bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2021‒02‒21
twenty-one papers selected by
Richard Halfpenny
Staffordshire University

  1. PLoS Negl Trop Dis. 2021 Feb 18. 15(2): e0009173
      BACKGROUND: As an invasive mosquito species in the United States, Aedes albopictus is a potential vector of arboviruses including dengue, chikungunya, and Zika, and may also be involved in occasional transmission of other arboviruses such as West Nile, Saint Louis encephalitis, eastern equine encephalitis, and La Crosse viruses. Aedes albopictus feeds on a wide variety of vertebrate hosts, wild and domestic, as well as humans.METHODOLOGY/PRINCIPAL FINDINGS: In order to investigate blood feeding patterns of Ae. albopictus, engorged specimens were collected from a variety of habitat types using the Centers for Disease Control and Prevention light traps, Biogents Sentinel 2 traps, and modified Reiter gravid traps in southeast Virginia. Sources of blood meals were determined by the analysis of mitochondrial cytochrome b gene sequences amplified in PCR assays. Our aims were to quantify degrees of Ae. albopictus interactions with vertebrate hosts as sources of blood meals, investigate arboviral infection status, assess the influence of key socioecological conditions on spatial variability in blood feeding, and investigate temporal differences in blood feeding by season. Analysis of 961 engorged specimens of Ae. albopictus sampled between 2017-2019 indicated that 96%, 4%, and less than 1% obtained blood meals from mammalian, reptilian, and avian hosts, respectively. Domestic cats were the most frequently identified (50.5%) hosts followed by Virginia opossums (17.1%), white-tailed deer (12.2%), and humans (7.3%), together representing 87.1% of all identified blood hosts. We found spatial patterns in blood feeding linked to socioecological conditions and seasonal shifts in Ae. albopictus blood feeding with implications for understanding human biting and disease risk. In Suffolk Virginia in areas of lower human development, the likelihood of human blood feeding increased as median household income increased and human blood feeding was more likely early in the season (May-June) compared to later (July-October). Screening of the head and thorax of engorged Ae. albopictus mosquitoes by cell culture and RT-PCR resulted in a single isolate of Potosi virus.
    CONCLUSION AND SIGNIFICANCE: Understanding mosquito-host interactions in nature is vital for evaluating vectorial capacity of mosquitoes. These interactions with competent reservoir hosts support transmission, maintenance, and amplification of zoonotic agents of human diseases. Results of our study in conjunction with abundance in urban/suburban settings, virus isolation from field-collected mosquitoes, and vector competence of Ae. albopictus, highlight the potential involvement of this species in the transmission of a number of arboviruses such as dengue, chikungunya, and Zika to humans. Limited interaction with avian hosts suggests that Ae. albopictus is unlikely to serve as a bridge vector of arboviruses such as West Nile and eastern equine encephalitis in the study region, but that possibility cannot be entirely ruled out.
  2. Malar J. 2021 Feb 16. 20(1): 95
      BACKGROUND: Ethiopia has made great strides in malaria control over the last two decades. However, this progress has not been uniform and one concern has been reported high rates of malaria transmission in large agricultural development areas in western Ethiopia. Improved vector control is one way this transmission might be addressed, but little is known about malaria vectors in this part of the country.METHODS: To better understand the vector species involved in malaria transmission and their behaviour, human landing collections were conducted in Dangur woreda, Benishangul-Gumuz, between July and December 2017. This period encompasses the months with the highest rain and the peak mosquito population. Mosquitoes were identified to species and tested for the presence of Plasmodium sporozoites.
    RESULTS: The predominant species of the Anopheles collected was Anopheles arabiensis (1,733; i.e. 61.3 % of the entire Anopheles), which was also the only species identified with sporozoites (Plasmodium falciparum and Plasmodium vivax). Anopheles arabiensis was collected as early in the evening as 18:00 h-19:00 h, and host-seeking continued until 5:00 h-6:00 h. Nearly equal numbers were collected indoors and outdoors. The calculated entomological inoculation rate for An. arabiensis for the study period was 1.41 infectious bites per month. More An. arabiensis were collected inside and outside worker's shelters than in fields where workers were working at night.
