Early rise of West Nile fever in Israel, June 2024.

This report describes an unusual surge of West Nile fever in Israel in June 2024, during which 125 cases were diagnosed, compared with 4 cases on average during June in previous years (2014-23). Of the cases, 64 (62.1%) had neuroinvasive disease and 12 (9.6%) died; the 2024 case fatality rate was not significantly elevated vs the average rate in 2014-23. The early rise could be related to a temperature increase in spring and early summer of 2024.

Isolation of Heartland Virus from Lone Star Ticks, Georgia, USA, 2019.

Report of a human death and exposure of white-tailed deer to Heartland virus (HRTV) in Georgia, USA, prompted the sampling of questing ticks during 2018-2019 in 26 sites near where seropositive deer were captured and the residence of the human case-patient. We processed 9,294 Amblyomma americanum ticks in pools by virus isolation in Vero E6 cells and reverse transcription PCR. Positive pools underwent whole-genome sequencing. Three pools were positive for HRTV (minimum infection rate 0.46/1,000 ticks) and none for Bourbon virus. Cell cultures confirmed HRTV presence in 2 pools. Genome sequencing, achieved for the 3 HRTV isolates, showed high similarity among samples but marked differences with previously sequenced HRTV isolates. The isolation and genomic characterization of HRTV from A. americanum ticks in Georgia confirm virus presence in the state. Clinicians and public health professionals should be aware of this emerging tickborne pathogen.

Protective effect of house screening against indoor Aedes aegypti in Mérida, Mexico: A cluster randomised controlled trial.

OBJECTIVE: To evaluate the protective effect of house screening (HS) on indoor Aedes aegypti infestation, abundance and arboviral infection in Merida, Mexico. METHODS: In 2019, we performed a cluster randomised controlled trial (6 control and 6 intervention areas: 100 households/area). Intervention clusters received permanently fixed fiberglass HS on all windows and doors. The study included two cross-sectional entomologic surveys, one baseline (dry season in May 2019) and one post-intervention (PI, rainy season between September and October 2019). The presence and number of indoor Aedes females and blood-fed females (indoor mosquito infestation) as well as arboviral infections with dengue (DENV) and Zika (ZIKV) viruses were evaluated in a subsample of 30 houses within each cluster. RESULTS: HS houses had significantly lower risk for having Aedes aegypti female mosquitoes (odds ratio [OR] = 0.56, 95% CI 0.33-0.97, p = 0.04) and blood-fed females (OR = 0.53, 95% CI 0.28-0.97, p = 0.04) than unscreened households from the control arm. Compared to control houses, HS houses had significantly lower indoor Ae. aegypti abundance (rate ratio [RR] = 0.50, 95% CI 0.30-0.83, p = 0.01), blood-fed Ae. aegypti females (RR = 0.48, 95% CI 0.27-0.85, p = 0.01) and female Ae. aegypti positive for arboviruses (OR = 0.29, 95% CI 0.10-0.86, p = 0.02). The estimated intervention efficacy in reducing Ae. aegypti arbovirus infection was 71%. CONCLUSIONS: These results provide evidence supporting the use of HS as an effective pesticide-free method to control house infestations with Aedes aegypti and reduce the transmission of Aedes-transmitted viruses such as DENV, chikungunya (CHIKV) and ZIKV.

Plant-feeding phlebotomine sand flies, vectors of leishmaniasis, prefer Cannabis sativa.

Blood-sucking phlebotomine sand flies (Diptera: Psychodidae) transmit leishmaniasis as well as arboviral diseases and bartonellosis. Sand fly females become infected with Leishmania parasites and transmit them while imbibing vertebrates' blood, required as a source of protein for maturation of eggs. In addition, both females and males consume plant-derived sugar meals as a source of energy. Plant meals may comprise sugary solutions such as nectar or honeydew (secreted by plant-sucking homopteran insects), as well as phloem sap that sand flies obtain by piercing leaves and stems with their needle-like mouthparts. Hence, the structure of plant communities can influence the distribution and epidemiology of leishmaniasis. We designed a next-generation sequencing (NGS)-based assay for determining the source of sand fly plant meals, based upon the chloroplast DNA gene ribulose bisphosphate carboxylase large chain (rbcL). Here, we report on the predilection of several sand fly species, vectors of leishmaniasis in different parts of the world, for feeding on Cannabis sativa We infer this preference based on the substantial percentage of sand flies that had fed on C. sativa plants despite the apparent "absence" of these plants from most of the field sites. We discuss the conceivable implications of the affinity of sand flies for C. sativa on their vectorial capacity for Leishmania and the putative exploitation of their attraction to C. sativa for the control of sand fly-borne diseases.

