bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2021‒03‒28
fifteen papers selected by
Richard Halfpenny
Staffordshire University

  1. PLoS Negl Trop Dis. 2021 Mar;15(3): e0009153
      Dengue is considered non-endemic to mainland China. However, travellers frequently import the virus from overseas and local mosquito species can then spread the disease in the population. As a consequence, mainland China still experiences large dengue outbreaks. Temperature plays a key role in these outbreaks: it affects the development and survival of the vector and the replication rate of the virus. To better understand its implication in the transmission risk of dengue, we developed a delay differential equation model that explicitly simulates temperature-dependent development periods and tested it with collected field data for the Asian tiger mosquito, Aedes albopictus. The model predicts mosquito occurrence locations with a high accuracy (Cohen's κ of 0.78) and realistically replicates mosquito population dynamics. Analysing the infection dynamics during the 2014 dengue outbreak that occurred in Guangzhou showed that the outbreak could have lasted for another four weeks if mosquito control interventions had not been undertaken. Finally, we analyse the dengue transmission risk in mainland China. We find that southern China, including Guangzhou, can have more than seven months of dengue transmission per year while even Beijing, in the temperate north, can have dengue transmission during hot summer months. The results demonstrate the importance of using detailed vector and infection ecology, especially when vector-borne disease transmission risk is modelled over a broad range of climatic zones.
  2. Med Vet Entomol. 2021 Mar 21.
      Mosquito species Aedes aegypti and Aedes albopictus are vectors of dengue worldwide. Mosquito vector control through maintaining larvivorous fish in water bodies is generally suggested, however, its underlying role towards oviposition preference of these dengue vectors is unknown in the Sri Lankan context. The current study investigated the effect of chemical exudates from larvivorous fish species Poecilia reticulata, Rasbora daniconius and Applocheilus dayi on the oviposition preference of Aedes mosquitoes. The number of eggs laid by each mosquito species was determined using ovitraps that contained water conditioned by the fish species both separately and in combination. The ovitraps were placed inside insect cages containing engorged gravid Aedes females. Both the mosquito species had the least preference of oviposition in water conditioned by A. dayi followed by R. daniconius. The highest preference of oviposition was shown for water conditioned by P. reticulata. The current study indicated that oviposition site selection in Ae. aegypti and Ae. albopictus was reduced by A. dayi and R. daniconius, however, it was not influenced by the fish combinations used. Further studies are warranted to understand the chemical cues associated with larvivorous fish towards the oviposition preference in Aedes mosquitoes.
    Keywords:  Aedes aegypti; Aedes albopictus; larvivorous fish; oviposition; oviposition preference
  3. Biomedica. 2021 03 19. 41(1): 153-160
      Introduction: The vector-borne diseases program in México has an established network of ovitraps for entomological surveillance of Aedes spp. In response to reports of Aedes albopictus in the periphery of Mérida, the state capital of Yucatán, the Ministry of Health increased the specificity of this surveillance. Objective: To describe the presence and distribution of Ae. albopictus in Mérida and its relative abundance compared to Aedes aegypti in ovitraps of the vector control program. Materials and methods: During October, 2019, 91 ovitraps were randomly selected from 31 neighborhoods of Mérida. Mosquitoes were reared at the insectary of the Collaborative Unit for Entomological Bioassays of the Autonomous University of Yucatán from eggs collected in the field. Relative abundance was determined for adult individuals of each identified species and neighborhood. Results: 32 % of the neighborhoods were positive for Ae. albopictus and 100 % for Ae. aegypti. A total of 28 adults of Ae. albopictus (10 females and 18 males) were obtained from ovitraps. No correlation was observed between the abundance of Ae. aegypti and Ae. albopictus for both adults and females (p>0.05) at the neighborhood level. Conclusions: The results confirm that Ae. albopictus coexisted with Ae. aegypti in Mérida at the time of the study. The low relative abundance suggests that Ae. albopictus was in the initial phase of invasion.
