Larviciding has become the new attraction in malaria control. Already many West African countries including Ghana are planning to adopt larviciding as one of the new approaches to malaria control in the sub-region.
Plans have been concluded by the Economic Community of West African States (ECOWAS) under a tripartite agreement with Venezuela and Cuba in Latin America for financial and technical support to set up factories to produce chemicals for larviciding.
The WHO, is however, not convinced that it is the way to go. It says larviciding has a superficial, temporary and transient effect on the malaria burden, and therefore finds it misleading when people make claims about it being as effective as insecticide treated nets (ITNs) and indoor residual spraying (IRS).
To the world health body, critical questions remain to be answered on whether it is possible to deliver larviciding on a large scale cost-effectively, with the requisite quality and completeness of cover and be sustained.
It said although recent trials and pilot operations in East African Highlands have brought renewed interest in the potential of larviciding to supplement ITNs and IRS, more studies are needed about anti-larval measures.
“This evidence is encouraging, and justifies further operational research to confirm that these findings can be repeated in similar settings elsewhere. Only a few studies are available on the efficacy or effectiveness of larviciding in Africa. This makes it difficult to draw generalized conclusions on it.”
While calling for an in-depth study by a multi-disciplinary team to design a multi-sectoral programme, the WHO cited the herculean effort that brought success in larviciding in parts of
Malaysia and Indonesia, where a detailed knowledge of species' habitats led to tailor-made methods of environmental manipulation and sustained cost-effective control.
The WHO also pointed out that one important reason for the use of larviciding in northern Europe and the USA is to control nuisance-biting, not disease transmission, as is the case in sub-Saharan Africa.
“Thus, the fact that larviciding is used for mosquito control in Europe and North America does not imply that it is the intervention of choice for malaria control in the tropics,” the WHO said.
Among the key weaknesses of larviciding, the WHO identifies its heavy dependence on skilled local entomologists and operational resources as posing a challenge to malaria control programmes, considering the fact that larviciding must compete for public resources with other interventions that are proven life-savers and easier to implement.
Although ITNs and IRS require sustained entomological monitoring to guide decisions about vector control, larviciding is said to demand even more entomological experts to ensure that control programmes at the national and local level are based on decisions on where larval control is appropriate.
Each locality needs its own intervention plan, targeting the most productive local sites, and based on local entomological knowledge. This need for local adaptation and local entomo-logical skills is a critical limitation on scaling-up of all kinds of larval source management measures, the WHO explained in its report on larviciding.
The WHO operational manual on larvicidal control management, July 2013 has stressed that the approach should be tailored to local environmental condition and should be based on only comprehensive feasibility and cost effectiveness study.
'Promoting the widespread use of larva source management in rural areas of Sub-Saharan Africa would be premature,” according to information on the website.
Few, fixed and findable
A review by the WHO Malaria Policy Advisory Committee about 3 years ago, recommended that larviciding should only have limited role in malaria control and only be used in areas where mosquito breeding sites are “few, fixed and findable.”
In other words, larviciding is effective only when specially adapted to each locality, and must be carried out thoroughly and selectively only in identifiable areas.
In sub-Saharan Africa, larviciding should be used only as a supplement to the core interventions (ITNs or IRS) and never be seen as a substitute for ITNs or IRS in areas with significant website. malaria risk, said the WHO.
The WHO is concerned that the rise in larviciding could result in a diversion of financial resources away from scientifically-proven vector control tools like bed nets and spraying.
The WHO is not alone in its stance. Some scientists are also uncomfortable with larviciding, which involves the regular application of biological or chemical insecticide to water bodies to reduce and kill mosquito larvae and pupae.
A Public Health Specialist, Professor Fred Binka, thinks it is inappropriate to use the approach in an environment of high transmission of malaria. “We are not in a position to use larviciding; it will be a complete waste of taxpayers' money. We cannot get rid of mosquitoes,” he said, adding that larvicide could only be useful in an environment of low malaria transmission.
Prof. Binka, who is also the Vice Chancellor of the University of Health and Allied Sciences in the Volta Region of Ghana, told AMMREN in an interview that it is not suitable to use
larvicide to kill mosquitoes because Ghana has high transmission of malaria with many breeding grounds across the country. The right approach to control malaria, he said, is to increase the use of ITNs, indoor spraying and ensure that patients are tested before treatment. He described this procedure as the “the best in our circumstances.”
He noted with regret that the use of are ITNs is still very low with only about 200,000 using the net, increasing to 11 million only last two years when Global Fund stepped in to supply mosquito nets.
In most endemic settings, the appropriate way to use larviciding is as a supplement to ITNs or IRS. The consensus among vector control specialists, based on currently available evidence, is that in most situations, universal coverage of larviciding across large areas and populations is unlikely to be feasible.
Prof Binka expressed the need for the government to invest more in the tried and tested malaria control methods like bed nets.
This information needs to be brought to the attention of policy makers in WHO member-states to ensure that larviciding is only implemented where it is appropriate, and that vector control resources are used where they expected to be cost-effective.
Ghana's National Malaria Control Programme Manager, Dr. Constance Bart-Plange, shares the view of Prof. Binka. She told AMMREN in an interview that what is needed is the combination of tools, which could include larviciding, pointing out that when a malaria vaccine is introduced, hopefully in 2015, it will be added to the other tools to help address the malaria menace.
She explained that Ghana is currently using multiple interventions in her malaria control efforts to put her on the path of malaria elimination.
Malaria is a life threatening blood disease transmitted from person-to-person through the bite of the female anopheles mosquito which needs the human blood for her egg and kills fast if not treated quickly. However, some of the larvicide products that had entered the market have not been received by the WHO Pesticide Evaluation Scheme to assess their safety and efficiency.
Studies on integrated malaria vector control with microbial larvi
cide and ITN in Western Kenya recently showed that though the use of larvicid
e reduced malaria vector of mosquito larvae and adult by 90 per cent, the effectiveness of the approach for reducing the incidence of malaria among vulnerable children remains unproven.
By Salifu Abdul-Rahaman