Introgression between Anopheles gambiae and Anopheles coluzzii in Burkina Faso and its associations with kdr resistance and Plasmodium infection.

BACKGROUND: Insecticide resistance in Anopheles coluzzii mosquitoes has become widespread throughout West Africa including in Burkina Faso. The insecticide resistance allele (kdr or L1014F) is a prime indicator that is highly correlated with phenotypic resistance in West Africa. Studies from Benin, Ghana and Mali have suggested that the source of the L1014F is introgression of the 2L divergence island via interspecific hybridization with Anopheles gambiae. The goal of this study was to characterize local mosquito populations in the Nouna Department, Burkina Faso with respect to: (i) the extent of introgression between An. coluzzii and An. gambiae, (ii) the frequency of the L1014F mutation and (iii) Plasmodium infection rates. METHODS: A total of 95 mosquitoes were collected from ten sites surrounding Nouna town in Kossi Province, Burkina Faso in 2012. The species composition, the extent of introgression in An. coluzzii mosquitoes and their Plasmodium infection rates were identified with a modified version of the "Divergence Island SNP" (DIS) genotyping assay. RESULTS: The mosquito collection contained 70.5% An. coluzzii, 89.3% of which carried a 3 Mb genomic region on the 2L chromosome with L1014F insecticide resistance mutation that was introgressed from An. gambiae. In addition, 22.4% in the introgressed An. coluzzii specimens were infected with Plasmodium falciparum, whereas none of the non-introgressed ("pure") An. coluzzii were infected. CONCLUSION: This paper is the first report providing divergence island SNP genotypes for natural population of Burkina Faso and corresponding Plasmodium infection rates. These observations warrant further study and could have a major impact on future malaria control strategies in Burkina Faso.

First detection of Leishmania donovani in sand flies from Cameroon and its epidemiological implications.

OBJECTIVES: A sound knowledge of the vector-host-parasite transmission dynamics is a prerequisite for adequate control measures of vector-borne diseases. To achieve this, an entomological investigation was conducted in the cutaneous leishmaniasis (CL) endemic focus of Mokolo District, northern Cameroon to identify the insect vector(s) of the disease. METHODS: Phlebotomine sand flies were collected in and around Mokolo using New Standard CDC Miniature Light Traps. Individual sand flies were used for morphological species identification, and the remainder of the body for DNA analysis. Sand flies were demonstrated to harbour Leishmania spp. parasites using ITS1 PCR. Mitochondrial vertebrate-specific Cytochrome b -PCR was used to identify blood meals ingested by female sand flies. PCR amplicons were sequenced for Leishmania and blood sources discrimination. RESULTS: This study revealed the presence of Leishmania donovani complex DNA (n = 1) in Phlebotomus duboscqi and of lizard-borne Leishmania tarentolae-like DNA (n = 3) in Sergentomyia spp. in 79 sand fly specimens from Mokolo district. CONCLUSIONS: The causative agent of CL could not be detected in potential vectors. Instead, we found evidence for visceral leishmaniasis (VL) parasites in Phlebotomus duboscqi as well as enzootic reptile parasites in the Mokolo area. We recommend that an epidemiological survey be carried out in the area to evaluate the prevalence and eventually describe the clinical manifestations of VL in the human population. Political instability in neighbouring countries and the resulting refugee migration are likely explanations for the emergence of VL in Mokolo.

Surveillance and detection of Haemaphysalis longicornis (Acari: Ixodidae) in protected areas from Georgia, USA.

