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Correlation between Larvicide Susceptibility and Quiescence in Aedes aegypti

Description

Mosquitoes are estimated to kill roughly 700,000 people each year through the transmission of vector-borne diseases. Vector control via insecticides is a widely used method in order to combat the spread of mosquito populations; however, this comes at a cost.

Mosquitoes are estimated to kill roughly 700,000 people each year through the transmission of vector-borne diseases. Vector control via insecticides is a widely used method in order to combat the spread of mosquito populations; however, this comes at a cost. Resistance to insecticides has the potential to increase vector-borne disease rates. Aedes aegypti is an invasive mosquito species in Arizona and is a known potential vector for a variety of infectious diseases including dengue, chikungunya, Zika, and yellow fever. In contrast to many other mosquito species Ae. aegypti mosquito eggs can undergo quiescence, an active state of dormancy, over long periods of time. Variation in quiescent periods correlates to climatic rainfall alterations and can ultimately influence hatching and mating between multiple generations. I have studied the effect of quiescence on larvicide (i.e., temephos) susceptibility using mosquito eggs collected from a susceptible lab strain and stored under optimal temperature and humidity conditions. After undergoing various quiescent periods (3, 7, 14, 28, 84, and 182 days), the experimental eggs as well as 7-day quiescent control eggs were hatched and reared to 3rd instar larvae. Temephos susceptibility was tested using the WHO bioassay procedure at lethal concentration (LC) 20, LC50, LC80, diagnostic dose (twice LC99), plus an untreated control. Each concentration dose was replicated four times with 20 larvae each. The 3-day experimental group was excluded from analysis because the mortality was significantly lower than the 7-day for both the experimental and control groups. The 3 day experimental eggs displayed decreased mortality which did not align with the hypothesis, as the quiescence period elongates under optimal conditions, susceptibility to insecticides decreases, and this could have likely resulted from unintentional selection for increased fitness and faster developing eggs because the larvae that developed to 3rd instar first were those used for larvicide testing. ANOVA testing demonstrates variability in the LC80 experimental group which suggests the need for further investigation into high dose temephos concentrations. For the experimental LC20 linear regression, there were significant differences in mortality. The results indicate mortality gradually decreases when the quiescence period elongates, therefore there are significant differences in insecticide susceptibility when quiescence is 182 days (or longer), compared to when quiescence is 7 days. Further investigation into field mosquito’s genetic diversity, insecticide resistance profile, and environmental conditions should be considered.

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2021-05

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Plasmodium Cost of Resistance and Life Stage Development within the Mosquito Vector

Description

Hundreds of thousands of people die annually from malaria; a protozoan of the genus Plasmodium is responsible for this mortality. The Plasmodium parasite undergoes several life stages within the mosquito vector, the transition between which require passage across the lumen

Hundreds of thousands of people die annually from malaria; a protozoan of the genus Plasmodium is responsible for this mortality. The Plasmodium parasite undergoes several life stages within the mosquito vector, the transition between which require passage across the lumen of the mosquito midgut. It has been observed that in about 15% of parasites that develop ookinetes in the mosquito abdomen, sporozoites never develop in the salivary glands, indicating that passage across the midgut lumen is a significant barrier in parasite development (Gamage-Mendis et al., 1993). We aim to investigate a possible correlation between passage through the midgut lumen and drug-resistance trends in Plasmodium falciparum parasites. This study contains a total of 1024 Anopheles mosquitoes: 187 Anopheles gambiae and 837 Anopheles funestus samples collected in high malaria transmission areas of Mozambique between March and June of 2016. Sanger sequencing will be used to determine the prevalence of known resistance alleles for anti-malarial drugs: chloroquine resistance transporter (pfcrt), multidrug resistance (pfmdr1) gene, dihydropteroate synthase (pfdhps) and dihydrofolate reductase (pfdhfr). We compare prevalence of resistance between abdomen and head/thorax in order to determine whether drug resistant parasites are disproportionately hindered during their passage through the midgut lumen. A statistically significant difference between resistance alleles in the two studied body sections supports the efficacy of new anti-malarial gene surveillance strategies in areas of high malaria transmission.

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2021-05

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Aedes aegypti Thermal Choice Experiment

Description

The non-native mosquito Aedes aegypti has become a common nuisance in Maricopa county. Associated with human settlement, Ae. aegypti is known to reproduce in standing water sources both indoors and outdoors, within vessels such as tires, flowerpots, and neglected swimming

The non-native mosquito Aedes aegypti has become a common nuisance in Maricopa county. Associated with human settlement, Ae. aegypti is known to reproduce in standing water sources both indoors and outdoors, within vessels such as tires, flowerpots, and neglected swimming pools (Jansen & Beebe, 2010). Ae. aegypti and the related Ae. albopictus are the primary vectors of the arboviral diseases chikungunya, Zika, yellow fever and dengue. Ae. aegypti tends to blood feed multiple times per gonotrophic cycle (cycle of feeding and egg laying) which, alongside a preference for human blood and close association with human habitation, contributes to an increased risk of Ae. aegypti borne virus transmission (Scott & Takken, 2012). Between 2010-2017, 153 travel-associated cases of dengue were reported in the whole of Arizona (Rivera et al., 2020); while there have been no documented locally transmitted cases of Aedes borne diseases in Maricopa county, there are no apparent reasons why local transmission can’t occur in the future via local Aedes aegypti mosquitoes infected after feeding from travelling viremic hosts. Incidents of local dengue transmission in New York (Rivera et al., 2020) and Barcelona (European Center for Disease Control [ECDC], 2019) suggest that outbreaks of Aedes borne arbovirus’ can occur in regions more temperate than the current endemic range of Aedes borne diseases. Further, while the fact that Ae. aegypti eggs have a high mortality rate when exposed to cold temperatures limits the ability for Ae aegypti to establish stable breeding populations in temperate climates (Thomas, Obermayr, Fischer, Kreyling, & Beierkuhnlein, 2012), global increases in temperature will expand the possible ranges of Ae aegypti and Aedes borne diseases.

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2020-05

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Mathematical Assessment of the Impact of Insecticide-Based Intervention on Malaria Transmission Dynamics

Description

Malaria is a deadly, infectious, parasitic disease which is caused by Plasmodium parasites and transmitted between humans via the bite of adult female Anopheles mosquitoes. The primary insecticide-based interventions used to control malaria are indoor residual spraying (IRS) and long-lasting

Malaria is a deadly, infectious, parasitic disease which is caused by Plasmodium parasites and transmitted between humans via the bite of adult female Anopheles mosquitoes. The primary insecticide-based interventions used to control malaria are indoor residual spraying (IRS) and long-lasting insecticide nets (LLINs). Larvicides are another insecticide-based intervention which is less commonly used. In this study, a mathematical model for malaria transmission dynamics in an endemic region which incorporates the use of IRS, LLINS, and larvicides is presented. The model is rigorously analyzed to gain insight into the asymptotic stability of the disease-free equilibrium. Simulations of the model show that individual insecticide-based interventions will not realistically control malaria in regions with high endemicity, but an integrated vector management strategy involving the use of multiple interventions could lead to the effective control of the disease. This study suggests that the use of larvicides alongside IRS and LLINs in endemic regions may be more effective than using only IRS and LLINs.

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2022-05