    CONCLUSIONS: Anopheles arabiensis is likely to be the primary vector of malaria in the agricultural development areas studied. High rates of human biting took place inside and outdoor near workers' residential housing. Improved and targeted vector control in this area might considerably reduce malaria transmission.
    Keywords:  Agricultural development; Anopheles arabiensis; Ethiopia; Malaria; Migrant workers
  3. J Infect Dis. 2021 Jan 28. pii: jiab049. [Epub ahead of print]
      BACKGROUND: There is a steady rise in the global incidence of Aedes-borne arbovirus disease. It has become urgent to develop alternative solutions for mosquito vector control. We developed a new method of sterilization of male mosquitoes, with the goal to suppress a local Aedes aegypti population and to prevent the spread of dengue.METHODS: Sterile male mosquitoes were produced from a locally acquired Ae. aegypti colony by using a treatment that includes double-stranded RNA and thiotepa. A field study was conducted, with sterile mosquito releases being performed on a weekly basis in predefined areas. Two intervention periods (INT1 and INT2) were carried out, with treatment and control areas reversed between INT1 and INT2.
    RESULTS: During INT1, releases in the treated area resulted in up to 91.4% reduction of live progeny of field Ae. aegypti mosquitoes recorded over time, while the control neighborhoods (no releases of sterile male mosquitoes) remained highly infested. The successful implementation of the program during INT1 and INT2 were associated with a 15.9-fold and 13.7-fold lower incidences of dengue in the treated area compared to the control areas, respectively.
    CONCLUSIONS: Our data show the success of this new SIT-based program in preventing the spread of dengue.
    Keywords:   Aedes aegypti ; SIT; dengue; dsRNA; suppression; thiotepa
  4. J Am Mosq Control Assoc. 2020 Sep 01. 36(3): 189-196
      A field study investigated penetration of outdoor ground ultra-low-volume (ULV) aerosol and thermal fog adulticide applications into a dwelling to control the dengue vector Aedes aegypti (L). Four applications of Kontrol 4-4 (4.6% permethrin active ingredient [AI], 4.6% piperonyl butoxide) at the maximum label rate were made at 25-30 m in front of a house at Camp Blanding Joint Training Center, Starke, FL, during summer 2016. The ULV sprayer and thermal fogger nozzles were oriented horizontally, and vehicle travel speeds were 16 and 24 km/h, respectively. All doors and windows of the house were left open. Spray efficacy was assessed using caged female mosquitoes positioned 30 cm above ground, outside and inside of the house. Interior cages were placed in open areas and cryptic sites (i.e., in a closet or cardboard box). A spinner holding 2 rods sized 3 mm × 75 mm was deployed next to each cage (except cryptic sites) to sample droplets and to quantify AI deposition. Thirty minutes after application, cages were removed, slides collected, and mosquitoes transferred to clean cages in the laboratory where mortality was assessed at 24 h posttreatment. The ULV application to the south side of the house produced 100% mortality in outdoor and indoor cages and 24% mortality at cryptic sites. Similarly applied thermal fog resulted in 85% mortality outdoors, 34% indoors, and only 4% in cages at cryptic sites. Application of either method from the west resulted in 19-61% mortality outdoors and 0.5-6.5% indoors. Droplet volume median diameter (Dv0.5) on rods from the ULV application was significantly larger compared with the thermal fogger outdoors, but similar indoors. Outdoors and indoors, the AI deposition from ULV was significantly higher than from thermal fog. Our results show the potential for controlling dengue vectors inside houses with outdoor ground ULV applications in areas where doors and windows are left open for ventilation.
    Keywords:  Insecticide application; Kontrol 4-4; penetration; permethrin; ultra-low volume
  5. Trop Biomed. 2019 Mar 01. 36(1): 310-314
      We report the presence of Zika virus RNA in naturally infected field captured Aedes aegypti and Ae. albopictus mosquito larvae in Malaysia from May 2016 to April 2017. Zika virus RNA was detected (n = 30) in the larvae of both Aedes mosquito species. Phylogenetic analysis of the NS5 partial sequence of all positive samples shows that the circulating Zika virus in the field collected larvae are of the Asian lineage.
