Bridging Biodiversity and Health: The Global Biodiversity Information Facility's initiative on open data on vectors of human diseases

There is an increased awareness of the importance of data publication, data sharing, and open science to support research, monitoring and control of vector-borne disease (VBD). Here we describe the efforts of the Global Biodiversity Information Facility (GBIF) as well as the World Health Special Programme on Research and Training in Diseases of Poverty (TDR) to promote publication of data related to vectors of diseases. In 2020, a GBIF task group of experts was formed to provide advice and support efforts aimed at enhancing the coverage and accessibility of data on vectors of human diseases within GBIF. Various strategies, such as organizing training courses and publishing data papers, were used to increase this content. This editorial introduces the outcome of a second call for data papers partnered by the TDR, GBIF and GigaScience Press in the journal GigaByte. Biodiversity and infectious diseases are linked in complex ways. These links can involve changes from the microorganism level to that of the habitat, and there are many ways in which these factors interact to affect human health. One way to tackle disease control and possibly elimination, is to provide stakeholders with access to a wide range of data shared under the FAIR principles, so it is possible to support early detection, analyses and evaluation, and to promote policy improvements and/or development.

Effects of mosquito age and batch size on knockdown and mortality of laboratory-reared Anopheles dirus, Anopheles minimus, and wild-caught Anopheles harrisoni (Diptera: Culicidae) exposed to transfluthrin using WHO tube and CDC bottle bioassays

WHO tube and CDC bottle bioassays are currently available for insecticide resistance monitoring and malaria transmission research. Multiple parameters including mosquito density, age, and nutritional status may affect the readout in these bioassays' tests. This study aims to assess the effects of experimental factors on knockdown and mortality measurements in dominant malaria vectors in Thailand following exposure to sublethal and lethal doses of transfluthrin. The effects of (i) 3 different mosquito batch sizes (5, 10, and 20 individuals) and (ii) 2 age groups (3-5 and 20-23 days old) on outcomes measured using the WHO tube (14.7 µg/cm2) and CDC bottle bioassay discriminating concentration (0.006 µg/cm2) against 2 laboratory strains: Anopheles dirus Peyton & Harrison and Anopheles minimus Theobald (species A) and wild-caught Anopheles harrisoni Harbach & Manguin (species C). Our results showed higher knockdown at 1-h exposure using WHO tube and CDC bottle bioassays containing 20 individuals compared to batches containing 10 and 5 individuals. Older mosquitoes showed greater susceptibility than younger test population, especially for An. mininus. Our study supports WHO recommendations for using 3- to 5-day-old mosquitoes. It also validates Praulin et al. (2022) proposal to divide the cohort into smaller batches with more test replicates when it is not practicable to test 25 mosquitoes per replicate.

Evolution and spread of Plasmodium falciparum mutations associated with resistance to sulfadoxine-pyrimethamine in central Africa: a cross-sectional study

BACKGROUND

Efficacy of sulfadoxine-pyrimethamine, the malaria chemoprophylaxis used in pregnant women, and in children when combined with amodiaquine, is threatened by the accumulation of mutations in the Plasmodium falciparum dihydropteroate synthase (pfdhps) and dihydrofolate reductase (pfdhfr) genes. Data on the prevalence of resistant alleles in central Africa and the new pfdhps I431V mutation, particularly associated with other mutations to form the pfdhps vagKgs allele, are scarce. We explored the frequency and geographical distribution of pfdhps and pfdhfr mutations in central Africa in 2014-18, and assessed the evolutionary origin of the vagKgs allele.

METHODS

Samples were collected at 18 health-care centres in seven countries (Angola, Cameroon, Central African Republic, Democratic Republic of the Congo, Gabon, Nigeria, and Republic of the Congo) from patients who showed possible symptoms of malaria between March 1, 2014, and Oct 31, 2018. Samples that were positive for P falciparum were transported to a laboratory in Toulouse, France, and genotyped. The frequency of pfdhfr and pfdhps mutations was studied in 1749 samples. Microsatellites in pfdhps flanking regions and whole-genome analysis compared with parasite genomes from the data-sharing network MalariaGEN were performed on samples carrying the vagKgs allele.

FINDINGS

Mapping of the prevalence of single nucleotide polymorphisms and corresponding alleles of pfdhfr and pfdhps showed a substantial spread of alleles associated with sulfadoxine-pyrimethamine resistance in central Africa during the 2014-18 period, especially an increase going west to east in pfdhps alleles carrying the K540E and A581G mutations. A high prevalence of the pfdhps I431V mutation was observed in Cameroon (exceeding 50% in the northern region) and Nigeria. Genomic analysis showed a recent African emergence and a clonal expansion of the most frequent pfdhps vagKgs allele.

INTERPRETATION

Reduced sulfadoxine-pyrimethamine efficacy due to increased resistance is a worrying situation, especially because the malaria transmission level is high in central Africa. Although the resistance phenotype remains to be confirmed, the emergence and spread of the vagKgs allele in west and central Africa could challenge the use of sulfadoxine-pyrimethamine.

FUNDING

Toulouse Institute for Infectious and Inflammatory Diseases.

Synergistic Repellent and Irritant Effects of a Mixture of β-Caryophyllene Oxide and Vetiver Oil against Mosquito Vectors

Repellents play a major role in reducing the risk of mosquito-borne diseases by preventing mosquito bites. The present study evaluated the mosquito-repellent activity of β-caryophyllene oxide 1% (BCO), vetiver oil 2.5% (VO), and their binary mixtures (BCO + VO (1:1), BCO + VO (2:1), BCO + VO (1:2)) against four laboratory-colonized mosquito species, Aedes aegypti (L.), Aedes albopictus (Skuse), Anopheles minimus Theobald, and Culex quinquefasciatus Say, using an excito-repellency assay system. In general, the compound mixtures produced a much stronger response in the mosquitoes than single compounds, regardless of the test conditions or species. The greatest synergetic effect was achieved with the combination of BCO + VO (1:2) in both contact and noncontact trials with An. minimus (74.07-78.18%) and Cx. quinquefasciatus (55.36-83.64%). Knockdown responses to the binary mixture of BCO + VO were observed for Ae. albopictus, An. minimus, and Cx. quinquefasciatus, in the range of 18.18-33.33%. The synergistic repellent activity of BCO and VO used in this study may support increased opportunities to develop safer alternatives to synthetic repellents for personal protection against mosquitoes.

Distribution of mosquitoes (Diptera: Culicidae) in Thailand: a dataset

Mosquitoes play a crucial role as primary vectors for various infectious diseases in Thailand. Therefore, accurate distribution information is vital for effectively combating and better controlling mosquito-borne diseases. Here, we present a curated dataset of the mosquito distribution in Thailand comprising 12,278 records of at least 117 mosquito species (Diptera: Culicidae). The main genera included in the dataset are Aedes, Anopheles, Armigeres, Culex, and Mansonia. From 2007 to 2023, data were collected through routine mosquito surveillance and research projects from 1,725 locations across 66 (out of 77) Thai provinces. The majority of the data were extracted from a Thai database of the Thailand Malaria Elimination Program. To facilitate broader access to mosquito-related data and support further exploration of the Thai mosquito fauna, the data were translated into English. Our dataset has been published in the Global Biodiversity Information Facility, making it available for researchers worldwide.

Biodiversity data supports research on human infectious diseases: Global trends, challenges, and opportunities

The unprecedented generation of large volumes of biodiversity data is consistently contributing to a wide range of disciplines, including disease ecology. Emerging infectious diseases are usually zoonoses caused by multi-host pathogens. Therefore, their understanding may require the access to biodiversity data related to the ecology and the occurrence of the species involved. Nevertheless, despite several data-mobilization initiatives, the usage of biodiversity data for research into disease dynamics has not yet been fully leveraged. To explore current contribution, trends, and to identify limitations, we characterized biodiversity data usage in scientific publications related to human health, contrasting patterns of studies citing the Global Biodiversity Information Facility (GBIF) with those obtaining data from other sources. We found that the studies mainly obtained data from scientific literature and other not aggregated or standardized sources. Most of the studies explored pathogen species and, particularly those with GBIF-mediated data, tended to explore and reuse data of multiple species (>2). Data sources varied according to the taxa and epidemiological roles of the species involved. Biodiversity data repositories were mainly used for species related to hosts, reservoirs, and vectors, and barely used as a source of pathogens data, which was usually obtained from human and animal-health related institutions. While both GBIF- and not GBIF-mediated data studies explored similar diseases and topics, they presented discipline biases and different analytical approaches. Research on emerging infectious diseases may require the access to geographical and ecological data of multiple species. The One Health challenge requires interdisciplinary collaboration and data sharing, which is facilitated by aggregated repositories and platforms. The contribution of biodiversity data to understand infectious disease dynamics should be acknowledged, strengthened, and promoted.

