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KRISTAL DALE F. CORPUZ – #6536448
Malaria is one of the most prevalent and sometimes fatal disease that is caused by Plasmodium spp. which uses mosquitoes (Anopheles spp.) to transmit and infect human often via blood-meal of the infective female mosquito. Cases usually occurs in warm regions (tropical and subtropical) including Thailand, but the species of vector and pathogen may vary. Based on literatures, only Anopheles spp. can transmit the pathogen and cause malaria. On the other hand, Aedes aegypti which is also an important mosquito species, has the capacity to carry and transmit viruses that can cause dengue, yellow fever, Zika, and Chikungunya. Same with malaria transmission, these viruses infect a human through blood-meal of the infective female Aedes mosquito. In this scenario, vector-pathogen or parasite relationship is evident. Aedes aegypti is not a malaria vector in Thailand because some factors affects the vector-parasite relationship which includes the transmission cycle, parasite-infection specificity, and the mosquito immune defenses. In the first place, Aedes spp. is not a primary vector of malaria which means for one that the pathogen’s infective stage can not be detected in the mosquito (although some current literature found out that there might be some cases of detection but the pathogen still failed to further develop to be able to get transmitted). In terms of parasite-infection specificity or the outcome of exposure of the Aedes aegypti to Plasmodium spp., it is as refractory wherein the pathogen fails to initiate development inside the mosquito due to its physiological and/or biochemical incompatability. Lastly, the Aedes aegypti’s innate immunity and the pathogen’s response to this determine the incompatability and beneficial trade-off. In summary, Aedes aegypti’s inability to be a malaria vector is attributed to its vector competence which subsequently affects the vectorial capacity of the said mosquito.
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KRISTAL DALE F. CORPUZ – #6536448
The transmission pattern of pathogen by mosquitoes as the vector (organism that could transmit a pathogen) and/or as definitive host (harbors the parasite for sexual reproduction and development) refers to the process wherein a pathogen is transferred or transmitted to a susceptible organism usually serving as an intermediate host (harbors the larval stage or asexual form of pathogen) that could lead to the manifestations of a mosquito-borne disease.
By means of transmission mechanism, a pathogen can be transmitted via [i] parent-to-offspring (vertical transmission), [ii] biting (horizontal transmission), and [iii] mating of mosquitoes (venereal transmission). Parent-to-offspring transmission gives way for the pathogen from the adult mosquito to be transferred directly either to the eggs or in the embryo; Through biting or blood-meal, the mosquito can either inject the pathogen inside another organism (e.g. human) and undergo intrinsic incubation until the onset of symptoms of a disease, or the other way around to which the mosquito ingests the pathogen from human and undergo extrinsic incubation inside the mosquito; And in terms of mating, adult mosquitoes can be both infected by the pathogen present in either of them.
Upon ingestion, depending on the pathogen, different mosquito parts or compartments (oral, gut, salivary gland, fecal, hemolymph) are infected leading to different routes to which transmission is made possible. Although it could be simply passing the pathogen to another organism, it can also be influenced by some factors including changes in the environment (climate, geography, temperature, other biotic and abiotic components), vector or mosquito behavior (host-seeking and biting, extrinsic incubation, sporogonic cycle, distribution and movement, longevity, susceptibility to pathogen), societal changes, as well as population movement and density especially of the intermediate hosts. These factors play importance in the whole transmission pattern and cycle because certain changes could be drivers for e.g. increased transmission rate, shortening of incubation period, erratic disease distribution and prevalence.
