Optimization of the feeding rate of Anopheles farauti s.s. colony mosquitoes in direct membrane feeding assays

Effects of Carbohydrate Intake on Anopheles darlingi and Anopheles deaneorum Fitness under Lab-Reared Conditions

The maintenance of a highly productive colony of anopheline mosquitoes requires standardized methods in order to obtain a sufficient number of homogeneous individuals for malaria research. In this context, nutritional status may affect survival, fecundity, and the capacity to support pathogen development. Here we assess the effects of carbohydrate sources on fecundity, survival, and susceptibility to Plasmodium vivax infection in colonies of Anopheles darlingi and Anopheles deaneorum mosquitoes. Newly emerged females from each species were fed either 10% sugar or 15% honey solutions until the end of each experiment. The type of carbohydrate meal did not impact any entomological parameters for An. deaneorum, except for survival. For both species, honey meal significantly increased median survival post-emergence by three to four days, probably due to its nutritional value. For An. darlingi fed with honey, a higher mean frequency in stage 5 was observed at 48 h post-blood-meal, which could indicate a delay in the digestion process. However, no effects on fecundity parameters were observed. Regarding susceptibility, An. darlingi fed with sugar exhibited a low intensity of sporozoites, although any negative effects of sucrose on sporozoites invasions in the salivary glands are unknown. Based on the increase in mosquito survival, a carbohydrate source composed of 15% honey solution could be better for maintaining An. darlingi and An. deaneorum in the lab-rearing context.

Infectivity of symptomatic Plasmodium vivax cases to different generations of wild-caught and laboratory-adapted Anopheles arabiensis using a membrane feeding assay, Ethiopia

When measuring human to mosquito transmission of Plasmodium spp., laboratory-adapted (colony) mosquitoes can be utilized. To connect transmission studies to the local epidemiology, it can be important to comprehend the relationship between infectivity in laboratory-adapted (colony) and wild-caught (wild) mosquitoes of the same species. Microscopically confirmed Plasmodium vivax cases were recruited from health facilities in Arba Minch town, and a nested polymerase chain reaction (nPCR) was used for subsequent confirmation. We performed paired membrane-feeding assays using colony An. arabiensis and three generations of wild origin An. arabiensis. Anopheles arabiensis aged 3-6 days were fed after being starved for 8-14 h. Microscopically, the oocyst development was evaluated at day 7 after feeding. Circumsporozoite proteins (CSPs) assay was carried out by enzyme-linked immunosorbent assay (ELISA). In 19 paired feeding experiments, the feeding efficiency was more than doubled in colony (median: 62.5%; interquartile range, IQR: 35-78%) than in wild mosquitoes (median: 28.5%; IQR: 17.5-40%; P < 0.001). Among the 19 P. vivax gametocyte-positive blood samples, 63.2% (n = 12) were infective to wild An. arabiensis and 73.7% (n = 14) were infective to colony An. arabiensis. The median infection rate was twice as high (26%) in the colony than in the wild (13%) An. arabiensis, although the difference was marginally insignificant (P = 0.06). Although the observed difference was not statistically significant (P = 0.19), the median number of oocysts per midgut was more than twice as high (17.8/midgut) in colony than in wild (7.2/midgut) An. arabiensis. The median feeding efficiency was 26.5% (IQR: 18-37%) in F1, 29.3% (IQR: 28-40%) in F2 and 31.2% (IQR: 30-37%) in F3 generations of wild An. arabiensis. Also, no significant difference was observed in oocyst infection rate and load between generations of wild An. arabiensis. CSP rate of P. vivax was 3.1% (3/97; 95% CI: 0.6-8.8%) in wild and 3.6% (3/84; 95% CI: 0.7-10.1%) in colony An. arabiensis. The results of the present study revealed that oocyst infection and load/midgut, and CSP rate were roughly comparable, indicating that colony mosquitoes can be employed for infectivity studies, while larger sample sizes may be necessary in future studies.

Comparative analysis of glass and Hemotek membrane feeding systems for malaria transmission research

BACKGROUND

Glass membrane feeders are used in malaria research for artificial blood feeding. This study investigates the use of Hemotek membrane feeders as a standardized alternative feeding system.

METHODS

Hemotek feeders were compared with glass feeders by assessing mosquito feeding rate, imbibed blood meal volume and Plasmodium falciparum infection intensity on mosquito guts.

