Journal of Vaccine Research 2024, Vol.14, No.2, 85-94 http://medscipublisher.com/index.php/jvr 86 2 Overview of Malaria 2.1 Explanation of malaria and its causative agents Malaria is a life-threatening disease caused by Plasmodium parasites, which are transmitted to humans through the bites of infected female Anopheles mosquitoes. There are five species of Plasmodium that cause malaria in humans: Plasmodium falciparum, P. vivax, P. ovale, P. malariae, and P. knowlesi. Among these, P. falciparum is the most deadly and prevalent, particularly in Africa (Wang et al., 2009; Crompton et al., 2010). The complex lifecycle of Plasmodium involves both human and mosquito hosts, making the development of effective control measures challenging (Wang et al., 2009). 2.2 Transmission cycle The transmission cycle of malaria involves several stages. When an infected mosquito bites a human, it injects sporozoites into the bloodstream. These sporozoites travel to the liver, where they mature and multiply. After a period of development, the parasites enter the bloodstream and infect red blood cells, leading to the symptomatic phase of the disease. Some of these parasites develop into sexual forms called gametocytes, which are taken up by mosquitoes during a blood meal. Inside the mosquito, the gametocytes undergo further development, eventually forming sporozoites that migrate to the mosquito's salivary glands, ready to infect another human host (Wang et al., 2009; Crompton et al., 2010; Theisen et al., 2017). 2.3 Global burden Malaria remains a significant global health issue, particularly in sub-Saharan Africa, where it is a leading cause of morbidity and mortality. The disease disproportionately affects children under five and pregnant women. Despite extensive control efforts, including the use of insecticide-treated nets and indoor residual spraying, malaria continues to pose a substantial public health challenge. The development of effective vaccines and novel vector control strategies is crucial for reducing the global burden of malaria (Benelli and Beier, 2017; Ogeto et al., 2020; Wilson et al., 2020). The RTS,S vaccine, targeting the pre-erythrocytic stage of the parasite, is one of the most advanced candidates and has shown partial efficacy in clinical trials (Crompton et al., 2010; Ogeto et al., 2020). In summary, malaria is a complex disease caused by Plasmodium parasites, with a lifecycle involving both human and mosquito hosts. The global burden of malaria remains high, necessitating continued efforts in vaccine development and vector control to achieve significant reductions in disease incidence and mortality. 3 Advances in Vector Management 3.1 Insecticide-treated nets (ITNs) and indoor residual spraying (IRS) Insecticide-treated nets (ITNs) and indoor residual spraying (IRS) are two primary vector control strategies used to combat malaria. ITNs involve the use of mosquito nets treated with insecticides, primarily pyrethroids, which are safe for prolonged contact with human skin. IRS, on the other hand, involves spraying the interior walls of homes with insecticides to kill mosquitoes that rest indoors. Combining ITNs with IRS has been shown to enhance malaria control, especially in areas where mosquitoes have developed resistance to pyrethroids (Pluess et al., 2010; Protopopoff et al., 2015; Pryce et al., 2022). Studies have demonstrated that adding IRS to ITNs can significantly reduce malaria prevalence and incidence. For instance, a study in Northern Tanzania found that combining IRS with ITNs reduced the density of Anopheles mosquitoes by 84% and the entomological inoculation rate (EIR) by 90% compared to ITNs alone (Protopopoff et al., 2015). Similarly, research in Mozambique showed that IRS with non-pyrethroid insecticides, such as pirimiphos-methyl, in addition to ITNs, reduced malaria vector densities and human exposure to malaria vectors (Chaccour et al., 2018; Wagman et al., 2021). 3.2 Biological control methods Biological control methods involve the use of natural predators, pathogens, or competitors to control mosquito populations. These methods are environmentally friendly and can be integrated with other vector control strategies. One promising biological control method is the use of larvivorous fish, which feed on mosquito larvae in water
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