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Epidemiology, Disease Transmission, Prevention, and Control
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
It is sometimes possible to interrupt transmission by acting on the reservoir of infection. Rats are controlled to prevent plague in man, for example. The vector of a disease may be a target. Destroying Anopheles mosquitoes by spraying or source reduction or by using a mosquito net to act as a barrier between the mosquitoes and the human host will often prevent malaria (Figure 21.8). If the reservoir is a human, isolation may accompany therapy to prevent spread of infection until treatment is completed.
Vector-Borne Disease Surveillance
Published in Jerome Goddard, Public Health Entomology, 2022
Adult mosquitoes, especially Anopheles, can be found during the daytime resting in both natural and artificial shelters. These areas include houses, barns, sheds, privies, bridges, culverts, hollow trees, overhanging cliffs, and foliage. Counts of mosquitoes utilizing daytime resting shelters can give a good indication of population density. Mosquitoes found in these shelters can be easily collected with an aspirator. In areas where no resting shelters are found, an investigator may install an artificial shelter such as a wooden box, approximately 60 cm x 60 cm, so that these sites can be routinely sampled. Many mosquitoes that do not usually bite can be collected in this way.
The Search for the Host
Published in Jacques Derek Charlwood, The Ecology of Malaria Vectors, 2019
Among the Anopheles, biting activity is also distributed unevenly throughout the night. In Africa, the vectors tend to bite late at night when their preferred hosts, humans, are asleep and therefore unlikely to indulge in defensive behaviours (Figure 3.2).
Plasmodium infection and drug cure for malaria vaccine development
Published in Expert Review of Vaccines, 2021
Reshma J. Nevagi, Michael F. Good, Danielle I. Stanisic
Malaria is transmitted to humans through the bite of a Plasmodium spp.-infected female Anopheles mosquito. During a bloodmeal, sporozoites in the salivary glands of the mosquito are transferred into the dermis of human skin (Figure 1) [2]. They then migrate to the liver via the bloodstream, infect hepatocytes and mature into hepatic schizonts. P. vivax and P. ovale have dormant liver-stage parasites (hypnozoites) that may reactivate, leading to relapses months or even years after the recovery of patients from the first episode of malaria. Upon rupture of an infected hepatic schizont, tens of thousands of merozoites are released into the bloodstream where they invade erythrocytes and continue to develop through the different erythrocytic stages (rings, trophozoites and schizonts), before the erythrocyte ruptures to release daughter merozoites. These merozoites also invade erythrocytes and the ongoing cycles of asexual replication enable parasite growth in the blood. During each replication cycle, some of the parasites develop into sexual-stage gametocytes which are ingested by mosquitoes during a bloodmeal. In the mosquito, male and female gametocytes mate within the gut forming diploid zygotes, which then become ookinetes. The ookinetes migrate to the midgut of the mosquito, pass through the gut wall and form oocysts. Sporozoites are formed after meiotic division of the oocysts. Sporozoites migrate to the salivary glands of the female Anopheles mosquito, ready to transmit the infection to another human host and continue the cycle of transmission.
Transmission-Blocking Vaccines: Harnessing Herd Immunity for Malaria Elimination
Published in Expert Review of Vaccines, 2021
Family compounds could suffice as clusters to measure herd protection in some settings, if infections circulate at that level. This could occur within individual households in some areas, based on the behavior of female Anopheles mosquitoes. Female mosquitoes blood-feed and then oviposit within a few days at the nearest water source, raising the prospect that they might preferentially return to the same family compound. Data support the possibility of household transmission: risk of infection for an individual is related to the infection status of other household members [105]; malaria infections cluster within households [106,107]; single-household clusters can persist for months [108]; and in general, Anopheles movement extends less than 2 km [109]. Mosquitoes may limit their movement when sites for oviposition are nearby and readily accessible, and this possibility should be evaluated as a criterion for selecting vaccination clusters.
Structural vaccinology of malaria transmission-blocking vaccines
Published in Expert Review of Vaccines, 2021
Transmission of parasites from one human to another relies on the generation of male and female gametocytes in the human host [4] (Figure 1(a)). These sexual stage parasites are ingested during a blood meal by an Anopheles mosquito and differentiate within the mosquito midgut to form microgametes and macrogametes. Microgametes then penetrate macrogametes to form zygotes, which then develop into motile and elongated ookinetes. Ookinetes invade the midgut wall of the mosquito where they develop into oocysts, which then grow, rupture, and release sporozoites. Sporozoites ultimately relocate to the mosquito’s salivary glands, enabling inoculation into the next human host to continue the malaria life cycle and transmission of disease (Figure 1(a)) (https://www.cdc.gov/malaria/about/biology/index.html).