To relate stability of malaria transmission to biologic characteristics of vector mosquitoes throughout the world, we derived an index representing the contribution of regionally dominant vector mosquitoes to the force of transmission. This construct incorporated published estimates describing the proportion of blood meals taken from human hosts, daily survival of the vector, and duration of the transmission season and of extrinsic incubation. The result of the calculation was displayed globally on a 0.5 degrees grid. We found that these biologic characteristics of diverse vector mosquitoes interact with climate to explain much of the regional variation in the intensity of transmission. Due to the superior capacity of many tropical mosquitoes as vectors of malaria, particularly those in sub-Saharan Africa, antimalaria interventions conducted in the tropics face greater challenges than were faced by formerly endemic nations in more temperate climes.

BackgroundIndoor-based anti-vector interventions remain the preferred means of reducing risk of malaria transmission in malaria endemic areas around the world. Despite demonstrated success in reducing human-mosquito interactions, these methods are effective solely against endophilic vectors. It may be that outdoor locations serve as an important venue of host seeking by Anopheles gambiae sensu lato (s.l.) mosquitoes where indoor vector suppression measures are employed. This paper describes the host seeking activity of anopheline mosquito vectors in the Punta Europa region of Bioko Island, Equatorial Guinea. In this area, An. gambiae sensu stricto (s.s.) is the primary malaria vector. The goal of the paper is to evaluate the importance of An gambiae s.l. outdoor host seeking behaviour and discuss its implications for anti-vector interventions.MethodsThe venue and temporal characteristics of host seeking by anopheline vectors in a hyperendemic setting was evaluated using human landing collections conducted inside and outside homes in three villages during both the wet and dry seasons in 2007 and 2008. Additionally, five bi-monthly human landing collections were conducted throughout 2009. Collections were segregated hourly to provide a time distribution of host-seeking behaviour.ResultsSurprisingly high levels of outdoor biting by An. gambiae senso stricto and An. melas vectors were observed throughout the night, including during the early evening and morning hours when human hosts are often outdoors. As reported previously, An. gambiae s.s. is the primary malaria vector in the Punta Europa region, where it seeks hosts outdoors at least as much as it does indoors. Further, approximately 40% of An. gambiae s.l. are feeding at times when people are often outdoors, where they are not protected by IRS or LLINs. Repeated sampling over two consecutive dry-wet season cycles indicates that this result is independent of seasonality.ConclusionsAn. gambiae s.l. mosquitoes currently seek hosts in outdoor venues as much as indoors in the Punta Europa region of Bioko Island. This contrasts with an earlier pre-intervention observation of exclusive endophagy of An. gambiae in this region. In light of this finding, it is proposed that the long term indoor application of insecticides may have resulted in an adaptive shift toward outdoor host seeking in An. gambiae s.s. on Bioko Island.

To determine whether proximity to flowering maize enhances the development of larval anopheline mosquitoes breeding in turbid water and when crowded, we evaluated the development of larval Anopheles arabiensis under various conditions of turbidity, larval density, and proximity to pollen-shedding maize in simulated breeding puddles in a malaria-endemic site. In naturally formed puddles, water turbidity, as well as larval density, increased as the rainy season progressed. In sites remote from flowering maize, more pupae developed and the resulting adults were larger in relatively clear water than in turbid water, and larval crowding inhibited development. In close proximity to flowering maize, however, larval development was little affected by water turbidity and larval crowding. Larvae of this member of the African An. gambiae complex of mosquitoes develop readily in turbid water and when crowded, provided that their breeding sites are located where maize pollen is abundant.

The role of epidemic malaria as a distinct epidemiologic entity posing unique intervention challenges is reviewed from a global perspective. Epidemic malaria derives from particular interactions of vectors, parasites, and various environmental and anthropogenic determinants. Malaria epidemics generally afflict immunologically vulnerable populations, and their explosiveness can strain the capacity of health facilities, causing case fatality rates to increase five-fold or more during outbreaks. People of all ages remain susceptible to the full range of clinical effects. This flatter demographic profile may translate into larger economic consequences, although the full economic impact of epidemic malaria remains undefined. Specialized intervention approaches are recommended for epidemic-prone areas, including enhanced surveillance activities and intensified antivector interventions. Such considerations are particularly critical during a time when malaria epidemics are occurring more frequently in Africa and throughout the world.

Objective To provide the international community with an estimate of the amount of financial resources needed to scale up malaria control to reach international goals, including allocations by country, year and intervention as well as an indication of the current funding gap. Methods A costing model was used to estimate the total costs of scaling up a set of widely recommended interventions, supporting services and programme strengthening activities in each of the 81 most heavily affected malaria-endemic countries. Two scenarios were evaluated, using different assumptions about the effect of interventions on the needs for diagnosis and treatment. Current health expenditures and funding for malaria control were compared to estimated needs. Findings A total of US$ 38 to 45 billion will be required from 2006 to 2015. The average cost during this period is US$ 3.8 to 4.5 billion per year. The average costs for Africa are US$ 1.7 billion and US$ 2.2 billion per year in the optimistic and pessimistic scenarios, respectively; outside Africa, the corresponding costs are US$ 2.1 billion and US$ 2.4 billion. Conclusion While these estimates should not be used as a template for country-level planning, they provide an indication of the scale and scope of resources required and can help donors to collaborate towards meeting a global benchmark and targeting funding to countries in greatest need. The analysis highlights the need for much greater resources to achieve the goals and targets for malaria control set by the international community.