bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2020‒11‒22
23 papers selected by
Richard Halfpenny
Staffordshire University

  1. Malar J. 2020 Nov 19. 19(1): 415
      BACKGROUND: Since the advent of the Green Revolution, pesticides have played an important role in the global management of invertebrate pests including vector mosquitoes. Despite optimal efficacy, insects often display insensitivity to synthetic insecticides owing to prolonged exposure that may select for resistance development. Such insecticide insensitivity may regress national and regional coordination in mosquito vector management and indeed malaria control. In Botswana, prolonged use of synthetic insecticides against malaria vectors have been practiced without monitoring of targeted mosquito species susceptibility status.METHODS: Here, susceptibility status of a malaria vector (Anopheles arabiensis), was assessed against World Health Organization-recommended insecticides, across three malaria endemic districts. Adult virgin female mosquitoes (2-5 days old) emerging from wild-collected larvae were exposed to standardized insecticide-impregnated papers with discriminating doses.
    RESULTS: The results showed resistance dynamics were variable in space, presumably as a result of spatial differences in insecticide use across malaria endemic districts and the types of insecticides used in the country. Overall, there was a reduced susceptibility of An. arabiensis for the pyrethroid lambda-cyhalothrin and for dichloro diphenyl trichloroethane [DDT], which have similar modes of action and have been used in the country for many years. The Okavango district exhibited the greatest reduction in susceptibility, followed by Ngamiland and then Bobirwa, reflective of national intervention strategy spraying intensities. Vector mosquitoes were, however, highly susceptible to carbamates and organophosphates irrespective of region.
    CONCLUSIONS: These results provide important findings of vector susceptibility to insecticides recommended for vector control. The results highlight the need to implement insecticide application regimes that more effectively including regionally integrated resistance management strategies for effective malaria control and elimination.
    Keywords:  DDT; Knockdown time; Pyrethroids; Southern africa; Susceptibility bioassays
  2. Malar J. 2020 Nov 20. 19(1): 418
      BACKGROUND: Host preference is a critical determinant of human exposure to vector-borne infections and the impact of vector control interventions. Widespread use of long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS) across sub-Saharan Africa, which protect humans against mosquitoes, may select for altered host preference traits of malaria vectors over the long term. Here, the host preferences of Anopheles arabiensis and Anopheles gambiae sensu stricto (s.s.) were experimentally assessed in the field, using direct host-preference assays in two distinct ecological settings in Tanzania.METHODS: Eight Ifakara Tent Trap (ITT), four baited with humans and four with bovine calves, were simultaneously used to catch malaria vectors in open field sites in urban and rural Tanzania. The numbers of mosquitoes collected in human-baited traps versus calf-baited traps were used to estimate human feeding preference for each site's vector species.
    RESULTS: The estimated proportion [95% confidence interval (CI)] of mosquitoes attacking humans rather than cattle was 0.60 [0.40, 0.77] for An. arabiensis in the rural setting and 0.61 [0.32, 0.85] for An. gambiae s.s. in the urban setting, indicating no preference for either host in both cases (P = 0.32 and 0.46, respectively) and no difference in preference between the two (Odds Ratio (OR) [95%] = 0.95 [0.30, 3.01], P = 0.924). However, only a quarter of An. arabiensis in the urban setting attacked humans (0.25 [0.09, 0.53]), indicating a preference for cattle that approached significance (P = 0.08). Indeed, urban An. arabiensis were less likely to attack humans rather than cattle when compared to the same species in the rural setting (OR [95%] = 0.21 [0.05, 0.91], P = 0.037).
    CONCLUSION: Urban An. arabiensis had a stronger preference for cattle than the rural population and urban An. gambiae s.s. showed no clear preference for either humans or cattle. In the urban setting, both species exhibited stronger tendencies to attack cattle than previous studies of the same species in rural contexts. Cattle keeping may, therefore, particularly limit the impact of human-targeted vector control interventions in Dar es Salaam and perhaps in other African towns and cities.