    Keywords:  Aedes; mosquito vectors; vector control; vector-borne diseases; México
  4. Front Zool. 2021 Mar 09. 18(1): 10
      BACKGROUND: The yellow fever mosquito, Aedes aegypti, is the principal vector of medically-important infectious viruses that cause severe illness such as dengue fever, yellow fever and Zika. The transmission potential of mosquitoes for these arboviruses is largely shaped by their life history traits, such as size, survival and fecundity. These life history traits, to some degree, depend on environmental conditions, such as larval and adult nutrition (e.g., nectar availability). Both these types of nutrition are known to affect the energetic reserves and life history traits of adults, but whether and how nutrition obtained during larval and adult stages have an interactive influence on mosquito life history traits remains largely unknown.RESULTS: Here, we experimentally manipulated mosquito diets to create two nutritional levels at larval and adult stages, that is, a high or low amount of larval food (HL or LL) during larval stage, and a good and poor adult food (GA or PA, represents normal or weak concentration of sucrose) during adult stage. We then compared the size, survival and fecundity of female mosquitoes reared from these nutritional regimes. We found that larval and adult nutrition affected size and survival, respectively, without interactions, while both larval and adult nutrition influenced fecundity. There was a positive relationship between fecundity and size. In addition, this positive relationship was not affected by nutrition.
    CONCLUSIONS: These findings highlight how larval and adult nutrition differentially influence female mosquito life history traits, suggesting that studies evaluating nutritional effects on vectorial capacity traits should account for environmental variation across life stages.
    Keywords:  Egg number; Hazard ratios; Mosquito longevity; Nutritional stress; Survival curves; Wing length
  5. Zootaxa. 2021 Jan 27. 4920(1): zootaxa.4920.1.7
      A thorough knowledge of the presence and spatio-temporal distribution patterns of vector species are pivotal to assess the risk of mosquito-borne diseases in Europe. In 2018, a Culex larva was collected during routine monitoring activities to intercept exotic Aedes mosquito species in the port of Antwerp (Kallo, Belgium). The larva, collected from a pond in mid-September, was morphologically identified as Culex modestus, and this identification was subsequently confirmed by COI barcoding. It is the first confirmed record of this West Nile virus bridge vector in Belgium. The present study also demonstrates the value of DNA-based identification techniques to validate the presence of potential vector species.
    Keywords:  Diptera, biodiversity, DNA-based identification, larva, monitoring, mosquito, new record
  6. Malar J. 2021 Mar 20. 20(1): 159
      Eswatini was the first country in sub-Saharan Africa to pass a National Malaria Elimination Policy in 2011, and later set a target for elimination by the year 2020. This case study aimed to review the malaria surveillance data of Eswatini collected over 8 years between 2012 and 2019 to evaluate the country's efforts that targeted malaria elimination by 2020. Coverage of indoor residual spraying (IRS) for vector control and data on malaria cases were provided by the National Malaria Programme (NMP) of Eswatini. The data included all cases treated for malaria in all health facilities. The data was analysed descriptively. Over the 8 years, a total of 5511 patients reported to the health facilities with malaria symptoms. The case investigation rate through the routine surveillance system increased from 50% in 2012 to 84% in 2019. Incidence per 1000 population at risk fluctuated over the years, but in general increased from 0.70 in 2012 to 1.65 in 2019, with the highest incidence of 3.19 reported in 2017. IRS data showed inconsistency in spraying over the 8 years. Most of the cases were diagnosed by rapid diagnostic test (RDT) kits in government (87.6%), mission (89.1%), private (87%) and company/industry-owned facilities (84.3%), either singly or in combination with microscopy. Eswatini has fallen short of achieving malaria elimination by 2020. Malaria cases are still consistently reported, albeit at low rates, with occasional localized outbreaks. To achieve elimination, it is critical to optimize timely and well-targeted IRS and to consider rational expansion of tools for an integrated malaria control approach in Eswatini by including tools such as larval source management, long-lasting insecticidal nets (LLINs), screening of mosquito house entry points, and chemoprophylaxis. The establishment of rigorous routine entomological surveillance should also be prioritized to determine the local malaria vectors' ecology, potential species diversity, the role of secondary vectors and insecticide resistance.
    Keywords:  Elimination; Integrated vector management; Malaria; Surveillance
  7. Trop Parasitol. 2020 Jul-Dec;10(2):10(2): 130-135
      Background and Objectives: In recent years, resurgence of mosquito-borne diseases has become a serious health problem in India. In the present study, Stigmatogobius sadanundio, a common indigenous fish, has been tested for its biocontrol potentiality for controlling Culex quinquefasciatus larvae. This small larvivorous fish can consume large number of Culex larvae even in the presence of alternate prey. This is the first report on the mosquito control ability of this fish.Materials and Methods: Experimental fishes were captured from tidal canals of Rupnarayan River in Purba Medinipur district, West Bengal. Mosquito larvae, pupae, and chironomid larvae were collected from Tamralipta municipality drainage system. Predation efficacy of the fish was evaluated on C. quinquefasciatus larvae and pupae as well as on Chironomus ramosus larvae which were collected from the drainage system of Tamralipta municipality and reared in the laboratory maintaining similar water parameters. Prey were offered to the fish separately and in paired combination to study its dietary preference.
