bims-mosdis 2021-01-31 papers

bims-mosdis

Biomed News

on Mosquito distribution and disease

Issue of 2021–01–31
fiveteen papers selected by
Richard Halfpenny, Staffordshire University

Parasitism of Aedes albopictus by Ascogregarina taiwanensis lowers its competitive ability against Aedes triseriatus.
Patterns of human exposure to early-evening and outdoor biting mosquitoes and residual malaria transmission in Ethiopia.
Bionomics and ecology of Anopheles merus along the East and Southern Africa coast.
Effectiveness of adulticide and larvicide in controlling high densities of Aedes aegypti in urban environments.
Malaria vectors diversity, insecticide resistance and transmission during the rainy season in peri-urban villages of south-western Burkina Faso.
Which indoor residual spraying insecticide best complements standard pyrethroid long-lasting insecticidal nets for improved control of pyrethroid resistant malaria vectors?
Fine-scale distribution of malaria mosquitoes biting or resting outside human dwellings in three low-altitude Tanzanian villages.
The entomological impact of passive metofluthrin emanators against indoor Aedes aegypti: A randomized field trial.
New Records of Anopheles benarrochi B (Diptera: Culicidae) in Malaria Hotspots in the Amazon Regions of Ecuador and Peru.
Evaluation of Long-Lasting Insecticidal Nets (DuraNet®) Under laboratory and Semi-Field Conditions Using Experimental Huts Against Anopheles Mosquitoes in Jimma Zone, Southwestern Ethiopia.
Pyriproxyfen Ingested With Attractive Toxic Sugar Baits Is Carried by the Feces and Reduces the Reproductive Potential of Adult Female Aedes aegypti (Diptera: Culicidae).
Anopheles stephensi Mosquitoes as Vectors of Plasmodium vivax and falciparum, Horn of Africa, 2019.
Malaria in Southern Venezuela: The hottest hotspot in Latin America.
A single-dose live attenuated chimeric vaccine candidate against Zika virus.
Biodiversity of mosquitoes and Mansonia uniformis as a potential vector of Wuchereria bancrofti in Hulu Sungai Utara District, South Kalimantan, Indonesia.

Parasit Vectors. 2021 Jan 25. 14(1): 79

Parasitism of Aedes albopictus by Ascogregarina taiwanensis lowers its competitive ability against Aedes triseriatus.

Emma Stump, Lauren M Childs, Melody Walker.

   BACKGROUND: Mosquitoes are vectors for diseases such as dengue, malaria and La Crosse virus that significantly impact the human population. When multiple mosquito species are present, the competition between species may alter population dynamics as well as disease spread. Two mosquito species, Aedes albopictus and Aedes triseriatus, both inhabit areas where La Crosse virus is found. Infection of Aedes albopictus by the parasite Ascogregarina taiwanensis and Aedes triseriatus by the parasite Ascogregarina barretti can decrease a mosquito's fitness, respectively. In particular, the decrease in fitness of Aedes albopictus occurs through the impact of Ascogregarina taiwanensis on female fecundity, larval development rate, and larval mortality and may impact its initial competitive advantage over Aedes triseriatus during invasion.
METHODS: We examine the effects of parasitism of gregarine parasites on Aedes albopictus and triseriatus population dynamics and competition with a focus on when Aedes albopictus is new to an area. We build a compartmental model including competition between Aedes albopictus and triseriatus while under parasitism of the gregarine parasites. Using parameters based on the literature, we simulate the dynamics and analyze the equilibrium population proportion of the two species. We consider the presence of both parasites and potential dilution effects.
RESULTS: We show that increased levels of parasitism in Aedes albopictus will decrease the initial competitive advantage of the species over Aedes triseriatus and increase the survivorship of Aedes triseriatus. We find Aedes albopictus is better able to invade when there is more extreme parasitism of Aedes triseriatus. Furthermore, although the transient dynamics differ, dilution of the parasite density through uptake by both species does not alter the equilibrium population sizes of either species.
CONCLUSIONS: Mosquito population dynamics are affected by many factors, such as abiotic factors (e.g. temperature and humidity) and competition between mosquito species. This is especially true when multiple mosquito species are vying to live in the same area. Knowledge of how population dynamics are affected by gregarine parasites among competing species can inform future mosquito control efforts and help prevent the spread of vector-borne disease.

