Anopheles drivers of persisting malaria transmission in Guna Yala, Panamá: an operational investigation

Background Though most of Panamá is free from malaria, localized foci of transmission persist, including in the Guna Yala region. Government-led entomological surveillance using an entomological surveillance planning tool (ESPT) sought to answer programmatically-relevant questions that would enhance the understanding of both local entomological drivers of transmission and gaps in protection that result in persisting malaria transmission to guide local vector control decision-making. Methods The ESPT was used to design a sampling plan centered around the collection of minimum essential indicators to investigate the relevance of LLINs and IRS in the communities of Permé and Puerto Obaldía, Guna Yala, as well as to pinpoint any remaining spaces and times where humans are exposed to Anopheles bites (gaps in protection). Adult Anopheles were collected at three time points via human landing catches (HLCs), CDC Light Traps (LT), and pyrethrum spray catches (PSCs) during the rainy and dry seasons. Mosquitoes were identified to species via molecular methods. Insecticide susceptibility testing of the main vector species to fenitrothion was conducted. Results In total, 7537 adult Anopheles were collected from both sites. Of the 493 specimens molecularly confirmed to species, two thirds (n = 340) were identified as Nyssorhynchus albimanus, followed by Anopheles aquasalis. Overall Anopheles human biting rates (HBRs) were higher outdoors than indoors, and were higher in Permé than in Puerto Obaldía: nightly outdoor HBR ranged from 2.71 bites per person per night (bpn) (Puerto Obaldía), to 221.00 bpn (Permé), whereas indoor nightly HBR ranged from 0.70 bpn (Puerto Obaldía) to 81.90 bpn (Permé). Generally, peak biting occurred during the early evening. The CDC LT trap yields were significantly lower than that of HLCs and this collection method was dropped after the first collection. Pyrethrum spray catches resulted in only three indoor resting Anopheles collected. Insecticide resistance (IR) of Ny. albimanus to fenitrothion was confirmed, with only 65.5% mortality at the diagnostic time. Conclusion The early evening exophagic behaviour of Anopheles vectors, the absence of indoor resting behaviours, and the presence of resistance to the primary intervention insecticide demonstrate limitations of the current malaria strategy, including indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs), and point to both gaps in protection and to the drivers of persisting malaria transmission in Guna Yala. These findings highlight the need for continued and directed entomological surveillance, based on programmatic questions, that generates entomological evidence to inform an adaptive malaria elimination strategy.

Study of behavioral patterns and infection analyses in anopheline species involved in the transmission of malaria in Buriticupu and São José de Ribamar municipality, Maranhão State, Brazil

Anopheles darlingi Root and Anopheles aquasalis Curry are the main vectors of malaria that occur in the State of Maranhão. Entomological surveys based on the behavior and infectivity of these vectors are important for the elaboration of disease control strategies. The objectives of this work were to study the behavioral patterns of mosquitoes, determining population and hematophagic peaks, dietary preferences, infectivity rate and characterization of breeding sites in two municipalities in the State of Maranhão: Buriticupu and São José of Ribamar. Larvae and pupae were collected in breeding sites and adult females in home environments. Mosquito behavior, their dietary preferences and Plasmodium spp infection rates were analyzed. The vegetation and physicochemical patterns in the breeding sites found are in agreement with those described for species from the Amazon region and the Brazilian Atlantic coast. Anopheles darlingi was the most prevalent mosquito in Buriticupu breeding and home environments. This species was found mainly fed on human blood and naturally infected with Plasmodium vivax Grassi & Feletti and Plasmodium falciparum Welch. Anopheles aquasalis was more frequent in breeding sites in São José de Ribamar, as well as in home environments, whose specimens were mainly fed with human and bird blood. The main peaks of mosquito occurrence in Buriticupu were between 6 pm to 9 pm and in São José de Ribamar we did not record a definite peak. In the first municipality A. darlingi showed dominance over Anopheles albitarsis Lynch Arribálzaga s.l., Anopheles oswaldoi Peryassú, Anopheles nuneztovari Gabaldón and Anopheles evansae Brèthes,, besides presenting a correlation with rainfall. In the second municipality, A. aquasalis was dominant over A. albitarsis s.l. and there was a correlation between these two species and the rainy season. We conclude that the collected data contribute to elucidate the dynamics of malaria transmission in the region and guide the control actions directed to the elimination of the disease in the country.

Microanatomy of the American Malaria Vector Anopheles aquasalis (Diptera: Culicidae: Anophelinae) Midgut: Ultrastructural and Histochemical Observations

The mosquito gut is divided into foregut, midgut, and hindgut. The midgut functions in storage and digestion of the bloodmeal. This study used light, scanning (SEM), and transmission (TEM) electron microscopy to analyze in detail the microanatomy and morphology of the midgut of nonblood-fed Anopheles aquasalis females. The midgut epithelium is a monolayer of columnar epithelial cells that is composed of two populations: microvillar epithelial cells and basal cells. The microvillar epithelial cells can be further subdivided into light and dark cells, based on their affinities to toluidine blue and their electron density. FITC-labeling of the anterior midgut and posterior midgut with lectins resulted in different fluorescence intensities, indicating differences in carbohydrate residues. SEM revealed a complex muscle network composed of circular and longitudinal fibers that surround the entire midgut. In summary, the use of a diverse set of morphological methods revealed the general microanatomy of the midgut and associated tissues of An. aquasalis, which is a major vector of Plasmodium spp. (Haemosporida: Plasmodiidae) in America.

The Basic Plan of the Adult Heart Is Conserved Across Different Species of Adult Mosquitoes, But the Morphology of Heart-Associated Tissues Varies

The heart is a pivotal organ in insects because it performs a number of different tasks, such as circulating nutrients, hormones, and excreta. In this study, the morphologies of the heart and associated tissues, including pericardial cells (PCs) and alary muscles (AMs), in the hematophagous mosquitoes Anopheles aquasalis Curry (Diptera: Culicidae), Aedes aegypti L. (Diptera: Culicidae), and Culex quinquefasciatus Say (Diptera: Culicidae), and the phytophagous Toxorhynchites theobaldi Dyar & Knab (Diptera: Culicidae) were compared using different microscopy techniques. Mosquito hearts are located across the median dorsal region of the whole abdomen. Paired incurrent openings in the heart wall (ostia) are found in the intersegmental regions (segments 2–7) of the abdomen, while an excurrent opening is located in the terminal cone of Ae. aegypti. The sides of the heart contain PC that are more numerous in An. aquasalis and Th. theobaldi. In these two species, PC form a cord of as closely aggregated cells, but in Ae. aegypti and Cx. quinquefasciatus, PC occur in pairs with two or four PC pairs per intersegmental region. In Th. theobaldi, AM binds to all regions of the heart, whereas in other mosquitoes they only bind in the intersegmental regions. The basic plan of the adult heart was conserved across all the adult mosquitoes investigated in this study. This conserved organization was expected because this organ plays an important role in the maintenance of individual homeostasis. However, the species had different PC and of AM morphologies. These morphological differences seem to be related to distinct physiological requirements of mosquito circulatory system.