The invasion of the Asian longhorned tick, Haemaphysalis longicornis Neumann, into the United States poses a significant ecological, veterinarian, and public health threat. We conducted a comprehensive tick survey using standard tick flagging protocol for collection over 3 field seasons, March-August, and 56 surveyed sites to identify the presence of H. longicornis in the native ecosystem and prove its establishment according to USDA criteria. Of the total 56 state parks and wildlife management areas (WMA) surveyed, only one was found to be invaded by H. longicornis; detection of H. longicornis occurred at Buck Shoals Wildlife Management area in White County, GA. This site is maintained by the state of Georgia, has no agricultural animals present, and hosts a large white-tailed deer population. After the initial detection of H. longicornis in 2022, an additional field season occurred in 2023, where H. longicornis was confirmed as established based on USDA criteria. The increase in H. longicornis populations from 2021 to 2023 at Buck Shoals WMA points to the rapid spread of this tick within the environment. Our findings provide evidence of the rapid establishment of H. longicornis in the southern edge of suitability for this tick and within the native ecosystem beyond farmlands and private land.

Wolbachia pipientis (Rickettsiales: Rickettsiaceae) mediated effects on the fitness and performance of Aedes aegypti (Diptera: Culicidae) under variable temperatures and initial larval densities.

Wolbachia pipientis (Hertig, 1936), also referred as Wolbachia, is a bacterium present across insect taxa, certain strains of which have been demonstrated to impact the fitness and capacity to transmit viruses in mosquitoes, particularly Aedes aegypti (Linnaeus, 1762). Most studies examine these impacts in limited sets of environmental regimes. Here we seek to understand the impacts of environmentally relevant conditions such as larval density, temperature, and their interaction on wAlbB-infected A. aegypti. Using a factorial design, we measured wAlbB stability (relative density, post-emergence in females, and in progeny), the ability for wAlbB to induce cytoplasmic incompatibility, and bacterial effects on mosquito fitness (fecundity, fertility, and body mass) and performance (adult survival and time to pupation) across 2 temperature regimes (fluctuating and constant) and 2 initial larval densities (low and high). Fluctuating daily regimes of temperature (27 to 40 °C) led to decreased post-emergence wAlbB density and increased wAlbB density in eggs compared to constant temperature (27 °C). An increased fecundity was found in wAlbB-carrying females reared at fluctuating temperatures compared to uninfected wild-type females. wAlbB-carrying adult females showed significantly increased survival than wild-type females. Contrarily, wAlbB-carrying adult males exhibited a significantly lower survival than wild-type males. We found differential effects of assessed treatments (Wolbachia infection status, temperature, and larval density) across mosquito sexes and life stages. Taken together, our results indicate that realistic conditions may not impact dramatically the stability of wAlbB infection in A. aegypti. Nonetheless, understanding the ecological consequence of A. aegypti-wAlbB interaction is complex due to life history tradeoffs under conditions faced by natural populations.

Evidence of Ongoing Transmission of Zika Virus in Mérida, Mexico.

Since the Zika virus (ZIKV) pandemic in 2015-2017, there has been a near absence of reported cases in the Americas outside of Brazil. However, the conditions for Aedes-borne transmission persist in Latin America, and the threat of ZIKV transmission is increasing as population immunity wanes. Mexico has reported only 70 cases of laboratory-confirmed ZIKV infection since 2020, with no cases recorded in the Yucatán peninsula. Here, we provide evidence of active ZIKV transmission, despite the absence of official case reports, in the city of Mérida, Mexico, the capital of the state of Yucatán. Capitalizing on an existing cohort, we detected cases in participants with symptoms consistent with flavivirus infection from 2021 to 2022. Serum samples from suspected cases were tested for ZIKV RNA by polymerase chain reaction or ZIKV-reactive IgM by ELISA. To provide more specific evidence of exposure, focus reduction neutralization tests were performed on ELISA-positive samples. Overall, we observed 25 suspected ZIKV infections for an estimated incidence of 2.8 symptomatic cases per 1,000 persons per year. Our findings emphasize the continuing threat of ZIKV transmission in the setting of decreased surveillance and reporting.

