Is malaria prevalence really declining?

Malaria study areas. Note the non presence of the DRC and  Angola.. along with all of the other areas that are missing. Do we really know what's going on with malaria?

Malaria study areas. Note the non presence of the DRC and Angola.. along with all of the other areas that are missing. Do we really know what’s going on with malaria?

The development community (and the world) has been celebrating dramatic and unprecedented reductions in the number of malaria cases around the world throughout the past decade and a half. Billions of dollars have been thrown at the disease, which is a major killer of children and an incredible hindrance to development.

A new study which just appeared in Malaria Journal, however, calls this optimism into question.

This review presents two central arguments: (i) that empirical studies measuring change are biased towards low transmission settings and not necessarily representative of high-endemic Africa where declines will be hardest-won; and (ii) that current modelled estimates of broad scale intervention impact are inadequate and now need to be augmented by detailed measurements of change across the diversity of African transmission settings.

So, our ability to accurately determine whether transmission intensity has declined is hampered by the fact that most studies of the disease occur in areas of low transmission. This would make sense. It is much easier for us to evaluate the malaria situation in Kenyan context than in the Democratic Republic of Congo due to availability of surveillance infrastructure, official mechanisms which allow research projects to move forward, and security issues.

The obvious problem with this, is the relationship of governance, economy an instability to malaria itself. People in the poorest countries are at the highest risk for malaria and people in the poorest parts of the poorest countries are at the highest risk of all. The trouble is, despite being the populations we are most concerned about, they are the hardest to reach, and the hardest to help.

Worse yet, the estimates of malaria prevalence found in a number of studies were considerably lower than estimates for the entire African continent.

The combined study area represented by measurements of change was 3.6 million km2 (Figure 1), approximately 16% of the area of Africa at any risk of malaria [9]. The level of endemicity within these studied areas (mean PfPR2-10 = 16%) was systematically lower than across the continent as a whole (mean PfPR2-10 = 31%) (Figure 2). While 40% of endemic Africa experienced ‘high-endemic’ transmission in 2010 (PfPR2-10 in excess of 40%) [9], only 9% of the studied areas were from these high transmission settings.

This is a huge issue and one that shouldn’t be limited to malaria. While it is helpful to hear good news of malaria declines in formerly afflicted areas, we need to be careful about overstating the impact of interventions. Funding for malaria projects such as the distribution of insecticide treated bed nets was incredibly high throughout the 00’s but it is unlikely that trend will continue. Offering an positive picture can show that our efforts are valuable, but might also lead policy makers and donors to suggest that money be put toward other goals. If Sri Lanka is any indication, where malaria was nearly eliminated at one time but experienced a rapid and devastating resurgence, even a brief relaxation of malaria control efforts could erase current gains completely.

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About Pete Larson

Assistant Professor of Epidemiology at the Nagasaki University Institute for Tropical Medicine

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