  6. PLoS Negl Trop Dis. 2021 Feb 16. 15(2): e0008492
      Vector control largely relies on neurotoxic chemicals, and insecticide resistance (IR) directly threatens their effectiveness. In some cases, specific alleles cause IR, and knowledge of the genetic diversity and gene flow among mosquito populations is crucial to track their arrival, rise, and spread. Here we evaluated Aedes aegypti populations' susceptibility status, collected in 2016 from six different municipalities of Rio de Janeiro state (RJ), to temephos, pyriproxyfen, malathion, and deltamethrin. We collected eggs of Ae. aegypti in Campos dos Goytacazes (Cgy), Itaperuna (Ipn), Iguaba Grande (Igg), Itaboraí (Ibr), Mangaratiba (Mgr), and Vassouras (Vsr). We followed the World Health Organization (WHO) guidelines and investigated the degree of susceptibility/resistance of mosquitoes to these insecticides. We used the Rockefeller strain as a susceptible positive control. We genotyped the V1016I and F1534C knockdown resistance (kdr) alleles using qPCR TaqMan SNP genotyping assay. Besides, with the use of Ae. aegypti SNP-chip, we performed genomic population analyses by genotyping more than 15,000 biallelic SNPs in mosquitoes from each population. We added previous data from populations from other countries to evaluate the ancestry of RJ populations. All RJ Ae. aegypti populations were susceptible to pyriproxyfen and malathion and highly resistant to deltamethrin. The resistance ratios for temephos was below 3,0 in Cgy, Ibr, and Igg populations, representing the lowest rates since IR monitoring started in this Brazilian region. We found the kdr alleles in high frequencies in all populations, partially justifying the observed resistance to pyrethroid. Population genetics analysis showed that Ae. aegypti revealed potential higher migration among some RJ localities and low genetic structure for most of them. Future population genetic studies, together with IR data in Ae aegypti on a broader scale, can help us predict the gene flow within and among the Brazilian States, allowing us to track the dynamics of arrival and changes in the frequency of IR alleles, providing critical information to improving vector control program.
  7. BMC Infect Dis. 2021 Feb 19. 21(1): 194
      BACKGROUND: Long-lasting insecticidal nets (LLINs) are currently the primary method of malaria control in sub-Saharan Africa and have contributed to a significant reduction in malaria burden over the past 15 years. However, this progress is threatened by the wide-scale selection of insecticide-resistant malaria vectors. It is, therefore, important to accelerate the generation of evidence for new classes of LLINs.METHODS: This protocol presents a three-arm superiority, single-blinded, cluster randomized controlled trial to evaluate the impact of 2 novel dual-active ingredient LLINs on epidemiological and entomological outcomes in Benin, a malaria-endemic area with highly pyrethroid-resistant vector populations. The study arms consist of (i) Royal Guard® LLIN, a net combining a pyrethroid (alpha-cypermethrin) plus an insect growth regulator (pyriproxyfen), which in the adult female is known to disrupt reproduction and egg fertility; (ii) Interceptor G2® LLIN, a net incorporating two adulticides (alpha-cypermethrin and chlorfenapyr) with different modes of action; and (iii) the control arm, Interceptor® LLIN, a pyrethroid (alpha-cypermethrin) only LLIN. In all arms, one net for every 2 people will be distributed to each household. Sixty clusters were identified and randomised 1:1:1 to each study arm. The primary outcome is malaria case incidence measured over 24 months through active case detection in a cohort of 25 children aged 6 months to 10 years, randomly selected from each cluster. Secondary outcomes include 1) malaria infection prevalence (all ages) and prevalence of moderate to severe anaemia in children under 5 years old, measured at 6 and 18 months post-intervention; 2) entomological indices measured every 3 months using human landing catches over 24 months. Insecticide resistance intensity will also be monitored over the study period.
    DISCUSSION: This study is the second cluster randomised controlled trial to evaluate the efficacy of these next-generation LLINs to control malaria transmitted by insecticide-resistant mosquitoes. The results of this study will form part of the WHO evidence-based review to support potential public health recommendations of these nets and shape malaria control strategies of sub-Saharan Africa for the next decade.
