Category Archives: Larvicide

Zero Malaria Starts with Universal Coverage: Part 3 Innovations and New Interventions

Newer malaria interventions are coming on board, and whether these will be used of a large scale or targeted to certain epidemiological contexts remains to be seen. In each case, one will need to examine if in each context one can measure whether the intervention is universally accessible to and used by the intended population or subgroup.

After 30 years of research and testing, a malaria vaccine is ready to go through implementation testing in Malawi, Ghana and Kenya. This pilot of the vaccine, known as RTS,S, will be made available to children up to 2 years of age with the Malawi launching first during the week of World Malaria Day.

WHO explains that, “The malaria vaccine pilot aims to reach about 360,000 children per year across the three countries. Ministries of health will determine where the vaccine will be given; they will focus on areas with moderate-to-high malaria transmission, where the vaccine can have the greatest impact.” There will be a strong monitoring component to identify coverage levels as well as any implementation challenges and adverse effects that may only become visible in a larger scale intervention that the typical efficacy trials. Implementation is occurring in areas with a relatively strong existing malaria control effort, with an intent to learn how a vaccine can complement a total control package.

Mass Drug Administration (MDA, also known as preventive chemotherapy) has been a successful strategy for controlling and eliminating neglected tropical diseases with special reference to onchocerciasis, lymphatic filariasis, trachoma, soil transmitted helminths and schistosomiasis. MDA use in malaria has been limited due to a number of financial and logistical challenges, not the least of which is the need to achieve high coverage over several periods of distribution. This is why WHO recommends, “Use of MDA for the elimination of P. falciparum malaria can be considered in areas approaching interruption of transmission where there is good access to treatment, effective implementation of vector control and surveillance, and a minimal risk of re-introduction of infection.”

Another link with MDA for a different disease, onchocerciasis, has pointed to a potential new malaria intervention. Around ten years ago it was observed that after ivermectin treatment for onchocerciasis in Senegal survivorship of malaria vectors was reduced. Subsequently the potential effect of ivermectin has been intentionally researched with the outcome that, “Frequently repeated mass administrations of ivermectin during the malaria transmission season can reduce malaria episodes among children without significantly increasing harms in the populace.” Mathematical models for onchocerciasis control have predicted the need to achieve annual coverage targets below what could be called universal levels. Using ivermectin for mosquito control would require more frequent dosing and higher coverage.

Although not defined as ‘new’ it is important to include mention of additional vector interventions like larviciding and indoor residual spraying, as these present technical and coverage challenges. For example, larviciding interventions either chemical or biological, do not cover individuals. These focus on breeding sites in communities. This may require better use of the concept of geographical coverage as has been used in onchocerciasis control wherein the proportion of endemic villages reached is monitored.

For example, in Mali the NTD program aimed to achieve 80% program coverage of individuals eligible for preventive chemotherapy and 100% geographical coverage yearly. This means all villages should be reached. In reality, the program achieved 85% geographical coverage for lymphatic filariasis and over 90% for onchocerciasis.

In conclusion, we have seen that defining as well as achieving universal coverage of malaria interventions is a challenging prospect. For example, do we base our monitoring on households, villages, or populations? Do we have the funds and technical capacity to implement and sustain the level of coverage required to have an impact on malaria transmission and move toward elimination? Are we able to introduce new, complimentary and appropriate interventions as a country moves closer to elimination?

What do we know about larvicides?

In SciDec.net we read that, “Cuba has announced plans to build biolarvicide factories in Brazil and several African countries in a bid to tackle malaria and dengue fever.” The move is based on apparent successes of efforts such as those in Angola where the Director-general of Labiofam says that, “Angola, for instance, has reduced malaria incidence by 50 per cent, and some areas have seen a 70 per cent fall,” with similar results in Accra, Ghana.

WHO says that larviciding is “indicated only for vectors which tend to breed in permanent or semi-permanent water bodies that can be identified and treated, and where the density of the human population to be protected is sufficiently high to justify the treatment with relatively short cycles of all breeding places.” What actual documented evidence is there from Angola and elsewhere in Africa about the use and effectiveness of larviciding?

An article on the history of malaria control in Liberia reviews early efforts to use synthetic insecticides for indoor residual spraying and larviciding.  Unfortunately, “These projects encountered a spate of difficulties that foreshadowed the general retreat from malaria eradication efforts across tropical Africa by the mid-1960s.” What has changed now that we are in the days of rolling back malaria?

A newly published article on mosquito larval source management in areas experiencing flooding in The Gambia concluded that …

The intervention was associated with a reduction in habitats with late stage anopheline larvae and an 88% reduction in larval densities. The effect of the intervention on mosquito densities was not pronounced and was confounded by the distance of villages to the major breeding sites and year. There was no reduction in clinical malaria or anemia. Ground applications of non-residual larvicides with simple equipment are not effective in riverine areas with extensive flooding, where many habitats are poorly demarcated, highly mobile, and inaccessible on foot.

dscn7743sm.JPGA key approach to the use of larvicides may be integrated vector management, where there is not reliance on one control measure alone. In the Kenyan highlands researchers found that, “Vector control with microbial larvicides enhanced the malaria control achieved with ITNs alone. Anti-larval measures are a promising complement to ITN distribution in the economically important highland areas and similar transmission settings in Africa.”

Larviciding was found to have a positive effect in reducing childhood malaria in Tanzania where “larviciding reduced malaria prevalence and complemented existing protection provided by insecticide-treated nets. Larviciding may represent a useful option for integrated vector management in Africa, particularly in its rapidly growing urban centres.”

The two promising articles from Kenya and Tanzania would be strengthened if large scale operations like those described for Angola were better documented and published because as was seen in Liberia many years ago it was the basic operational issues that limited program effectiveness.

Devine and Killeen report in discuss some of the practical issues of larviciding in Malaria Journal and note that, “The effective operational implementation of these campaigns is difficult, time consuming, and expensive,” in part because of “The myriad and cryptic nature of aquatic habitats and the difficulty in identifying and targeting the most productive of these (which) makes maximizing that impact very challenging.”

Devine and Killeen recommend a “new auto-dissemination methodology” based on a “detailed characterization of oviposition behaviour and of the effective transfer distances between feeding, resting and aquatic resources.” Again, these are good ideas, but what of evaluation of current large scale approaches underway? In addition, as RTI suggests programs must establish “baseline information on the acute, intermediate, and chronic effects of chemicals used in malaria vector control on workers and the general population.”

The basic question remains – what can we learn about the right conditions for larvicide use as a major tool in integrated vector management for malaria? All partners in rolling back malaria have a responsibility for helping this learning process by documenting and publishing their experiences. Maybe the proceedings of the recent Labiofam Conference in Havana will be published soon.