Behavioral avoidance and biological safety of vetiver oil and its constituents against Aedes aegypti (L.), Aedes albopictus (Skuse) and Culex quinquefasciatus Say

Numerous plant-based repellents are widely used for personal protection against host-seeking mosquitoes. Vitiveria zizanioides (L.) Nash essential oil and its constituents have demonstrated various mosquito repellent activities. In this study, three chemical actions of vetiver oil and five constituents (terpinen-4-ol, α-terpineol, valencene, vetiverol and vetivone) were characterized against Aedes aegypti, Aedes albopictus and Culex quinquefasciatus by using the high-throughput screening assay system (HITSS). Significant contact escape responses in Ae. aegypti and Ae. albopictus to all test compounds at concentrations between 2.5 and 5% were observed. Spatial repellency responses were also observed in some tested mosquito populations depending upon concentrations. The most significant toxic response on mosquitoes was found at the highest concentration, except for vetivone which had no toxic effect on Ae. aegypti and Ae. albopictus. Results on phototoxic and genotoxic hazard revealed that vetiver oil and their constituents showed no phototoxic potential or any significant genotoxic response. In conclusion, vetiver oil and two constituents, valencene and vetiverol, are potentials as active ingredients for mosquito repellency and present no toxicity.

Scientific achievements and reflections after 20 years of vector biology and control research at the Pu Teuy mosquito field research station, Thailand

Additional vector control tools are needed to supplement current strategies to achieve malaria elimination and control of Aedes-borne diseases in many settings in Thailand and the Greater Mekong Sub-region. Within the next decade, the vector control community, Kasetsart University (KU), and the Ministry of Higher Education, Science, Research and Innovation must take full advantage of these tools that combine different active ingredients with different modes of action. Pu Teuy Mosquito Field Research Station (MFRS), Department of Entomology, Faculty of Agriculture, Kasetsart University (KU), Thailand was established in 2001 and has grown into a leading facility for performing high-quality vector biology and control studies and evaluation of public health insecticides that are operationally relevant. Several onsite mosquito research platforms have been established including experimental huts, a 40-m long semi-field screening enclosure, mosquito insectary, field-laboratory, and living quarters for students and researchers. Field research and assessments ranged from 'basic' investigations on mosquito biology, taxonomy and genetics to more 'applied' studies on responses of mosquitoes to insecticides including repellency, behavioural avoidance and toxicity. In the course of two decades, 51 peer-reviewed articles have been published, and 7 masters and 16 doctoral degrees in Entomology have been awarded to national and international students. Continued support of key national stakeholders will sustain MFRS as a Greater Mekong Subregion centre of excellence and a resource for both insecticide trials and entomological research.

Trophic Behavior and Species Diversity of the Anopheles barbirostris Complex (Diptera: Culicidae) in Thailand

Species of the Anopheles barbirostris complex (Myzorhynchus Series of the subgenus Anopheles) are potential vectors of malaria and filariasis parasites. Owing to the lack of reliable identification methods, the biting activity and host preference of the species within this complex have not been previous described. In this study, the trophic behavior and host preferences of the species in the complex were determined in Thailand, and a map of their geographical distributions constructed. Adult female mosquitoes in Chanthaburi and Prachuap Khiri Khan provinces were collected using human landings (indoor and outdoor) and cow-bait. Morphological characters were used to initially identify the mosquitoes, and then, species were further separated by multiplex PCR. Four species were identified in the An. barbirostris complex: An. wejchoochotei Taai & Harbach (Diptera: Culicidae), An. saeungae Taai & Harbach (Diptera: Culicidae), An. dissidens Taai & Harbach (Diptera: Culicidae), and An. campestris Reid (Diptera: Culicidae). The species showed exophagic and zoophilic behavior, except An. wejchoochotei in Chanthaburi, which displayed slight endophilic behavior. Indoor and outdoor blood feeding behavior of An. wejchoochotei and An. saeungae peaked at 2000 h. An updated distribution map of the An. barbirostris complex in Thailand is presented. With a better understanding of the sibling vector species and their spatial distributions, more specific and effective control strategies for vectors of malaria and filariasis in Thailand can be achieved.

Defeating malaria in the North-East region: the forerunner for malaria elimination in India

India is a malaria endemic country which is targeting malaria elimination by 2027. Transmission intensities are low-to-moderate depending on the region supported by multiple disease vectors. Among these, comparatively North-East India contributes to high proportions of malaria cases annually, the majority of which are due to Plasmodium falciparum (90%). Anopheles minimus and An. baimaii (sibling species in the An. dirus complex) are widely prevalent and incriminated as vectors of malaria. Number of intervention tools were field-evaluated beginning 1988 to date against disease vectors and causative parasites to contain the spread of malaria. These included (i) insecticide-treated netting materials (ITNs) for vector control, (ii) rapid diagnostic tests (RDTs) for in situ diagnosis, and (iii) therapeutic efficacy of artemisinin-based combination therapies (ACTs) for improved drug-policy; all of which were incorporated in healthcare services resulting in substantial disease transmission reduction. Populations of both An. minimus and An. baimaii were observed depleting, instead An. culicifacies s.l. recorded to be fast invading degraded forests and assessed to be resistant to multiple insecticides. Of the two prevalent Plasmodium species, while P. vivax continued to be susceptible to chloroquine therapy, P. falciparum had emerged resistant to most available antimalarial drugs except ACTs over space and time and spreading to peninsular India threatening elimination efforts. Disease transmission trends were observed to be declining for which the state of Assam has made huge strides reporting steady fall in cases each passing year vis-à-vis Meghalaya, Mizoram and Tripura (all sharing international border with Bangladesh), in which malaria transmission remained uninterrupted. Consequently, control of malaria in the North-East region of India is of immediate importance and needs prioritization for intensified disease surveillance and control interventions coupled with improved access to healthcare services mitigating risk of disease outbreaks and spread of drug-resistant malaria helping realize the goal of malaria elimination in the country.

Homogeneity and Possible Replacement of Populations of the Dengue Vectors Aedes aegypti and Aedes albopictus in Indonesia

Currently, Aedes aegypti, the principal vector of dengue virus in Indonesia, has spread throughout the archipelago. Aedes albopictus is also present. Invasion and high adaptability of the Aedes mosquitoes to all of these areas are closely related to their ecology and biology. Between June 2016 and July 2017, larval and adult mosquito collections were conducted in 43 locations in 25 provinces of Indonesia using standardized sampling methods for dengue vector surveillance. The samples collected were analyzed for polymorphism and phylogenetic relationship using the mitochondrial cox1 gene and the nuclear ribosomal internal transcribed spacer 2 (ITS2). Almost all Ae. aegypti samples collected in this study (89%) belonged to the same haplotype. A similar situation is observed with the nuclear ITS2 marker. Populations of Ae. aegypti characterized few years ago were genetically different. A closely related observation was made with Aedes albopictus for which the current populations are different from those described earlier. Ae. aegypti populations were found to be highly homogenous all over Indonesia with all samples belonging to the same maternal lineage. Although difficult to demonstrate formally, there is a possibility of population replacement. Although to a lower extent, a similar conclusion was reached with Ae. albopictus.

Assessment of Mosquito Collection Methods for Dengue Surveillance

Several methods exist to collect and assess the abundance of dengue vector mosquitoes, i.e., morning adult collection, pupal collection, ovitraps, human landing, and larval collection. Several of these methods are officially implemented to monitor mosquito density and make decisions on treatments for dengue control. This monitoring is also constrained by the need to conduct this assessment on a “one point/one day” process, meaning that once the threshold of 100 households is reached, the assessment is made, and the collectors teams move to another place, thus preventing the use of long-term sampling methods. This diversity of methods might be a source of variability and lack of statistical significance. There is also a lack of published data regarding the efficacy of these methods. Furthermore, the Stegomyia indices are shown to be not reliable for assessing the risk of dengue outbreaks. A mosquito survey was, thus, conducted in 39 locations corresponding to 15 dengue endemic provinces in Indonesia by using the different adult and larval collection methods recommended nationwide. A total of 44,675 mosquitoes were collected. The single larva method was the most efficient. Out of a total of 89 dengue-positive pools, the most frequently encountered virus was DENV2, which made up half of the positive samples, followed by DENV3 and DENV1, respectively. Factor analysis of mixed data showed that no correlation could be found between any methods and the presence of dengue virus in mosquitoes. Moreover, no correlation could be found between any methods and the incidence of dengue. There was no consistency in the efficacy of a given method from one site to another. There was no correlation between any of the parameters considered, i.e., method, incidence of dengue, location, and the presence of dengue virus in mosquitoes.