    TRIAL REGISTRATION:, NCT03931473 , registered on 30 April 2019.
    Keywords:  Benin; Chlorfenapyr, pyriproxyfen, Royal Guard®; Cluster randomized controlled trial; Dual-active ingredient long-lasting insecticidal nets; Entomological inoculation rate; Interceptor® G2; Malaria case incidence; Malaria prevalence
  8. PLoS One. 2021 ;16(2): e0246932
      Mosquito diversity and disease transmission are influenced by landscape modifications, i.e., vectors and pathogens previously found only in forests are now found close to human environments due to anthropic changes. This study determined the diversity and distribution of mosquitoes in forest environments in order to analyze the potential vectors of Amazonian forest arboviruses. Mosquitoes were collected by 1) vertical stratification from forest canopy and ground areas using Hooper Pugedo (HP) light traps and human attraction and 2) horizontal stratification using HP light traps in peridomicile, forest edge, and forest environments near the Rio Pardo rural settlement, Amazonas, Brazil. A total of 3,750 mosquitoes were collected, representing 46 species. 3,139 individuals representing 46 species were sampled by vertical stratification. Both the Shannon-Weaver diversity index (H') and equitability (J') were higher in the canopy than on the ground. 611 individuals representing 13 species were sampled by horizontal stratification. H' decreased in the following order: forest edge > forest > peridomicile, and J' was greater at the forest edge and smaller in the peridomicile environment. Moreover, H' was higher for the human attraction collection method than the HP traps. A total of 671 pools were analyzed by RT-qPCR; three species were positive for Oropouche-like viruses (Ochlerotatus serratus, Psorophora cingulata, and Haemagogus tropicalis) and the minimum infection rate was 0.8%. The composition of mosquito species did not differ significantly between anthropic and forest environments in Rio Pardo. Some mosquito species, due to their abundance, dispersion in the three environments, and record of natural infection, were hypothesized to participate in the arbovirus transmission cycle in this Amazonian rural settlement.
  9. J Am Mosq Control Assoc. 2020 Sep 01. 36(3): 197-200
      Aedes albopictus is an important vector of several arboviruses that affect human health worldwide; thus, knowledge of its distribution is a key factor for the implementation of disease control strategies. In Mexico, Ae. albopictus was recorded for the first time in 1988 in Tamaulipas State (northeast), but currently it has been recorded in 14 of the 32 states in the country. In 2012, it was recorded for the first time in a single locality in Quintana Roo (Cancún). In this study, we provide new distribution information for Ae. albopictus in the center and south of Quintana Roo State and comment on its medical importance.
    Keywords:   Aedes albopictus ; Mexico; arbovirus; distribution
  10. J Am Mosq Control Assoc. 2020 Sep 01. 36(3): 201-203
      Four mosquito species-Anopheles (Nyssorhynchus) galvaoi, An. (Anopheles) mediopunctatus, Culex (Culex) lahillei, and Uranotaenia (Uranotaenia) geométrica-were recorded for the first time in northwestern Argentina. In addition, Psorophora (Grabhamia) confinnis and Cx. (Melanoconion) pedroi are reported for the first time in Jujuy Province, while Aedes (Ochlerotatus) hastatus, Coquillettidia (Rhynchotaenia) hermanoi, An. (Ano.) fluminensis, and An. (Ano.) punctimacula were reported for the first time in Tucumán Province.
    Keywords:  Culicidae; Jujuy; Salta; Tucumán; new records
  11. Environ Res. 2021 Feb 16. pii: S0013-9351(21)00187-0. [Epub ahead of print] 110893
      The environment, directly and indirectly, affects many mosquito traits in both the larval and adult stages. The availability of food resources is one of the key factors influencing these traits, although its role in mosquito fitness and pathogen transmission remains unclear. Larvae nutritional status determines their survivorship and growth, having also an impact on adult characteristics like longevity, body size, flight capacity or vector competence. During the adult stage, mosquito diet affects their survival rate, fecundity and host-seeking behaviour. It also affects mosquito susceptibility to infection, which may determine the vectorial capacity of mosquito populations. The aim of this review is to critically revise the current knowledge on the effects that both larval and adult quantity and quality of the diet have on mosquito life history traits, identifying the critical knowledge gaps and proposing future research lines. The quantity and quality of food available through their lifetime greatly determine adult body size, longevity or biting frequency, therefore affecting their competence for pathogen transmission. In addition, natural sugar sources for adult mosquitoes, i.e., specific plants providing high metabolic energy, might affect their host-seeking and vertebrate biting behaviour. However, most of the studies are carried out under laboratory conditions, highlighting the need for studies of feeding behaviour of mosquitoes under field conditions. This kind of studies will increase our knowledge of the impact of diets on pathogen transmission, helping to develop successful control plans for vector-borne diseases.
