Editorial: 2022 in review: vector biology

Résumé

Aedes aegypti mosquito by estimating critical parameters of vectorial capacity (vector abundance, human blood feeding rates, survivorship) that modulate transmission risk of dengue ─ the most widespread arboviral disease of humans globally which is expected to increase with projected population increase coupled with climate change and geographic expansion of the key vector (1). The study focused on Ae. aegypti populations in two environments in Kenya: peri-urban Rabai (coastal Region, dengue-endemic) and rural Kerio Valley (Rift Valley Region, no reported dengue outbreak). Correlations were then explored between each of these parameters and satellite derived weather parameters notably temperature, rainfall, and relative humidity. Results found differential survival abilities between populations in Rabai and Kerio Valley. Both vector abundance and human bloodfeeding rates were consistently lower in Kerio Valley indicating that dengue virus transmission risk could be strongly related to the degree of urbanization (1,2). In both environments, a negative association of Ae. aegypti survival (estimated by parity) and abundance modulated by weather conditions, notably temperature and relative humidity, was evident. These bionomic traits could be integrated with suitable ecological parameters into a modelling framework for risk prediction of dengue outbreak occurrence and spread trajectory.In their research article Gonçalves et al 2023, characterized the blood feeding patterns of the malaria (Anopheles arabiensis) and arboviral (Ae. aegypti, and Culex pipiens sensu lato (s.l.)) vectors employing enzyme-linked immunosorbent assay. The specimens were surveyed in three Santiago Island municipalities of Cape Verde (Praia, Santa Cruz, and Santa Catarina).The outcome, mainly single-host blood meals depict high human blood feeding for Ae. 44 consistent with the high anthropophagic tendency reported in literature (3); with An. 45 arabiensis exhibiting low levels of human feeding. pipiens s.l. was more random in its 46 trophic outlook compared to the other mosquito species despite high likelihood of human 47 feeding. Interestingly, strong negative association of Cx. pipiens s.l. feeding on dogs and goats was uncovered, similar to the An. arabiensis-human host relationship. Blood feeding 49 patterns generally assessed via blood meal analyses, reflect mosquito-host associations under 50 the influence of biologic and environmental factors (3,4). Thus, quantifying the strength of 51 such relationships should consider the effect of genetics, habitat, and seasonal host 52 adult host-seeking mosquitoes and the others mainly resting cohorts (PSC, CPs) or exiting 62 mosquitoes (WETs). An assessment of the other methods as alternative to HLC was made but 63 it was proposed that caution should be exercised in the interpretation of results because of the 64 likelihood of bias inherent in the different mosquito cohorts being targeted (host seeking vs 65 resting/exiting). Not all anophelines enter houses to allow for fair comparative assessments. A 66 record of higher anopheline richness and abundance both indoors and outdoors in HLC is not 67 unexpected as it remains superior in trapping species that prefer humans (5). It remains the 68 gold standard when incriminating anopheline species that can bite humans and so associated 69 with human malaria parasite transmission (5). Although inferior to HLC and targeting host 70 seeking mosquitoes, CDC-LTs are being considered as alternatives owing to ethical issues 71 with the former but efficiency can be improved by use of olfactory cues like carbon dioxide 72 or other host-derived odors (6). 73 74form) and (S)-(+)-(S-form) of the compound 1-octen-3-ol including the racemic mixture for 76 improved trapping of adult sandflies, vectors of Leishmania parasites that cause leishmaniasis 77 in humans, is reported. The isomers have been found to elicit differential behavioral 78 responses in other blood feeding insects such as mosquitoes. Because, the isomers are 79 commercially expensive, an elaborate procedure is described to synthesize the individual 80 isomers including enzymatic resolution of the enantiomeric mixtures incorporating a suite of 81 chemical analytical techniques. These include coupled gas chromatography (GC) and nuclear 82 magnetic resonance (NMR). Field trials using the individual compounds as baits in CDC light 83 traps revealed a higher sensitivity for R-compared to S-form only in Phlebotomus martini, 84 the vector of the Leishmania parasites that cause visceral leishmaniasis, a neglected tropical 85 disease which can be fatal if left untreated (7). This was evident in significantly increased 86 captures of the species but not in others dominated by Sergentomyia species. Sandflies in this latter genus are not known to be competent vectors of leishmaniasis. In practical terms, this specific isomer can incorporated in conventional traps to selectively enhance capture of 89 this species. This would be beneficial to surveillance programs. 90Overall, the collection highlighted the importance of active vector population 91 surveillance central to risk mapping of vector-borne diseases and guiding suitable control 92 strategies. Expansion of vector range is correlated with emergence of pathogens in humans. 93Particular attention is paid to data collection through active surveillance of key traits that 94 modulate the risk of disease transmission and spread and provide insights into differential 95 occurrence trends. Given the sporadic transmission foci (e.g., arboviruses) or low 96 transmission (e.g. malaria) in some settings deployment of sensitive vector monitoring of 97 adult populations is critical for the accurate assessment of disease epidemiology considering 98 pathogen infections, vector abundance and movement. Such sensitivity could be achieved by 99 further exploring the olfactory cues that mediate chemical communication in diverse disease 100 vectors (6).

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