Laboratory Evaluation of Efficacy of the Larvicide Spinosad Against AnophelesStephensi in Jigjiga, Ethiopia.

We report the efficacy of a commercial formulation of the insecticide spinosad against larvae of Anopheles stephensi populations found in the city of Jigjiga, Somali Region, eastern Ethiopia. Batches of 25 larvae (late III to early IV instars) collected from large water storage reservoirs associated with construction sites (the primary An. stephensi larval site in the dry season) were tested under laboratory conditions against each insecticide at a dose recommended by the manufacturer (Natular® G30, 0.02 g/5 liter), following World Health Organization guidelines. Mortality at 24-48 h postexposure was 100%. Results show that spinosad is effective against An. stephensi larvae and suggest that it may be a useful tool as part of larval source management plans aimed at controlling this invasive malaria vector in Ethiopia.

Residual efficacy of the neonicotinoid insecticide clothianidin against pyrethroid-resistant Aedes aegypti.

BACKGROUND: Here we report the residual efficacy of the neonicotinoid insecticide clothianidin against pyrethroid-resistant Aedes aegypti. We first conducted a range-finding evaluation of clothianidin on three different substrates (wall, wood, cloth) using three doses (100, 300 and 600 mg a.i. m-2 ) and conducting World Health Organization (WHO) cone bioassays to assess acute (24 h) and delayed (up to 7 days) mortality. In experimental houses located in Merida (Mexico) and using free-flying pyrethroid-resistant Ae. aegypti females, we quantified the acute and delayed mortality after a 24-h exposure to the targeted indoor residual spraying (TIRS) of two clothianidin doses (100 and 300 mg a.i. m-2 ). RESULTS: Range-finding studies with WHO cones showed low (<50%) acute mortality for all surfaces, doses and times post spraying. Delayed mortality was higher, with average values above or close to the 60% mark (and 95% confidence interval estimates crossing 80% for the 600 mg a.i. m-2 dose). In experimental houses, a similar low acute mortality was quantified (range of mortality across 12 months was 2-44% for 100 mg a.i. m-2 and 8-61% for 300 mg a.i/m2 ). However, delayed mortality showed a strong effect of clothianidin on free-flying Ae. aegypti, with values above 80% up to 7 months post-TIRS. CONCLUSION: Novel residual insecticide molecules have a promising outlook for Ae. aegypti control and can contribute to the expansion and adoption of TIRS in urban areas. clothianidin can contribute to the control of resistant Ae. aegypti and provide residual control for up to 7 months after application. © 2022 Society of Chemical Industry.

Building the vector in: construction practices and the invasion and persistence of Anopheles stephensi in Jigjiga, Ethiopia.

Anopheles stephensi is a major vector of malaria in Asia and the Arabian Peninsula, and its recent invasion into Africa poses a major threat to malaria control and elimination efforts on the continent. The mosquito is well adapted to urban environments, and its presence in Africa could potentially lead to an increase in malaria transmission in cities. Most of the knowledge about An stephensi ecology in Africa has been generated from studies conducted during the rainy season, when vectors are most abundant. Here, we provide evidence from the peak of the dry season in the city of Jigjiga in Ethiopia, and report An stephensi immature stages infesting predominantly in water reservoirs made to support construction operations (ie, in construction sites or associated with brick-manufacturing businesses). Political and economic changes in Ethiopia (particularly the Somali Region) have fuelled an unprecedented construction boom since 2018 that, in our opinion, has been instrumental in the establishment, persistence, and propagation of An stephensi via the year-round availability of perennial larval habitats associated with construction. We argue that larval source management during the dry season might provide a unique opportunity for focused control of An stephensi in Jigjiga and similar areas.

Targeted indoor residual insecticide applications shift Aedes aegypti age structure and arbovirus transmission potential.