    Keywords:  Anopheles; Entomological surveillance; Host preferences; Malaria; Residual transmission; Tanzania; Vector
  3. BMC Ecol. 2020 Nov 19. 20(1): 60
      BACKGROUND: The characteristics of a larval habitat is an important factor which affects the breeding pattern and population growth of mosquitoes Information about the larval habitat characteristics and pupal productivity can be utilized for the surveillance of the level of population growth, species diversity, and preferred breeding sites of mosquitoes, which are important aspects of integrated vector control. In the present study, mosquito larvae were collected from 22 natural habitats in five counties of the West Azerbaijan Province in the Northwest of Iran during May-November 2018. Physicochemical characteristics of the habitats were investigated. These included alkalinity, chloride (Cl) content, water temperature (°C), turbidity (NTU), Total Dissolved Solids (TDS) (ppm), Electrical Conductivity (EC) (μS/cm), and acidity (pH). The index of affinity between the collected species was calculated using Fager & McGowan test.RESULTS: A total of 2715 specimens were collected and identified. Seven different species belonging to four genera were identified in our study sites. The species included, Culex pipiens Linnaeus 1758, Culex theileri Theobald 1903, Culex mimeticus Noé 1899, Culex modestus Ficalbi 1947, Culiseta longiareolata Macquart 1838, Anopheles maculipennis Meigen 1818complex, and Aedes caspius Pallas 1771. There was a significant difference in chloride content and water temperature preferences among the different species (P < 0.05). Also, there was no significant difference in pH, Alkalinity, Turbidity, TDS, and EC preferences among the different species (P > 0.05). The affinity between the pair of species Cx. mimeticus/Cs. longiareolata was 0.526. There was no affinity between other pairs of species or the affinity was very weak.
    CONCLUSIONS: The physicochemical and biological characteristics of mosquito larval habitats play an important role in zoning of areas suitable for breeding and distribution. Surveillance of these characteristics can provide valuable information for entomological monitoring of mosquito vectors and for designing targeted control programs. Also, further studies should be undertaken in a wider geographical area, taking into account the complex characteristics of the physicochemical and ecological factors of the study area and their interaction with various mosquito species.
    Keywords:  Mosquito larval habitats; Oviposition sites; Species diversity
  4. Front Genet. 2020 ;11 602863
      Hainan is a tropical island in southern China with abundant mosquito species, putting Hainan at risk of mosquito-borne virus disease outbreaks. The population genetic diversity of most mosquito species on Hainan Island remains elusive. In this study, we report the diversity of mosquito species and the genetic diversity of the predominant species on Hainan. Field populations of adults or larvae were collected from 12 regions of Hainan Island in 2018 and 2019. A fragment of the mitochondrial cytochrome c oxidase subunit I (coxI) gene was sequenced from 1,228 mosquito samples and used for species identification and genetic diversity analysis. Twenty-three known mosquito species from the genera Aedes, Armigeres, Culex, Mansonia, and Anopheles and nine unconfirmed mosquito species were identified. Aedes albopictus, Armigeres subalbatus, and Culex pipiens quinquefasciatus were the most prevalent mosquito species on Hainan. The regions north of Danzhou, Tunchang, and Qionghai exhibited high mosquito diversity (26 species). The order of the total haplotype diversity and nucleotide diversity of the populations from high to low was as follows: Culex tritaeniorhynchus, Ar. subalbatus, Culex pallidothorax, Culex gelidus, Ae. albopictus, and C. p. quinquefasciatus. Tajima's D and Fu's F s tests showed that Ae. albopictus, C. p. quinquefasciatus, C. tritaeniorhynchus, and C. gelidus had experienced population expansion, while the Ar. subalbatus and C. pallidothorax populations were in genetic equilibrium. Significant genetic differentiation existed in the overall populations of Ae. albopictus, Ar. subalbatus, C. p. quinquefasciatus, and C. pallidothorax. The Ae. albopictus populations on Hainan were characterized by frequent gene exchange with populations from Guangdong and four other tropical countries, raising the risk of viral disease outbreaks in these regions. Two subgroups were reported in the Ar. subalbatus populations for the first time. Our findings may have important implications for vector control on Hainan Island.
    Keywords:  Aedes; Anopheles; Armigeres; Culex; Mansonia; cytochrome c oxidase subunit I
  5. PLoS Negl Trop Dis. 2020 Nov 17. 14(11): e0008846
      Zika virus (ZIKV) is an emerging mosquito-borne pathogen that can cause global public health threats. In the absence of effective antiviral medications, prevention measures rely largely on reducing the number of adult mosquito vectors by targeting juvenile stages. Despite the importance of juvenile mosquito control measures in reducing adult population size, a full understanding of the effects of these measures in determining mosquito phenotypic traits and in mosquito-arbovirus interactions is poorly understood. Pyriproxyfen is a juvenile hormone analog that primarily blocks adult emergence, but does not cause mortality in larvae. This mechanism has the potential to work in combination with other juvenile sources of mortality in nature such as predation to affect mosquito populations. Here, we experimentally evaluated the effects of juvenile exposure to pyriproxyfen and predatory mosquito Toxorhynchites rutilus on Aedes aegypti phenotypes and susceptibility to ZIKV infection and transmission. We discovered that combined effects of pyriproxyfen and Tx. rutilus led to higher inhibition of adult emergence in Ae. aegypti than observed in pyriproxyfen or Tx. rutilus treatments alone. Adult body size was larger in treatments containing Tx. rutilus and in treatments mimicking the daily mortality of predation compared to control or pyriproxyfen treatments. Susceptibility to infection with ZIKV in Ae. aegypti was reduced in predator treatment relative to those exposed to pyriproxyfen. Disseminated infection, transmission, and titers of ZIKV in Ae. aegypti were similar in all treatments relative to controls. Our data suggest that the combination of pyriproxyfen and Tx. rutilus can inhibit adult Ae. aegypti emergence but may confer a fitness advantage in survivors and does not inhibit their vector competence for ZIKV relative to controls. Understanding the ultimate consequences of juvenile mosquito control measures on subsequent adults' ability to transmit pathogens is critical to fully understand their overall impacts.
