bims-mosdis 2023-01-15 papers

bims-mosdis

Biomed News

on Mosquito distribution and disease

Issue of 2023–01–15
sixteen papers selected by
Richard Halfpenny, Staffordshire University

The role of anthropogenic container habitats as mosquito oviposition habitats in rural settlements in northern Tanzania.
A next-generation (DNA) sequencing (NGS)-based method for identifying the sources of sugar meals in mosquito vectors of West Nile virus in Israel.
Entomological monitoring data driving decision-making for appropriate and sustainable malaria vector control in Côte d'Ivoire.
Worldwide transmission and infection risk of mosquito vectors of West Nile, St. Louis encephalitis, Usutu and Japanese encephalitis viruses: a systematic review.
Residual efficacy of selected larvicides against Culex pipiens pipiens (Diptera: Culicidae) under laboratory and semi-field conditions.
Characterization of the anopheline vector breeding habitats: Implications for elimination of malaria in tribal inhabited Car Nicobar Island.
Utilizing citizen science to model the distribution of Aedes aegypti in West Africa.
Neuromodulation and differential learning across mosquito species.
First record of the mosquito Aedes (Downsiomyia) shehzadae (Diptera: Culicidae) in Australia: A unique discovery aided by citizen science.
Review of the Mimeticus Subgroup of Culex (Culex) (Diptera: Culicidae), With an Assessment of the Specific Status of Three Nominal Species Described From India.
Environmental Management and Sanitation as a Malaria Vector Control Strategy: A Qualitative Cross-Sectional Study Among Stakeholders, Sunyani Municipality, Ghana.
Unravelling the impact of insecticide-treated bed nets on childhood malaria in Malawi.
Range expansion of Aedes bahamensis (Diptera: Culicidae) into the Florida Keys.
Spatiotemporal dynamics of malaria in Zanzibar, 2015-2020.
Individual variation in Plasmodium vivax malaria risk: Are repeatedly infected people just unlucky?
Interactions between the gut micro-community and transcriptome of Culex pipiens pallens under low-temperature stress.

J Vector Ecol. 2022 Jun;47(1): 69-80

The role of anthropogenic container habitats as mosquito oviposition habitats in rural settlements in northern Tanzania.

Gordian Rocky Mataba, Linus Munishi, Luc Brendonck, Bram Vanschoenwinkel.

  In many areas, the main sources of mosquito vectors are not natural habitats but small artificial water bodies that are provided unintentionally by humans. Such container habitats have been linked to outbreaks of dengue fever and other arboviral diseases. However, in many parts of the world the possible risks associated with container habitats have not been assessed. Here, we focused on a human population expansion area in northern Tanzania with a high incidence of dengue and other cases of high fever. We explored the importance of anthropogenic container habitats for mosquito production in the Lake Manyara Basin. We also assessed how biotic and physicochemical habitat characteristics limit mosquito abundance in containers. Results showed that Aedes aegypti (Linnaeus), vector of dengue and other arboviruses, and Culex quinquefasciatus (Say), vector of filarial worms, were the dominant mosquitoes ovipositing in large numbers in different containers. Old tires were the dominant and most productive container habitat for mosquitoes in the region. However, there were strong differences among villages, illustrating that the mosquito burden associated with container habitats varies locally. We concluded that in this region, removal of artificial container habitats could be a simple strategy to reduce the mosquito-mediated disease burden within the local population.

Keywords:  Aedes aegypti; Culex quinquefasciatus; Lake Manyara basin; mosquito; oviposition

DOI:  https://doi.org/10.52707/1081-1710-47.1.69
J Vector Ecol. 2022 Jun;47(1): 109-116

A next-generation (DNA) sequencing (NGS)-based method for identifying the sources of sugar meals in mosquito vectors of West Nile virus in Israel.

Ibrahim Abbasi, Fouad Akad, Liora Studentsky, Irina Ben Avi, Laor Orshan, Alon Warburg.