    Keywords:  Mosquito diet; arbovirus; feeding behavior; pathogen infection; vectorial capacity
  12. Trop Biomed. 2019 Jun 01. 36(2): 550-558
      There was an increasing trend in dengue infection in Malaysia with many outbreaks that occurred in Petaling District, Selangor in 2013 - 2014. A high rise apartment in Petaling Jaya reported ten episodes of dengue outbreaks from June 2013 to June 2014. We studied the prolonged dengue hotspot at this residential complex in Petaling Jaya, Selangor and made recommendations to prevent future prolonged dengue outbreaks. This was a retrospective exploratory study by analysing secondary data on dengue outbreaks from years 2013 to 2014. Small group discussions, interview sessions with staff and site visits were carried out to obtain necessary information. Two hundred and ninety-one cases were notified during the dengue outbreaks from Epid week (EW) 25 in 2013 to EW 26 in 2014 with no mortality reported. Information entered into dengue databases might be incomplete or mixed up. Active case detection and environmental risks assessment based on cases were not carry out due to the massive outbreak. Basic information on the population in the outbreak locality was unavailable. Various control activities were carried out with varying outcomes. Community participation was poor with little cooperation from residents during health education and community-based mosquito breeding prevention activities. To ensure better management of dengue outbreaks and to prevent prolonged dengue outbreaks in the future, integrated case findings, effective control activities, extensive environmental assessment on the outbreak locality and adopting innovative community outreach initiative with sufficient staff are required to curb dengue vector.
  13. PLoS Negl Trop Dis. 2021 Feb 16. 15(2): e0008736
      Transmission foci of autochthonous malaria caused by Plasmodium vivax-like parasites have frequently been reported in the Atlantic Forest in Southeastern and Southern Brazil. Evidence suggests that malaria is a zoonosis in these areas as human infections by simian Plasmodium species have been detected, and the main vector of malaria in the Atlantic Forest, Anopheles (Kerteszia) cruzii, can blood feed on human and simian hosts. In view of the lack of models that seek to predict the dynamics of zoonotic transmission in this part of the Atlantic Forest, the present study proposes a new deterministic mathematical model that includes a transmission compartment for non-human primates and parameters that take into account vector displacement between the upper and lower forest strata. The effects of variations in the abundance and acrodendrophily of An. cruzii on the prevalence of infected humans in the study area and the basic reproduction number (R0) for malaria were analyzed. The model parameters are based on the literature and fitting of the empirical data. Simulations performed with the model indicate that (1) an increase in the abundance of the vector in relation to the total number of blood-seeking mosquitoes leads to an asymptotic increase in both the proportion of infected individuals at steady state and R0; (2) the proportion of infected humans at steady state is higher when displacement of the vector mosquito between the forest strata increases; and (3) in most scenarios, Plasmodium transmission cannot be sustained only between mosquitoes and humans, which implies that non-human primates play an important role in maintaining the transmission cycle. The proposed model contributes to a better understanding of the dynamics of malaria transmission in the Atlantic Forest.