  6. J Med Entomol. 2020 Oct 20. pii: tjaa214. [Epub ahead of print]
      Various products and insecticides are available that purport to reduce wild populations of adult mosquitoes. Recently, several manufacturers and general public comments on the internet have promoted devices that claim that ingestion of salt will significantly reduce populations of wild mosquitoes to near zero; there are no known scientific efficacy data that support these claims. We tested the survival of nine mosquito species of pest and public health importance across four adult diets: Water Only, Sugar Water Only (8.00%), Salt Water Only (1.03%), and Sugar + Salt Water. Species included the following: Aedes aegypti (L.), Aedes albopictus (Skuse), Aedes dorsalis (Meigen), Aedes notoscriptus (Skuse), Aedes vigilax (Skuse), Anopheles quadrimaculatus (Say), Culex pipiens (L.), Culex quinquefasciatus (Say), and Culex tarsalis (Coquillett). Male and female mosquitoes were placed in cages and allowed to feed on liquid diets under controlled environmental conditions for 1 wk. For seven of the nine species, adult survival was significantly higher in the presence (Sugar Water, Sugar + Salt Water) versus the absence (Water Only, Salt Only) of sugar, with no indication that salt had any effect on survival. Anopheles quadrimaculatus showed intermediate survival in Sugar + Salt to either Sugar Only or no sugar diets, whereas Aedes dorsalis showed low survival in Salt Only versus other diets. Based on our data and coupled with the fact that mosquitoes have physiological and behavioral adaptations that allow them to avoid or process excess salt (as found in blood meals), we conclude that there is no scientific foundation for salt-based control methods of mosquitoes.
    Keywords:  Culicidae; attractive toxic sugar bait; diet; sodium chloride; sucrose
  7. PLoS Negl Trop Dis. 2020 Nov 19. 14(11): e0008860
      Culex quinquefasciatus is one of the most important mosquito vectors of arboviruses. Currently, the fastest approach to control disease transmission is the application of synthetic adulticide insecticides. However, in highly populated urban centers the development of insecticide resistance in mosquito populations could impair insecticide efficacy and therefore, disease control. To assess the effect of resistance on vector control, females of Cx. quinquefasciatus collected from six mosquito control operational areas in Harris County, Texas, were treated in field cage tests at three different distances with the pyrethroid Permanone® 31-66 applied at the operational rate. Females were analyzed by sequencing and/or diagnostic PCR using de novo designed primers for detecting the kdr-like mutation in the voltage-gated sodium channel (L982F; TTA to TTT) (house fly kdr canonical mutation L1014F). Females from the Cx. quinquefasciatus susceptible Sebring strain and those from the six operational areas placed at 30.4 m from the treatment source were killed in the tests, while 14% of field-collected mosquitoes survived at 60.8 m, and 35% at 91.2 m from the source. The diagnostic PCR had a with 97.5% accuracy to detect the kdr-like mutation. Pyrethroid resistant mosquitoes carrying the L982F mutation were broadly distributed in Harris County at high frequency. Among mosquitoes analyzed (n = 1,028), the kdr-kdr genotype was prevalent (81.2%), the kdr-s genotype was 18%, and s-s mosquitoes were less than 1% (n = 8). A logistic regression model estimated an equal probability of survival for the genotypes kdr-kdr and kdr-s in all areas analyzed. Altogether, our results point to a high-risk situation for the pyrethroid-based arboviral disease control in Harris County.
  8. PLoS Negl Trop Dis. 2020 Nov 18. 14(11): e0008841
      The California Arbovirus Surveillance Program was initiated over 50 years ago to track endemic encephalitides and was enhanced in 2000 to include West Nile virus (WNV) infections in humans, mosquitoes, sentinel chickens, dead birds and horses. This comprehensive, statewide program is a function of strong partnerships among the California Department of Public Health (CDPH), the University of California, and local vector control and public health agencies. This manuscript summarizes WNV surveillance data in California since WNV was first detected in 2003 in southern California. From 2003 through 2018, 6,909 human cases of WNV disease, inclusive of 326 deaths, were reported to CDPH, as well as 730 asymptomatic WNV infections identified during screening of blood and organ donors. Of these, 4,073 (59.0%) were reported as West Nile neuroinvasive disease. California's WNV disease burden comprised 15% of all cases that were reported to the U.S. Centers for Disease Control and Prevention during this time, more than any other state. Additionally, 1,299 equine WNV cases were identified, along with detections of WNV in 23,322 dead birds, 31,695 mosquito pools, and 7,340 sentinel chickens. Annual enzootic detection of WNV typically preceded detection in humans and prompted enhanced intervention to reduce the risk of WNV transmission. Peak WNV activity occurred from July through October in the Central Valley and southern California. Less than five percent of WNV activity occurred in other regions of the state or outside of this time. WNV continues to be a major threat to public and wild avian health in California, particularly in Southern California and the Central Valley during summer and early fall months. Local and state public health partners must continue statewide human and mosquito surveillance and facilitate effective mosquito control and bite prevention measures.