  Mosquitoes of the genus Culex comprise important vectors of pathogenic arboviruses in our region, including West Nile and Rift Valley Fever viruses. To improve our understanding of the epidemiology and transmission dynamics of arboviruses, we need to study the behavior and ecology of their vectors. The feeding patterns of the vector mosquitoes can be very useful in determining how and where to focus control efforts. For example, determining the preferred blood hosts of the females can assist in the implementation of potentially efficacious strategies for focused control of mosquito females. Determining the plants from which both sexes derive their sugar meals can comprise the initial step towards the formulation of efficient lures for trapping mosquitoes. In the past, plant meal identification was based mainly on chemical detection of fructose and microscopical observations of cellulose particles in mosquito guts. More recent studies have utilized DNA barcoding capable of identifying plant food sources. In the current study, we identify multiple plant species from which large numbers of mosquitoes obtained their sugar meals in one experimental procedure. We employed next generation DNA sequencing to sequence the chloroplast specific plant genes atpB and rbcL.

Keywords:  Culex perexiguus; Culex pipiens; mosquito plant meals; next generation sequencing

DOI:  https://doi.org/10.52707/1081-1710-47.1.109
Malar J. 2023 Jan 12. 22(1): 14

Entomological monitoring data driving decision-making for appropriate and sustainable malaria vector control in Côte d'Ivoire.

Bernard Loukou Kouassi, Constant Edi, Allassane Foungoye Ouattara, Armand Kouassi Ekra, Louise Golou Bellai, Janice Gouaméné, Yves Alain Kadio Kacou, Jackson Koffi Ives Kouamé, Armel-Hermann Obo Béké, Firmain N'Dri Yokoli, Constant Guy N'Guessan Gbalegba, Emmanuel Tia, Roseline Monsan Yapo, Lucien Yao Konan, Roméo N'Tamon N'Tamon, Maurice Adja Akré, Alphonsine Amanan Koffi, Antoine Mea Tanoh, Pascal Zinzindohoué, Blaise Kouadio, Patricia L Yepassis-Zembrou, Allison Belemvire, Seth R Irish, Ndombour Gning Cissé, Cecilia Flatley, Joseph Chabi.

   BACKGROUND: Entomological surveillance provides critical information on vectors for appropriate malaria vector control and strategic decision-making. The widely documented insecticide resistance of malaria vectors in Côte d'Ivoire requires that any vector control intervention deployment be driven by entomological data to optimize its effectiveness and appropriate resource allocations. To achieve this goal, this study documents the results of monthly vector surveillance and insecticide susceptibility tests conducted in 2019 and a review of all previous entomological monitoring data used to guide vector control decision making. Furthermore, susceptibility to pirimiphos-methyl and clothianidin was assessed in addition to chlorfenapyr and pyrethroids (intensity and piperonyl butoxide (PBO) synergism) tests previously reported. Vector bionomic data were conducted monthly in four sites (Sakassou, Béoumi, Dabakala and Nassian) that were selected based on their reported high malaria incidence. Adult mosquitoes were collected using human landing catches (HLCs), pyrethrum spray catches (PSCs), and human-baited CDC light traps to assess vector density, behaviour, species composition and sporozoite infectivity.
RESULTS: Pirimiphos-methyl and clothianidin susceptibility was observed in 8 and 10 sites, respectively, while previous data reported chlorfenapyr (200 µg/bottle) susceptibility in 13 of the sites, high pyrethroid resistance intensity and increased mortality with PBO pre-exposure at all 17 tested sites. Anopheles gambiae sensu lato was the predominant malaria vector collected in all four bionomic sites. Vector density was relatively higher in Sakassou throughout the year with mean biting rates of 278.2 bites per person per night (b/p/n) compared to Béoumi, Dabakala and Nassian (mean of 48.5, 81.4 and 26.6 b/p/n, respectively). The mean entomological inoculation rate (EIR) was 4.44 infective bites per person per night (ib/p/n) in Sakassou, 0.34 ib/p/n in Beoumi, 1.17 ib/p/n in Dabakala and 1.02 ib/p/n in Nassian. The highest EIRs were recorded in October in Béoumi (1.71 ib/p/n) and Nassian (3.22 ib/p/n), in July in Dabakala (4.46 ib/p/n) and in May in Sakassou (15.6 ib/p/n).
CONCLUSION: Based on all results and data review, the National Malaria Control Programme developed and implemented a stratified insecticide-treated net (ITN) mass distribution in 2021 considering new generation ITNs. These results also supported the selection of clothianidin-based products and an optimal spraying time for the first indoor residual spraying (IRS) campaign in Sakassou and Nassian in 2020.