  14. Trop Biomed. 2019 Mar 01. 36(1): 209-223
      The state's retrospective findings indicate the incidence of malaria deaths, which is more during the onset of first monsoon season. Based upon this fact, our objective was to study the distribution pattern of major Anopheles vectors in two endemic districts viz. Kalahandi and Cuttack of Odisha, India that differ significantly according to malariogenic stratification, under the impact of first monsoon shower. A comparative study of vector abundance, predominance, their habitats, resting site preference, impact of abiotic rhythm (light/dark period) on vector distribution, gonotrophic status as well as sporozoite rate was established in a high and a low endemic district of Odisha, when the degree of malaria transmission elevates to its peak level Anopheles culicifacies was found to be predominant in hyperendemic Kalahandi district while Anopheles subpictus was abundant in hypo-endemic Cuttack district. Both primary vector An. culicifacies and the secondary vector An. subpictus mostly prefer CS (Cattle shed) compared to HD (Human dwelling) in Kalahandi district where as there was slight shifting of resting habitat of An. culicifacies from CS to HD in Cuttack district. Anopheles culicifacies prefers to rest on wall besides objects in Kalahandi while no such site preference was observed in Cuttack district. On the other hand, distribution of An. subpictus was highly influenced by the daily rhythm of light/dark cycle (i.e. day and night) in Cuttack. The gonotrophic condition revealed the high tendency of the predominant vectors towards endophilic resting. The sporozoite rate was 0.66% in Kalahandi and nil in Cuttack district. The proper monitoring of vector prevalence and distribution, at least during the peak transmission period can avert a perpetuated upsurge in malaria.
  15. Trop Biomed. 2019 Sep 01. 36(3): 610-619
      India contributes substantially to global malaria incidents. Vector dynamics is the significant determinant of malaria risk. Hence, knowledge on the interaction between rainfall, malaria cases and malaria vector density can be very useful for controlling malaria transmission. Kalahandi was screened for malaria cases, Anopheline vector density and their temporal relationship with rainfall. Epidemiological data was obtained from National Vector Borne Disease Control Programme, Odisha, India. Three years vector population study was carried out. Rainfall data was obtained from a database maintained by the Govt. of Odisha and was analysed using Univariate ANOVA and Pearson correlation co-efficient tests using R-prog. Malaria was found to be prevalent throughout the year attaining peak between July to August and another peak in December, amidst which the clinical malaria cases being recorded implied highest incidents in the month of July. The results estimated the seasonality of the population of An. culicifacies, An. fluviatilis and An. annularis over the region and determined the influence of rainfall on the vector population dynamics. Simple linear regression analysis suggested that at one month lag monthly rainfall (P=0.0007) was a significant meteorological factor. Rainfall seemed to be one of the best malaria predictors because of its positive correlation with proliferation of malaria cases in conjunction with An. culicifacies density making malaria a serious health issue in Kalahandi.
  16. J Travel Med. 2021 Jan 28. pii: taab015. [Epub ahead of print]
      BACKGROUND: There is concern about the risk of yellow fever (YF) establishment in Asia, owing to rising numbers of urban outbreaks in endemic countries and globalisation. Following an outbreak in Angola in 2016, YF cases were introduced into China. Prior to this, YF had never been recorded in Asia, despite climatic suitability and the presence of mosquitoes. An outbreak in Asia could result in widespread fatalities and huge economic impact. Therefore, quantifying the potential risk of YF outbreaks in Asia is a public health priority.METHODS: Using international flight data and YF incidence estimates from 2016, we quantified the risk of YF introduction via air travel into Asia. In locations with evidence of a competent mosquito population, the potential for autochthonous YF transmission was estimated using a temperature-dependent model of the reproduction number and a branching process model assuming a negative binomial distribution.
    RESULTS: 25 cities across Asia were estimated to be at risk of receiving at least one YF viraemic traveller during 2016. At their average temperatures, we estimated the probability of autochthonous transmission to be below 50% in all cities, which was primarily due to the limited number of estimated introductions that year.
    CONCLUSION: Despite the rise in air travel, we found low support for travel patterns between YF endemic countries and Asia resulting in autochthonous transmission during 2016. This supports the historic absence of YF in Asia and suggests it could be due to a limited number of introductions in previous years. Future increases in travel volumes or YF incidence can increase the number of introductions and the risk of autochthonous transmission. Given the high proportion of asymptomatic or mild infections and the challenges of YF surveillance, our model can be used to estimate the introduction and outbreak risk, and can provide useful information to surveillance systems.
