Journal of Mosquito Research 2024, Vol.14, No.4, 172-183 http://emtoscipublisher.com/index.php/jmr 174 3.2 Pathogen survival and multiplication within the mosquito host Once ingested, pathogens must survive and multiply within the mosquito host to ensure successful transmission. Arboviruses, for example, exploit the mosquito's physiological processes to enhance their replication. The ingestion of a blood meal activates the GABAergic system in mosquitoes, which suppresses antiviral innate immunity and facilitates arbovirus replication. Malaria parasites, on the other hand, undergo a complex life cycle within the mosquito, involving multiple developmental stages and bottlenecks. Only a small proportion of ingested gametocytes successfully develop into sporozoites, which are capable of infecting new hosts (Dong et al., 2009). The mosquito's immune system plays a crucial role in controlling pathogen propagation, employing mechanisms such as phagocytosis, melanization, and lysis to limit pathogen survival (Kumar et al., 2018). 3.3 Factors influencing pathogen uptake Several factors influence the uptake and subsequent transmission of pathogens by mosquitoes. Host immunity, for instance, can affect the availability and concentration of pathogens in the blood, thereby influencing the likelihood of mosquito infection (Carrington and Simmons, 2014). The gut microbiota of mosquitoes also plays a significant role in modulating pathogen acquisition and survival. The microbiota can inhibit the development of pathogens such as Plasmodium through the activation of the mosquito's immune responses. Additionally, the source of the blood meal can impact pathogen development; for example, the efficiency of malaria parasite development within mosquitoes is influenced by the type of host blood consumed during sporogony (Figure 1) (Emami et al., 2017). Understanding these factors is crucial for developing strategies to control mosquito-borne diseases. In summary, the acquisition of pathogens by mosquitoes involves complex interactions between the mosquito, the pathogen, and various environmental and biological factors. These interactions determine the efficiency of pathogen uptake, survival, and transmission, ultimately influencing the epidemiology of mosquito-borne diseases. Figure 1 Effect of second blood meal from different hosts (cow and human) on oocyst and sporozoite load in mosquitoes (Adapted from Emami et al., 2017) Image caption: Four days after the infectious blood, An. gambiae s.s. (Keele) and An. arabiensis (Ifakara) mosquitoes were offered a second blood meal of human or cow origin, or no second blood meal (control). Number of oocysts per midgut (panels a and d) were measured at day 10 post-infection. The total number of parasites per mosquito was estimated using quantitative PCR within the midgut (oocyst) stages at day 10 post-infection (panels b and e) and within the salivary glands at day 16 post-infection (panels c and f). The top panels (a,b,c) showAn. arabiensis (Ifakara), and the lower panels (c,d,e) showAn. gambiae s.s. (Keele). The infection load values are taken from the negative binomial model estimations. The median is represented as a thick solid line, the box represents the upper and lower quartile range, and the whiskers show the range. Outliers are shown as unfilled circles. Statistically different comparisons are shown by the brackets (***p ≤ 0.001; *p = 0.01) (Adapted from Emami et al., 2017)
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