While residual insecticide applications have the potential to decrease pathogen transmission by reducing the density of vectors and shifting the age structure of the adult mosquito population towards younger stages of development, this double entomological impact has not been documented for Aedes aegypti. Aedes collected from households enrolled in a cluster-randomized trial evaluating the epidemiological impact of targeted indoor residual spraying (TIRS) in Merida, Mexico, were dissected and their age structure characterized by the Polovodova combined with Christopher's ovariole growth methods. In total, 813 females were dissected to characterize age structure at 1, 3, 6, and 9 months post-TIRS. Significant differences in the proportion of nulliparous Ae. aegypti females between the treatment groups was found at one-month post-TIRS (control: 35% vs. intervention: 59%), three months (20% vs. 49%) but not at six or nine months post-TIRS. TIRS significantly shiftted Ae. aegypti age structure towards younger stages and led to a non-linear reduction in survivorship compared to the control arm. Reduced survivorship also reduced the number of arbovirus transmitting females (those who survived the extrinsic incubation period). Our findings provide strong evidence of the full entomological impact of TIRS, with important implications for quantifying the epidemiological impact of vector control methods.

Preventive residual insecticide applications successfully controlled Aedes aegypti in Yucatan, Mexico.

Insecticide-based approaches remain a key pillar for Aedes-borne virus (ABV, dengue, chikungunya, Zika) control, yet they are challenged by the limited effect of traditional outdoor insecticide campaigns responding to reported arboviral cases and by the emergence of insecticide resistance in mosquitoes. A three-arm Phase II unblinded entomological cluster randomized trial was conducted in Merida, Yucatan State, Mexico, to quantify the entomological impact of targeted indoor residual spraying (TIRS, application of residual insecticides in Ae. aegypti indoor resting sites) applied preventively 2 months before the beginning of the arbovirus transmission season. Trial arms involved the use of two insecticides with unrelated modes of action (Actellic 300CS, pirimiphos-methyl, and SumiShield 50WG, clothianidin) and a control arm where TIRS was not applied. Entomological impact was quantified by Prokopack adult collections performed indoors during 10 min per house. Regardless of the insecticide, conducting a preventive TIRS application led to significant reductions in indoor Ae. aegypti densities, which were maintained at the same levels as in the low arbovirus transmission period (Actellic 300CS reduced Ae. aegypti density up to 8 months, whereas SumiShield 50WG up to 6 months). The proportional reduction in Ae. aegypti abundance in treatment houses compared to control houses was 50-70% for Actellic 300CS and 43-63% for SumiShield 50WG. Total operational costs including insecticide ranged from US$4.2 to US$10.5 per house, depending on the insecticide cost. Conducting preventive residual insecticide applications can maintain Ae. aegypti densities at low levels year-round with important implications for preventing ABVs in the Americas and beyond.

Experimental evaluation of a metofluthrin passive emanator against Aedes albopictus.

BACKGROUND: With the recent occurrence of locally transmitted Aedes-borne viruses in the continental United States and Europe, and a lack of effective vaccines, new approaches to control Aedes aegypti and Aedes albopictus are needed. In sub-tropical urban settings in the US, Ae. albopictus is a dominant nuisance and arbovirus vector species. Unfortunately, the vector control toolbox against Ae. albopictus is not as well developed as for Ae. aegypti. Here, we evaluate the efficacy, longevity, and range of protectiveness of a novel passive metofluthrin emanator (10% active ingredient in a polyethylene mesh) against Ae. albopictus indoors and outdoors. METHODS: Four studies were conducted comparing the presence of the metofluthrin emanator to a control lacking emanator with interest in quantifying efficacy by human landing counts. Studies evaluated the effect of an emanator at varying distances from one or more human volunteers indoors and outdoors. Efficacy of emanators over time since activation was also evaluated. RESULTS: Mixed-effects models determined that sitting in close proximity to an emanator reduced landings by 89.5% outdoors and by 74.6% indoors. The emanator was determined protective when located immediately next to a human volunteer outdoors but not uniformly protective when located further away. The emanator was protective at all tested distances from the device indoors. Mortality of mosquitoes exposed to metofluthrin emanators was ~2x higher than those who were not exposed in indoor conditions. Finally, a Generalized Additive Model determined that emanators used continuously outdoors lost their effect after 2.5 weeks and stopped inducing paralysis in mosquitoes after 3.8 weeks of use. CONCLUSIONS: We show strong and lasting efficacy of 10% metofluthrin emanators against field Ae. albopictus both in indoor and outdoor conditions. Metofluthrin emanators can protect people from Ae. albopictus bites, representing a viable option for reducing human-mosquito contacts at home and beyond.

