The third paper in The Lancet Series on Malaria Elimination addresses operational strategies to achieve and maintain malaria elimination, and is written by Dr Bruno Moonen, The Clinton Health Access Initiative, Nairobi, Kenya, and Professor Geoffrey Targett, London School of Hygiene and Tropical Medicine, UK, and colleagues.
Unlike previous countries that have eliminated malaria, many countries considering elimination today have medium to high transmission potential. In addition, in the absence of a global eradication campaign, modern population movements mean many people infected with malaria will cross borders. Despite this a combination of initiatives have meant that several countries (Zambia, Ethiopia, Rwanda, Eritrea, Zanzibar [Tanzania], Senegal) have achieved remarkable declines in malaria disease and mortality, where the disease was a major life-threatening infection. These initiatives include the Roll Back Malaria (RBM) Scaling-up for Impact (SUFI) strategy and the UN Secretary General's call for Universal Coverage, supported by an increase in funding from the Global Fund to Fight Aids, Tuberculosis and Malaria, the President's Malaria Initiative and the World Bank Booster programme.
The authors stress however, that even in countries that have successfully controlled malaria, the next stage might need further scale-up of interventions such as insecticide-treated bednets, indoor residual spraying, and will always require a more rapid detection and diagnosis of malaria infections and treatment with appropriate drugs. As such these methods, although more intense, are no different from control.
Moving from control to elimination cannot simply be business as usual or more of the same. It is only after a low rate of malaria transmission has been achieved (community parasite prevalence of less than 1%) that activities of elimination substantially differ from those of control. The most important difference between elimination and control programmes is the concentration of activities to identify and attack clusters of asymptomatic as well as clinical infections since both allow transmission to continue.
To rely on passive case detection (identifying cases that present at reporting health facilities) is not enough since not all infections become symptomatic, and not all symptomatic cases seek care in a health facility, too often having to rely on home treatment. The Zanzibar research showed that passive detection (routine data collection) only detects 40% of infections; thus active case finding must be included.
Active case detection methods can be broadly categorized as "re-active" or "pro-active". Reactive case detection—following a passively detected clinical case back home—is based on the fact that malaria cases tend to cluster geographically. Pro-active case detection is the hunting for cases, especially during certain seasons or in high-risk groups or areas. Mass-blood screening has occurred in Brazil, Morocco, Taiwan and China.
Once reservoirs of malaria infection have been drained, malaria-endemic countries considering elimination need to prevent importation of infections through proactive case detection at the border, screening of high-risk migrants, and implementation of cross-border and regional initiatives that can reduce transmission at the source of migration.
Although elimination of the malaria vector itself has been discussed over the years, this has been deemed operationally unachievable, mainly because the breeding sites of mosquitoes are too diverse and widespread. Even if the local parasite reservoir has been eliminated, restricting imported cases as above remains a priority as long as a competent vector is present.
Maintaining the current elimination states in the USA and Europe does, however, only need passive case detection due to lack of vectors for transmission and strong health systems. Despite this, the USA still experienced 1298 cases in 2008, and the UK had 1495 cases in 2009. All these cases were officially recorded as imported.
To interrupt transmission, active and passive surveillance to detect a high proportion if not all new infections needs to be complemented by effective treatment that ideally kills all stages of the parasite for all five malaria species.
Artemisinin-combination therapies—the standard treatment for malaria in most countries—kill developing gametocytes (the sexual stage of the parasite that the mosquito picks up from the human host) of P falciparum but an added single dose of primaquine is likely to be beneficial to interrupt transmission.
Primaquine is also the only registered drug available to kill the liver/dormant stages of P vivax that persist undetected for several years. However this requires a course of treatment lasting 2 weeks, and primaquine is not safe for use in people lacking the enzyme glucose-6-phosphate dehydrogenase, since it causes haemolysis (see press release paper 1).
Because detecting asymptomatic cases is expensive, mass drug administration or mass screening and treatment could be used, but are not currently recommended by WHO.
The authors note that the cost of an elimination programme will be at least as high as that for control for many years though, in time, it might be possible to scale back some expensive and intensive vector control measures. However, the costs should be set against the benefits of having a malaria-free country.
They conclude: "The road to elimination will not be short and the development of new approaches and novel technologies will be necessary. Malaria and mosquitoes are evolving all the time and must be met with an equally resilient attack."
Dr Bruno Moonen, The Clinton Health Access Initiative, Nairobi, Kenya. T) + 254 733 331119 E) bmoonen@clintonhealthaccess.org
Alternative contact for Bruno Moonen: Jennifer Gregorie, Clinton Health Access Initiative, Boston, USA. T) +1 617 774 0110 E) jgregoire@clintonhealthaccess.org
Prof Geoffrey Targett, London School of Hygiene & Tropical Medicine, London, UK. T) +44 (0)20 7299 4708 / +44 (0)7971 479684 E) geoff.targett@lshtm.ac.uk
For full Series paper 3, see: http://press.thelancet.com/malelim3.pdf
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