Keywords:  Aedes albopictus; Aedes triseriatus; Ascogregarina barretti; Ascogregarina taiwanensis; Competition; Mosquito population dynamics; Parasitism

DOI:  https://doi.org/10.1186/s13071-021-04581-0
Acta Trop. 2021 Jan 21. pii: S0001-706X(21)00016-4. [Epub ahead of print] 105837

Patterns of human exposure to early-evening and outdoor biting mosquitoes and residual malaria transmission in Ethiopia.

Teshome Degefa, Andrew K Githeko, Ming-Chie Lee, Guiyun Yan, Delenasaw Yewhalaw.

  Ethiopia has shown a notable progress in reducing malaria burden over the past decade, mainly due to the scaleup of vector control interventions such as long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS). Based on the progress, the country has set goals to eliminate malaria by 2030. However, residual malaria transmission due to early-evening and outdoor biting vectors could pose a challenge to malaria elimination efforts. This study assessed vector behavior, patterns of human exposure to vector bites and residual malaria transmission in southwestern Ethiopia. Anopheles mosquitoes were collected monthly from January to December 2018 using human landing catches (HLCs), human-baited double net traps, CDC light traps and pyrethrum spray catches. Human behavior data were collected using questionnaire to estimate the magnitude of exposure to mosquito bites occurring indoors and outdoors at various times of the night. Enzyme-linked immunosorbent assay (ELISA) was used to determine mosquito blood meal sources and sporozoite infections. A total of 2,038 female Anopheles mosquitoes comprising Anopheles arabiensis (30.8%), An. pharoensis (40.5%), An. coustani (28.1%), An. squamosus (0.3%) and An. funestus group (0.2%) were collected. Anopheles arabiensis and An. pharoensis were 2.4 and 2.5 times more likely to seek hosts outdoors than indoors, respectively. However, 66% of human exposure to An. arabiensis and 39% of exposure to An. pharoensis bites occurred indoors for LLIN non-users. For LLIN users, 75% of exposure to An. arabiensis bites occurred outdoors while 23% occurred indoors before bed time. Likewise, 84% of exposure to An. pharoensis bites occurred outdoors while 15% occurred indoors before people retired to bed. Anopheles arabiensis and An. pharoensis were 4.1 and 4.8 times more likely to feed on bovine than human, respectively. Based on the HLC, an estimated indoor and outdoor EIR of An. arabiensis was 6.2 and 1.4 infective bites/person/year, respectively, whereas An. pharoensis had an estimated outdoor EIR of 3.0 infective bites/person/year. In conclusion, An. arabiensis and An. pharoensis showed exophagic and zoophagic behavior. Human exposure to An. arabiensis bites occurred mostly indoors for LLIN non-users, while most of the exposure to both An. arabiensis and An. pharoensis bites occurred outdoors for LLIN users. Malaria transmission by An. arabiensis occurred both indoors and outdoors, whereas An. pharoensis contributed exclusively to outdoor transmission. Additional control tools targeting early-evening and outdoor biting malaria vectors are required to complement the current control interventions to control residual transmission and ultimately achieve malaria elimination.

Keywords:  Ethiopia; Exposure; Human behavior; Malaria: Vector behavior; Residual transmission

DOI:  https://doi.org/10.1016/j.actatropica.2021.105837
Parasit Vectors. 2021 Jan 28. 14(1): 84

Bionomics and ecology of Anopheles merus along the East and Southern Africa coast.

Brian Bartilol, Irene Omedo, Charles Mbogo, Joseph Mwangangi, Martin K Rono.

  Malaria transmission persists despite the scale-up of interventions such as long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). Understanding the entomological drivers of transmission is key for the design of effective and sustainable tools to address the challenge. Recent research findings indicate a shift in vector populations from the notorious Anopheles gambiae (s.s.) as a dominant vector to other species as one of the factors contributing to the persistence of malaria transmission. However, there are gaps in the literature regarding the minor vector species which are increasingly taking a lead role in malaria transmission. Currently, minor malaria vectors have behavioural plasticity, which allows their evasion of vector control tools currently in use. To address this, we have reviewed the role of Anopheles merus, a saltwater mosquito species that is becoming an important vector of malaria transmission along the East and Southern African coast. We performed a literature review from PubMed and Google Scholar and reviewed over 50 publications relating to An. merus's bionomics, taxonomy, spatial-temporal distribution and role in malaria transmission. We found that An. merus is an important vector of malaria and that it contributes to residual malaria transmission because of its exophilic tendencies, insecticide resistance and densities that peak during the dry seasons as the freshwater mosquitoes decline. Spatial and temporal studies have also shown that this species has increased its geographical range, densities and vectorial capacity over time. In this review, we highlight the resting behaviour and breeding habitats of this mosquito, which could be targeted for surveillance studies and control interventions.