SARS-CoV-2 antibody prevalence in a pediatric cohort of unvaccinated children in Mérida, Yucatán, México.

The prevalence of SARS-CoV-2 exposure in children during the global COVID-19 pandemic has been underestimated due to lack of testing and the relatively mild symptoms in adolescents. Understanding the exposure rates in the pediatric population is essential as children are the last to receive vaccines and can act as a source for SARS-CoV-2 mutants that may threaten vaccine escape. This cross-sectional study aims to quantify the prevalence of anti-SARS-CoV-2 serum antibodies in children in a major city in México in the Spring of 2021 and determine if there are any demographic or socioeconomic correlating factors. We obtained socioeconomic information and blood samples from 1,005 children from 50 neighborhood clusters in Mérida, Yucatán, México. We then tested the sera of these participants for anti-SARS-CoV-2 IgG and IgM antibodies using lateral flow immunochromatography. We found that 25.5% of children in our cohort were positive for anti-SARS-CoV-2 antibodies and there was no correlation between age and antibody prevalence. Children that lived with large families were statistically more likely to have antibodies against SARS-CoV-2. Spatial analyses identified two hotspots of high SARS-CoV-2 seroprevalence in the west of the city. These results indicate that a large urban population of unvaccinated children has been exposed to SARS-CoV-2 and that a major correlating factor was the number of people within the child's household with a minor correlation with particular geographical hotspots. There is also a larger population of children that may be susceptible to future infection upon easing of social distancing measures. These findings suggest that in future pandemic scenarios, limited public health resources can be best utilized on children living in large households in urban areas.

Natural Aedes-Borne Virus Infection Detected in Male Adult Aedes aegypti (Diptera: Culicidae) Collected From Urban Settings in Mérida, Yucatán, México.

Aedes-borne viruses (ABVs) such as dengue (DENV), chikungunya (CHIKV), and Zika (ZIKV) contribute significantly to the global burden of infectious diseases, disproportionately affecting disadvantaged populations from tropical and subtropical urban areas. ABVs can be transmitted from female mosquitoes to their progeny by vertical transmission via transovarial and/or trans-egg vertical transmission and contribute to the maintenance of infected-mosquito populations year-round in endemic regions. This study describes the natural infection rate of DENV, CHIKV, and ZIKV in field-caught male Aedes (Sergentomyia) aegypti (Linnaeus) mosquitoes from Mérida, Yucatán, México, as a proxy for the occurrence of vertical virus transmission. We used indoor sequential sampling with Prokopack aspirators to collect all mosquitoes inside houses from ABV hotspots areas. Collections were performed in a DENV and CHIKV post-epidemic phase and during a period of active ZIKV transmission. We individually RT-qPCR tested all indoor collected Ae. aegypti males (1,278) followed by Sanger sequencing analysis for final confirmation. A total of 6.7% male mosquitoes were positive for ABV (CHIKV = 5.7%; DENV = 0.9%; ZIKV = 0.1%) and came from 21.0% (30/143) houses infested with males. Most ABV-positive male mosquitoes were positive for CHIKV (84.8%). The distribution of ABV-positive Ae. aegypti males was aggregated in a few households, with two houses having 11 ABV-positive males each. We found a positive association between ABV-positive males and females per house. These findings suggested the occurrence of vertical arbovirus transmission within the mosquito populations in an ABV-endemic area and, a mechanism contributing to viral maintenance and virus re-emergence among humans in post-epidemic periods.

Efficacy of targeted indoor residual spraying with the pyrrole insecticide chlorfenapyr against pyrethroid-resistant Aedes aegypti.