RESULTS

While mosquito feeding rate and blood meal volume were comparable between Hemotek and glass feeders, a loss in transmission was observed using the Hemotek feeder with a conventional collagen membrane. There was no difference in transmission between both feeders when Parafilm was used as the membrane.

CONCLUSIONS

Hemotek feeders with a Parafilm membrane can be used as an alternative feeding system for malaria transmission research.

Asia-Pacific ICEMR: Understanding Malaria Transmission to Accelerate Malaria Elimination in the Asia Pacific Region

Gaining an in-depth understanding of malaria transmission requires integrated, multifaceted research approaches. The Asia-Pacific International Center of Excellence in Malaria Research (ICEMR) is applying specifically developed molecular and immunological assays, in-depth entomological assessments, and advanced statistical and mathematical modeling approaches to a rich series of longitudinal cohort and cross-sectional studies in Papua New Guinea and Cambodia. This is revealing both the essential contribution of forest-based transmission and the particular challenges posed by Plasmodium vivax to malaria elimination in Cambodia. In Papua New Guinea, these studies document the complex host-vector-parasite interactions that are underlying both the stunning reductions in malaria burden from 2006 to 2014 and the significant resurgence in transmission in 2016 to 2018. Here we describe the novel analytical, surveillance, molecular, and immunological tools that are being applied in our ongoing Asia-Pacific ICEMR research program.

Modified World Health Organization (WHO) Tunnel Test for Higher Throughput Evaluation of Insecticide-Treated Nets (ITNs) Considering the Effect of Alternative Hosts, Exposure Time, and Mosquito Density

The standard World Health Organization (WHO) tunnel test is a reliable laboratory bioassay used for “free-flying” testing of insecticide-treated nets (ITNs) bio-efficacy where mosquitoes pass through a ITN sample to reach a live animal bait. Multiple parameters (i.e., bait, exposure time, and mosquito density) may affect the outcomes measured in tunnel tests. Therefore, a comparison was conducted of alternative hosts, exposure time, and lower mosquito density against the current gold standard test (100 mosquitoes, animal bait, and 12-h exposure) as outlined in the WHO ITN evaluation guideline. This was done with the aim to make the tunnel test cheaper and with higher throughput to meet the large sample sizes needed for bio-efficacy durability monitoring of chlorfenapyr ITNs that must be evaluated in “free-flying” bioassays. Methods: A series of experiments were conducted in the WHO tunnel test to evaluate the impact of the following factors on bio-efficacy endpoints of mosquito mortality at 24-h (M24) and 72-h (M72) and blood-feeding success (BFS): (1) baits (rabbit, membrane, human arm); (2) exposure time in the tunnel (1 h vs. 12 h); and (3) mosquito density (50 vs. 100). Finally, an alternative bioassay using a membrane with 50 mosquitoes (membrane-50) was compared to the gold standard bioassay (rabbit with 100 mosquitoes, rabbit-100). Pyrethroid-resistant Anopheles arabiensis and pyrethroid susceptible Anopheles gambiae were used to evaluate Interceptor® and Interceptor® G2 ITNs. Results: Using a human arm as bait gave a very different BFS, which impacted measurements of M24 and M72. The same trends in M24, M72 and BFS were observed for both Interceptor® ITN and Interceptor® G2 unwashed and washed 20 times measured using the gold standard WHO tunnel test (rabbit-100) or rabbit with 50 mosquitoes (rabbit-50). M24, M72 and BFS were not statistically different when either 50 or 100 mosquitoes were used with rabbit bait in the tunnel bioassay for either the susceptible or resistant strains. No systematic difference was observed between rabbit-50 and rabbit-100 in the agreement by the Bland and Altman method (B&A). The mean difference was 4.54% (−22.54–31.62) in BFS and 1.71% (−28.71–32.12) in M72 for rabbit-50 versus rabbit-100. Similar M24, M72 and lower BFS was measured by membrane-50 compared to rabbit-100. No systematic difference was observed in the agreement between membrane-50 and rabbit-100, by B&A. The mean difference was 9.06% (−11.42–29.64) for BSF and −5.44% (−50.3–39.45) for M72. Both membrane-50, rabbit-50 and rabbit-100 predicted the superiority of Interceptor® G2 over Interceptor® ITN for the resistant strain on M72. Conclusion: These results demonstrate that WHO tunnel tests using rabbit bait may be run with 50 mosquitoes to increase sample sizes needed for bio-efficacy durability monitoring of ITNs in “free-flying” bioassays. Using a membrane feeder with 50 mosquitoes is a potential replacement for the WHO tunnel bioassay with animal bait if control blood feeding rates can be improved to 50% because blood feeding impacts mosquito survival after exposure to insecticides.