Keywords:  Anopheles merus; Indoor residual spraying; Insecticide resistance; Plasmodium falciparum

DOI:  https://doi.org/10.1186/s13071-021-04582-z
PLoS One. 2021 ;16(1): e0246046

Effectiveness of adulticide and larvicide in controlling high densities of Aedes aegypti in urban environments.

André B B Wilke, Chalmers Vasquez, Augusto Carvajal, Monica Ramirez, Gabriel Cardenas, William D Petrie, John C Beier.

Current management and control of Aedes aegypti populations in urban areas are based on the spraying of insecticides. Here, we evaluated the effectiveness of spraying larvicide (Bacillus thuringiensis israelensis) using a truck-mounted Buffalo Turbine and adulticide (Deltamethrin) using a Grizzly ULV Sprayer in an urban area with high densities of Ae. aegypti and many cryptic and difficult to reach aquatic breeding habitats. Experiments were conducted in a tire shop located in Miami-Dade County, Florida with approximately 100,000 used airplane tires. Insecticide interventions were performed after a baseline survey consisting of 3 weeks of collections, followed by two insecticide interventions: (i) application of the adulticide followed by the application of larvicide on the subsequent week; and (ii) application of both adulticide and larvicide on two consecutive weeks. The first insecticide intervention resulted in a non-significant decrease in the relative abundance of Ae. aegypti. On the other hand, the second insecticide intervention significantly reduced the Ae. aegypti relative abundance (P < 0.002). Our results demonstrated that the combined insecticide interventions on two consecutive weeks significantly reduced the relative abundance of Ae. aegypti. This result indicated that the larvicide was successfully propelled reaching cryptical and difficult to reach aquatic habitats. However, even though the number of mosquitoes was greatly reduced, it was still greatly above the 10-mosquito threshold by trap night used by the Miami-Dade Mosquito Control Division to deploy an inspector to survey the area. Considering the lack of new and effective mosquito control tools, efficient and mobile insecticide propellers such as Buffalo Turbine can be of great help to manage mosquito populations in urban areas.

DOI: https://doi.org/10.1371/journal.pone.0246046
Malar J. 2021 Jan 25. 20(1): 63

Malaria vectors diversity, insecticide resistance and transmission during the rainy season in peri-urban villages of south-western Burkina Faso.

Dieudonné Diloma Soma, Serge Bèwadéyir Poda, Aristide Sawdetuo Hien, Moussa Namountougou, Ibrahim Sangaré, John Marie Emmanuel Sawadogo, Florence Fournet, Georges Anicet Ouédraogo, Abdoulaye Diabaté, Nicolas Moiroux, Roch Kounbobr Dabiré.

   BACKGROUND: This study reports an updated description on malaria vector diversity, behaviour, insecticide resistance and malaria transmission in the Diébougou and Dano peri-urban areas, Burkina Faso.
METHODS: Mosquitoes were caught monthly using CDC light traps and pyrethrum spray catches. Mosquitoes were identified using morphological taxonomic keys. PCR techniques were used to identify the species of the Anopheles gambiae complex and insecticide resistance mechanisms in a subset of Anopheles vectors. The Plasmodium sporozoite infection status and origins of blood meals of female mosquitoes were determined by ELISA methods. Larvae were collected, breed in the insectary and tested for phenotypic resistance against four insecticides using WHO bioassays.
RESULTS: This study contributed to update the entomological data in two peri-urban areas of Southwest Burkina Faso. Anopheles populations were mostly anthropophilic and endophilic in both areas and exhibit high susceptibility to an organophosphate insecticide. This offers an alternative for the control of these pyrethroid-resistant populations. These data might help the National Malaria Control Programme for decision-making about vector control planning and resistance management.
CONCLUSIONS: This study contributed to update the entomological data in two peri-urban areas of Southwest Burkina Faso. Anopheles populations were mostly anthropophilic and endophilic in both areas and exhibit high susceptibility to an organophosphate insecticide. This offers an alternative for the control of these pyrethroid-resistant populations. These data might help the National Malaria Control Programme for decision-making about vector control planning and resistance management.