  17. Malar J. 2021 Feb 19. 20(1): 104
      BACKGROUND: Climate and environmental factors could be one of the primary factors that drive malaria transmission and it remains to challenge the malaria elimination efforts. Hence, this study was aimed to evaluate the effects of meteorological factors and topography on the incidence of malaria in the Boricha district in Sidama regional state of Ethiopia.METHODS: Malaria morbidity data recorded from 2010 to 2017 were obtained from all public health facilities of Boricha District in the Sidama regional state of Ethiopia. The monthly malaria cases, rainfall, and temperature (minimum, maximum, and average) were used to fit the ARIMA model to compute the malaria transmission dynamics and also to forecast future incidence. The effects of the meteorological variables and altitude were assessed with a negative binomial regression model using R version 4.0.0. Cross-correlation analysis was employed to compute the delayed effects of meteorological variables on malaria incidence.
    RESULTS: Temperature, rainfall, and elevation were the major determinants of malaria incidence in the study area. A regression model of previous monthly rainfall at lag 0 and Lag 2, monthly mean maximum temperature at lag 2 and Lag 3, and monthly mean minimum temperature at lag 3 were found as the best prediction model for monthly malaria incidence. Malaria cases at 1801-1900 m above sea level were 1.48 times more likely to occur than elevation ≥ 2000 m.
    CONCLUSIONS: Meteorological factors and altitude were the major drivers of malaria incidence in the study area. Thus, evidence-based interventions tailored to each determinant are required to achieve the malaria elimination target of the country.
    Keywords:  Altitude; Boricha; Ethiopia; Malaria; Rainfall; Temperature
  18. PLoS Comput Biol. 2021 Feb 16. 17(2): e1008658
      During sporogony, malaria-causing parasites infect a mosquito, reproduce and migrate to the mosquito salivary glands where they can be transmitted the next time blood feeding occurs. The time required for sporogony, known as the extrinsic incubation period (EIP), is an important determinant of malaria transmission intensity. The EIP is typically estimated as the time for a given percentile, x, of infected mosquitoes to develop salivary gland sporozoites (the infectious parasite life stage), which is denoted by EIPx. Many mechanisms, however, affect the observed sporozoite prevalence including the human-to-mosquito transmission probability and possibly differences in mosquito mortality according to infection status. To account for these various mechanisms, we present a mechanistic mathematical model, which explicitly models key processes at the parasite, mosquito and observational scales. Fitting this model to experimental data, we find greater variation in the EIP than previously thought: we estimated the range between EIP10 and EIP90 (at 27°C) as 4.5 days compared to 0.9 days using existing statistical methods. This pattern holds over the range of study temperatures included in the dataset. Increasing temperature from 21°C to 34°C decreased the EIP50 from 16.1 to 8.8 days. Our work highlights the importance of mechanistic modelling of sporogony to (1) improve estimates of malaria transmission under different environmental conditions or disease control programs and (2) evaluate novel interventions that target the mosquito life stages of the parasite.
  19. Mol Ecol Resour. 2021 Feb 15.
      The two most efficient and most recently radiated Afrotropical vectors of human malaria - Anopheles coluzzii and An. gambiae - are identified by single-locus diagnostic PCR assays based on species-specific markers in a 4 Mb region on chromosome-X centromere. Inherently, these diagnostic assays cannot detect interspecific autosomal admixture shown to be extensive at the westernmost and easternmost extremes of the species range. The main aim of this work was to develop novel, easy-to-implement tools for genotyping An. coluzzii and An. gambiae-specific Ancestral Informative Markers (AIMs) identified from the Anopheles gambiae 1000 genomes (Ag1000G) project. First, we took advantage of this large set of data in order to develop a multi-locus approach to genotype 26 AIMs on all chromosome arms valid across the species range. Second, we tested the multi-locus assay on samples from Guinea Bissau, The Gambia and Senegal, three countries spanning the westernmost hybridization zone, where conventional species diagnostic is problematic due to the putative presence of a novel "hybrid form". The multi-locus assay was able to capture patterns of admixture reflecting those revealed by the whole set of AIMs and provided new original data on interspecific admixture in the region. Third, we developed an easy-to-use, cost-effective PCR approach for genotyping two AIMs on chromosome-3 among those included in the multi-locus approach, opening the possibility for advanced identification of species and of admixed specimens during routine large scale entomological surveys, particularly, but not exclusively, at the extremes of the range, where WGS data highlighted unexpected autosomal admixture.
