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PMI and Swiss Cheese

July 6, 2016 - 13:07 -- William Jobin

There is dangerous obstacle - we call it the Immunity Trap - in malaria prevention strategies which is most dangerous for countries which have relied on the ephemeral methods recommended by WHO and used by PMI, but which have not included permanent methods. In the 19 African countries in the US Presidential Malaria Initiative administered by the PMI for the last decade, of the 30 million who have lost their immunity, about half are also no longer protected by house spraying because of the high cost of new biocides. These unprotected and non-immune people in malaria endemic areas, are at the mercy of future US Presidents, and possible budget cuts.

Swiss Cheese Strategy

What to do? As suppression of malaria transmission continues, and as large, non-immune populations build up, permanent methods should be added to the ephemeral ones. Addition of other methods is known as the Swiss Cheese Strategy, in which several layers of cheese (methods) - even with their attendant holes - are overlapped so that the holes do not match, to finally give complete coverage (and a tasty sandwich – Emmentaler anyone?).

These multiple strategies should include improved housing and also elimination or management of larval habitats, which have the additional advantage of being permanent. Improved housing includes closure of eaves and screening of windows and doors (see Tusting et al, in Malaria Journal 2016 15:320).

Hopefully, the decade of malaria suppression in the PMI countries will also have resulted in improved economic conditions for the population, resulting in many other self-financed improvements, such as small electric fans which disturb the hunting system of anophelines. Also there are social and environmental changes which should help. Paradoxically, the spread of urbanization across Africa has resulted in local suppression of malaria because of increased environmental contamination of water and air, which is tough on malaria mosquitoes.

The Immunity Trap should not be taken lightly by the folks who run the PMI; a few wet years could kick off disastrous epidemics in the 19 African countries, similar to the one which occurred in central Sudan in the early 1990’s. Beware of this Trap Tim, along with your 13 million unprotected and non-immune people!