Control of Urban Zika Vectors: Should We Return to the Successful PAHO/WHO Strategy?

in Research Jun 1, 2023 By Paul Reiter From PloS Medicine

We keep hearing that vector control is our only weapon against Zika.

The problem is: How?

We assume that the urban vectors of the virus are Aedes aegypti and Ae. albopictus. They are also the principal vectors of urban dengue and chikungunya, in which case the spectacular increase in the global prevalence and incidence of both diseases [1] is harsh condemnation of our current control strategies. The stark truth is that over the past 50 years no country anywhere in the world (with the possible exception of Singapore) can claim sustained suppression of transmission of these viruses [2].

A plethora of factors has been blamed: explosive growth of urban areas, globalization of pathogens and vectors, limited government resources, excessive reliance on insecticides, ineffectual application technology, incorrect application methods, insecticide resistance, poor training of field personnel, the “throw-away society”, a “quick fix” mentality, inadequate garbage collection, irregular water supply, inadequate public education and overemphasis on the “top down” role of governments rather than the “bottom up” role of the community, and more.

In the past, nevertheless, there were two remarkable examples of success: the source-reduction campaigns that began at the turn of the 20th century, and the Ae. aegypti Eradication Campaign—coordinated by the Pan-American Health Organization (PAHO)—that followed in the late 1940s. The goal of the latter was complete eradication of the species from the entire western hemisphere and indeed, by 1962, eighteen countries had been declared totally free of the mosquito and of dengue [3]. Unfortunately, for a variety of reasons—including insecticide resistance and failure to sustain efforts in regions where the campaign had been successful—the project was abandoned and both mosquito and virus quickly regained their lost territory.

The challenges that confronted the eradication campaign are dwarfed by the obstacles that we face today. The problem is primarily urban: Ae. aegypti is ubiquitous and abundant in urban areas throughout the tropics. In addition, in the past 30 years, Ae. albopictus has invaded many tropical and temperate regions world-wide.

To understand the abundance of both we must be mindful of their origins as forest species. In that habitat they did not breed in ground-pools or marshlands but in a well-defined niche: tree-holes, plant axils, fruit husks, rock-holes and other small natural containers. They have adopted the human peri-domestic environment by exploiting the profusion of artificial containers in the human jungle—water storage vessels, discarded tires, blocked gutters, broken china, cracked buckets, defunct toilet bowls, saucers under flowerpots, flower vases, water-storage vessels, abandoned kiddie play-pens and so-on …

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