  9. J Vector Ecol. 2020 Dec;45(2): 312-320
      The mosquito Aedes albopictus is a vector of several arboviruses transmitted to humans. They have a sylvatic behavior, occurring in rural areas. However, reports of their adaptation to anthropic environments have been increasing. The aim of this study is to investigate the presence and distribution of Ae. albopictus in the Metropolitan Region of Belém in the Brazilian Amazon and evaluate its preference for either natural or artificial breeding sites under the weather conditions of the Amazon. Ovitraps (artificial breeding sites) and bamboo internodes (natural breeding sites) were deployed in neighborhood peridomiciles during the dry and rainy seasons. The results showed that the presence of Ae. albopictus was recorded in 71.4% of the neighborhoods during the dry season and in 69.2% neighborhoods during the rainy season, thus indicating a wide distribution in the region. A significant increase in the frequency of the capture of mosquitoes in areas with higher vegetation cover was observed during the dry season (R2 = 0.2995; p=0.018) but not during the rainy season (R2 = 0.044; p=0.43). Comparing the weekly frequency of Ae. albopictus on positive bamboos and OVT, no significant difference was observed between them (t= 0.559; df= 23; p=0.58). A significant increase in the number of positive breeding sites was observed with increased rainfall for both bamboo (R2 = 0.33; p= 0.002) and OVT (R2 = 0.24; p= 0.013). This is the first report of Ae. albopictus in the metropolitan area of Belém. The findings suggest a wide distribution in the studied area, preferably in areas with more extensive vegetation cover. Additionally, the mosquito population showed the ability to use both natural and artificial habitats.
    Keywords:  Aedes albopictus; larval habitat preference; mosquitoes; oviposition; vector
  10. J Vector Ecol. 2020 Dec;45(2): 155-179
      Vector control is an important component of the interventions aimed at mosquito-borne disease control. Current and future mosquito control strategies are likely to rely largely on the understanding of the behavior of the vector, by exploiting mosquito biology and behavior, while using cost-effective, carefully timed larvicidal and high-impact, low-volume adulticidal applications. Here we review the knowledge on the ecology of mosquito oviposition behavior with emphasis on the potential role of infochemicals in surveillance and control of mosquito-borne diseases. A search of PubMed, Embase, Web of Science, Global Health Archive, and Google Scholar databases was conducted using the keywords mosquito, infochemical, pheromone, kairomone, allomone, synomone, apneumone, attractant, host-seeking, and oviposition. Articles in English from 1974 to 2019 were reviewed to gain comprehensive understanding of current knowledge on infochemicals in mosquito resource-searching behavior. Oviposition of many mosquito species is mediated by infochemicals that comprise pheromones, kairomones, synomones, allomones, and apneumones. The novel putative infochemicals that mediate oviposition in the mosquito subfamilies Anophelinae and Culicinae were identified. The role of infochemicals in surveillance and control of these and other mosquito tribes is discussed with respect to origin of the chemical cues and how these affect gravid mosquitoes. Oviposition attractants and deterrents can potentially be used for manipulation of mosquito behavior by making protected resources unsuitable for mosquitoes (push) while luring them towards attractive sources (pull). In this review, strategies of targeting breeding sites with environmentally friendly larvicides with the aim to develop appropriate trap-and-kill techniques are discussed.
