Implementation of G6PD testing and primaquine for P. vivax radical cure: operational perspectives from Thailand and Cambodia

Following progressive success in reducing the burden of malaria over the past two decades, countries ofthe Asia Pacific are now aiming for elimination of malaria by 2030. Plasmodium falciparum and Plasmodiumvivax are the two main malaria species that are endemic in the region. P. vivax is generally perceived to beless severe but will be harder to eliminate, owing partly to its dormant liver stage (known as a hypnozoite)that can cause multiple relapses following an initial clinical episode caused by a mosquito-borne infection.Primaquine is the only anti-hypnozoite drug against P. vivax relapse currently available, with tafenoquine inthe pipeline. However, both drugs may cause severe haemolysis in individuals with deficiency of the enzymeglucose-6-phosphate dehydrogenase (G6PD), a hereditary defect. The overall incidence of malaria hassignificantly declined in both Thailand and Cambodia over the last 15 years. However, P. vivax has replacedP. falciparum as the dominant species in large parts of both countries. This paper presents the experience ofthe national malaria control programmes of the two countries, in their efforts to implement safe primaquinetherapy for the radical cure, i.e. relapse prevention, of P. vivax malaria by introducing a rapid, point-of-caretest to screen for G6PD deficiency.

Efficacy of the Merozoite Surface Protein 1 of Plasmodium Vivax as an Antigen for ELISA to Diagnose Malaria

Malaria is still a major health problem in Thailand and its incidence is currently rising in Korea. To identify a useful antigen for the diagnosis of malaria patients, a cDNA expression library from malaria parasites was constructed and screened out immunologically. One clone was selected in view of its predominant reactivity with the patient sera. The recombinant malaria parasite antigen (Pv30) with 27 kDa as a C-terminal His-tag fusion protein that was produced in Escherichia coli was identified through immunoblot analysis. The deduced amino acid sequence had the sequence homology with the merozoite surface protein 1 (MSP1) genes of Plasmodium falciparum and P. yoelii, each by 41% and 42%, respectively. Measurement of serum IgG and IgM antibody to Pv30 by enzyme-linked immunosorbent assay (ELISA) was evaluated as a serodiagnostic test for malaria patients in Thailand (endemic area) and Korea (recently reemerging area). The sensitivity of P. vivax, P. falciparum, and P. malariae was 96.3% (26 /27), 90.6% (29/32), and 100% (6/6), respectively, and the specificity was 63.5% (40/63) in Thailand samples. The sensitivity of P. vivax was 98.8% (88/89), and the specificity was 96.6% (86/89) in Korean samples. Pv30 appears to be a good and reliable recombinant antigen for serodiagonosis of malaria in a nonendemic area.

Mekong malaria. II. Update of malaria, multi-drug resistance and economic development in the Mekong region of Southeast Asia.

In an expansion of the first Mekong Malaria monograph published in 1999, this second monograph updates the malaria database in the countries comprising the Mekong region of Southeast Asia. The update adds another 3 years' information to cover cumulative data from the 6 Mekong countries (Cambodia, China/Yunnan, Lao PDR, Myanmar, Thailand, Viet Nam) for the six-year period 1999-2001. The objective is to generate a more comprehensive regional perspective in what is a global epicenter of drug resistant falciparum malaria, in order to improve malaria control on a regional basis in the context of social and economic change. The further application of geographical information systems (GIS) to the analysis has underscored the overall asymmetry of disease patterns in the region, with increased emphasis on population mobility in disease spread. Of great importance is the continuing expansion of resistance of P. falciparum to antimalarial drugs in common use and the increasing employment of differing drug combinations as a result. The variation in drug policy among the 6 countries still represents a major obstacle to the institution of region-wide restrictions on drug misuse. An important step forward has been the establishment of 36 sentinel sites throughout the 6 countries, with the objective of standardizing the drug monitoring process; while not all sentinel sites are fully operational yet, the initial implementation has already given encouraging results in relation to disease monitoring. Some decreases in malaria mortality have been recorded. The disease patterns delineated by GIS are particularly instructive when focused on inter-country distribution, which is where more local collaborative effort can be made to rationalize resource utilization and policy development. Placing disease data in the context of socio-economic trends within and between countries serves to further identify the needs and the potential for placing emphasis on resource rationalization on a regional basis. Despite the difficulties, the 6-year time frame represented in this monograph gives confidence that the now well established collaboration is becoming a major factor in improving malaria control on a regional basis and hopefully redressing to a substantial degree the key problem of spread of drug resistance regionally and eventually globally.