BACKGROUND: There is an increased need to mitigate the emergence of insecticide resistance and incorporate new formulations and modes of application to control the urban vector Aedes aegypti. Most research and development of insecticide formulations for the control of Ae. aegypti has focused on their peridomestic use as truck-mounted ULV-sprays or thermal fogs despite the widespread knowledge that most resting Ae. aegypti are found indoors. A recent modification of indoor residual spraying (IRS), termed targeted IRS (TIRS) works by restricting applications to 1.5 m down to the floor and on key Ae. aegypti resting sites (under furniture). TIRS also opens the possibility of evaluating novel residual insecticide formulations currently being developed for malaria IRS. METHODS: We evaluated the residual efficacy of chlorfenapyr, formulated as Sylando 240SC, for 12 months on free-flying field-derived pyrethroid-resistant Ae. aegypti using a novel experimental house design in Merida, Mexico. On a monthly basis, 600 female Ae. aegypti were released into the houses and left indoors with access to sugar solution for 24 hours. After the exposure period, dead and alive mosquitoes were counted in houses treated with chlorfenapyr as well as untreated control houses to calculate 24-h mortality. An evaluation for these exposed cohorts of surviving mosquitoes was extended up to seven days under laboratory conditions to quantify "delayed mortality". RESULTS: Mean acute (24-h) mortality of pyrethroid-resistant Ae. aegypti ranged 80-97% over 5 months, dropping below 30% after 7 months post-TIRS. If delayed mortality was considered (quantifying mosquito mortality up to 7 days after exposure), residual efficacy was above 90% for up to 7 months post-TIRS application. Generalized Additive Mixed Models quantified a residual efficacy of chlorfenapyr of 225 days (ca. 7.5 months). CONCLUSIONS: Chlorfenapyr represents a new option for TIRS control of Ae. aegypti in urban areas, providing a highly-effective time of protection against indoor Ae. aegypti females of up to 7 months.

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

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.

Natural arbovirus infection rate and detectability of indoor female Aedes aegypti from Mérida, Yucatán, Mexico.

Arbovirus infection in Aedes aegypti has historically been quantified from a sample of the adult population by pooling collected mosquitoes to increase detectability. However, there is a significant knowledge gap about the magnitude of natural arbovirus infection within areas of active transmission, as well as the sensitivity of detection of such an approach. We used indoor Ae. aegypti sequential sampling with Prokopack aspirators to collect all mosquitoes inside 200 houses with suspected active ABV transmission from the city of Mérida, Mexico, and tested all collected specimens by RT-PCR to quantify: a) the absolute arbovirus infection rate in individually tested Ae. aegypti females; b) the sensitivity of using Prokopack aspirators in detecting ABV-infected mosquitoes; and c) the sensitivity of entomological inoculation rate (EIR) and vectorial capacity (VC), two measures ABV transmission potential, to different estimates of indoor Ae. aegypti abundance. The total number of Ae. aegypti (total catch, the sum of all Ae. aegypti across all collection intervals) as well as the number on the first 10-min of collection (sample, equivalent to a routine adult aspiration session) were calculated. We individually tested by RT-PCR 2,161 Aedes aegypti females and found that 7.7% of them were positive to any ABV. Most infections were CHIKV (77.7%), followed by DENV (11.4%) and ZIKV (9.0%). The distribution of infected Aedes aegypti was overdispersed; 33% houses contributed 81% of the infected mosquitoes. A significant association between ABV infection and Ae. aegypti total catch indoors was found (binomial GLMM, Odds Ratio > 1). A 10-min indoor Prokopack collection led to a low sensitivity of detecting ABV infection (16.3% for detecting infected mosquitoes and 23.4% for detecting infected houses). When averaged across all infested houses, mean EIR ranged between 0.04 and 0.06 infective bites per person per day, and mean VC was 0.6 infectious vectors generated from a population feeding on a single infected host per house/day. Both measures were significantly and positively associated with Ae. aegypti total catch indoors. Our findings provide evidence that the accurate estimation and quantification of arbovirus infection rate and transmission risk is a function of the sampling effort, the local abundance of Aedes aegypti and the intensity of arbovirus circulation.