Fewer malaria cases, more artesunate resistance on Thai border

By Helen Albert, Senior medwireNews Reporter

Results from an observational study show that the number of reported malaria cases in children and pregnant women on the Thai-Myanmar border has decreased significantly over the past decade.

However, the researchers found that resistance to first-line mefloquine-artesunate combination therapy has increased dramatically, with a significant increase in resistance observed in 2011.

"Alternative fixed combination treatments are needed urgently to replace the failing first-line regimen of mefloquine and artesunate," write the authors in PLoS Medicine.

Fran?ois Nosten (University of Oxford, UK) and colleagues analyzed observational data on malaria collected from the Thai-Myanmar border between October 1999 and September 2011, during which time the number of cross border health facilities increased from two to 11 and a focus on early diagnosis and treatment (EDT) was instituted.

The team assessed changes in the incidence and prevalence of malaria from a cohort of pregnant women and cross-sectional surveys. The number of visits to the health centers and their outcomes were also recorded.

Nosten and co-investigators found that the number of health center visits for malaria decreased significantly in children under 5 years of age, from 78% in 1999 to 7% in 2011. Similarly, the incidence of malaria in pregnant women decreased from 1.1 to 0.1 episodes per pregnant-woman year from 1999 to 2011.

The researchers also found that the ratio of Plasmodium falciparum to Plasmodium vivax decreased from 1.4 to 0.7 over the study period and that the cumulative proportion of pregnant women infected with P. falciparum during this time decreased from 24.3% to 3.4%.

Notably, the treatment efficacy of mefloquine-artesunate decreased significantly from a 0% slide-confirmed positivity for malaria at day 3 of treatment in 2000 to 28% slide positivity at 3 days in 2011.

"Our results and results from elsewhere indicate that an aggressive strategy based on EDT of cases, combined with vector control and information to the population, is the way forward to eliminate malaria," write the authors.

They concede that "it is uncertain whether this strategy alone could achieve complete elimination over time," and acknowledge that the observational nature of their study limits the application of the results in the field.

"Adjunctive approaches should be evaluated, such as the use of low-dose primaquine to reduce transmission further, mass drug administrations, more sensitive detection of sub-microscopic infections using molecular methods, or targeted use of the new malaria vaccine, if it is approved," they suggest.

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