Review of Issues on Residual Malaria Transmission

Residual malaria transmission is the actual maintained inoculation of Plasmodium, in spite of a well-designed and implemented vector control programs, and is of great concern for malaria elimination. Residual malaria transmission occurs under several possible circumstances, among which the presence of exophilic vector species, such as Anopheles dirus, or indoor- and outdoor-biting vectors, such as Anopheles nili, or specific behavior, such as feeding on humans indoors, then resting or leaving the house the same night (such as Anopheles moucheti) or also changes in behavior induced by insecticides applied inside houses, such as the well-known deterrent effect of permethrin-treated nets or the irritant effect of DDT. The use of insecticides may change the composition of local Anopheles populations, such as A. arabiensis taking up the place of A. gambiae in Senegal, A. aquasalis replacing A. darlingi in Guyana, or A. harrisoni superseding A. minimus in Vietnam. The change in behavior, such as biting activity earlier than usually reported—for example, Anopheles funestus after a large-scale distribution of long-lasting insecticidal nets—or insecticide resistance, in particular the current spread of pyrethroid resistance, could hamper the efficacy of classic pyrethroid-treated long-lasting insecticidal nets and maintained transmission. These issues must be well documented in every situation to elaborate, implement, monitor, and evaluate tailored vector control programs, keeping in mind that they must be conceived as integrated programs with several well and appropriately coordinated approaches, combining entomological but also parasitological, clinical, and social methods and analyses. A successful integrated vector control program must then be designed to reduce transmission and incidence rates of malaria morbidity and overall mortality.

Fast Expansion of the Asian-Pacific Genotype of the Chikungunya Virus in Indonesia

Chikungunya is repeatedly affecting Indonesia through successive outbreaks. The Asian genotype has been present in Asia since the late 1950s while the ECSA-IOL (East/Central/South Africa - Indian Ocean Lineage) genotype invaded Asia in 2005. In order to determine the extension of the circulation of the chikungunya virus (CHIKV) in Indonesia, mosquitoes were collected in 28 different sites from 12 Indonesian provinces in 2016-2017. The E1 subunit of the CHIKV envelope gene was sequenced while mosquitoes were genotyped using the mitochondrial cox1 (cytochrome C oxidase subunit 1) gene to determine whether a specific population was involved in the vectoring of CHIKV. A total of 37 CHIKV samples were found in 28 Aedes aegypti, 8 Aedes albopictus and 1 Aedes butleri out of 15,362 samples collected and tested. These viruses, like all Indonesian CHIKV since 2000, belonged to a genotype we propose to call the Asian-Pacific genotype. It also comprises the Yap isolates and viruses having emerged in Polynesia, the Caribbean and South America. They differ from the CHIKV of the Asian genotype found earlier in Indonesia indicating a replacement. These results raise the question of the mechanisms behind this fast and massive replacement.

Evaluation of fecal immunoassays for canine Echinococcus infection in China

Human echinococcosis is present worldwide but it is in China that disease prevalence is the highest. In western China, especially in the Tibetan Plateau, the burden of echinococcosis is the most important. Dogs are a major definitive host of Echinococcus and monitoring the presence of Echinococcus worms in dogs is therefore essential to efficiently control the disease. Detection kits based on three different technologies including sandwich ELISA, (indirect) ELISA, and gold immunodiffusion, are currently marketed and used in China. The objective of this work was to assess the efficacy of these kits, in particular with respect to sensitivity and specificity. Four fecal antigen detection kits for canine infection reflecting the three technologies were obtained from companies and tested in parallel on 220 fecal samples. The results indicate that the performance is lower than expected, in particular in terms of sensitivity. The best results were obtained with the sandwich ELISA technology. The gold immunofiltration yielded the poorest results. In all cases, further development is needed to improve the performance of these kits which are key components for the control of echinococcosis.

Although present worldwide, human echinococcosis is at its highest prevalence in western China and particularly in the Tibetan Plateau. Controlling echinococcosis is a national priority and routine monitoring must be established. Dogs are the main infection source in China and surveying Echinococcus worms in dogs is therefore a research priority. Commercial detection kits are currently in use in China to monitor the presence of Echinococcus in dogs. The kits are based on three different technologies including sandwich ELISA with two monoclonal antibodies, (indirect) ELISA, and gold immunodiffusion. National survey programmes are essential for the control of echinococcosis and it is thus very important to assess the efficacy of these kits for the programmes. This work was therefore undertaken to assess efficacy of the kits, in particular with respect to sensitivity and specificity. Four fecal antigen detection kits for canine infection reflecting the three technologies were obtained from companies and tested in parallel on 220 fecal samples. The performance was lower than expected, in particular for their sensitivity which ranged between 51.5% and 83.9% with only two samples displaying a worm burden lower than 100. Three out of four kits showed non-specific cross-reactions with other parasites. The best results were obtained with the sandwich ELISA technology, whereas gold immunofiltration yielded the poorest results. However, in all cases, further development is strongly needed to improve the performance of these kits which are key components for the control of echinococcosis.

[Lessons from the Malaria Vector Control Program Based on Indoors Residual Spraying with DDT or Dieldrin in the Pilot Zone of Bobo-Dioulasso: Failure or Success?]

During five years, from 1953, a village scale indoors residual spraying (IRS) was done in the pilot zone of Bobo-Dioulasso, Burkina Faso, with DDT or dieldrin (DLN) or even HCH with a conceptually both entomological and parasitological evaluation [18].Compared to the control area, DDT induced an approximatively 95% and 67% reduction in the landing rate of Anopheles gambiae, respectively inside and outside human houses but due to its irritant action, DDT greatly increased their exophagic behaviour. However, DLN had no impact on the landing rate of An. gambiae either indoors or outdoors due to the already noticed resistance of this species to this insecticide. The sporozoitic index of An. gambiae was reduced by 96% in the DDT treated areas and by 70% in the DLN treated area.DDT reduced the landing rates of Anopheles funestus by 98% and 91%, inside and outside treated houses respectively. With DLN, these reductions were 98% and 97%, respectively. The sporozoitic index of An. funestus was reduced by 95% in areas treated with DDT.Thus, vector control has reduced malaria transmission due to the two main vectors, An. gambiae and An. funestus, by some 99.8% in DDT treated villages compared to control villages. DLN reduced transmission from An. funestus by 99.9%, but almost not from An. gambiae . Overall, the implementation of vector control based on indoor residual spraying with DDT or DLN reduced by 99.9% the transmission of human Plasmodium in the villages of the pilot zone and therefore the program can be considered as entomologically successful.In children aged 2-9 years (target group for endemicity indices) the splenic index was 84.3% (n = 979) in the control area and 44.4% (n = 8920) in the treated areas (difference -47.3%), the plasmodial prevalence was 60.6% (n = 946) in the control zone and 38.0% (n = 7242) in the treated zones (difference - 37%) but the relatively high level of plasmodic or splenic index in treated villages showed that transmission was maintained at such a level that the program could be considered as a "semi-failure".Besides, the gametocytic indices remained at the same levels (3.28%, n = 946 in the control zone and 3.04%, n = 7242 in the treated zones) indicating the maintenance of the "reservoir of parasites" and the remaining possibilities of transmission.Compared to the control area, the index of new contamination was significantly lower in infants 0-3 months and 4 to 6 months in DDT treated villages but not in infants 7 to 12 months demonstrating that the control vector had some efficacy in the prevention of plasmodial infection but "all newborns were infected within one year" demonstrating that P. falciparum transmission was not completely stopped.In spite of its striking drop, the transmission was not fully stopped, and the programme was considered as a "semi-failure" or even a "failure" and inducing a complete shift in malaria control policy from vector control to mass drug chemotherapy (with several drugs, chloroquine, primaquine, pyriméthamine etc) without complete stop of transmission either. In fact, such vector control operations by DDT may have different analysis; in one side they can be considered an entomological success but, in another side, the actual reduction of plasmodic and splenic indices was not enough to be considered as successful. It was clear that both vector and parasite must be implemented in an integrated programme taking care of insecticide and drug resistance. Nevertheless, such programme, even not as successful as expected, could be considered as encouraging and not "disappointing" as it was. Important lessons can be learned from such large-scale field trial in spite of several methodological and operational issues.