    Keywords:  Culicidae; control; infochemicals; mosquito behavior; olfactory cues; oviposition; surveillance
  11. Emerg Microbes Infect. 2020 Nov 20. 1-39
      Usutu virus (USUV) and West Nile virus (WNV) are closely related mosquito-borne flaviviruses that are mainly transmitted between bird hosts by vector mosquitoes. Infections in humans are incidental but can cause severe disease. USUV is endemic in large parts of Europe, while WNV mainly circulates in Southern Europe. In recent years, WNV is also frequently detected in Northern Europe, thereby expanding the area where both viruses co-circulate. However, it remains unclear how USUV may affect the future spread of WNV and the likelihood of human co-infection. Here we investigated whether co-infections with both viruses in cell lines and their primary mosquito vector, Culex pipiens, affect virus replication and transmission dynamics. We show that USUV is outcompeted by WNV in mammalian, avian and mosquito cells during co-infection. Mosquitoes that were exposed to both viruses simultaneously via infectious blood meal displayed significantly reduced USUV transmission compared to mosquitoes that were only exposed to USUV (from 15% to 3%), while the infection and transmission of WNV was unaffected. In contrast, when mosquitoes were pre-infected with USUV via infectious blood meal, WNV transmission was significantly reduced (from 44% to 17%). Injection experiments established the involvement of the midgut in the observed USUV-mediated WNV inhibition. The competition between USUV and WNV during co-infection clearly indicates that the chance of concurrent USUV and WNV transmission via a single mosquito bite is low. The competitive relation between USUV and WNV may impact virus transmission dynamics in the field and affect the epidemiology of WNV in Europe.
    Keywords:  Competition; Mosquito; Usutu virus; Vector competence; West Nile virus
  12. Trop Med Int Health. 2020 Nov 15.
      OBJECTIVE: We tested the hypothesis that Zika virus (ZIKV) immunity may protect against dengue virus (DENV) infection, disease severity, or human amplification, based on analysis of epidemiological data from our long-term surveillance study (2009 - 2016) in the city of Salvador, Brazil that indicated a substantial reduction in the frequency of laboratory-confirmed dengue cases following the Zika outbreak.METHODS: To assess whether similar patterns were observed across the Americas, we did a broader explorative investigation of historical series (2004 to 2019) of suspected cases of dengue fever, covering 20 DENV-endemic South and Central American countries. We used segmented linear regressions of single group interrupted time series (ITS) analysis to evaluate whether the Zika epidemic had a statistical effect on the trends of annual dengue incidence.
    RESULTS: We observed in our 16-year historical series that in all countries, the incidence of dengue exhibited periodic oscillations over time, with a general trend of statistically significant increase during the pre-Zika period overall and for 11 of the 20 countries. Following the peak of the first population exposure to ZIKV in the Americas, in 2016, the overall rate of reported dengue cases in 2017 and 2018 in the countries under study sharply dropped (P<0.05) and was the lowest reported since 2005. Individually in each country, a statistically significant reduction in the annual dengue incidence beginning in 2016 or in 2017-2018 occurred in 13 of the 20 studied countries. However, in 2019, reports of suspected dengue cases increased across the Americas. In Brazil, Dominican Republic, Guatemala, and Honduras, dengue incidence was >5 times higher in 2019 than in 2017 and 2018, and, in 2019, they had the greater dengue incidence than in all previous years throughout the historical series.
    CONCLUSIONS: The widespread decline in suspected dengue cases recorded in 2017 and 2018 lends further support to our previous epidemiological hypothesis of ZIKV induced cross-species immunity to DENV. However, the cross-protection appears to be transient (around 2 years). Long-term, prospective follow-ups of dengue reports are needed to confirm (or refute) these findings, which could have significant public health implications, in particular regarding DENV vaccine development and application.
    Keywords:  The Americas; Zika virus; cross-protection; dengue virus; herd immunity
  13. Korean J Parasitol. 2020 Oct;58(5): 551-558
      The flaviviruses are small single-stranded RNA viruses that are typically transmitted by mosquitoes or tick vectors and are etiological agents of acute zoonotic infections. The viruses are found around the world and account for significant cases of human diseases. We investigated population of culicine mosquitoes in central region of Korean Peninsula, Incheon Metropolitan City and Hwaseong-si. Aedes vexans nipponii was the most frequently collected mosquitoes (56.5%), followed by Ochlerotatus dorsalis (23.6%), Anopheles spp. (10.9%), and Culex pipiens complex (5.9%). In rural regions of Hwaseong, Aedes vexans nipponii was the highest population (62.9%), followed by Ochlerotatus dorsalis (23.9%) and Anopheles spp. (12.0%). In another rural region of Incheon (habitat of migratory birds), Culex pipiens complex was the highest population (31.4%), followed by Ochlerotatus dorsalis (30.5%), and Aedes vexans vexans (27.5%). Culex pipiens complex was the predominant species in the urban region (84.7%). Culicine mosquitoes were identified at the species level, pooled up to 30 mosquitoes each, and tested for flaviviral RNA using the SYBR Green-based RT-PCR and confirmed by cDNA sequencing. Three of the assayed 2,683 pools (989 pools without Anopheles spp.) were positive for Culex flaviviruses, an insect-specific virus, from Culex pipiens pallens collected at the habitats for migratory birds in Incheon. The maximum likelihood estimation (the estimated number) for Culex pipiens pallens positive for Culex flavivirus was 25. Although viruses responsible for mosquito-borne diseases were not identified, we encourage intensified monitoring and long-term surveillance of both vector and viruses in the interest of global public health.