    Keywords:  ecological speciation; hybridization; malaria vector
  20. J Am Mosq Control Assoc. 2020 Sep 01. 36(3): 204-207
      Little is known regarding the comparative source-sink relationships between primary mosquito breeding sites (source) and neighboring (sink) environments in heterogeneous landscapes. An exploration of those relationships may provide unique insights into the utility of open-space buffer zone mitigation strategies currently being considered by urban planners to reduce contact between mosquitoes and humans. We investigated the source-sink relationships between a highly productive mosquito habitat and adjacent residential (developed) and rural (undeveloped) coastal environments. Our results suggest that source-sink relationships are unaffected by environment. This conclusion is supported by the high level of synchronicity in daily saltmarsh mosquito abundance observed among all surveyed environments (β = 0.67-0.79, P < 0.001). This synchronicity occurred despite the uniqueness of each surveyed environment and the considerable distances of open water and land (2.2-2.6 km) between them. Trap catches, which we interpret as expected mosquito biting nuisance, were high in both residential and rural coastal landscapes (309.4 ± 52.84 and 405.3 ± 62.41 mosquitoes/day, respectively). These observations suggest that existing and planned open-space buffer zones will do little to reduce the biting burden caused by highly vagile saltmarsh mosquitoes. This strengthens the need for empirically informed planning guidelines that alert urban planners to the real risks of human residential encroachment on land that is close to highly vagile mosquito habitat.
    Keywords:  Buffer zones; Public Health; coastal development; mosquitoes; nuisance
  21. Malar J. 2021 Feb 18. 20(1): 101
      BACKGROUND: The Government of Madhya Pradesh employed Indoor Residual Spraying (IRS) with alpha-cypermethrin synthetic pyrethroids in sub-centres with Annual Parasite Incidence (API) from 2 to 4.99. In sub-centres with API more than 5, Long-Lasting Insecticidal Nets (LLINs) were distributed. At the request of the State Government, the Malaria Elimination Demonstration Project (MEDP) staff observed and provided support to both IRS and LLINs campaigns. In the year 2017, the study team monitored only the IRS campaigns, however, in the year 2018, the supportive supervision was provided to the IRS campaign teams along with post-distribution monitoring of the LLINs.METHODS: The study was carried out during IRS spraying using a pre-tested, closed-ended monitoring checklist which consisted of two parts- observations of spraying team and observation of sprayed houses. For LLINs, a sample of the households that received the bed nets was taken for the study. For IRS, the spraying teams were monitored for quality and technique for a total of 159 times in 2017 and 183 times in the year 2018, respectively. For post spraying observations, a total of 1261 and 1791 households were observed in the years 2017 and 2018, respectively. The use of LLINs was observed in 5 % of the households in 2018 and 2020, which is about 2,000 houses in each survey where each house received about 2.5 LLINs per household. The results of surveys were compared to assess impact of supportive supervision and monitoring.
    RESULTS: Significant improvement was noted after supportive supervision in year 2018 in various aspects of spraying. Preparedness of spraying, such as advance information to villagers, presence of equipment and records improved by up to 70 %. The methodology of spraying preparation improved from 50 to 90 %, spraying technique improved from 54 to 80 %, and proper use equipment during spraying improved from 51 to 92 %. After eight months post distribution of the LLINs in 2019, improvement was seen in regular usage of LLINs by 28 %. It was found that on-spot demonstrations during distribution and carrying of LLINs when sleeping outside homes increased by 56 %. Results of IEC campaigns revealed the reduction in adverse effects by 64 % and increase in awareness by 97 %.
    CONCLUSIONS: Effective supervision improved the quality of IRS and usage of LLINs in the study area. Based on these results, continued training and monitoring of staff that is deployed to spraying houses and distribute bed nets was suggested. The study also revealed that proper IEC/BCC drives help increase community acceptance of vector control measures and their rational usage.