Species diversity and insecticide resistance within the Anopheles hyrcanus group in Ubon Ratchathani Province, Thailand

Background

Members of the Anopheles hyrcanus group have been incriminated as important malaria vectors. This study aims to identify the species and explore the insecticide susceptibility profile within the Anopheles hyrcanus group in Ubon Ratchathani Province, northeastern Thailand where increasing numbers of malaria cases were reported in 2014.

Methods

Between 2013 and 2015, five rounds of mosquito collections were conducted using human landing and cattle bait techniques during both the rainy and dry seasons. Anopheles mosquitoes were morphologically identified and their insecticide susceptibility status was investigated. Synergist bioassays were carried out with An. hyrcanus (s.l.) due to their resistance to all insecticides. An ITS2-PCR assay was conducted to identify to species the Hyrcanus group specimens.

Results

Out of 10,361 Anopheles females collected, representing 18 taxa in 2 subgenera, 71.8% were morphologically identified as belonging to the Hyrcanus Group (subgenus Anopheles), followed by An. barbirostris group (7.9%), An. nivipes (6.5%), An. philippinensis (5.9%) and the other 14 Anopheles species. Specimens of the Hyrcanus Group were more prevalent during the rainy season and were found to be highly zoophilic. Anopheles hyrcanus (s.l.) was active throughout the night, with an early peak of activity between 18:00 h and 21:00 h. ITS2-PCR assay conducted on 603 DNA samples from specimens within the Hyrcanus Group showed the presence of five sisters species. Anopheles peditaeniatus was the most abundant species (90.5%, n = 546), followed by An. nitidus (4.5%, n = 27), An. nigerrimus (4.3%, n = 26), An. argyropus (0.5%, n = 3), and An. sinensis (0.2%, n = 1). All An. hyrcanus (s.l.) specimens that were found resistant to insecticides (deltamethrin 0.05%, permethrin 0.75% and DDT 4% and synergist tests) belonged to An. peditaeniatus. The degree of resistance in An. peditaeniatus to each of these three insecticides was approximately 50%. Addition of PBO (Piperonyl butoxide), but not DEF (S.S.S-tributyl phosphotritioate), seemed to restore susceptibility, indicating a potential role of oxidases as a detoxifying enzyme resistance mechanism.

Conclusions

A better understanding of mosquito diversity related to host preference, biting activity and insecticide resistance status will facilitate the implementation of locally adapted vector control strategies.

Excito-repellency and biological safety of β-caryophyllene oxide against Aedes albopictus and Anopheles dirus (Diptera: Culicidae)

The activity of β-caryophyllene oxide as either a contact or noncontact repellent was evaluated against two laboratory strains (Aedes albopictus and Anopheles dirus) using an excito-repellency test system. N, N-Diethyl-3-methylbenzamide (DEET) was used as a standard reference baseline for comparative purposes. β-Caryophyllene oxide and DEET were tested at concentrations of 0.1, 0.25, 0.5 and 1.0% (v/v). In addition, the phototoxic and genotoxic effects of β-caryophyllene oxide were investigated on Balb/c 3T3 mouse fibroblasts (3T3-L1) and Chinese hamster ovary cell line (CHO-K1). The results demonstrated that the higher concentrations of test compounds (0.5 and 1.0%) produced greater behavioral responses. Aedes albopictus was more sensitive to β-caryophyllene oxide than An. dirus. Moderate avoidance response rates (25-56% escape) of Ae. albopictus at 0.5% and 1.0% β-caryophyllene oxide were observed in contact and noncontact trials compared with low response rates from An. dirus (26-31% escape). DEET at ≤1% displayed lower irritancy and repellency (1-38%) than β-caryophyllene oxide when tested against the two mosquito species. Knockdown responses (37%) were only observed in An. dirus exposed to 1% β-caryophyllene oxide in the contact trial. β-Caryophyllene oxide did not show any phototoxic potential (PIF= 0.38) nor was there any significant genotoxic response as indicated by no increase in micro-nucleated cells with or without metabolic activation. β-Caryophyllene oxide could be considered as a safe repellent, effective against mosquitoes.

Stegomyia Indices and Risk of Dengue Transmission: A Lack of Correlation

Dengue is present in 128 countries worldwide and is still expanding. There is currently no treatment or universally approved vaccine available. Therefore, prevention and control of mosquito vectors remain the most efficient ways of managing the risk of dengue outbreaks. The Stegomyia indices have been developed as quantitative indicators of the risk of dengue outbreaks. However, conflictual data are circulating about their reliability. We report in this article the first extensive study on Stegomyia indices, covering 78 locations of differing environmental and socio-economic conditions, climate, and population density across Indonesia, from West Sumatra to Papua. A total of 65,876 mosquito larvae and pupae were collected for the study. A correlation was found between incidence and human population density. No correlation was found between the incidence of dengue and the Stegomyia indices.

Bacterial Microbiome in Wild-Caught Anopheles Mosquitoes in Western Thailand

Among the complex microbial community living in the mosquito midgut, some bacteria (e.g., Enterobacter spp.) can deliver effector molecules with anti-Plasmodium effects suppressing the development of malaria parasites (Plasmodium falciparum) before the öokinete can penetrate the mosquito midgut epithelium. Despite knowledge of this phenomenon, only a few studies have defined the diversity of microbiota in wild-caught adult Anopheles species. The objective of this study was to analyze and compare the bacterial microbiota in different Anopheles species, including representatives of the primary malaria vectors in western Thailand. Wild female Anopheles species were sampled from malaria-endemic areas in Tak and Mae Hong Son provinces near the Thai-Myanmar border. Midgut/abdominal bacterial diversity was assessed by examining the 16S rRNA gene, V3 hypervariable region, using PCR-Temporal Temperature Gel Electrophoresis (PCR-TTGE) profiling and sequence analysis. A total of 24 bacterial genera were identified from eight Anopheles species. Five bacterial genera were newly reported in Anopheles mosquitoes (Ferrimonas, Megasphaera, Pectobacterium, Shimwellia, and Trabulsiella). Five genera, including Megasphaera, were detected exclusively in a single-malaria (Plasmodium vivax) infected Anopheles minimus and not observed in other non-infected mosquitoes. The use of PCR-TTGE provides the first characterization of the midgut bacterial microbiome present in wild adult Anopheles in Thailand. Evidence that microbiota might impact pathogen development (suppression) in Anopheles and thereby reduce the risk of pathogen transmission deserves more studies to describe the presence and better understand the biological role of bacteria in natural mosquito populations.

Excito-repellent activity of β-caryophyllene oxide against Aedes aegypti and Anopheles minimus

Contact irritant and non-contact repellent activities of β-caryophyllene oxide were evaluated against laboratory strains of female Aedes aegypti (USDA strain), a major arbovirus vector and Anopheles minimus (KU strain), a major malaria parasite vector, compared with the synthetic repellent DEET, using an excito-repellency test system. β-caryophyllene oxide and DEET were tested at concentrations of 0.1, 0.25, 0.5 and 1.0% (v/v). Anopheles minimus was found to be more sensitive to β-caryophyllene oxide than that of Ae. aegypti and exhibited high avoidance response rates (86-96% escape) at 0.5% and 1.0% concentrations in contact and non-contact trials compared with Ae. aegypti (22-59% escape). However, at the same concentrations, DEET displayed lower irritancy and repellency capacities against these two mosquito species (range 0-54% escape) compared to β-caryophyllene oxide. The analysis of escape responses showed significant differences between mosquito species at all concentrations (P < 0.05) except for 0.1%. For both species, there were significant differences in irritant and repellent responses between β-caryophyllene oxide and DEET at higher concentrations (0.5 and 1.0%).

Genetic homogeneity of Anopheles maculatus in Indonesia and origin of a novel species present in Central Java

Background

Anopheles maculatus (s.s.) is an important vector of malaria in Indonesia. Previously it was considered the only member of the Maculatus Group present in Indonesia. A novel species was recently identified in the Kulon Progo District in Central Java. Until recently, few investigations have been conducted looking at An. maculatus genetic diversity in Indonesia, including allopatric island populations.

Methods

Indonesian An. maculatus (s.l.) samples were collected in several locations in Java, Lesser Sunda Island group, Sumatra and in Kulon Progo (Yogyakarta, central Java) where a novel species has been identified. Samples from a 30-year-old colony of the Kulon Progo population were also included in the analysis. Maximum-likelihood analysis established the phylogenies of the ITS2 (nuclear) and cox1 (mitochondrial) markers. Putative times of separation were based on cox1 genetic distances.

Results

Two species of the Maculatus Group are present in Indonesia. The novel sibling species is more closely related to Anopheles dispar than to An. maculatus (s.s.). Anopheles maculatus (s.s.) samples are homogeneous based on the ITS2 sequences. Indonesian samples and An. dispar belong to the same cox1 maternal lineage and differ from all other known members of the Maculatus Group. Divergence time between the different populations found in Java was estimated using an established cox1 mutation rate.