Infectivity of Symptomatic Malaria Patients to Anopheles farauti Colony Mosquitoes in Papua New Guinea

Plasmodium transmission from humans to mosquitoes is an understudied bottleneck in the transmission of malaria. Direct membrane feeding assays (DMFA) allow detailed malaria transmission studies from humans to mosquitoes. Especially for Plasmodium vivax, which cannot be cultured long-term under laboratory conditions, implementation of DMFAs requires proximity to P. vivax endemic areas. In this study, we investigated the infectivity of symptomatic Plasmodium infections to Anopheles farauti colony mosquitoes in Papua New Guinea (PNG). A total of 182 DMFAs were performed with venous blood collected from rapid diagnostic test (RDT) positive symptomatic malaria patients and subsequently analysed by light microscopy and quantitative real time polymerase chain reaction (qPCR). DMFAs resulted in mosquito infections in 20.9% (38/182) of cases. By light microscopy and qPCR, 10 – 11% of P. falciparum and 32 – 44% of P. vivax positive individuals infected An. farauti. Fifty-eight percent of P. vivax and 15% of P. falciparum gametocytaemic infections infected An farauti.

Dose-Dependent Blood-Feeding Activity and Ovarian Alterations to PM2.5 in Aedes aegypti

Simple Summary

Aedes aegypti (Ae. aegypti) is a mosquito that transmits arboviruses and responds to various biological and environmental stressors, including temperature, rainfall, and humidity. However, there is a lack of knowledge about fine particulate matter (PM_2.5) effects on arbovirus vectors. We hypothesized that fine particulate matter (PM_2.5) may affect Ae. aegypti blood-feeding rate and organs. We set up an environmental chamber that could adjust the concentration of PM_2.5 and observed their blood-feeding activity. We observed a dose–response relationship between PM_2.5 level and blood-feeding rate in adult female Ae. aegypti mosquitoes. In addition, histopathological study showed some changes in the ovaries. Vacuolated or vacuolar degeneration characterized by a formation of non-lipid small droplets in the cytoplasm was observed. This demonstrated the degenerative stage of the cells before developing hydropic degeneration or another advanced stage of cellular damage. The present study explored the effects of PM_2.5 exposure on the blood-feeding rate and organ integrity in the major arboviral vector Ae. Aegypti, providing information on the potential but indirect operational impact of PM_2.5 exposure on the survival and transmission capabilities of this major vector. Our findings may contribute towards the conceptualization and implementation of mosquito control measures with due consideration of the effects of ambient PM_2.5 on their populations.

Abstract

High levels of fine particulate matter (PM_2.5) air pollution are a concern for human health. Several studies have examined the effects of air pollution on human and animal health. However, there is a lack of knowledge about its effects on arbovirus vectors. Thus, we investigated whether PM_2.5 concentration alters the blood-feeding activity of Ae. aegypti mosquitoes. We investigated the effect on the females’ propensity to blood feed at eight concentrations of PM_2.5 ranging from 100 to 1000 μg/m³. Correlation analysis showed blood-feeding activity had a significant strong negative correlation with concentration of PM_2.5 (r_p = −0.85; p ≤ 0.00001). Exploratory linear and non-linear models showed an exponential decay relationship was the best fitting model (corrected Akaike’s information criterion, 193.0; Akaike’s weight, 0.766; adjusted R², 0.780). Ultrastructural study demonstrated PM_2.5 did not obstruct the respiratory system, but some fine particles were present on the antenna and abdominal body parts. Ovaries showed a dose–response relationship between PM_2.5 level and vacuolated degeneration. In conclusion, the blood-feeding behavior of Ae. aegypti females may have an exponential decay relationship with PM_2.5 level, and their ovaries may demonstrate dose-dependent degeneration. These findings may be important in understanding the vector’s biology and disease transmission in settings with high PM_2.5 levels. These results are important to understand blood-feeding and feeding pattern of mosquitoes during PM_2.5 pollution, which is important for disease transmission and vector control.