    Results: S. sadanundio is a diurnal predator consuming significantly large number of prey during daytime. It prefers mosquito and chironomid larvae over mosquito pupae. The rate of predation was very high during 1st h of predation. It consumed more chironomid larvae in the presence of mosquito larvae during daytime but consumed large number of mosquito larvae as compared to other larvivorous fish.
    Conclusion: S. sadanundio, an indigenous fish, is an effective biocontrol agent for the larvae of C. quinquefasciatus in laboratory condition. Even though the presence of alternate prey chironomid larvae influences the predation rate, it consumed large number of mosquito larvae. However, careful controlled field trials must be conducted before this fish is used as a biocontrol agent.
    Keywords:  Biocontrol; Chironomus larvae; Culex larvae; Stigmatogobius sadanundio; larvivorous fish
  8. PLoS Negl Trop Dis. 2021 Mar;15(3): e0009205
      BACKGROUND: In Malaysia, dengue remains a top priority disease and usage of insecticides is the main method for dengue vector control. Limited baseline insecticide resistance data in dengue hotspots has prompted us to conduct this study. The present study reports the use of a map on the insecticide susceptibility status of Aedes aegypti and Aedes albopictus to provide a quick visualization and overview of the distribution of insecticide resistance.METHOD AND RESULTS: The insecticide resistance status of Aedes populations collected from 24 dengue hotspot areas from the period of December 2018 until June 2019 was proactively monitored using the World Health Organization standard protocol for adult and larval susceptibility testing was conducted, together with elucidation of the mechanisms involved in observed resistance. For resistance monitoring, susceptibility to three adulticides (permethrin, deltamethrin, and malathion) was tested, as well as susceptibility to the larvicide, temephos. Data showed significant resistance to both deltamethrin and permethrin (pyrethroid insecticides), and to malathion (organophosphate insecticide) in all sampled Aedes aegypti populations, while variable resistance patterns were found in the sampled Aedes albopictus populations. Temephos resistance was observed when larvae were tested using the diagnostic dosage of 0.012mg/L but not at the operational dosage of 1mg/L for both species.
    CONCLUSION: The present study highlights evidence of a potential threat to the effectiveness of insecticides currently used in dengue vector control, and the urgent requirement for insecticide resistance management to be integrated into the National Dengue Control Program.
  9. Parasit Vectors. 2021 Mar 20. 14(1): 169
      BACKGROUND: Sichuan province is located in the southwest of China, and was previously a malaria-endemic region. Although no indigenous malaria case has been reported since 2011, the number of imported cases is on the rise. Insecticide-based vector control has played a central role in the prevention of malaria epidemics. However, the efficacy of this strategy is gravely challenged by the development of insecticide resistance. Regular monitoring of insecticide resistance is essential to inform evidence-based vector control. Unfortunately, almost no information is currently available on the status of insecticide resistance and associated mechanisms in Anopheles sinensis, the dominant malaria vector in Sichuan. In this study, efforts were invested in detecting the presence and frequency of insecticide resistance-associated mutations in three genes that encode target proteins of several classes of commonly used insecticides.METHODS: A total of 446 adults of An. sinensis, collected from 12 locations across Sichuan province of China, were inspected for resistance-conferring mutations in three genes that respectively encode acetylcholinesterase (AChE), voltage-gated sodium channel (VGSC), and GABA receptor (RDL) by DNA Sanger sequencing.
    RESULTS: The G119S mutation in AChE was detected at high frequencies (0.40-0.73). The predominant ace-1 genotype was GGC/AGC (119GS) heterozygotes. Diverse variations at codon 1014 were found in VGSC, leading to three different amino acid substitutions (L1014F/C/S). The 1014F was the predominant resistance allele and was distributed in all 12 populations at varying frequencies from 0.03 to 0.86. The A296S mutation in RDL was frequently present in Sichuan, with 296SS accounting for more than 80% of individuals in six of the 12 populations. Notably, in samples collected from Chengdu (DJY) and Deyang (DYMZ), almost 30% of individuals were found to be resistant homozygotes for all three targets.
    CONCLUSIONS: Resistance-related mutations in three target proteins of the four main classes of insecticides were prevalent in most populations. This survey reveals a worrisome situation of multiple resistance genotypes in Sichuan malaria vector. The data strengthen the need for regular monitoring of insecticide resistance and establishing a region-customized vector intervention strategy.