Conclusions

A novel species within the Maculatus Group, most closely related to An. dispar, is confirmed present in the Kulon Progo area of Central Java. The divergence of this species from An. maculatus (s.s.) is explained by the stable refugia in the Kulon Progo area during the quaternary period of intense volcanic activity throughout most of Java. This novel species awaits detailed morphological description before applying a formal species name. For the interim, it is proposed that the Kulon Progo population be designated An. maculatus var. menoreh to distinguish it from An. maculatus (s.s.).

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3598-1) contains supplementary material, which is available to authorized users.

Imported malaria cases in former endemic and non-malaria endemic areas in China: are there differences in case profile and time to response?

BACKGROUND

China has achieved zero indigenous malaria case report in 2017. However, along with the increasing of international cooperation development, there is an increasing number of imported malaria cases from Chinese nationals returning from malaria-affected countries. Previous studies have focused on malaria endemic areas in China. There is thus limited information on non-endemic areas in China, especially on the performance of malaria surveillance and response in health facilities.

METHODS

A comparative retrospective study was carried out based on routine malaria surveillance data collected from 2013 to 2017. All imported malaria cases reported within the mainland of China were included. Variables used in the comparative analysis between cases in former endemic and former non-endemic areas, included age, gender and occupation, destination of overseas travel, Plasmodium species and patient health outcome. Monthly aggregated data was used to compare seasonal and spatial characteristics. Geographical distribution and spatial-temporal aggregation analyses were conducted. Time to diagnosis and report, method of diagnosis, and level of reporting/diagnosing health facilities were used to assess performance of health facilities.

RESULTS

A total of 16 733 malaria cases, out of which 90 were fatal, were recorded in 31 provinces. The majority of cases (96.2%) were reported from former malaria endemic areas while 3.8% were reported from former non-malaria endemic areas. Patients in the age class from 19 to 59 years and males made the highest proportion of cases in both areas. There were significant differences between occupational categories in the two areas (P <  0.001). In former endemic areas, the largest proportion of cases was among outdoor workers (80%). Two peaks (June, January) and three peaks (June, September and January) were found in former endemic and former non-endemic areas, respectively. Time between the onset of symptoms and diagnosis at clinics was significantly different between the two areas at different level of health facilities (P <  0.05).

CONCLUSIONS

All the former non-endemic areas are now reporting imported malaria cases. However, the largest proportion of imported cases is still reported from former endemic areas. Health facilities in former endemic areas outperformed those in former non-endemic areas. Information, treatment, and surveillance must be provided for expatriates while capacity building and continuous training must be implemented at health facilities in China.

Malaria Vectors and Species Complexes in Thailand: Implications for Vector Control

There are seven Anopheles species incriminated as important (primary) malaria vectors in Thailand. These vectors belong to species complexes or are in closely related groups that are difficult to separate morphologically. Precise species identification, using molecular methods, enables control operations to target only important vectors and to increase understanding of their specific ecological requirements, bionomic characteristics, and behavioral traits. This review focuses on adult mosquito behavior, vector transmission capacity, and geographical distribution of malaria vectors in Thailand identified using genetic and molecular identification methods between 1994 and 2019. A better understanding of Anopheles biodiversity, biology, behavior, vector capacity, and distribution in Thailand and neighboring countries in the Greater Mekong Subregion (GMS) will facilitate more effective and efficient vector-control strategies and consequently contribute to a further decrease in the malaria burden.

Diversity and biting patterns of Anopheles species in a malaria endemic area, Umphang Valley, Tak Province, western Thailand

Malaria is highly endemic in Umphang Valley, a district in the western edge of Tak Province, along the boundary with Kayin State of Myanmar. Although there are high indigenous malaria cases in this area every year, nothing about malaria vectors and their transmission role have been investigated before this study. The objective of this work is to characterize the Anopheles species diversity and trophic behavior of malaria vectors in the transmission area of Umphang Valley. Females of Anopheles mosquitoes were collected every two months during a two-year period. Mosquito collections were using standard collection technique, indoor and outdoor human landing collections and outdoor cattle bait collection. Anopheles mosquitoes were identified using morphological characters and multiplex AS-PCR assay for the identification of sibling species within groups and complexes present. From a total of 16,468 Anopheles females, 2723 specimens (16.54%) were collected from humans and 13,745 specimens (83.46%) were captured from cattle. From human landing collections, 2447 specimens (89.86%) of Anopheles minimus were obtained, followed by 119 Anopheles peditaeniatus (4.37%), 62 Anopheles maculatus (2.28%), 17 Anopheles dirus (0.6%), 15 Anopheles aconitus (0.5%) and 6 Anopheles sawadwongporni (0.2%) respectively. Seven putative malaria vectors, including An. minimus, An. dirus, An. baimaii, An. sawadwongporni, An. maculatus, An. pseudowillmori and An. aconitus were documented from this study and trophic behavior of each respective species were observed. Such information is definitely crucial for defining the vector capacity of each single species and for designing appropriate vector prevention and control strategies against target vector species.

First evidence of the presence of genotype-1 of Japanese encephalitis virus in Culex gelidus in Indonesia

Background

Japanese encephalitis has become a public health threat in Indonesia. Three genotypes have been recorded in Indonesia, i.e. genotype II (GII), genotype III (GIII) and genotype IV (GIV). Genotype I (GI) and genotype V (GV) have never been reported in Indonesia.

Results

A Japanese encephalitis virus (JEV) belonging to the genotype I-a (GI-a) has been isolated for the first time from a Culex gelidus mosquito in the Province of Jambi, Indonesia. This virus is related to a 1983 isolate from Thailand whereas the infected Cx. gelidus mosquito belonged to a Chinese haplotype.

Conclusions

Surveillance of JEV and mosquito dissemination is recommended.

Japanese encephalitis in Indonesia: An update on epidemiology and transmission ecology

The Japanese Encephalitis (JE) virus circulation in Indonesia was first documented in Lombok in 1960, and the virus was first isolated in 1972 from Culex tritaeniorhynchus in Bekasi, West Java and Kapuk, West Jakarta. Since then, Indonesia has been recognized as an endemic country for JE transmission. Up to now, JE cases have been found in at least 29 provinces, with Bali, West Kalimantan, East Nusa Tenggara, West Java and East Java, being the areas of highest incidence. However, routine surveillance on JE has not been established at the national level even though many surveys were conducted. JEV has been isolated from 10 mosquito species: Culex tritaeniorhynchus, Cx. gelidus, Cx. vishnui, Cx. fuscocephala, Cx. bitaeniorhynchus, Cx. quinquefasciatus, Anopheles vagus, An. kochi, An. annularis, and Armigeres subalbatus. Culex tritaeniorhynchus is the main JE vector in Indonesia. JE has been detected throughout the Indonesian archipelago from West to East. However, due to a lack of routine, systematic and standardized diagnostic approaches, the JE burden has still not been clearly established yet. Long term and systematic JE surveillance across Indonesia is a priority, the burden needs to be better assessed and appropriate control measures must be implemented.

Anopheles Vectors in Mainland China While Approaching Malaria Elimination

China is approaching malaria elimination; however, well-documented information on malaria vectors is still missing, which could hinder the development of appropriate surveillance strategies and WHO certification. This review summarizes the nationwide distribution of malaria vectors, their bionomic characteristics, control measures, and related studies. After several years of effort, the area of distribution of the principal malaria vectors was reduced, in particular for Anopheles lesteri (synonym: An. anthropophagus) and Anopheles dirus s.l., which nearly disappeared from their former endemic regions. Anopheles sinensis is becoming the predominant species in southwestern China. The bionomic characteristics of these species have changed, and resistance to insecticides was reported. There is a need to update surveillance tools and investigate the role of secondary vectors in malaria transmission.

