic attendance.

Clinics of the Anti-Malaria Program of Thailand play an important part in the control of malaria morbidity and mortality, treating over 60% of reported cases yearly. Interviews were conducted both with attenders at three clinics in Mae Sot District and among those reporting malaria illness but not attending. Distance travelled to the clinic, costs of travel and frequency of other treatment prior to clinic attendance were all highest among patients at the large centralized clinic, moderate in a peripheral fixed clinic, and lowest in a village-based mobile clinic. Reported length of illness prior to attendance was similar for all three clinics. As many as 91% of villagers interviewed chose not to treat their illness in a malaria clinic. These non-attenders reported longer illness time and higher expenditures on treatment than clinic patients. Provision of village-based clinics can improve access. However, the widespread reliance on non-Program treatment of malaria suggests the need for policies to address these alternative therapeutic modes.

Evaluation of malaria clinics in Maesot, Thailand: use of serology to assess coverage.

The clinics of the anti-malaria programme in Thailand serve an increasingly important role in the strategy for control of malaria within a context of multi-drug resistant falciparum malaria. Figures from clinics in Maesot District show a predominance of young males among positive cases treated (56% of all cases). In contrast, sero-epidemiological findings from a random sample of over 500 villagers in the area show similar exposure rates among males and females of equal age. There were no statistically significant differences between males and females 0-15 and 16-30 years old in percentages positive by indirect fluorescent antibody tests or enzyme-linked immunosorbent assays (ELISA), mean level of ELISA positivity, or rate of sero-conversion. Differences in level of positivity did occur between males and females over 30. An index constructed from the serological findings indicated under-representation of children and women of all ages in clinics but suggested that coverage of children could be improved by the provision of a community-based, fixed-schedule mobile clinic.