Keywords:  Anopheles gambiae; Côte d’Ivoire; Decision-making; IRS; ITNs; Insecticide resistance monitoring; Malaria; Vector bionomics

DOI:  https://doi.org/10.1186/s12936-023-04439-z
Sci Rep. 2023 Jan 06. 13(1): 308

Worldwide transmission and infection risk of mosquito vectors of West Nile, St. Louis encephalitis, Usutu and Japanese encephalitis viruses: a systematic review.

María José Tolsá-García, Magdalena Laura Wehmeyer, Renke Lühken, David Roiz.

The increasing trend of mosquito-borne pathogens demands more accurate global estimations of infection and transmission risks between mosquitoes. Here, we systematically review field and laboratory studies to assess the natural field infection and experimental laboratory transmission risk in Culex mosquitoes. We studied four worldwide flaviviruses: West Nile, Usutu, Japanese encephalitis, and St. Louis encephalitis, belonging to the Japanese encephalitis Serocomplex (JES). The PRISMA statement was carried out for both approaches. The Transmission-Infection Risk of the diverse mosquito species for the different viruses was estimated through seven variables. We considered 130 and 95 articles for field and experimental approach, respectively. We identified 30 species naturally infected, and 23 species capable to transmit some of the four flaviviruses. For the JES, the highest Transmission-Infection Risk estimate was recorded in Culex quinquefasciatus (North America). The maximum Infection-Transmission Risk values for West Nile was Culex restuans, for Usutu it was Culex pipiens (Europe), for St. Louis encephalitis Culex quinquefasciatus (North America), and for Japanese encephalitis Culex gelidus (Oceania). We conclude that on a worldwide scale, a combination of field and experimental data offers a better way of understanding natural infection and transmission risks between mosquito populations.

DOI: https://doi.org/10.1038/s41598-022-27236-1
Environ Sci Pollut Res Int. 2023 Jan 10.

Residual efficacy of selected larvicides against Culex pipiens pipiens (Diptera: Culicidae) under laboratory and semi-field conditions.

Maria K Sakka, Charalampos S Ioannou, Nikos T Papadopoulos, Christos G Athanassiou.

  Mosquitoes are a threat worldwide since they are vectors of important pathogens and parasites such as malaria, dengue, yellow fever, and West Nile. The residual toxicity of several commercial mosquito larvicides was evaluated for the control of Culex pipiens pipiens under controlled laboratory and semi-field conditions during late spring and summer of 2013. The evaluation included six different active ingredient formulations, i.e., diflubenzuron Du-Dim), Bacillus thuringiensis var. israelensis (Bti) (Vectobac), spinosad (Mozkill), S-methoprene (Biopren), temephos (Abate), and polydimethylsiloxane (PDMS) (Aquatain), that are currently registered of and had been registered in the past for mosquito control. Under controlled laboratory conditions, the residual activity ranged from 1 week (S-methoprene) up to 2 months (spinosad, PDMS). Exposure of larvicides under semi-field conditions resulted in noticeable differences regarding their efficacy as compared to the laboratory bioassays. Exposure of S-methoprene, Bti, and spinosad, for up to 3 days, resulted in similar adult emergence to the controls. On the other hand, the residual efficacy of diflubenzuron, temephos, and PDMS ranged from 14 to 28 days, depending on the season of exposure. Longevity and fecundity of adults that had emerged from surviving larvae, in most of the cases tested, did not differ significantly from that of the controls. The results of the present study demonstrate the necessity of both field and laboratory studies to draw safe conclusions regarding the efficacy of larvicides against mosquitoes and the selection of the proper formulation for each application scenario. In addition, defining the seasonal variation in the residual toxicity of the tested formulations could be useful for improving mosquitos' management programs.

