The second paper in The Lancet Series on Malaria Elimination ranks each malaria endemic country by their current feasibility for achieving elimination of both P. falciparum and P. vivax malaria relative to others, and is written by Dr Andrew J Tatem, Emerging Pathogens Institute, University of Florida, Gainesville, FL, USA and colleagues.
The 108 countries that have eliminated malaria to date had several things in common, including malaria originally of low risk and relatively low levels of incoming population movements from countries with endemic malaria. Other factors that have contributed to elimination have been political stability, good general health systems, absence of conflict and populations at risk that are easily accessible. Many countries currently burdened with malaria are missing some or all of these factors. The development of databases and mathematical models on these aspects related to malaria elimination now facilitates construction of an evidence-based framework for setting technical support and financing priorities.
Only subjective assessments of elimination feasibility currently exist at the global scale. The authors say an elimination strategy needs a strong evidence base, and currently this only exists for P. falciparum, not P. vivax malaria. The authors have now assembled data collected across the world into a single database and combined it with statistical and mathematical models to map the P. falciparum transmission reductions required to achieve elimination. This data has also contributed towards the derivation of evidence-based relative rankings for technical, operational and combined elimination feasibility.
When plotted onto a world map, countries on the fringes of the malaria map generally have the highest feasibility for elimination of malaria. Technically, P. falciparum malaria could be eliminated in most of the world if transmission could be reduced from 2007 rates by 90%, (below the critical threshold for malaria to sustain itself). Such a reduction would need to be maintained for 10—15 years.
Due to differences between P. falciparum and P. vivax, elimination strategies are likely to be species specific (and thus so are country rankings for elimination). Near-term elimination strategies for P. vivax will require tackling the dormant liver phase of the parasite by treatment with primaquine. However, this drug can causes haemolysis (see press release paper 1). An estimated 5% to 20% of people in P. vivax endemic areas have this enzyme deficiency, and a rapid, on-the-spot specific test to reveal deficiency is not yet available and is urgently needed.
The rankings for P. falciparum show that Somalia, Chad, Yemen and DR Congo will all face substantial difficulties in eliminating P. falciparum compared to other P. falciparum malaria-endemic countries. Most countries with the highest feasibility for P. falciparum elimination relative to others are among the most economically developed in the three continental regions, such as the Dominican Republic, Saudi Arabia, Brazil, and Iran, or those with small, fairly accessible populations at risk, such as Honduras, Djibouti, and Belize. Higher absolute spending per head and low numbers of people at risk put Botswana, Swaziland and Rwanda at an operational advantage for elimination compared to other countries in sub-Saharan Africa.
The authors say: "In general, elimination from countries in the Americas is most feasible using current tools, and least feasible for most sub-Saharan African countries. However, forest and fringe malaria dominates in the Americas, and the elimination of malaria in the continent overall will depend heavily on the feasibility of elimination in the Amazon basin." They add however that Venezuela and Ecuador are examples of American countries where elimination is relatively less feasible, due partly in both cases to difficult to access populations exposed to stable P. vivax transmission.
Political instability and relatively weak health systems mean that Pakistan and Afghanistan currently appear to be less likely to succeed with elimination than other endemic Asian countries. Yet while Yemen on its own is also a relatively weak candidate for elimination, a recent joint elimination programme launched with the much wealthier Saudi Arabia could considerably enhance its prospects. The authors state that regional initiatives will be crucially important to the elimination prospects of individual countries (see African and Asian examples in paper one press release).
In southeast Asia, (eg, Indonesia, Laos) elimination of P. vivax is likely to pose a challenge Additionally, Burma and its neighbouring countries ( Cambodia, Vietnam) form the region where drug resistance commonly develops first and where there is now concern that this is happening to the artemisinin drugs on which we are so dependent for treatment.
The authors conclude: "Our analysis represents a starting point, and it now needs more critical use and adaptation to meet the agenda of international agencies that govern priority setting for malaria control."
Dr Tatem adds: "While global evidence-based assessments of elimination feasibility such as this can objectively assess the merits of regional and national malaria intervention plans, countries should undertake detailed feasibility assessments before embarking on an elimination campaign."
Dr Andrew J Tatem, Emerging Pathogens Institute, University of Florida, Gainesville, FL, USA. T) +1 352-273-9373 / +1 352-219-8639 E) atatem@ufl.edu
Note to editors: *Anopheles stephensi is one of the only malaria spreading mosquitoes that prefers urban habitats - therefore, as India increasingly becomes more and more urban, more and more ideal habitat will be created for the mosquito
For full Series paper 2, see: http://press.thelancet.com/malelim2.pdf
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The Lancet