    Keywords:  Mosquito; climate change; flavivirus; insect-specific flavivirus; surveillance
  14. Trans R Soc Trop Med Hyg. 2020 Nov 16. pii: traa131. [Epub ahead of print]
      BACKGROUND: Understanding and describing the regional and climatic patterns associated with increasing dengue epidemics in Nepal is critical to improving vector and disease surveillance and targeting control efforts.METHODS: We investigated the spatial and temporal patterns of annual dengue incidence in Nepal from 2010 to 2019, and the impacts of seasonal meteorological conditions (mean maximum, minimum temperature and precipitation) and elevation on those patterns.
    RESULTS: More than 25 000 laboratory-confirmed dengue cases were reported from 2010 to 2019. Epidemiological trends suggest that dengue epidemics are cyclical with major outbreaks occurring at 2- to 3-y intervals. A significant negative relationship between dengue incidence and increasing elevation (metres above sea level) driven by temperature was observed (p<0.05) with dengue risk being greatest below 500 m. Risk was moderate between 500 and 1500 m and decreased substantially above 1500 m. Over the last decade, increased nightly temperatures during the monsoon months correlated with increased transmission (p<0.05). No other significant relationship was observed between annual dengue cases or incidence and climatological factors.
    CONCLUSIONS: The spatial analysis and interpretation of dengue incidence over the last decade in Nepal confirms that dengue is now a well-established public health threat of increasing importance, particularly in low elevation zones and urbanised areas with a tropical or subtropical climate. Seasonal variations in temperature during the monsoon months are associated with increased transmission.
    Keywords:   Aedes ; Nepal; climate; dengue; elevation; epidemiology
  15. Science. 2020 Nov 20. 370(6519): 991-996
      The drivers and patterns of zoonotic virus emergence in the human population are poorly understood. The mosquito Aedes aegypti is a major arbovirus vector native to Africa that invaded most of the world's tropical belt over the past four centuries, after the evolution of a "domestic" form that specialized in biting humans and breeding in water storage containers. Here, we show that human specialization and subsequent spread of A. aegypti out of Africa were accompanied by an increase in its intrinsic ability to acquire and transmit the emerging human pathogen Zika virus. Thus, the recent evolution and global expansion of A. aegypti promoted arbovirus emergence not solely through increased vector-host contact but also as a result of enhanced vector susceptibility.
  16. J Med Entomol. 2020 Nov 21. pii: tjaa249. [Epub ahead of print]
      Aedes (Stegomyia) aegypti (Linnaeus, 1762) is a mosquito species of significant medical importance. The use of this vector in research studies usually requires a large number of mosquitoes as well as rearing and maintenance in a laboratory-controlled environment. However, laboratory conditions may be different from field environments, presenting stressful challenges such as low food concentration, especially during larval stages, which may, in turn, impair vector biology. Therefore, we tested herein if larval food availability (0.004, 0.009, 0.020, and 0.070% diets) would affect overall adult insect fitness. We observed slower development in mosquitoes fed a 0.004% diet 15 d post-eclosion (DPE) and shorter mean time in mosquitoes fed a 0.020% diet (7 DPE). Larval diet and adult mosquito weight were positively correlated, and heavier females fed higher larval diets exhibited greater blood feeding capacity and oviposition. In addition, larval diet concentrations led to median adult lifespan variations (male/female in days-0.004%: 30 ± 1.41, 45 ± 1.3; 0.009%: 31.5 ± 1.33, 41 ± 1.43; 0.020%: 26 ± 1.18, 41 ± 1.45; 0.070%: 29 ± 1.07, 44 ± 1.34), reduced tolerance to deltamethrin (1 mg/m2) and changes in detoxification enzyme activities. Moreover, in the larval 0.070% diet, females presented higher Zika susceptibility (plaque-forming unit [PFU]: 1.218 × 106) compared with other diets (0.004%: 1.31 × 105; 0.009%: 2.0 × 105; 0.020%: 1.25 × 105 PFU). Altogether, our study demonstrates that larval diet restriction results not only in larval developmental arrest but also in adult fitness impairment, which must be considered in future assessments.
    Keywords:   Aedes aegypti ; fitness; larval feeding; mosquito
  17. Insects. 2020 Nov 17. pii: E808. [Epub ahead of print]11(11):
      The mosquito species Aedes albopictus has successfully colonized many areas at temperate latitudes, representing a major public health concern. As mosquito bionomics is critically affected by temperature, we experimentally investigated the influence of different constant rearing temperatures (10, 15, 25, and 30 °C) on the survival rates, fecundity, and developmental times of different life stages of Ae. albopictus using a laboratory colony established from specimens collected in northern Italy. We compared our results with previously published data obtained with subtropical populations. We found that temperate Ae. albopictus immature stages are better adapted to colder temperatures: temperate larvae were able to develop even at 10 °C and at 15 °C, larval survivorship was comparable to the one observed at warmer conditions. Nonetheless, at these lower temperatures, we did not observe any blood-feeding activity. Adult longevity and fecundity were substantially greater at 25 °C with respect to the other tested temperatures. Our findings highlight the ability of Ae. albopictus to quickly adapt to colder environments and provide new important insights on the bionomics of this species at temperate latitudes.