Keywords:  Bti; Control; Diflubenzuron; Larvicides; Mosquitoes; Polydimethylsiloxane; S-methoprene; Spinosad; Temephos

DOI:  https://doi.org/10.1007/s11356-022-24654-6
Indian J Med Res. 2022 Aug;156(2): 240-249

Characterization of the anopheline vector breeding habitats: Implications for elimination of malaria in tribal inhabited Car Nicobar Island.

I P Sunish, A N Shriram, Amitabha De, A P Sugunan, P Vijayachari.

   Background & objectives: Malaria is an important public health problem in Andaman & Nicobar archipelago. Among the three districts, Nicobar is the most endemic district where API is >2. In this district, the malaria incidence in Car Nicobar Tehsil has declined steadily over the past 10 years. A renewed initiative to consolidate this gain is being made with the ultimate objective of achieving zero indigenous transmission of malaria in Car Nicobar. So, the present study undertook a close environmental monitoring of water bodies for assessing changes in the risk potential of mosquito vector breeding habitats which can augment the elimination programme.
Methods: The breeding habitats of anopheline mosquitoes were sampled in 16 areas of Car Nicobar Island for eight time periods during 2017-2020. Along with anophelines, various associated water parameters (n=60) were estimated, viz. physicochemical (n=13), and biological, which included culicine mosquito immatures, insect predators (n=5), phytoplanktons (n=31) and zooplanktons (n=10).
Results: In the 16 study sites, overall 1126 surface water stagnating bodies constituting 21 different habitat types were surveyed. Of these, 17 were positive for anopheline breeding. Water bodies from three villages were consistently found to be positive for anopheline breeding. However, early instars of anopheline larvae were more abundant compared to the late instars. Four anopheline species were recorded, including Anopheles sundaicus, A. barbirostris, A. insulaeflorum and A. subpictus, in which 48 per cent were A. sundaicus. Multivariable analysis indicated that anopheline density was significantly higher in permanent water bodies than in temporary habitats (P<0.05) (high risk of anophelines). The highest pH (≥8.2), dissolved solids (≥0.39) levels showed significantly (P<0.05) decreased larval densities (lower risk of breeding), adjusted with breeding sites and season. Nitrite levels increased (P=0.022) larval densities.
Interpretation & conclusions: The present study facilitated estimating the productive period of a larval habitat enabling target larval sources to reduce adult populations. Implementing larviciding strategy before monsoon season is presumably the most cost-effective strategy. The output can be utilized for environmental monitoring of mosquito breeding risk in other malaria endemic areas, particularly where medium/large water bodies are the predominant breeding sites for malaria vectors.

Keywords:  Anophelines; Car Nicobar; malaria; risk factors

DOI:  https://doi.org/10.4103/ijmr.ijmr_3189_21
J Vector Ecol. 2022 Jun;47(1): 117-127

Utilizing citizen science to model the distribution of Aedes aegypti in West Africa.

Elizabeth A Freeman, Elizabeth J Carlton, Sara Paull, Samuel Dadzie, Andrea Buchwald.