Keywords:  Bionomics; Burkina Faso; Resistance; Vector

DOI:  https://doi.org/10.1186/s12936-020-03554-5
PLoS One. 2021 ;16(1): e0245804

Which indoor residual spraying insecticide best complements standard pyrethroid long-lasting insecticidal nets for improved control of pyrethroid resistant malaria vectors?

Thomas Syme, Augustin Fongnikin, Damien Todjinou, Renaud Govoetchan, Martial Gbegbo, Mark Rowland, Martin Akogbeto, Corine Ngufor.

BACKGROUND: Where resources are available, non-pyrethroid IRS can be deployed to complement standard pyrethroid LLINs with the aim of achieving improved vector control and managing insecticide resistance. The impact of the combination may however depend on the type of IRS insecticide deployed. Studies comparing combinations of pyrethroid LLINs with different types of non-pyrethroid IRS products will be necessary for decision making.
METHODS: The efficacy of combining a standard pyrethroid LLIN (DuraNet®) with IRS insecticides from three chemical classes (bendiocarb, chlorfenapyr and pirimiphos-methyl CS) was evaluated in an experimental hut trial against wild pyrethroid-resistant Anopheles gambiae s.l. in Cové, Benin. The combinations were also compared to each intervention alone. WHO cylinder and CDC bottle bioassays were performed to assess susceptibility of the local An. gambiae s.l. vector population at the Cové hut site to insecticides used in the combinations.
RESULTS: Susceptibility bioassays revealed that the vector population at Cové, was resistant to pyrethroids (<20% mortality) but susceptible to carbamates, chlorfenapyr and organophosphates (≥98% mortality). Mortality of wild free-flying pyrethroid resistant An. gambiae s.l. entering the hut with the untreated net control (4%) did not differ significantly from DuraNet® alone (8%, p = 0.169). Pirimiphos-methyl CS IRS induced the highest mortality both on its own (85%) and in combination with DuraNet® (81%). Mortality with the DuraNet® + chlorfenapyr IRS combination was significantly higher than each intervention alone (46% vs. 33% and 8%, p<0.05) demonstrating an additive effect. The DuraNet® + bendiocarb IRS combination induced significantly lower mortality compared to the other combinations (32%, p<0.05). Blood-feeding inhibition was very low with the IRS treatments alone (3-5%) but increased significantly when they were combined with DuraNet® (61% - 71%, p<0.05). Blood-feeding rates in the combinations were similar to the net alone. Adding bendiocarb IRS to DuraNet® induced significantly lower levels of mosquito feeding compared to adding chlorfenapyr IRS (28% vs. 37%, p = 0.015).
CONCLUSIONS: Adding non-pyrethroid IRS to standard pyrethroid-only LLINs against a pyrethroid-resistant vector population which is susceptible to the IRS insecticide, can provide higher levels of vector mosquito control compared to the pyrethroid net alone or IRS alone. Adding pirimiphos-methyl CS IRS may provide substantial improvements in vector control while adding chlorfenapyr IRS can demonstrate an additive effect relative to both interventions alone. Adding bendiocarb IRS may show limited enhancements in vector control owing to its short residual effect.

DOI: https://doi.org/10.1371/journal.pone.0245804
PLoS One. 2021 ;16(1): e0245750

Fine-scale distribution of malaria mosquitoes biting or resting outside human dwellings in three low-altitude Tanzanian villages.

Arnold S Mmbando, Emmanuel W Kaindoa, Halfan S Ngowo, Johnson K Swai, Nancy S Matowo, Masoud Kilalangongono, Godfrey P Lingamba, Joseph P Mgando, Isaac H Namango, Fredros O Okumu, Luca Nelli.

