Factors Contributing to Malaria Transmission

Factors Contributing to Malaria 🦟 Transmission

Malaria is an acute febrile illness caused by Plasmodium parasites, which are spread to people through the bites of infected female Anopheles mosquitoes.

Malaria in humans results from infection by any of five species of Plasmodium transmitted by approximately 50 species of mosquitoes, all belonging to the genus Anopheles. In sub-Saharan Africa, the majority of deaths are caused by P. falciparum and transmitted by An. gambiae s.s. and its close relative Anopheles arabiensis.

Human Factors

Socio-Economic Status

Higher socioeconomic status is associated with a number of factors that lead to reduced malaria transmission, from piped water and better refuse collection to better education, higher exposure to TV and radio prevention campaigns, and increased ability to afford prevention methods and treatment. These factors contribute to a better awareness of vector breeding sites, malaria transmission, and control among people of higher socioeconomic status. The higher socioeconomic status of urban dwellers is a major factor contributing to their reduced risk of contracting malaria within cities, socioeconomic factors contribute to increased transmission in poorer areas with slum-like conditions.

Household Factors

Better-quality housing decreases the risk of malaria as it minimizes entry points for mosquitoes during the night. Floors comprised of earth bricks are also associated with lower malaria risk as inhabitants are more likely to sleep on raised beds to avoid ground moisture, in turn eluding bites from An. gambiae mosquitoes which search for blood close to the ground [16]. Electricity use was associated with increased malaria risk, as the alternative of biomass fuel burning produces smoke that is thought to deter mosquitoes from entering houses.

Community Factors

Hygiene, sanitation, and waste collection are key determinants of malaria transmission which, while household responsibilities, have a community-level effect on disease transmission. As an example, the more the households dispose of waste properly, the lower the risk of liquid waste collecting in pools of stagnant water and forming vector breeding sites. Toilets are also potential areas of mosquito activity, and septic tanks within communities are a potential source of vector breeding sites.

Natural Vector Breeding Sites and Environmental Factors

The heavy burden of malaria in rural Africa is testimony to the ability of natural breeding sites to sustain vector populations. Natural breeding sites, although less common in urban areas, are nevertheless present. Field studies suggest that anopheline larvae are most likely to be found in permanent, shallow, sunlit pools of water of perimeter greater than 10m. Temporary pools are less favoured because they may not provide sufficient time for eggs to develop and emerge as adults. It has also been suggested that they are more likely to be disturbed by human activity. A high groundwater table is particularly conducive to breeding sites as the absence of surface runoff allows pools of stagnant water to develop Of the natural vector breeding sites, the most common are ponds and swamps.

Rivers and Floodplains

Rivers and their floodplains provide great breeding grounds for mosquitoes in riverside urban communities. Large fields with loamy/clay soils tend to collect stagnant water from rivers and provide optimal conditions for anopheline breeding.

Altitudes

Altitude is commonly thought to play an important role in limiting malaria in the tropical highlands by negatively influencing the development of vector species.

Artificial Vector Breeding Sites

It is widely regarded that artificial rather than natural vector breeding sites provide the most abundant sources of mosquito larvae in African urban centres. Also, water tanks, construction sites, and swimming pools are included. Some others are sites, such as tyre tracks and swimming pools, contain all life stages of An. gambiae, suggesting that they are particularly productive habitats and are found mainly in poorly-drained, periurban areas.

Urban Agriculture

It provides optimal conditions for vector breeding, leading to a higher risk of malaria transmission in its vicinity. Agricultural trenches create ideal breeding sites due to the formation of shallow water between seed beds. Other breeding sites include irrigation wells, noncemented wells, ditches for furrow systems, and human footprints.

Drains, Ditches, and Gutters

While agriculture provides the most productive urban vector breeding sites, drains and ditches may provide more common habitats. Blockages are often due to poor sanitation and lead to reduced water flow and accumulation of stagnant water pools which are ideal for mosquito breeding. Gutters provide a similar breeding site for mosquitoes in both the wet and dry seasons.

Swimming pools

Unused swimming pools provide a particularly productive habitat for Anopheles immature stages.

Water Pipes

Water pipes can lead to breeding site formation in a variety of ways, most frequently when they are broken and pools of water collect. Pipes often break as a result of poor installation or quality, clay soil expansion and contraction, construction work, and as an opportunity to procure free water for sale or consumption. Water sources that are further away from pipes are more likely to be anopheline positive because water flow from nearby pipes may disturb the water surface, reducing the breeding site quality . Artificial water storage containers can also serve as breeding sites, and car washing has been found to provide excellent habitats for larval development.