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Eliminated ... and Staying That Way

By Rachel Wallach

Once a country eliminates malaria, the parasitic disease often stays away indefinitely even if the interventions are not continued—a new finding that may hold powerful implications for nations assessing their approach to the disease.

Johns Hopkins Malaria Research Institute faculty recently conducted a review of malaria elimination data. Under the Global Eradication Effort beginning in the late 1940s, some 79 countries had approached or achieved elimination before the international funds supporting the effort dried up in 1969. Contrary to their expectation that the mosquito-borne disease would reappear in countries that discontinued the interventions, the researchers found that those nations that achieved elimination have remained malaria-free, while most of those that came close experienced a resurgence.

“If you think about it, it’s a bit shocking. Why should going all the way to zero be better than going most of the way to zero?” asks David L. Smith, PhD, MA, MS, an Epidemiology professor and one of the study’s authors.

The researchers don’t yet have an answer to that question, but there are several possibilities. During the same period, many economies were developing and health systems improving. So researchers tried to tease apart the role those factors may play, versus the role of elimination itself in causing changes that result in malaria staying away. “The most critical question is, does [elimination] cause its own stability, or is it caused by something else?” Smith asks.

It’s a complicated web, but it does seem likely that economic development has a hand in it, Smith says. People with more resources are more likely to get treatment and less likely to be a significant factor in malaria transmission. At the same time, elimination should lead to greater wealth, as children miss less school and adults are more productive.

Meanwhile, Smith says, if a nation’s health system is good enough to get rid of malaria, it’s probably also good enough to contain transmission: In the process of achieving elimination, health systems become so well developed that it’s difficult for transmission to occur. (When patients are treated with appropriate drug regimens within the first week after a malaria fever appears, they will not become infectious, Smith says.)

The WHO estimates that 149 million to 274 million cases of malaria occur annually in 99 countries, causing 537,000 to 907,000 deaths, with the majority occurring in young children in Africa. Elimination is both expensive and risky. Expensive because it requires an intensive combination of household insecticide spraying and the distribution of treated bed nets. Risky because if a resurgence occurs, the population—which has lost its immunity—is at greater risk. So while it may be tempting to think every country should jump on the elimination bandwagon, it’s essential for any country to assess feasibility carefully based on its specific conditions, Smith says. For example, Angola has achieved a relatively high level of malaria control, but frequent border crossings with its neighbor the Democratic Republic of Congo create opportunities for transmission that lower its potential for elimination.

The new research is a distinct departure from traditional malaria research, which Smith and his colleagues believe holds unnecessarily low expectations for the possibilities of elimination succeeding in countries that are ready. Clive Shiff, PhD, associate professor in Molecular Microbiology and Immunology, is not optimistic about prospects for elimination in central Africa, India and other parts of Asia. He points out, for example, that malaria is well controlled in much of Zambia, where he is principal investigator on research into malaria epidemiology and control, but in the northern areas, 50 percent of the population is still infected at any given time.

While many unknowns remain, the study does suggest that the value of elimination has been underestimated, indicating the potential for elimination strategies, under the right conditions, to be very successful in the long run. But elimination in any country will not happen without significant increases in international funding.

As economic development continues, some elimination will occur on its own, Smith says, but an infusion of funds could speed up the process and save children’s lives.