BACKGROUND: While malaria transmission in Africa still happens primarily inside houses, there is a substantial proportion of Anopheles mosquitoes that bite or rest outdoors. This situation may compromise the performance of indoor insecticidal interventions such as insecticide-treated nets (ITNs). This study investigated the distribution of malaria mosquitoes biting or resting outside dwellings in three low-altitude villages in south-eastern Tanzania. The likelihood of malaria infections outdoors was also assessed.
METHODS: Nightly trapping was done outdoors for 12 months to collect resting mosquitoes (using resting bucket traps) and host-seeking mosquitoes (using odour-baited Suna® traps). The mosquitoes were sorted by species and physiological states. Pooled samples of Anopheles were tested to estimate proportions infected with Plasmodium falciparum parasites, estimate proportions carrying human blood as opposed to other vertebrate blood and identify sibling species in the Anopheles gambiae complex and An. funestus group. Environmental and anthropogenic factors were observed and recorded within 100 meters from each trapping positions. Generalised additive models were used to investigate relationships between these variables and vector densities, produce predictive maps of expected abundance and compare outcomes within and between villages.
RESULTS: A high degree of fine-scale heterogeneity in Anopheles densities was observed between and within villages. Water bodies covered with vegetation were associated with 22% higher densities of An. arabiensis and 51% lower densities of An. funestus. Increasing densities of houses and people outdoors were both associated with reduced densities of An. arabiensis and An. funestus. Vector densities were highest around the end of the rainy season and beginning of the dry seasons. More than half (14) 58.3% of blood-fed An. arabiensis had bovine blood, (6) 25% had human blood. None of the Anopheles mosquitoes caught outdoors was found infected with malaria parasites.
CONCLUSION: Outdoor densities of both host-seeking and resting Anopheles mosquitoes had significant heterogeneities between and within villages, and were influenced by multiple environmental and anthropogenic factors. Despite the high Anopheles densities outside dwellings, the substantial proportion of non-human blood-meals and absence of malaria-infected mosquitoes after 12 months of nightly trapping suggests very low-levels of outdoor malaria transmission in these villages.

DOI: https://doi.org/10.1371/journal.pone.0245750
PLoS Negl Trop Dis. 2021 Jan 26. 15(1): e0009036

The entomological impact of passive metofluthrin emanators against indoor Aedes aegypti: A randomized field trial.

Gregor J Devine, Gonzalo M Vazquez-Prokopec, Wilbert Bibiano-Marín, Norma Pavia-Ruz, Azael Che-Mendoza, Anuar Medina-Barreiro, Josue Villegas, Gabriela Gonzalez-Olvera, Mike W Dunbar, Oselyne Ong, Scott A Ritchie, Thomas S Churcher, Oscar D Kirstein, Pablo Manrique-Saide.

BACKGROUND: In the absence of vaccines or drugs, insecticides are the mainstay of Aedes-borne disease control. Their utility is challenged by the slow deployment of resources, poor community compliance and inadequate household coverage. Novel application methods are required.
METHODOLOGY AND PRINCIPAL FINDINGS: A 10% w/w metofluthrin "emanator" that passively disseminates insecticide from an impregnated net was evaluated in a randomized trial of 200 houses in Mexico. The devices were introduced at a rate of 1 per room and replaced at 3-week intervals. During each of 7 consecutive deployment cycles, indoor resting mosquitoes were sampled using aspirator collections. Assessments of mosquito landing behaviours were made in a subset of houses. Pre-treatment, there were no differences in Aedes aegypti indices between houses recruited to the control and treatment arms. Immediately after metofluthrin deployment, the entomological indices between the trial arms diverged. Averaged across the trial, there were significant reductions in Abundance Rate Ratios for total Ae. aegypti, female abundance and females that contained blood meals (2.5, 2.4 and 2.3-times fewer mosquitoes respectively; P<0.001). Average efficacy was 60.2% for total adults, 58.3% for females, and 57.2% for blood-fed females. The emanators also reduced mosquito landings by 90% from 12.5 to 1.2 per 10-minute sampling period (P<0.05). Homozygous forms of the pyrethroid resistant kdr alleles V410L, V1016L and F1534C were common in the target mosquito population; found in 39%, 24% and 95% of mosquitoes collected during the trial.
CONCLUSIONS/SIGNIFICANCE: This is the first randomized control trial to evaluate the entomological impact of any volatile pyrethroid on urban Ae. aegypti. It demonstrates that volatile pyrethroids can have a sustained impact on Ae. aegypti population densities and human-vector contact indoors. These effects occur despite the presence of pyrethroid-resistant alleles in the target population. Formulations like these may have considerable utility for public health vector control responses.

DOI: https://doi.org/10.1371/journal.pntd.0009036
J Med Entomol. 2021 Jan 28. pii: tjaa293. [Epub ahead of print]

New Records of Anopheles benarrochi B (Diptera: Culicidae) in Malaria Hotspots in the Amazon Regions of Ecuador and Peru.

Diego Morales Viteri, Manuela Herrera-Varela, Maribel Albuja, Cristina Quiroga, Gloria Diaz, Clara Del Aguila Morante, Dario Ramirez, Joseph M Vinetz, Sara A Bickersmith, Jan E Conn.