  In the rapidly urbanizing region of West Africa, Aedes mosquitoes pose an emerging threat of infectious disease that is compounded by limited vector surveillance. Citizen science has been proposed as a way to fill surveillance gaps by training local residents to collect and share information on disease vectors. Understanding the distribution of arbovirus vectors in West Africa can inform researchers and public health officials on where to conduct disease surveillance and focus public health interventions. We utilized citizen science data collected through NASA's GLOBE Observer mobile phone application and data from a previously published literature review on Aedes mosquito distribution to examine the contribution of citizen science to understanding the distribution of Ae. aegypti in West Africa using Maximum Entropy modeling. Combining citizen science and literature-derived observations improved the fit of the model compared to models created by each data source alone but did not alleviate location bias within the models, likely due to lack of widespread observations. Understanding Ae. aegypti distribution will require greater investment in Aedes mosquito surveillance in the region, and citizen science should be utilized as a tool in this mission to increase the reach of surveillance.

Keywords:  Aedes; GLOBE Observer; Maximum Entropy; West Africa; citizen science; mosquito distribution; niche modeling

DOI:  https://doi.org/10.52707/1081-1710-47.1.117
Proc Biol Sci. 2023 Jan 11. 290(1990): 20222118

Neuromodulation and differential learning across mosquito species.

Gabriella H Wolff, Chloé Lahondère, Clément Vinauger, Elizabeth Rylance, Jeffrey A Riffell.

  Mosquitoes can change their feeding behaviours based on past experiences, such as shifting from biting animals to biting humans or avoiding defensive hosts (Wolff & Riffell 2018 J. Exp. Biol. 221, jeb157131. (doi:10.1242/jeb.157131)). Dopamine is a critical neuromodulator for insects, allowing flexibility in their feeding preferences, but its role in the primary olfactory centre, the antennal lobe (AL), remains unclear (Vinauger et al. 2018 Curr. Biol. 28, 333-344.e8. (doi:10.1016/j.cub.2017.12.015)). It is also unknown whether mosquitoes can learn some odours and not others, or whether different species learn the same odour cues. We assayed aversive olfactory learning in four mosquito species with different host preferences, and found that they differentially learn odours salient to their preferred host. Mosquitoes that prefer humans learned odours found in mammalian skin, but not a flower odour, and a nectar-feeding species only learned a floral odour. Comparing the brains of these four species revealed significantly different innervation patterns in the AL by dopaminergic neurons. Calcium imaging in the Aedes aegypti AL and three-dimensional image analyses of dopaminergic innervation show that glomeruli tuned to learnable odours have significantly higher dopaminergic innervation. Changes in dopamine expression in the insect AL may be an evolutionary mechanism to adapt olfactory learning circuitry without changing brain structure and confer to mosquitoes an ability to adapt to new hosts.

Keywords:  dopamine; learning and memory; mosquito; olfaction

DOI:  https://doi.org/10.1098/rspb.2022.2118
J Vector Ecol. 2022 Jun;47(1): 133-137

First record of the mosquito Aedes (Downsiomyia) shehzadae (Diptera: Culicidae) in Australia: A unique discovery aided by citizen science.

Cameron Webb, John Clancy, Stephen L Doggett, Erica McAlister, Craig Williams, Stephen Fricker, Andrew van den Hurk, Bryan Lessard, John Lenagan, Marlene Walter.

DOI: https://doi.org/10.52707/1081-1710-47.1.133
J Med Entomol. 2023 Jan 13. pii: tjac188. [Epub ahead of print]

Review of the Mimeticus Subgroup of Culex (Culex) (Diptera: Culicidae), With an Assessment of the Specific Status of Three Nominal Species Described From India.

Pradya Somboon, Thanari Phanitchakun, Rinzin Namgay, Ralph E Harbach.

  The Mimeticus Subgroup of the subgenus Culex, genus Culex Linnaeus, is reviewed and revised. Mitochondrial COI sequences of species of the subgroup available in GenBank were analysed to verify the identity of voucher specimens. The specific status of three species described from India, Cx. gaugleri Suman, Cx. katezari Karlekar, Andrew & Deshpande, and Cx. kodaikanalensis Suman, Veer & Chandra, was examined and found to be unsupportable. Culex gaugleri and Cx. kodaikanalensis are synonyms of Cx. jacksoni based on the similarity of DNA sequences and dubious evidence of morphological differentiation. Culex katezari is recognized as a nomen dubium because the morphological description and molecular information provided by the authors are insufficient for its identification. A number of specimens registered in GenBank were found to be misidentified. In addition, available data indicate that the Mimeticus Subgroup may include at least three unrecognized species, referred to informally as Cx. mimeticus form B, Cx. mimulus form X, and Cx. mimulus form Y.