Malaria overdiagnosis and subsequent overconsumption of antimalarial drugs in Angola: Consequences and effects on human health

Microscopic blood smear examinations done in health centers of Angola demonstrated a large overdiagnosis of malaria cases with an average rate of errors as high as 85%. Overall 83% of patients who received Coartem^® had an inappropriate treatment. Overestimated malaria diagnosis was noticed even when specific symptoms were part of the clinical observation, antimalarial treatments being subsequently given. Then, malaria overdiagnosis has three main consequences, (i) the lack of data reliability is of great concern, impeding epidemiological records and evaluation of the actual influence of operations as scheduled by the National Malaria Control Programme; (ii) the large misuse of antimalarial drug can increase the selective pressure for resistant strain and can make a false consideration of drug resistant P. falciparum crisis; and (iii) the need of strengthening national health centers in term of human, with training in microscopy, and equipment resources to improve malaria diagnosis with a large scale use of rapid diagnostic tests associated with thick blood smears, backed up by a "quality control" developed by the national health authorities. Monitoring of malaria cases was done in three Angolan health centers of Alto Liro (Lobito town) and neighbor villages of Cambambi and Asseque (Benguéla Province) to evaluate the real burden of malaria. Carriers of Plasmodium among patients of newly-borne to 14 years old, with or without fever, were analyzed and compared to presumptive malaria cases diagnosed in these health centers. Presumptive malaria cases were diagnosed six times more than the positive thick blood smears done on the same children. In Alto Liro health center, the percentage of diagnosis error reached 98%, while in Cambambi and Asseque it was of 79% and 78% respectively. The percentage of confirmed malaria cases was significantly higher during the dry (20.2%) than the rainy (13.2%) season. These observations in three peripheral health centers confirmed what has already been noticed in other malaria endemic regions, and highlight the need for an accurate evaluation of the Malaria control programme implemented in Angola.

Diversity of the Bacterial Microbiota of Anopheles Mosquitoes from Binh Phuoc Province, Vietnam

The naturally acquired microbiota of Anopheles can influence vector’s susceptibility to Plasmodium and its capacity to transmit them. Microbiota modification is a new challenge to limit disease transmission but it still needs advanced knowledges on bacterial community in Anopheles, especially in wild and infected specimens from diverse origin and species. Bacterial culture and 16S rRNA gene-PCR associated to Temporal Temperature Gradient Electrophoresis (TTGE) were applied to explore the bacterial diversity in the abdomen of 100 wild specimens (eight Anopheles species) collected in the Binh Phuoc Province, Vietnam. Culture and PCR-TTGE were complementary. The bacterial richness of the mosquito collection encompassed 105 genera belonging to seven phyla, mostly Proteobacteria, Firmicutes, and Actinobacteria. Staphylococcus, Clostridium, and Bacillus in Firmicutes were the most prevalent genera. However, Proteobacteria represented by 57 genera was the most diversified phylum in Anopheles microbiota. The high overall of Anopheles-associated bacteria is confirmed with, to our knowledge, 51 genera described for the first time in Anopheles microbiota. However, the diversity per specimen was low with average diversity index and the average Shannon–Wiener score (H) of 4.843 and 5.569, respectively. The most represented bacterial genera were present in <30% of the specimens. Consequently, the core microbiota share by Anopheles from Binh Phuoc was very narrow, suggesting that Anopheles microbiota was greatly influenced by local environments. The repertory of bacterial genera in two specimens of An. dirus and An. pampanai naturally infected by Plasmodium vivax was also described as preliminary results. Finally, this study completed the repertory of bacteria associated to wild Anopheles. Anopheles associated-bacteria appeared specimen-dependent rather than mosquitoe species- or group-dependent. Their origin and the existence of Anopheles-specific bacterial taxa are discussed.

Biology, distribution and control of Anopheles (Cellia) minimus in the context of malaria transmission in northeastern India

Among six dominant mosquito vector species involved in malaria transmission in India, Anopheles minimus is a major species in northeast India and held responsible for focal disease outbreaks characterized by high-rise of Plasmodium falciparum infections and attributable death cases. It has been now genetically characterized that among the three-member species of the Minimus Complex spread in Asia, An. minimus (former species A) is prevalent in India including northeastern states and east-central state of Odisha. It is recorded in all seasons and accounts for perennial transmission evidenced by records of sporozoite infections. This species is highly anthropophilic, and largely endophilic and endophagic, recorded breeding throughout the year in slow flowing seepage water streams. The populations of An. minimus in India are reported to be highly diverse indicating population expansion with obvious implications for judicious application of vector control interventions. Given the rapid ecological changes due to deforestation, population migration and expansion and developmental activities, there is scope for further research on the existence of potential additional sibling species within the An. minimus complex and bionomics studies on a large geographical scale for species sanitation. For control of vector populations, DDT continues to be applied on account of retaining susceptibility status even after decades of residual spraying. Anopheles minimus is a highly adaptive species and requires continuous and sustained efforts for its effective control to check transmission and spread of drug-resistant malaria. Anopheles minimus populations are reportedly diminishing in northeastern India whereas it has staged comeback in east-central State of Odisha after decades of disappearance with its eco-biological characteristics intact. It is the high time to siege the opportunity for strengthening interventions against this species for its population diminution to sub-optimal levels for reducing transmission in achieving malaria elimination by target date of 2030.

Comparative Excito-Repellency of Three Cambodian Plant-Derived Extracts Against Two Mosquito Vector Species, Aedes aegypti and Anopheles minimus

A study of the behavioral responses of Aedes aegypti and Anopheles minimus to 3 Cambodian plant extracts at 3 different concentrations (1%, 2.5%, and 5%) was performed using an excito-repellency test system. These 3 plants were Strophanthus scandens, Capparis micracantha, and Dioscorea hispida, selected according to traditional healer's knowledge, bibliographic studies and market surveys. Results showed that S. scandens leaves' hexane extract was the only one to exert repellency against Ae. aegypti with 23.3% of escaped mosquitoes at a concentration of 5%. Capparis micracantha was responsible for an irritant activity against An. minimus with 20.2% of escaped mosquitoes at a concentration of 2.5% and 22.8% escaping at a concentration of 5%. Dioscorea hispida showed an irritant activity on both mosquito species with 23.2% of escaped Ae. aegypti at a concentration of 5% and about 20% of escaped An. minimus at 2.5% and 5%. This is the first report on the irritant and repellent activities of S. scandens , D. hispida , and C. micracantha against mosquito species.

Diversity of the Bacterial Microbiota of Anopheles Mosquitoes from Binh Phuoc Province, Vietnam

The naturally acquired microbiota of Anopheles can influence vector's susceptibility to Plasmodium and its capacity to transmit them. Microbiota modification is a new challenge to limit disease transmission but it still needs advanced knowledges on bacterial community in Anopheles, especially in wild and infected specimens from diverse origin and species. Bacterial culture and 16S rRNA gene-PCR associated to Temporal Temperature Gradient Electrophoresis (TTGE) were applied to explore the bacterial diversity in the abdomen of 100 wild specimens (eight Anopheles species) collected in the Binh Phuoc Province, Vietnam. Culture and PCR-TTGE were complementary. The bacterial richness of the mosquito collection encompassed 105 genera belonging to seven phyla, mostly Proteobacteria, Firmicutes, and Actinobacteria. Staphylococcus, Clostridium, and Bacillus in Firmicutes were the most prevalent genera. However, Proteobacteria represented by 57 genera was the most diversified phylum in Anopheles microbiota. The high overall of Anopheles-associated bacteria is confirmed with, to our knowledge, 51 genera described for the first time in Anopheles microbiota. However, the diversity per specimen was low with average diversity index and the average Shannon-Wiener score (H) of 4.843 and 5.569, respectively. The most represented bacterial genera were present in <30% of the specimens. Consequently, the core microbiota share by Anopheles from Binh Phuoc was very narrow, suggesting that Anopheles microbiota was greatly influenced by local environments. The repertory of bacterial genera in two specimens of An. dirus and An. pampanai naturally infected by Plasmodium vivax was also described as preliminary results. Finally, this study completed the repertory of bacteria associated to wild Anopheles. Anopheles associated-bacteria appeared specimen-dependent rather than mosquitoe species- or group-dependent. Their origin and the existence of Anopheles-specific bacterial taxa are discussed.

Spatio-temporal variations of Anopheles coluzzii and An. gambiae and their Plasmodium infectivity rates in Lobito, Angola

From 2003 to 2007, entomological surveys were conducted in Lobito town (Benguela Province, Angola) to determine which Anopheles species were present and to identify the vectors responsible for malaria transmission in areas where workers of the Sonamet Company live. Two types of surveys were conducted: (1) time and space surveys in the low and upper parts of Lobito during the rainy and dry periods; (2) a two-year longitudinal study in Sonamet workers' houses provided with long-lasting insecticide-treated nets (LLIN), "PermaNet," along with the neighboring community. Both species, An. coluzzii (M molecular form) and An. gambiae (S molecular form), were collected. Anopheles coluzzii was predominant during the dry season in the low part of Lobito where larvae develop in natural ponds and temporary pools. However, during the rainy season, An. gambiae was found in higher proportions in the upper part of the town where larvae were collected in domestic water tanks built near houses. Anopheles melas and An. listeri were captured in higher numbers during the dry season and in the low part of Lobito where larvae develop in stagnant brackish water pools. The infectivity rates of An. gambiae s.l. varied from 0.90% to 3.41%.