  The increase in malaria transmission in the Amazon region motivated vector control units of the Ministry of Health of Ecuador and Peru to investigate Anopheles (Diptera: Culicidae) species present in transmission hotspots. Mosquitoes were collected using prokopack aspirators and CDC light traps (Ecuador) and human landing catch in Peru. In Ecuador, 84 Anopheles were captured from Pastaza, Morona Santiago, and Orellana provinces and identified morphologically [An. (An.) apicimacula Dyar and Knab, An. (Nys.) near benarrochi, An. (Nys.) near oswaldoi, An. (Nys.) near strodei, An. (An.) nimbus (Theobald, 1902), and An. (Nyssorhynchus) sp.]. In Peru, 1,150 Anopheles were collected in Andoas District. A subsample of 166 specimens was stored under silica and identified as An. near oswaldoi, An. darlingi, and An. (An.) mattogrossensis Lutz and Neiva. COI barcode region sequences were obtained for 137 adults (107 from Peru, 30 from Ecuador) identified by ITS2 PCR-RFLP as An. benarrochi Gabaldon, Cova Garcia, and Lopez and retained in the final analysis. Haplotypes from the present study plus An. benarrochi B GenBank sequences grouped separately from Brazilian An. benarrochi GenBank sequences by 44 mutation steps, indicating that the present study specimens were An. benarrochi B. Our findings confirm the presence of An. benarrochi B in Ecuador and reported here for the first time from the Amazonian provinces of Orellana and Morona Santiago. Furthermore, we confirm that the species collected in Andoas District in the Datem del Maranon Province, Peru, is An. benarrochi B, and we observed that it is highly anthropophilic. Overall, the known distribution of An. benarrochi B has been extended and includes southern Colombia, much of Peru and eastern Ecuador.

Keywords:  Ecuador; Peru; anopheline identification; malaria hotspot

DOI:  https://doi.org/10.1093/jme/tjaa293
Environ Health Insights. 2021 ;15 1178630220974730

Evaluation of Long-Lasting Insecticidal Nets (DuraNet®) Under laboratory and Semi-Field Conditions Using Experimental Huts Against Anopheles Mosquitoes in Jimma Zone, Southwestern Ethiopia.

Brhane Gebremariam, Wondwosen Birke, Wuhib Zeine, Argaw Ambelu, Delenasaw Yewhalaw.

   Background: Long-Lasting Insecticidal Nets (LLINs) efficacy could be compromised due to a lot of influences together with user compliance and vector population insecticide resistance status. Thus, this study was to assess the biological efficacy of DuraNet® with the help of the World Health Organization cone bioassay and field experimental hut.
Methods: A laboratory and a semi-field conditions experimental huts against Anopheles Mosquitoes were conducted in southwestern Ethiopia from September 2015 to January 2016. The bio efficacy of DuraNet® was evaluated using the WHO cone bioassay test and then its field efficacy was evaluated using experimental huts against the malaria vector population.
Results: World Health Organization cone bioassay tests against pyrethroid-resistant An. arabiensis led to mean percent mortality and knockdown of 78% and 93%, respectively. Washing of DuraNet® successively reduced its efficacy from 93% knockdown (0 wash) to 45% knockdown (20 washes). Similarly, mean mortality decreased from 84% (0 wash) to 47% (20 washes). A total of 1575 female mosquitoes were collected over 40 nights out of which 1373(87.8%) were An. gambiae s.l., 116 (7.4%) were Anopheles coustani and 107 (6.8%) were An. pharoensis. The mean blood-feeding rate was significantly lower (P < .001) in hut containing unwashed DuraNet® when compared to hut containing untreated DuraNet®. The mean mortality rate was significantly higher (P < .001) in hut containing DuraNet® when compared to hut containing untreated DuraNet®. Unwashed DuraNet® showed the highest personal protection 88.7% and 100% against An. Arabiensis and An. pharoensis, respectively.
Conclusion: Both DuraNet® and PermaNet 2.0 moderate efficacy against a pyrethroid-resistant population of An. arabiensis from Ethiopia. The bio efficacy of DuraNet® was found below the WHO recommendation. Therefore, the real impact of the observed insecticide resistance against DuraNet® to be further studied under phase-III trials, the need for new alternative vector control tools remains critical.

