Malaria epidemic is a major public health problem. In Africa alone, malaria is a disease that is estimated to kill a million people per annum. According to CDC impact survey 2018, malaria occurs mostly in poor tropical and subtropical areas of the world. In many of the countries affected by malaria especially in Sub-Saharan Africa, it is a leading cause of illness and death. In areas with high transmission, the most vulnerable groups are young children, who have not developed immunity to malaria yet and pregnant women whose immunity have been reduced by pregnancy. In 2016, malaria caused an estimated 216 million clinical episodes and 455,000 deaths. An estimated 91% of deaths in 2016 were in the WHO African region.
There are four species that affect humans, P. falciparum, P. maleriae, P. vivax and P. ovale. The predominant parasite species is P. falciparum, which is the specie that is most likely to cause severe malaria and death. Malaria drugs targets different stages of the parasite development in human. However, widespread resistance has been evolving to the original antimalaria drugs and the newer alternatives are being developed to replace them. Although the development and introduction of artimisinin derived drugs with their higher efficacy in combination with other longer acting drugs has offered hope and appears to be the way forward to combat malaria, the economic and logistical obstacles of changing many poor countries health policies are barriers that needs to be overcome. Malaria imposes substantial economic burden on both individuals and the governments. Direct cost for illness, treatment and premature death has been estimated to be at least US$ 12 billion per year. The cost in retard economic growth is even more.
Since the discovery of Ronald Ross in 1897 that mosquitoes are the vectors of the malaria parasite, vector control has become an important part of malaria control programs. Several strategies have been designed and put into place to reduce the mosquito population and others are currently being investigated as possible solutions for rendering the mosquito vector less competent to transmit malaria. Among these strategies are environmental management, insecticide treatments and molecular approaches.
Environmental control strategy focuses on environmental modification, manipulation, changes in human behavior and habitat. Vector control strategies employ in this area involves reduction of mosquito population through draining of wetlands, removal of potential breeding habitats, use of house screens and use of lavivorous fishes. Although some level of success have been recorded in two African countries (Egypt and Zambia), the wide array of mosquito vector and diverse habitat requirements coupled with the formation of temporary pools during rainy season have made these approaches impractical. Biological approach involves the use of lavivorous fishes and microbial agents. These methods are currently being limited by the effect of the lavivorous fishes on native fauna and the specificity of the microbial agent.
Chemical method involves the use of chemical agents. Early approach relied on the use of corper acetoarsenite and petroleum byproducts but their use has been discontinued due to high toxicity and increase in water bodies. Soon after the discovery of dichlorodiphenyltrichloroethane (DDT), the focus of malaria control strategy shifted from early vector control to mosquito adult population. The outstanding result obtained through the use of DDT and other synthetic insecticide in USA, Southern Europe and Southern Africa created a false impression that malaria can be eradicated from the planet. However with the emergence of insecticide resistance, rejection of the use of DDT due to ecological effect and changes in mosquito feeding habit, this optimism is soon eroded. Currently insecticide use still plays a significant role in malaria control programs through the use of insecticide treated nets and indoor residual spraying especially in malaria endemic countries. Pyrethorid-insecticide treated nets have been regarded as an excellent tool in malaria eradication in developing countries. These approaches focus on feeding habit of mosquito and only reduce their lifespan.
The inherent challenges involve in the successful implementation of malaria control programs revolves around socioeconomic, biological and political issues. The challenges in biological terms include varied mosquito vector specie and wide array of habitat choices. Molecular approaches have been hampered by the development of plasmodium resistance specie. According to WHO, mosquitos have become resistance to all types of insecticide available in certain areas. The molecular mechanisms of resistance are not yet understood.
The identification of anti-plasmodium factors through understanding vector biology and the biology of malaria transmission opens new door to new elimination strategy and effective malaria control. Most new ideas in this field make use of molecular data and methods to add to the insights of entomologists from the pre-genomic era and explain the molecular mechanisms behind vector-parasite interactions and mosquito biology and behavior. For example the genomic analysis carried out by sequencing the A. gambia genome can be disrupted or exploited in an attempt to control malaria. Another area of interest is mosquito olfaction: the use of odorant receptors to control mosquito population. This makes olfaction a possible basis for target control. Studies have shown that transmission is completed if the infected female mosquito finds a new vertebrate a process that is mediated by the ability of the mosquito to sense its host through heat, shape and body odor which provides opportunity for possible interference with mosquito olfaction through altering of vector-host relationship and various functions of the mosquito.
It is therefore becoming obvious that a comprehensive approach is required in order to make significant progress toward malaria eradication. Drugs and vaccine development may not be sufficient to halt transmission, vector based strategy has proven effective in other areas. Not only do vector based strategy have effect on transmission processes, it also alter pre-transmission stages which make also makes it a preventive strategy with exciting promises towards malaria elimination.
Innovation and development toward malaria eradication requires three components: 1. understanding of the molecular, physiological and biology mosquito population 2. Understanding parasite, vector and host relationship 3. Developing potential delivery mechanisms. Synergy between these three elements plays an important role towards eradication of malaria.
Well said. Nice work Abimbola