Keywords:  DNA; morphology; mosquito; systematics; taxonomy

DOI:  https://doi.org/10.1093/jme/tjac188
Environ Health Insights. 2023 ;17 11786302221146890

Environmental Management and Sanitation as a Malaria Vector Control Strategy: A Qualitative Cross-Sectional Study Among Stakeholders, Sunyani Municipality, Ghana.

Samuel Yaw Agyemang-Badu, Esi Awuah, Sampson Oduro-Kwarteng, Justice Yao Woelinam Dzamesi, Nazri Che Dom, Girum Gebremeskel Kanno.

   Background: For centuries malaria infection remains a public health burden globally as well as in the Sunyani Municipality. This exploratory qualitative study aimed to assess the prospects of environmental management and sanitation (EMS) as a malaria vector control strategy among key stakeholders involved in the prevention and control of malaria in Sunyani Municipality, Ghana.
Method: We used an exploratory qualitative study and a designed focus group discussion (FGD) guide (with specific research questions) to solicit opinions and/or views among Malaria Control Focal Persons, Environmental Health Officers (Health Inspectors), and Honourable Assembly Members. Data were collected between December 2019 and February 2020. The responses were analyzed according to the specific research questions.
Result: Findings from this study shows that high government support and/or political will by investing in environmental sanitation infrastructure, creating the enabling environment for strict enforcement of environmental sanitation bye-laws by Environmental Health Officers/Health Inspectors, effective and efficient collaboration among key stakeholders and organization of communal labor activities is likely to help reduce the majority of the mosquito breeding sites.
Conclusion: The prospects of environmental management and sanitation (EMS) as a vector control strategy, look promisingly very high, pertinent, and workable and a likelihood game changer of winning the fight against malaria due to the residual transmission that is happening outdoors. However, EMS can be employed as a supplementary method to the current core vector control methods if the following conditions and bottlenecks are addressed and in place: (a) Effective collaboration among key stakeholders at all levels; (b) Adequate allocation of funds to the Environmental Health and Sanitation Department; (c) Enactment of robust educational campaigns across all educational levels and via different media; (d) Recognition, empowerment, and adequate resourcing of Environmental Health Officers; (e) Adherence to the building regulations to prevent encroachment of natural wetlands; (f) Revision of fees/fines and prosecution of sanitary offenders; (g) Enactment of an Environmental Sanitation Day (ESD), and establishment of the Environmental Health and Sanitation Fund (EHSF).

Keywords:  Environmental management and sanitation; Ghana; environmental health officers; focus group discussion; malaria vector control; stakeholders; sunyani municipality

DOI:  https://doi.org/10.1177/11786302221146890
Malar J. 2023 Jan 13. 22(1): 16

Unravelling the impact of insecticide-treated bed nets on childhood malaria in Malawi.

Julie-Anne A Tangena, Donnie Mategula, Luigi Sedda, Peter M Atkinson.