Keywords:  Anopheles arabiensis; Anopheles gambiae; DuraNet®; Ethiopia; Knockdown; cone bioassay; experimental hut

DOI:  https://doi.org/10.1177/1178630220974730
J Med Entomol. 2021 Jan 28. pii: tjaa265. [Epub ahead of print]

Pyriproxyfen Ingested With Attractive Toxic Sugar Baits Is Carried by the Feces and Reduces the Reproductive Potential of Adult Female Aedes aegypti (Diptera: Culicidae).

Tarsis Tamar Pereira Silva, Aurea Vieira Teixeira, Alexandre de Almeida E Silva.

  In the search for new strategies to control Aedes aegypti Linnaeus (Diptera: Culicidae), several studies have successfully related pyriproxyfen (PPF) tarsal transference to breeding sites (autodissemination), as well as the sterilization potential of females exposed to PPF. Potential PPF autodissemination by mosquito feces after the ingestion of sugar baits has also been proposed. Therefore, the present work evaluated several parameters, e.g., fecal production, residuality under dry and aqueous conditions, PPF excretion affecting emergence inhibition (EI) by fecal deposits of Ae. aegypti fed with attractive toxic sugar baits (ATSBs) containing PPF as well as their reproductive potential. Females were fed with ATSBs offered as droplets and the feces were collected using filter paper and transferred to plastic cups with L3 larvae to evaluate EI. The residual effect of feces in aqueous and dry conditions and PPF excretion on EI was obtained by keeping the feces in water or dried for different time intervals and using feces collected at 24-h intervals, respectively. Females received a bloodmeal after feeding on ATSBs, eggs and larval counting expressed the reproductive potential. The fecal mass was not affected by PPF concentration, but EI increased from 33 to 54% as the PPF concentration increased. The PPF excretion in the feces exceeded 96 h. The residual effect in the EI for feces kept in water was reduced by more than 60% after 30 d but was not affected under dry conditions. The fecundity and fertility of the females were reduced up to 51% and 97%, respectively.

Keywords:  chemical control; fecal deposits; insect growth regulator (IGR)

DOI:  https://doi.org/10.1093/jme/tjaa265
Emerg Infect Dis. 2021 Feb;27(2): 603-607

Anopheles stephensi Mosquitoes as Vectors of Plasmodium vivax and falciparum, Horn of Africa, 2019.

Fitsum G Tadesse, Temesgen Ashine, Hiwot Teka, Endashaw Esayas, Louisa A Messenger, Wakweya Chali, Lisette Meerstein-Kessel, Thomas Walker, Sinknesh Wolde Behaksra, Kjerstin Lanke, Roel Heutink, Claire L Jeffries, Daniel Abebe Mekonnen, Elifaged Hailemeskel, Surafel K Tebeje, Temesgen Tafesse, Abrham Gashaw, Tizita Tsegaye, Tadele Emiru, Kigozi Simon, Eyuel Asemahegn Bogale, Gedeon Yohannes, Soriya Kedir, Girma Shumie, Senya Asfer Sabir, Peter Mumba, Dereje Dengela, Jan H Kolaczinski, Anne Wilson, Thomas S Churcher, Sheleme Chibsa, Matthew Murphy, Meshesha Balkew, Seth Irish, Chris Drakeley, Endalamaw Gadisa, Teun Bousema.

  Anopheles stephensi mosquitoes, efficient vectors in parts of Asia and Africa, were found in 75.3% of water sources surveyed and contributed to 80.9% of wild-caught Anopheles mosquitoes in Awash Sebat Kilo, Ethiopia. High susceptibility of these mosquitoes to Plasmodium falciparum and vivax infection presents a challenge for malaria control in the Horn of Africa.

Keywords:  Anopheles stephensi; Horn of Africa; Plasmodium falciparum; Plasmodium vivax; emerging; membrane feeding; mosquitoes; outbreak; parasites; transmission; urban malaria; vector competence

DOI:  https://doi.org/10.3201/eid2702.200019
PLoS Negl Trop Dis. 2021 Jan 25. 15(1): e0008211

Malaria in Southern Venezuela: The hottest hotspot in Latin America.

Maria Eugenia Grillet, Jorge E Moreno, Juan V Hernández-Villena, Maria F Vincenti-González, Oscar Noya, Adriana Tami, Alberto Paniz-Mondolfi, Martin Llewellyn, Rachel Lowe, Ananías A Escalante, Jan E Conn.

