Chemical mosquito controls ineffective inZika fight7 December 2016

Transmission electron microscope image of negative-stained, Fortaleza-strain Zika virus (red), isolated from amicrocephaly case in Brazil. The virus is associated withcellular membranes in the center. Credit: NIAID

Some existing methods for controlling Zika-carrying mosquitos are not effective and may evenbe counter-productive, according to research byscientists at the University of East Anglia (UEA).

A review of previous studies into mosquito controlinterventions shows that there is a lack of clear evidence behind many of the strategies used toprevent the transmissions of insect-borne diseaseslike Zika virus, dengue and yellow fever.

Published today in the journal PLOS NeglectedTropical Diseases, the study led by Prof PaulHunter from UEA's Norwich Medical School looked

at various control strategies which have been usedover the years and the evidence of their success.Methods examined including biological controlssuch as introducing mosquito larvae-eatingcrustaceans or fish to water containers, chemicalcontrols like pesticides and larvicides, andcommunity educational campaigns.

It found that while biological interventions didappear to reduce numbers of disease-carryinginsects more than chemical controls, the quality ofthe evidence was often poor, weakening ourunderstanding of how best to combat diseases likeZika and dengue.

While some studies showed chemical insecticidesand larvicides reduced mosquito numbers by up to76 per cent, others showed no significant reductionand the overall results across all studies wereinconsistent. Overall study of the evidence for theeffectiveness of chemical spraying around domesticareas was weak, and any reduction of mosquitoswasn't sustained.

Prof Hunter said: "Although chemical measures arewidely used and expected to be effective, weconsider most of the evidence in favour of chemicalspraying to be quite poor.

"In fact there is some evidence that spraying maybe counterproductive as it generates a false senseof security such that people no longer put effort intoremoving mosquito breeding sites around thehome."

Currently, the World Health Organisation (WHO)recommends integrated approaches, whichcombine more than one type of control method totackle all life stages of mosquitos and which fullyengage communities to control these diseases. Inparticular WHO advice is that the elimination ofmosquito breeding sites is the most effectiveintervention for protecting populations.

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Prof Hunter said: "Although there is limitedevidence relating to integrated campaignscombining multiple methods of control, the WHO iscorrect to reiterate that the most effectiveintervention is likely to be the elimination ofmosquito breeding sites. This requires sustainedand ongoing education campaigns."

Most of the studies reviewed in the paper reportedoutcomes based on reduction of insects followinginterventions rather than reduction in the incidenceof disease.

"There is a real need for more high-qualityresearch," said Prof Hunter. "There is mixedevidence about whether simply reducing insectnumbers actually reduces disease. So futureresearch needs to cover longer durations, withbetter methodology, and must report on disease-related outcomes rather than just mosquitoreduction."

The review also highlights the need to consider thecost effectiveness of control strategies.

Prof Hunter said: "Public health funding tends toalready be quite limited in low-to-middle incomecountries where mosquitos are endemic, so moreevidence on how best to spend these limited fundsis essential.

"Educational campaigns and communityengagement are paramount in reducing breedinghabitats around domestic environments andinterrupting the cycle of disease transmission, butongoing resources need to be allocated to ensureeducation continues and is maintained."

Recently, the WHO has declared that Zika, likeEbola, is no longer a "public health emergency ofinternational concern". However, co-author DrMaha Bouzid stresses this does not mean that thedisease has been defeated nor that the affectedpeople have resumed normal lives.

She said: "Considering the number of countrieswith active transmission, neurological disorders inadults and the lifelong repercussions on babiesborn with microcephaly, the containment of thecurrent Zika epidemic is far from achieved. This in

addition to the significant global burden of dengueand the recent resurgence of Yellow fever highlightthe need for evidence based interventions tocontrol mosquito transmitted diseases."

This research was partially funded by theRESPONSES project and the National Institute forHealth Research Health Protection Research Unit(NIHR HPRU) in Emergency Preparedness andResponse at Kings College London in partnershipwith Public Health England (PHE).

'Public health interventions Aedes control in thetime of Zikavirus- A meta-review on effectiveness ofvector control strategies' is published in the journal PLOS Neglected Tropical Diseases.

Provided by University of East Anglia

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APA citation: Chemical mosquito controls ineffective in Zika fight (2016, December 7) retrieved 6 April2022 from https://medicalxpress.com/news/2016-12-chemical-mosquito-ineffective-zika.html

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