   BACKGROUND: To achieve malaria elimination it is essential to understand the impact of insecticide-treated net (ITNs) programmes. Here, the impact of ITN access and use on malaria prevalence in children in Malawi was investigated using Malaria Indicator Survey (MIS) data.
METHODS: MIS data from 2012, 2014 and 2017 were used to investigate the relationship between malaria prevalence in children (6-59 months) and ITN use. Generalized linear modelling (GLM), geostatistical mixed regression modelling and non-stationary GLM were undertaken to evaluate trends, spatial patterns and local dynamics, respectively.
RESULTS: Malaria prevalence in Malawi was 27.1% (95% CI 23.1-31.2%) in 2012 and similar in both 2014 (32.1%, 95% CI 25.5-38.7) and 2017 (23.9%, 95% CI 20.3-27.4%). ITN coverage and use increased during the same time period, with household ITN access growing from 19.0% (95% CI 15.6-22.3%) of households with at least 1 ITN for every 2 people sleeping in the house the night before to 41.7% (95% CI 39.1-44.4%) and ITN use from 41.1% (95% CI 37.3-44.9%) of the population sleeping under an ITN the previous night to 57.4% (95% CI 55.0-59.9%). Both the geostatistical and non-stationary GLM regression models showed child malaria prevalence had a negative association with ITN population access and a positive association with ITN use although affected by large uncertainties. The non-stationary GLM highlighted the spatital heterogeneity in the relationship between childhood malaria and ITN dynamics across the country.
CONCLUSION: Malaria prevalence in children under five had a negative association with ITN population access and a positive association with ITN use, with spatial heterogeneity in these relationships across Malawi. This study presents an important modelling approach that allows malaria control programmes to spatially disentangle the impact of interventions on malaria cases.

Keywords:  Bed net use; Insecticide-treated bed net; Malaria indicator survey; Malawi

DOI:  https://doi.org/10.1186/s12936-023-04448-y
J Vector Ecol. 2022 Jun;47(1): 128-129

Range expansion of Aedes bahamensis (Diptera: Culicidae) into the Florida Keys.

Sierra Short, Valerie Dos Santos, Lawrence J Hribar.

DOI: https://doi.org/10.52707/1081-1710-47.1.128
BMJ Glob Health. 2023 Jan;pii: e009566. [Epub ahead of print]8(1):

Spatiotemporal dynamics of malaria in Zanzibar, 2015-2020.

Donal Bisanzio, Shabbir Lalji, Faiza B Abbas, Mohamed H Ali, Wahida Hassan, Humphrey R Mkali, Abdul-Wahid Al-Mafazy, Joseph J Joseph, Ssanyu Nyinondi, Chonge Kitojo, Naomi Serbantez, Erik Reaves, Erin Eckert, Jeremiah M Ngondi, Richard Reithinger.

   BACKGROUND: Despite high coverage of malaria interventions, malaria elimination in Zanzibar remains elusive, with the annual number of cases increasing gradually over the last 3 years.
OBJECTIVE: The aims of the study were to (1) assess the spatiotemporal dynamics of malaria in Zanzibar between 2015 and 2020 and (2) identify malaria hotspots that would allow Zanzibar to develop an epidemiological stratification for more effective and granular intervention targeting.
METHODS: In this study, we analysed data routinely collected by Zanzibar's Malaria Case Notification (MCN) system. The system collects sociodemographic and epidemiological data from all malaria cases. Cases are passively detected at health facilities (ie, primary index cases) and through case follow-up and reactive case detection (ie, secondary cases). Analyses were performed to identify the spatial heterogeneity of case reporting at shehia (ward) level during transmission seasons.
RESULTS: From 1 January 2015 to 30 April 2020, the MCN system reported 22 686 index cases. Number of cases reported showed a declining trends from 2015 to 2016, followed by an increase from 2017 to 2020. More than 40% of cases had a travel history outside Zanzibar in the month prior to testing positive for malaria. The proportion of followed up index cases was approximately 70% for all years. Out of 387 shehias, 79 (20.4%) were identified as malaria hotspots in any given year; these hotspots reported 52% of all index cases during the study period. Of the 79 hotspot shehias, 12 were hotspots in more than 4 years, that is, considered temporally stable, reporting 14.5% of all index cases.
CONCLUSIONS: Our findings confirm that the scale-up of malaria interventions has greatly reduced malaria transmission in Zanzibar since 2006. Analyses identified hotspots, some of which were stable across multiple years. Malaria efforts should progress from a universal intervention coverage approach to an approach that is more tailored to a select number of hotspot shehias.