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KRISTAL DALE F. CORPUZ – #6536448
In general, flies are part of the Class Insecta and Order Diptera which is a paraphyletic grouping of the most primitive flies characterized by having three body regions (head, thorax, abdomen), three pairs of legs, typically two functional wings, and one pair of antennae with more antennal segments than the other orders. Some flies can transmit a pathogen that can potentially cause a disease in animals or human which includes the biting midges (Family Ceratopogonidae, Genus Culicoides). Biting midges undergo complete metamorphosis from adult laying eggs to larva to pupa and finally an adult again. The adult biting midges’ distinguishing features are: small (2-5 mm) and dark, long filamentous antenna with 15 segments, hooped thorax with humeral pits and bears a pair of spotted or broad mottled wings without scales, lacks proboscis which set them apart from mosquitoes but mouthpart is composed of three pairs of cutting and slashing elements that causes wound. Only the female adult takes a blood-meal necessary for the maturation of eggs, while both male and female feed on nectar, and biting behavior is usually observed during dusk or dawn often in swarms in nearby water. Aside from the biting nuisance and stress, various Culicoides species have been documented to be vectors of different pathogens: Mansonella spp. (Mansonellosis), Orbiviruses, bluetongue virus (BTV), epizootic hemorrhagic disease virus (EHDV), African horse sickness virus (AHSV), Orthobunyaviruses, Oropouche virus (OROV), Akabane virus (AKAV), Schmallenberg virus (SBV), bovine ephemeral fever, Plasmodium agamae, and Leucocytozoon. Culicoides transmit pathogens when adult female takes infected blood-meal, and after laying eggs will be ready to feed again which could involve transmission of the pathogenic organism in the animal or human host.
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KRISTAL DALE F. CORPUZ – #6536448
In general, flies are part of the Class Insecta and Order Diptera which is a paraphyletic grouping of the most primitive flies characterized by having three body regions (head, thorax, abdomen), three pairs of legs, typically two functional wings, and one pair of antennae with more antennal segments than the other orders. Some flies can transmit a pathogen that can potentially cause a disease in animals or human which includes the biting midges (Family Ceratopogonidae, Genus Culicoides). The adult biting midges’ distinguishing features are: small (2-5 mm) and dark, long filamentous antenna with 15 segments, hooped thorax with humeral pits and bears a pair of spotted or broad mottled wings without scales, lacks proboscis which set them apart from mosquitoes but mouthpart is composed of three pairs of cutting and slashing elements that causes wound. Only the female adult takes a blood-meal necessary for the maturation of eggs, while both male and female feed on nectar, and biting behavior is usually observed during dusk or dawn often in swarms in nearby water. Aside from the biting nuisance and stress, various Culicoides species have been documented to be vectors of different pathogens: Mansonella spp. (Mansonellosis), Orbiviruses, bluetongue virus (BTV), epizootic hemmorhagic disease virus (EHDV), African horse sickness virus (AHSV), Orthobunyaviruses, Oropouche virus (OROV), Akabane virus (AKAV), Schmallenberg virus (SBV), bovone ephemeral fever, Plasmodium agamae, Leucocytozoon. Culicoides transmit pathogens when adult female takes infected blood-meal and after laying eggs will be ready to feed again which could involve transmission of the pathogenic organism in the animal or human host.
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KRISTAL DALE F. CORPUZ – Student ID: 6536448
1. How the mosquito can transmit the pathogen?
Not all species of mosquito transmit a pathogen, but in order to do so, a mosquito should be a susceptible arthropod (insect). Inside the mosquito, the parasite’s oocysts develop in the gut until the sporozoites transfer to the salivary gland. Through biological transmission or when the mosquito bites, the sporozoites (infective stage) will be injected into the human (intermediate host) where it will continue its developmental stages. The pattern of pathogen transmission can be identified as (a) vertical – from adult vector to egg, (b) horizontal – from biting host 1 to host 2, and (c) venereal – through mating of vector.2. What tool and how to determine the malaria transmission?
Vector surveillance is a useful tool or method in gathering information regarding (for example) the malaria transmission. Through this method, observations will be made considering the mosquito biting behavior, biting frequency profile, adult and larval mosquito capture, and cases of malaria incidence. Aside from the principle and importance of the vectorial capacity, the EIR and IRR can also be used as indicators in understanding and monitoring the risk of transmission in a given area.
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