Bacterial diversity associated with wild caught Anopheles mosquitoes from Dak Nong Province, Vietnam using culture and DNA fingerprint

Background

Microbiota of Anopheles midgut can modulate vector immunity and block Plasmodium development. Investigation on the bacterial biodiversity in Anopheles, and specifically on the identification of bacteria that might be used in malaria transmission blocking approaches, has been mainly conducted on malaria vectors of Africa. Vietnam is an endemic country for both malaria and Bancroftian filariasis whose parasitic agents can be transmitted by the same Anopheles species. No information on the microbiota of Anopheles mosquitoes in Vietnam was available previous to this study.

Method

The culture dependent approach, using different mediums, and culture independent (16S rRNA PCR – TTGE) method were used to investigate the bacterial biodiversity in the abdomen of 5 Anopheles species collected from Dak Nong Province, central-south Vietnam. Molecular methods, sequencing and phylogenetic analysis were used to characterize the microbiota.

Results and Discussion

The microbiota in wild-caught Anopheles was diverse with the presence of 47 bacterial OTUs belonging to 30 genera, including bacterial genera impacting Plasmodium development. The bacteria were affiliated with 4 phyla, Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria, the latter being the dominant phylum. Four bacterial genera are newly described in Anopheles mosquitoes including Coxiella, Yersinia, Xanthomonas, and Knoellia. The bacterial diversity per specimen was low ranging from 1 to 4. The results show the importance of pairing culture and fingerprint methods to better screen the bacterial community in Anopheles mosquitoes.

Conclusion

Sampled Anopheles species from central-south Vietnam contained a diverse bacterial microbiota that needs to be investigated further in order to develop new malaria control approaches. The combination of both culture and DNA fingerprint methods allowed a thorough and complementary screening of the bacterial community in Anopheles mosquitoes.

Diversity of Anopheles species and trophic behavior of putative malaria vectors in two malaria endemic areas of northwestern Thailand

We determined the species diversity, blood-feeding behavior, and host preference of Anopheles mosquitoes in two malaria endemic areas of Tak (Mae Sot District) and Mae Hong Son (Sop Moei District) Provinces, located along the Thai border with Myanmar, during a consecutive two-year period. Anopheline mosquitoes were collected using indoor and outdoor human-landing captures and outdoor cow-baited collections. Mosquitoes were initially identified using morphological characters, followed by the appropriate multiplex AS-PCR assay for the identification of sibling species within Anopheles (Cellia) complexes and groups present. Real-time PCR was performed for parasite-specific detection in mosquitoes (Plasmodium spp. and Wuchereria bancrofti). A total of 7,129 Anopheles females were captured, 3,939 from Mae Sot and 3,190 from Sop Moei, with 58.6% and 37% of all anophelines identified as An. minimus, respectively. All three malaria vector complexes were detected in both areas. One species within the Minimus Complex (An. minimus) was present along with two related species in the Funestus Group, (An. aconitus, An. varuna), two species within the Dirus Complex (An. dirus, An. baimaii), and four species within the Maculatus Group (An. maculatus, An. sawadwongporni, An. pseudowillmori, and An. dravidicus). The trophic behavior of An. minimus, An. dirus, An. baimaii, An. maculatus, and An. sawadwongporni are described herein. The highest An. minimus densities were detected from February through April of both years. One specimen of An. minimus from Mae Sot was found positive for Plasmodium vivax.

Biting patterns and host preference of Anopheles epiroticus in Chang Island, Trat Province, eastern Thailand

A study of species diversity of Anopheles mosquitoes, biting patterns, and seasonal abundance of important mosquito vectors was conducted in two villages of Chang Island, Trat Province, in eastern Thailand, one located along the coast and the other in the low hills of the central interior of the island. Of 5,399 captured female anophelines, 70.25% belong to the subgenus Cellia and remaining specimens to the subgenus Anopheles. Five important putative malaria vectors were molecularly identified, including Anopheles epiroticus, Anopheles dirus, Anopheles sawadwongporni, Anopheles maculatus, and Anopheles minimus. Anopheles epiroticus was the most commonly collected species in the coastal site, whereas An. dirus was found to be most abundant in the forest-hill site. From both locations, a greater number of mosquitoes was collected during the dry season compared to the wet. Anopheles epiroticus showed greater exophagic and zoophilic behavior with the highest blood feeding densities occurring between 18:00 and 19:00. In contrast, An. dirus demonstrated an activity peak between midnight and 01:00. We conclude that An. epiroticus and An. dirus, in coastal and inland areas, respectively, appear to be the most epidemiologically important malaria vectors on Chang Island. As no studies of vector competency specific to Chang Island have been conducted, our conclusions that these two species play a primary role in malaria transmission are based on evidence from other localities in Thailand and mainland Southeast Asia. This information serves as a basis for designing improved vector control programs that target specific species, and if integrated with other interventions could result in the elimination of malaria transmission on the island.

Influence of Time of Assay on Behavioral Responses of Laboratory and Field Populations Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae) to DEET

Knowledge on test conditions that may influence behavioral responses of mosquitoes is critical when excito-repellency tests are conducted. The objective of this study was to investigate the effect of test time differences on normal circadian activity and behavioral responses of field and colonized Aedes aegypti (L.) (=Stegomyia aegypti) and Culex quinquefasciatus Say to DEET, one of the most common synthetic repellent active ingredients available. Two field populations of Ae. aegypti and Cx. quinquefasciatus from Kanchanaburi and Nonthaburi provinces, respectively, and two long-standing laboratory populations, Ae. aegypti obtained from the U.S. Department of Agriculture, and Cx. quinquefasciatus from the Ministry of Public Health, Thailand, were used. Each population was exposed to DEET during two different periods of time (0900-1500 hours) and (2100-0300 hours). Both field and laboratory Cx. quinquefasciatus showed marked differences in spatial repellent escape responses between day and nighttime periods but none in direct contact tests. No significant differences between day and nighttime testing periods were observed with field or laboratory Ae. aegypti, except a higher daytime escape response from noncontact DEET treatment. This study indicates that test time may influence the behavioral avoidance responses and is a potential confounder of excito-repellency evaluations.

Diversity of Anopheles mosquitoes in Binh Phuoc and Dak Nong Provinces of Vietnam and their relation to disease

Background

Human malaria is still a burden in Dak Nong and Binh Phuoc Provinces in south-central Vietnam that border Cambodia. Several Anopheles species that transmit human malarial Plasmodium may also transmit Wuchereria bancrofti, the nematode that causes Bancroftian lymphatic filariasis. The objective of this study was to investigate the role of Anopheles species in the transmission of these two pathogens in the two highly malaria endemic provinces of Vietnam.

Methods

Anopheles mosquitoes were collected in Dak Nong and Binh Phuoc Provinces in November and December of 2010 and 2011. Human landing catches, paired collections on human and buffalo, and resting captures were made with mouth aspirators. Collections were also made with light traps. Morphological and PCR-based methods were used to identify the species. Real-time PCR was used to detect Plasmodium species and W. bancrofti in individual mosquitoes.

Results

Twenty-four Anopheles species were identified among 797 captured mosquitoes. Anopheles dirus was found in both provinces and was the predominant species in Binh Phuoc Province; An. maculatus was the most prevalent species in Dak Nong Province. Anopheles minimus was collected only in Binh Phuoc Province. Some specimens of An. minimus and An. pampanai were misidentified based on morphology. Four specimens of An. scanloni were identified, and this is the first report of this species of the Dirus Complex in Vietnam. Two females, one An. dirus and one An. pampanai, collected in Binh Phuoc Province were infected with P. vivax, for an overall infection rate of 0.41% (2/486): 0.28% for An. dirus (1/361) and 20% for An. pampanai (1/5). No mosquitoes were found to be infected with P. falciparum, P. knowlesi or W. bancrofti in either province.

Conclusion

A diversity of Anopheles species occurs in Dak Nong and Binh Phuoc Provinces of Vietnam, several of which are considered to be actual and potential vectors of malarial protozoa and microfilariae. It is highly likely that two of the species, An. dirus and An. pampanai, are active in malaria transmission based on the detection of P. vivax in females of these species. This is the first report of An. scanloni in Vietnam.