    Keywords:  invasive species; mosquito bionomics; mosquito dynamics
  18. Malar J. 2020 Nov 16. 19(1): 410
      BACKGROUND: In the past decade substantial reduction in malaria morbidity and mortality has been observed through well-implemented case management and vector control strategies. India has also achieved a significant reduction in malaria burden in 2018 and has committed to eliminate malaria by 2030. The Mandla Malaria Elimination Demonstration Project (MEDP) was started in 2017 in 1233 villages of District Mandla to demonstrate malaria elimination in a tribal district with hard-to-reach areas was possible using active and passive surveillance, case management, vector control, and targeted information, education and communication campaigns. An operational plan was developed to strengthen the existing surveillance and malaria elimination systems, through fortnightly active case detection to ensure that all cases including those that are introduced into the communities are rapidly identified and treated promptly. The plan also focused on the reduction of human-mosquito contact through the use of Long-Lasting Insecticial Nets (LLINs) and Indoor Residual Spray (IRS). The operational plan was modified in view of the present COVID-19 pandemic by creating systems of assistance for the local administration for COVID-related work while ensuring the operational integrity of malaria elimination efforts.RESULTS: The use of MEDP study design and operational plan, with its built-in management control systems, has yielded significant (91%) reduction of indigenous cases of malaria during the period from June 2017 to May 2020. The malaria positivity rate was 0.33% in 2017-18, 0.13% in 2018-19, and 0.06% in 2019-20. Mass screening revealed 0.18% malaria positivity in September-October 2018, followed by 0.06% in June 2019, and 0.03% in December 2019, and these were mostly asymptomatic cases in the community. The project has been able to sustain the gains of the past three years during the ongoing COVID-19 pandemic.
    CONCLUSION: This paper provides the study design and the operational plan for malaria elimination in a high-burden district of Central India, which presented difficulties of hard to reach areas, forest malaria, and complex epidemiology of urban and rural malaria. The lessons learned could be used for malaria elimination efforts in rest of the country and other parts of South Asia with comparable demography and epidemiology.
    Keywords:  India; Malaria elimination; Monitoring and evaluation; Operational framework; Strategic planning
  19. J Vector Ecol. 2020 Dec;45(2): 306-311
      We present the first records of Anopheles (Anopheles) plumbeus Stephens, 1828 and Culex (Culex) torrentium Martini, 1925 in the autonomous region of Galicia (NW Spain), obtained through the Rede Galega de Vixilancia de Vectores (ReGaViVec). This entomological surveillance network, which was initiated in 2017 by the Xunta de Galicia in collaboration with the University of Vigo and the University of Santiago de Compostela, aims to detect the arrival of invasive vectors as well as to improve the knowledge about mosquito populations (Diptera: Culicidae) in the Galician territory. This study shows the first findings of these species in Galicia, which have been reported in six different locations throughout the region: five in the province of Pontevedra and one in the province of Lugo. The 51 captured specimens were collected at different stages of development between July and September, 2018 and 2019 by using specialized traps arranged in favorable regions for the settlement and development of culicids.
    Keywords:  Anopheles plumbeus; Culex torrentium; Galicia; Mosquitoes; surveillance
  20. Nat Commun. 2020 11 16. 11(1): 5801
      Historically endemic to Sub-Saharan Africa and South America, yellow fever is absent from the Asia-Pacific region. Yellow fever virus (YFV) is mainly transmitted by the anthropophilic Aedes mosquitoes whose distribution encompasses a large belt of tropical and sub tropical regions. Increasing exchanges between Africa and Asia have caused imported YFV incidents in non-endemic areas, which are threatening Asia with a new viral emergence. Here, using experimental infections of field-collected mosquitoes, we show that Asian-Pacific Aedes mosquitoes are competent vectors for YFV. We observe that Aedes aegypti populations from Singapore, Taiwan, Thailand, and New Caledonia are capable of transmitting YFV 14 days after oral infections, with a number of viral particles excreted from saliva reaching up to 23,000 viral particles. These findings represent the most comprehensive assessment of vector competence and show that Ae. aegypti mosquitoes from the Asia-Pacific region are highly competent to YFV, corroborating that vector populations are seemingly not a brake to the emergence of yellow fever in the region.