Malaria elimination in Latin America is becoming an elusive goal. Malaria cases reached a historical ~1 million in 2017 and 2018, with Venezuela contributing 53% and 51% of those cases, respectively. Historically, malaria incidence in southern Venezuela has accounted for most of the country's total number of cases. The efficient deployment of disease prevention measures and prediction of disease spread to new regions requires an in-depth understanding of spatial heterogeneity on malaria transmission dynamics. Herein, we characterized the spatial epidemiology of malaria in southern Venezuela from 2007 through 2017 and described the extent to which malaria distribution has changed country-wide over the recent years. We found that disease transmission was focal and more prevalent in the southeast region of southern Venezuela where two persistent hotspots of Plasmodium vivax (76%) and P. falciparum (18%) accounted for ~60% of the total number of cases. Such hotspots are linked to deforestation as a consequence of illegal gold mining activities. Incidence has increased nearly tenfold over the last decade, showing an explosive epidemic growth due to a significant lack of disease control programs. Our findings highlight the importance of spatially oriented interventions to contain the ongoing malaria epidemic in Venezuela. This work also provides baseline epidemiological data to assess cross-border malaria dynamics and advocates for innovative control efforts in the Latin American region.

DOI: https://doi.org/10.1371/journal.pntd.0008211
NPJ Vaccines. 2021 Jan 29. 6(1): 20

A single-dose live attenuated chimeric vaccine candidate against Zika virus.

Wei-Xin Chin, Regina Ching Hua Lee, Parveen Kaur, Tian Sheng Lew, Thinesshwary Yogarajah, Hao Yuin Kong, Zi-Yun Teo, Cyrill Kafi Salim, Rong-Rong Zhang, Xiao-Feng Li, Sylvie Alonso, Cheng-Feng Qin, Justin Jang Hann Chu.

The mosquito-borne Zika virus is an emerging pathogen from the Flavivirus genus for which there are no approved antivirals or vaccines. Using the clinically validated PDK-53 dengue virus vaccine strain as a backbone, we created a chimeric dengue/Zika virus, VacDZ, as a live attenuated vaccine candidate against Zika virus. VacDZ demonstrates key markers of attenuation: small plaque phenotype, temperature sensitivity, attenuation of neurovirulence in suckling mice, and attenuation of pathogenicity in interferon deficient adult AG129 mice. VacDZ may be administered as a traditional live virus vaccine, or as a DNA-launched vaccine that produces live VacDZ in vivo after delivery. Both vaccine formulations induce a protective immune response against Zika virus in AG129 mice, which includes neutralising antibodies and a strong Th1 response. This study demonstrates that VacDZ is a safe and effective vaccine candidate against Zika virus.

DOI: https://doi.org/10.1038/s41541-021-00282-y
Vet World. 2020 Dec;13(12): 2815-2821

Biodiversity of mosquitoes and Mansonia uniformis as a potential vector of Wuchereria bancrofti in Hulu Sungai Utara District, South Kalimantan, Indonesia.

Muhammad Rasyid Ridha, Nita Rahayu, Budi Hairani, Dian Perwitasari, Harninda Kusumaningtyas.

   Background and Aim: Lymphatic filariasis, also known as elephantiasis, still remains a problem in Indonesia. The primary causative species of this disease are the filarial worms Wuchereria bancrofti and Brugia spp. This study was conducted to identify the diversity of species and behavior of mosquitoes and to determine the mosquitoes that could be potential vectors of filariasis.
Materials and Methods: Mosquito samples derived from Hulu Sungai Utara (HSU) district in the 2017 multicenter study conducted in Indonesia were used in this cross-sectional study. The diversity of mosquito species was analyzed using the Shannon-Wiener diversity index. Mosquitoes were identified based on their species, and their DNA was isolated by polymerase chain reaction (PCR). Transcription-insulated isothermal PCR method was used to detect microfilariae/filaria larvae in the mosquitoes.
Results: Biodiversity was found in 14 species of mosquitoes belonging to five genera. The maximum number of mosquitoes was recorded from the species Mansonia dives, Culex vishnui, Culex quinquefasciatus, and Mansonia uniformis. W. bancrofti infection was detected in M. uniformis at an infectivity rate of 0.3% (n=311).
Conclusion: To the best of our knowledge, this is the first report of M. uniformis species as a vector of W. bancrofti in HSU district, Indonesia. More efficient and accurate studies are required to aid in the lymphatic filariasis elimination programs in this subregion.

Keywords:  Mansonia uniformis; Wuchereria bancrofti; biodiversity; mosquito

DOI:  https://doi.org/10.14202/vetworld.2020.2815-2821