    Keywords:  Acetylcholinesterase (AChE); Anopheles sinensis; Knockdown resistance (kdr); Sichuan province of China; Voltage-gated sodium channel (VGSC)
  10. J Infect Public Health. 2021 Mar 17. pii: S1876-0341(20)30748-6. [Epub ahead of print]14(4): 527-532
      BACKGROUND: Due to a high burden imposed on public health from malaria disease in Sub-Saharan Africa, the vector control strategy is a significant concern. Despite the implementation of malaria control interventions in Ethiopia, it remains a major public health problem. Moreover, none of the prior researches was conducted in this title specifically. Therefore, this study investigates the impact of vector control interventions on malaria based on panel data of 10 malaria endemic-regions from 2000 to 2018.METHODS: A reflexive analysis study based on before-and-after assessment was used to evaluate the impact of vector control interventions on malaria with a difference-in-difference approach, representing Period I for before and Period II for after strategic intervention. The random-effect model was also employed to explore the direct relationship between the study variables. The data exported to Stata version 13.0 for analysis.
    RESULTS: The study results suggest that the negative relationship between intervention strategy and malaria cases reported in comparison with its counterfactual, showing the increase in malaria cases during Period II comparing to Period I. The study explores a remarkable achievement on the decline in mean malaria-related death in all regions after the implementation of the strategy. Furthermore, a significant relationship between indoor residual spraying, insecticide-treated mosquito nets, and malaria was demonstrated within the strategic periods.
    CONCLUSION: Better results achieved in Period I on mean malaria cases. The results of Period II showed a decline in mean malaria related-death, which was encouraging. The study calls for a supplementary strategy to align with the existing program. The study demonstrates the need for extra efforts on the implementation of the programme and progress about malaria.
    Keywords:  Different-estimation approach; Impact; Indoor residual spraying; Insecticide-treated mosquito nets; Malaria; Random effect model
  11. Appl Microbiol Biotechnol. 2021 Mar 21.
      The impact of ambient relative humidity (RH) on conidial production of Metarhizium humberi IP 46 microsclerotia (MS) formulated in pellets or granules was investigated, and a promising granular formulation was tested against Aedes aegypti adults to confirm its efficacy. Microcrystalline cellulose (MC) and diatomaceous earth (DE) or a combination of vermiculite (VE), DE and silicon dioxide (SD) were tested as carriers in granular formulations containing MS. A range of 93-96.5% RH was critical for fungal development, and at least 96.5-98.5% RH was required for high conidial production on pellets or granules. Conidial production was clearly higher on pellets and granules prepared with VE than MC as the main carrier. VE granules containing MS were highly active against A. aegypti adults. Most mosquitoes were killed within 6 days after treatment regardless of the exposure time of adults to the formulation (1 min-24 h) or ambient humidity (75 or >98%). Production of conidia on dead adults varied between 7.3 × 106 and 2.2 × 107 conidia/individual, when exposed to MS granules for 12 h and 1 min, respectively. Granular formulations containing VE as the main carrier and MS as the active ingredient of M. humberi have strong potential for use against A. aegypti. KEY POINTS: • High conidial production on granular microsclerotial formulations at >96.5% RH • Vermiculite is more appropriate as a carrier than microcrystalline cellulose • Granules with IP 46 microsclerotia are highly active against Aedes aegypti adults.
    Keywords:  Biological control; Entomopathogenic fungus; Granule; Mosquito; Pellet
  12. Int Q Community Health Educ. 2021 Mar 22. 272684X211004943
      Mosquito-borne diseases are a major public health concern. Because of absence of effective therapy and vaccination to treat and prevent such vector-borne diseases, these initial cases have triggered strong concerns within medical communities, turning a bad dream into reality. To date, reducing the mosquito vector population remains the main strategy to control the transmission of mosquito borne diseases. In this connection, community-based perception recognized as an essential tool for long-term vector control management. In this study, a community perception survey was carried out in six selected study areas of Ganjam district of Odisha. A total of 3257 inhabitants from randomly chosen 600 no. of houses from 06 selected study areas were interviewed using a pre-tested structured questionnaire about various mosquito vector-borne diseases. As an outcome, we found that only 36% of people have basic knowledge and idea about vector-borne diseases, out of which only 14% know Anopheles as a causative agent whereas Aedes and Culex were very least concern. Regarding the source of knowledge, electronic media was the principal source of information, while the involvements of health personnel were least mentioned. Results of the current study indicates the necessity to plan health education program to bring important perceptions regarding vector-borne diseases at school and college level because the infrequent source of knowledge is the main cause of an increase in the disease incidence.