  21. Euro Surveill. 2020 Nov;25(46):
      In October 2020, the first case of autochthonous West Nile virus neuroinvasive disease was diagnosed in the Netherlands with a presumed infection in the last week of August. Investigations revealed five more cases of local West Nile virus (WNV) infection. The cases resided in a region where WNV was detected in a bird and mosquitoes in August 2020. Molecular analysis was successful for two cases and identified the presence of WNV lineage 2.
    Keywords:  WNF; WNND; West Nile virus; blood safety; meningitis; the Netherlands; zoonoses
  22. PeerJ. 2020 ;8 e9577
      Background: This study postulates that underlying environmental conditions and a susceptible population's socio-economic status should be explored simultaneously to adequately understand a vector borne disease infection risk. Here we focus on West Nile Virus (WNV), a mosquito borne pathogen, as a case study for spatial data visualization of environmental characteristics of a vector's habitat alongside human demographic composition for understanding potential public health risks of infectious disease. Multiple efforts have attempted to predict WNV environmental risk, while others have documented factors related to human vulnerability to the disease. However, analytical modeling that combines the two is difficult due to the number of potential explanatory variables, varying spatial resolutions of available data, and differing research questions that drove the initial data collection. We propose that the use of geovisualization may provide a glimpse into the large number of potential variables influencing the disease and help distill them into a smaller number that might reveal hidden and unknown patterns. This geovisual look at the data might then guide development of analytical models that can combine environmental and socio-economic data.Methods: Geovisualization was used to integrate an environmental model of the disease vector's habitat alongside human risk factors derived from socio-economic variables. County level WNV incidence rates from California, USA, were used to define a geographically constrained study area where environmental and socio-economic data were extracted from 1,133 census tracts. A previously developed mosquito habitat model that was significantly related to WNV infected dead birds was used to describe the environmental components of the study area. Self-organizing maps found 49 clusters, each of which contained census tracts that were more similar to each other in terms of WNV environmental and socio-economic data. Parallel coordinate plots permitted visualization of each cluster's data, uncovering patterns that allowed final census tract mapping exposing complex spatial patterns contained within the clusters.
    Results: Our results suggest that simultaneously visualizing environmental and socio-economic data supports a fuller understanding of the underlying spatial processes for risks to vector-borne disease. Unexpected patterns were revealed in our study that would be useful for developing future multilevel analytical models. For example, when the cluster that contained census tracts with the highest median age was examined, it was determined that those census tracts only contained moderate mosquito habitat risk. Likewise, the cluster that contained census tracts with the highest mosquito habitat risk had populations with moderate median age. Finally, the cluster that contained census tracts with the highest WNV human incidence rates had unexpectedly low mosquito habitat risk.
    Keywords:  Data mining; Parallel coordinate plots; Public health; Self organizing maps; West Nile Virus
  23. Infect Dis Poverty. 2020 Nov 19. 9(1): 158
      BACKGROUND: Malaria cases have declined significantly along the China-Myanmar border in the past 10 years and this region is going through a process from control to elimination. The aim of this study is to investigate the epidemiology of malaria along the border, will identify challenges in the progress from control to elimination.METHODS: National reported malaria cases from China and Myanmar, along with the data of 18 Chinese border counties and 23 townships in Myanmar were obtained from a web-based diseases information reporting system in China and the national malaria control program of Myanmar, respectively. Epidemiological data was analyzed, including the number of reported cases, annual parasite index and proportion of vivax infection. Spatial mapping of the annual parasite index (API) at county or township level in 2014 and 2018 was performed by ArcGIS. The relationship of malaria endemicity on both sides of the border was evaluated by regression analysis.
    RESULTS: The number of reported malaria cases and API declined in the border counties or townships. In 2014, 392 malaria cases were reported from 18 Chinese border counties, including 8.4% indigenous cases and 91.6% imported cases, while the highest API (0.11) was occurred in Yingjiang County. There have been no indigenous cases reported since 2017, but 164 imported cases were reported in 2018 and 97.6% were imported from Myanmar. The average API in 2014 in 23 Myanmar townships was significantly greater than that of 18 Chinese counties (P < 0.01). However, the API decreased significantly in Myanmar side from 2014 to 2018 (P < 0.01). The number of townships with an API between 0 and 1 increased to 15 in 2018, compared to only five in 2014, while still four townships had API > 10. Plasmodium vivax was the predominant species along the border. The number of reported malaria cases and the proportion of vivax infection in the 18 Chinese counties were strongly correlated with those of the 23 Myanmar townships (P < 0.05).
    CONCLUSIONS: Malaria elimination is approaching along the China-Myanmar border. However, in order to achieve the malaria elimination in this region and prevent the re-establishment of malaria in China after elimination, continued political, financial and scientific commitment is required.
    Keywords:  China–Myanmar border; Control; Elimination; Malaria