Keywords:  Epidemiology; Malaria; Public Health

DOI:  https://doi.org/10.1136/bmjgh-2022-009566
PLoS Negl Trop Dis. 2023 Jan;17(1): e0011020

Individual variation in Plasmodium vivax malaria risk: Are repeatedly infected people just unlucky?

Rodrigo M Corder, Ana Paula Arez, Marcelo U Ferreira.

Extensive research has examined why some people have frequent Plasmodium falciparum malaria episodes in sub-Saharan Africa while others remain free of disease most of the time. In contrast, malaria risk heterogeneity remains little studied in regions where P. vivax is the dominant species. Are repeatedly infected people in vivax malaria settings such as the Amazon just unlucky? Here, we briefly review evidence that human genetic polymorphism and acquired immunity after repeated exposure to parasites can modulate the risk of P. vivax infection and disease in predictable ways. One-fifth of the hosts account for 80% or more of the community-wide vivax malaria burden and contribute disproportionally to onward transmission, representing a priority target of more intensive interventions to achieve malaria elimination. Importantly, high-risk individuals eventually develop clinical immunity, even in areas with very low or residual malaria transmission, and may constitute a large but silent parasite reservoir.

DOI: https://doi.org/10.1371/journal.pntd.0011020
Parasit Vectors. 2023 Jan 12. 16(1): 12

Interactions between the gut micro-community and transcriptome of Culex pipiens pallens under low-temperature stress.

Wen-Xiang Lv, Peng Cheng, Jing-Jing Lei, Hui Peng, Chuan-Hui Zang, Zi-Wei Lou, Hong-Mei Liu, Xiu-Xia Guo, Hai-Yang Wang, Hai-Fang Wang, Chong-Xing Zhang, Li-Juan Liu, Mao-Qing Gong.

   BACKGROUND: Culex pipiens pallens (Diptera: Culicidae) can survive at low temperature for long periods. Understanding the effects of low-temperature stress on the gut microflora and gene expression levels in Cx. pipiens pallens, as well as their correlation, will contribute to the study of the overwintering mechanism of Cx. pipiens pallens.
METHODS: The gut bacteria were removed by antibiotic treatment, and the survival of Cx. pipiens pallens under low-temperature stress was observed and compared with the control group. Then, full-length 16S rRNA sequencing and the Illumina HiSeq X Ten sequencing platform were used to evaluate the gut microflora and gene expression levels in Cx. pipiens pallens under low-temperature stress.
RESULTS: Under the low-temperature stress of 7 °C, the median survival time of Cx. pipiens pallens in the antibiotic treatment group was significantly shortened by approximately 70% compared to that in the control group. The species diversity index (Shannon, Simpson, Ace, Chao1) of Cx. pipiens pallens decreased under low-temperature stress (7 °C). Non-metric multidimensional scaling (NMDS) analysis divided all the gut samples into two groups: control group and treatment group. Pseudomonas was the dominant taxon identified in the control group, followed by Elizabethkingia and Dyadobacter; in the treatment group, Pseudomonas was the dominant taxon, followed by Aeromonas and Comamonas. Of the 2417 differentially expressed genes (DEGs), 1316 were upregulated, and 1101 were downregulated. Functional GO terms were enriched in 23 biological processes, 20 cellular components and 21 molecular functions. KEGG annotation results showed that most of these genes were related to energy metabolism-related pathways. The results of Pearson's correlation analysis showed a significant correlation between the gut microcommunity at the genus level and several DEGs.
CONCLUSIONS: These results suggest that the mechanism of adaptation of Cx. pipiens pallens to low-temperature stress may be the result of interactions between the gut bacterial community and transcriptome.

Keywords:  16S rRNA; Culex pipiens pallens; Interaction; Low temperature; Transcriptome

DOI:  https://doi.org/10.1186/s13071-022-05643-7