Journal of Mosquito Research 2024, Vol.14, No.4, 172-183 http://emtoscipublisher.com/index.php/jmr 173 2 Mosquito Biology and Vector Competence 2.1 Anatomy and physiology relevant to pathogen transmission Mosquitoes are haematophagous insects, meaning they feed on blood, which is essential for the development of their eggs. The anatomy and physiology of mosquitoes are intricately linked to their role as vectors of pathogens. The process of pathogen transmission begins when a mosquito takes a blood meal from an infected host. The pathogens then propagate within the mosquito's tissues, particularly in the midgut, where they undergo various developmental stages before migrating to the salivary glands. From there, the pathogens can be transmitted to a new host during subsequent blood meals (Wu et al., 2019). The mosquito's immune system plays a crucial role in determining its vector competence, which is the ability to acquire, maintain, and transmit pathogens. The interaction between the mosquito's gut microbiota and its immune system can significantly influence vector competence (Farajollahi, 2011). For instance, certain microorganisms in the mosquito's gut can modulate the immune response, thereby affecting the mosquito's ability to transmit diseases. Additionally, genetic factors and the mosquito's evolutionary history also contribute to its susceptibility to different pathogens (Mitri and Vernick, 2012). 2.2 Lifecycle of mosquitoes: implications for disease spread The lifecycle of mosquitoes consists of four stages: egg, larva, pupa, and adult (Brugueras et al., 2020). The duration of each stage can vary depending on environmental conditions such as temperature and humidity. The adult stage is particularly significant for disease transmission, as only adult female mosquitoes feed on blood. The frequency and preference for blood meals can greatly influence the spread of diseases. For example, species like Anopheles gambiae and Aedes aegypti are known to take multiple blood meals during a single gonotrophic cycle, which increases their potential to transmit pathogens (Wilke et al., 2020). The lifecycle of mosquitoes also includes a process called sporogony, particularly in the case of malaria transmission by Anopheles mosquitoes. During sporogony, the malaria parasite undergoes several developmental stages within the mosquito, including gametocyte ingestion, fertilization in the midgut, and sporozoite formation in the salivary glands (Benelli et al., 2016). This complex lifecycle creates multiple bottlenecks, making it challenging for the parasite to complete its development and be transmitted to a new host (Beier, 1998). 2.3 Key species involved in human pathogen transmission Several mosquito species are key vectors of human pathogens. The Culex pipiens complex, for instance, includes species such as Culex pipiens and Culex quinquefasciatus, which are principal vectors of West Nile virus and St. Louis encephalitis virus. These species are highly adaptable to urban and suburban environments, contributing to their widespread distribution and role in disease transmission. Aedes aegypti and Aedes albopictus are other significant vectors, known for transmitting viruses such as dengue, Zika, and chikungunya. These species are highly invasive and have adapted well to urban environments, increasing their potential to spread diseases (Scott and Takken, 2012). Anopheles gambiae is the primary vector for malaria, and its vector competence is influenced by genetic, ecological, and immunological factors (Kain et al., 2022). Understanding the biology and vector competence of these key mosquito species is essential for developing effective control strategies to reduce the burden of mosquito-borne diseases (Gabrieli et al., 2021). 3 Pathogen Acquisition by Mosquitoes 3.1 Mechanisms of pathogen ingestion during blood feeding Mosquitoes acquire pathogens primarily through the ingestion of blood from an infected host. During blood feeding, mosquitoes ingest various pathogens, including viruses, bacteria, and parasites, which are present in the host's blood. For instance, arboviruses are acquired by naive mosquitoes from infected hosts during blood meals, and these viruses then propagate extensively within the mosquito's tissues. Similarly, malaria parasites are ingested by mosquitoes in the gametocyte stage during blood feeding on an infected host. These parasites undergo fertilization in the mosquito midgut, transforming into ookinetes, oocysts, and eventually sporozoites, which are then transmitted to a new host during subsequent blood meals (Beier, 1998).
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