Dappled Wings of Death

An minimus mosquito
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Anopheles minimus mosquito. Image Courtesy of Jim Gathany

Yesterday, August 20, marked World Mosquito Day: the day in 1897 that Ronald Ross, a British medical officer in India, discovered the malaria parasite in the “dapple-winged” mosquito—changing the course of history. The following day he drafted a poem including the lines:

O million-murdering Death.

I know this little thing

A myriad men will save

This “little thing a myriad men will save” indeed. Our understanding of the mosquito vector and her role in transmitting malaria and yellow fever—and now, of growing global importance, dengue, Zika and chikungunya—has transformed our world.

We seem to be winning some battles but struggle with others. Malaria remains a crushing burden in many communities, with an estimated 212 million cases worldwide in 2015—but this represents a 21% decrease in incidence and 29% decrease in mortality since 2010. Our struggles with Aedes, vectors of yellow fever, dengue, chikungunya and Zika, present a more troubling picture. Through globalization, urbanization and climate change, Aedes aegypti and Aedes albopictus continue to proliferate almost unchecked. More than 2.5 billion people—40% of the world’s population across 100 countries—live in areas at risk of Aedes-borne viruses. As former WHO Director-General Margret Chan famously told the 2016 World Health Assembly, “Above all, the spread of Zika, the resurgence of dengue, and the emerging threat from chikungunya are the price being paid for a massive policy failure that dropped the ball on mosquito control in the 1970s.”

Clearly, 120 years since Sir Ronald incriminated the mosquito and penned these famous lines, we need to step up. WHO and partners are renewing efforts to build capacities and respond to these mosquito-borne threats through the broad multi-sectoral Global Vector Control Response launched in June this year. Complementing the work of WHO are growing networks of national programs, institutions and partners through the Roll Back Malaria Vector Control Working Group, the Asia Pacific Malaria Elimination Network and the Pan African Mosquito Control Association.

As we think of that warm and humid August afternoon in India, remember the mosquito and the “million murdering death.” We’ve learned a lot and have made progress against Anopheles, but Aedes continue to challenge. It will be through these partnerships and networks, through the growing cadre of a new generation of public health entomologists in the Americas, Africa and Asia, that we realize the full benefit of “this little thing” Sir Ronald discovered 120 years ago.

 

Michael B. Macdonald Sc.D. (JHU SPH ’88) is former co-chair of the RBM VCWG.

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1 comment

Manuel Lluberas
August 21, 2017

In Africa, and a good portion of the rest of the world, malaria vector control is driven by the quest for a better net as a result of mosquitoes developing resistance to the insecticides in them. What seems to be forgotten in this equation is that these mosquitoes are becoming increasingly exophilic and exophagic (prefer outdoors and bite outdoors) in many parts of the continent. In areas where this is happening, a "better" formulation in the net fibers will have little or no effect on the vector population. In other regions, where the vector is already mostly exophagic and its biting behavior is mostly during the periods where mosquito nets will have no effect -like South America and parts of Asia- promoting and distributing these "better nets" will be equally futile. They may give the population and those promoting them a sense of security, but there will be little effect on malaria transmission.

Those promoting the use of mosquito nets as a malaria "vector control" method continue to focus their attention on producing a better mosquito net ignoring these fundamental points.

Integrated vector management with a strong source reduction component has been demonstrated to work. Unfortunately, for whatever the reasons, those in a position to implement a program that deploys as many mosquito control tools as possible continue to insist that larval source management is only effective when the sources of mosquitoes are "few, fixed and findable."

Dr. Fred Soper eradicated malaria vectors from an area in northern Brazil the size of Togo mostly through LSM in 1939 after he was told repeated that it could not be done. (And he did so without even a calculator!)

Sadly, the global campaign against malaria continues to promote the use of bed nets at the exclusion of every other vector control method and tool. A few years after Dr. Ross confirmed malaria was transmitted by a mosquito, he voiced his concern about malaria when he said "Malaria will continue to affect the world until the mosquito is taken seriously." Unfortunately, those in a position to affect some change continue to repeat a statement issued in 1903 by the Isthmian Canal Commission of the Panama Canal that read “To spend time and money chasing after mosquitoes … would be to squander time and money in a most irresponsible fashion.”

It is time to get serious about mosquito control.

Manuel

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