    Keywords:  Odisha; community perception; mosquito; vector-borne diseases
  13. PLoS Negl Trop Dis. 2021 Mar 22. 15(3): e0009273
      Rift Valley fever virus (RVFV) is a mosquito-transmitted virus with proven ability to emerge into naïve geographic areas. Limited field evidence suggests that RVFV is transmitted vertically from parent mosquito to offspring, but until now this mechanism has not been confirmed in the laboratory. Furthermore, this transmission mechanism has allowed for the prediction of RVFV epizootics based on rainfall patterns collected from satellite information. However, in spite of the relevance to the initiation of epizootic events, laboratory confirmation of vertical transmission has remained an elusive research aim for thirty-five years. Herein we present preliminary evidence of the vertical transmission of RVFV by Culex tarsalis mosquitoes after oral exposure to RVFV. Progeny from three successive gonotrophic cycles were reared to adults, with infectious RVFV confirmed in each developmental stage. Virus was detected in ovarian tissues of parental mosquitoes 7 days after imbibing an infectious bloodmeal. Infection was confirmed in progeny as early as the first gonotrophic cycle, with infection rates ranging from 2.0-10.0%. Virus titers among progeny were low, which may indicate a host mechanism suppressing replication.
  14. Am J Trop Med Hyg. 2021 Mar 22. pii: tpmd201304. [Epub ahead of print]
      Zoonotic knowlesi malaria has replaced human malaria as the most prevalent malaria disease in Malaysia. The persistence of knowlesi malaria in high-risk transmission areas or hotspots can be discouraging to existing malaria elimination efforts. In this study, retrospective data of laboratory-confirmed knowlesi malaria cases were obtained from the Sarawak Health Department to investigate the spatiotemporal patterns and clustering of knowlesi malaria in the state of Sarawak from 2008 to 2017. Purely spatial, purely temporal, and spatiotemporal analyses were performed using SaTScan software to define clustering of knowlesi malaria incidence. Purely spatial and spatiotemporal analyses indicated most likely clusters of knowlesi malaria in the northern region of Sarawak, along the Sarawak-Kalimantan border, and the inner central region of Sarawak between 2008 and 2017. Temporal cluster was detected between September 2016 and December 2017. This study provides evidence of the existence of statistically significant Plasmodium knowlesi malaria clusters in Sarawak, Malaysia. The analysis approach applied in this study showed potential in establishing surveillance and risk management system for knowlesi malaria control as Malaysia approaches human malaria elimination.
  15. Malar J. 2021 Mar 26. 20(1): 168
      BACKGROUND: Although it is accepted that long-lasting insecticidal net (LLIN) use is an effective means to prevent malaria, children aged 5 to 15 years do not appear to be sufficiently protected in Madagascar; the malaria prevalence is highest in this age group. The purpose of this research is to summarize recent qualitative studies describing LLIN use among the Malagasy people with a focus on children aged 5-15 years.METHODS: Qualitative data from three studies on malaria conducted between 2012 and 2016 in 10 districts of Madagascar were analysed. These studies cover all malaria epidemiological profiles and 10 of the 18 existing ethnic groups in Madagascar. A thematic analysis was conducted on the collected data from semi-structured interviews, direct observation data, and informal interviews.
    RESULTS: A total of 192 semi-structured interviews were conducted. LLINs are generally perceived positively because they protect the health and well-being of users. However, regional representations of mosquito nets may contribute to LLIN lower use by children over 5 years of age including the association between married status and LLIN use, which leads to the refusal of unmarried young men to sleep under LLINs; the custom of covering the dead with a mosquito net, which leads to fear of LLIN use; and taboos governing sleeping spaces for siblings of opposite sexes, which leads to LLIN shortages in households. Children under 5 years of age are known to be the most vulnerable age group for acquiring malaria and, therefore, are prioritized for LLIN use when there are limited supplies in households. In contrast, children over 5 years of age, who are perceived to be at less risk for malaria, often sleep without LLINs.
    CONCLUSIONS: Perceptions, social practices and regional beliefs regarding LLINs and vulnerability to malaria contribute to the nonuse of LLINs among children over 5 years of age in Madagascar. Modifying LLIN policies to account for these factors may increase LLIN use in this age group and reduce disease burden.
    Keywords:  Children over five; LLIN use; Madagascar; Malaria; Sociocultural factors