Pyrethroid susceptibility and behavioral avoidance in Anopheles epiroticus, a malaria vector in Thailand

The physiological susceptibility to insecticides and the behavioral responses of four wild-caught populations of female Anopheles epiroticus to synthetic pyrethroids (deltamethrin, permethrin, and alpha-cypermethrin) were assessed. Test populations were collected from different localities along the eastern coast, Trat (TR), Songkhla (SK), and Surat Thani (ST) and one population from the western coast, Phang Nga (PN). Results showed that all four populations of An. epiroticus were susceptible to all three synthetic pyrethroids tested. Behavioral responses to test compounds were characterized for all four populations using an excito-repellency test system. TR displayed the strongest contact excitation ('irritancy') escape response (76.8% exposed to deltamethrin, 74.1% permethrin, and 78.4% alpha-cypermethrin), followed by the PN population (24.4% deltamethrin, 35% permethrin, and 34.4% for alpha-cypermethrin) by rapidly escaping test chambers after direct contact with surfaces treated with each active ingredient compared with match-paired untreated controls. Moderate non-contact repellency responses to all three compounds were observed in the TR population but were comparatively weaker than paired contact tests. Few mosquitoes from the SK and ST populations escaped from test chambers, regardless of insecticide tested or type of trial. We conclude that contact excitation was a major behavioral response in two populations of An. epiroticus, whereas two other populations showed virtually no escape response following exposure to the three pyrethroids. The explanation for these large unexpected differences in avoidance responses between pyrethroid-susceptible populations of the same species is unclear and warrants further investigation.

Taxonomic assessment of Anopheles crawfordi and An. dangi of the Hyrcanus Group of subgenus Anopheles in Vietnam

Anopheles dangi, introduced as a new species of the Hyrcanus Group of subgenus Anopheles in an illustrated dichotomous key for the identification of the Anopheles mosquitoes of Vietnam published in 1987, was distinguished from Anopheles crawfordi based on the presence of a humeral pale spot on the base of the costal vein of the wing. However, this character has been known to occur occasionally in An. crawfordi. To determine whether An. dangi is distinct from An. crawfordi, we analyzed nucleotide sequences of the COI, COII and Cyt-b genes of mtDNA and the D3 gene of rDNA obtained from specimens collected in south-central Vietnam that were identified as An. dangi and An. crawfordi based on the presence or absence, respectively, of a humeral pale spot. Maximum Likelihood and Bayesian analyses of the sequences showed a low mean genetic distance of 0.004 for specimens identified as An. crawfordi and 0.008 for those identified as An. dangi. The mean genetic distance between the two nominal species was 0.006, compared with 0.077 for any group versus the outgroup taxa Anopheles dirus and Anopheles minimus, and the specimens of the two forms clustered in a single strongly supported clade. Consequently, An. dangi is merely a morphological variant of An. crawfordi and is deemed to be a synonym of that nominal species.

Species diversity and biting activity of Anopheles dirus and Anopheles baimaii (Diptera: Culicidae) in a malaria prone area of western Thailand

BACKGROUND

A survey of adult anopheline mosquito diversities, collected from September 2009 to August 2010, was conducted in a malaria endemic area of western Thailand. Two anopheline species complexes, Dirus and Minimus, along with the Maculatus group were observed. Of several species documented from within each complex and group, four important malaria vectors were identified, including An. dirus, An. baimaii, An. minimus, and An. sawadwongporni. Information on biting activity and host preference for any single species within the Dirus complex has never been assessed. Using specific molecular identification assays, the trophic behavior and biting activity of each sibling species within the Dirus complex were observed and analyzed for the Kanchanaburi Province, Thailand.

METHODS

Adult female mosquitoes were collected for two consecutive nights each month during a one year period. Three collection methods, human landing indoor (HLI), human landing outdoor (HLO), and cattle baited collections (CBC) were applied. Each team of collectors captured mosquitoes between 1800 and 0600 h.

RESULTS

From a total of 9,824 specimens, 656 belong to the Dirus complex (An. dirus 6.09% and An. baimaii 0.59%), 8,802 to the Minimus complex (An. minimus 4.95% and An. harrisoni 84.65%) and 366 to the Maculatus group (An. maculatus 2.43% and An. sawadwongporni 1.29%). Both An. dirus and An. baimaii demonstrated exophagic and zoophilic behaviors. Significantly greater numbers of An. dirus and An. baimaii were collected from cattle as compared to humans (P = 0.003 for An. dirus and P = 0.048 for An. baimaii).

CONCLUSIONS

Significantly greater numbers of An. dirus and An. baimaii were collected from cattle baited traps as compared to human landing collections (P < 0.05), demonstrating that both species show a strong zoophilic behavior. Knowledge of host-seeking behavior helps to define a species' capacity to acquire and transmit malaria and its contribution to the overall risk for disease transmission in the human population, as well as, assisting in the design and implementation of appropriate vector prevention and control strategies.

Human antibody response to Anopheles saliva for comparing the efficacy of three malaria vector control methods in Balombo, Angola

Human antibody (Ab) response to Anopheles whole saliva, used as biomarker of Anopheles exposure, was investigated over a period of two years (2008–2009), in children between 2 to 9 years old, before and after the introduction of three different malaria vector control methods; deltamethrin treated long lasting impregnated nets (LLIN) and insecticide treated plastic sheeting (ITPS) - Zero Fly®) (ITPS-ZF), deltamethrin impregnated Durable (Wall) Lining (ITPS-DL – Zerovector®) alone, and indoor residual spraying (IRS) with lambdacyhalothrin alone. These different vector control methods resulted in considerable decreases in all three entomological (82.4%), parasitological (54.8%) and immunological criteria analyzed. The highest reductions in the number of Anopheles collected and number of positive blood smears, respectively 82.1% and 58.3%, were found in Capango and Canjala where LLIN and ITPS-ZF were implemented. The immunological data based on the level of anti-saliva IgG Ab in children of all villages dropped significantly from 2008 to 2009, except in Chissequele. These results indicated that these three vector control methods significantly reduced malaria infections amongst the children studied and IRS significantly reduced the human-Anopheles contact. The number of Anopheles, positive blood smears, and the levels of anti-saliva IgG Ab were most reduced when LLIN and ITPS-ZF were used in combination, compared to the use of one vector control method alone, either ITPS-DL or IRS. Therefore, as a combination of two vector control methods is significantly more effective than one control method only, this control strategy should be further developed at a more global scale.

Assessment of geraniol-incorporated polymers to control Aedes albopictus (Diptera: Culicidae)

Effective control of mosquito borne diseases has proven extremely difficult with both vector and pathogen remaining entrenched and expanding in many disease endemic areas. When lacking an effective vaccine, vector control methods targeting both larval habitats and adult mosquito populations remain the primary strategy for reducing risk. Aedes albopictus from Thailand was used as a reference baseline for evaluation of natural insecticides incorporated in polymer disks and pellets and tested both in laboratory and field conditions. In laboratory and field tests, the highest larval mortality was obtained with disks or pellets containing IKHC (Insect Killer Highly Concentrate) from Fulltec AG Company. This product is reputed to contain geraniol as an active ingredient. With pellets, high mortality of Ae. albopictus larvae (92%) was observed in presence of 1 g of pellets per 500 ml of water at day 1st, and the mortality was 100% at day 1st for larvae in presence of 5 or 10 g of pellets. Fulltec AG Company has not accepted to give us the exact composition of their IKHC product. Therefore, we cannot recommend it, but the principle of using monoterpenes like geraniol, incorporated into polymer disks or pellets as natural larvicide needs more attention as it could be considered as a powerful alternative in mosquito vector control.

A global map of dominant malaria vectors

Background

Global maps, in particular those based on vector distributions, have long been used to help visualise the global extent of malaria. Few, however, have been created with the support of a comprehensive and extensive evidence-based approach.

Methods

Here we describe the generation of a global map of the dominant vector species (DVS) of malaria that makes use of predicted distribution maps for individual species or species complexes.

Results

Our global map highlights the spatial variability in the complexity of the vector situation. In Africa, An. gambiae, An. arabiensis and An. funestus are co-dominant across much of the continent, whereas in the Asian-Pacific region there is a highly complex situation with multi-species coexistence and variable species dominance.

Conclusions

The competence of the mapping methodology to accurately portray DVS distributions is discussed. The comprehensive and contemporary database of species-specific spatial occurrence (currently available on request) will be made directly available via the Malaria Atlas Project (MAP) website from early 2012.

The dominant Anopheles vectors of human malaria in the Asia-Pacific region: occurrence data, distribution maps and bionomic précis

BACKGROUND

The final article in a series of three publications examining the global distribution of 41 dominant vector species (DVS) of malaria is presented here. The first publication examined the DVS from the Americas, with the second covering those species present in Africa, Europe and the Middle East. Here we discuss the 19 DVS of the Asian-Pacific region. This region experiences a high diversity of vector species, many occurring sympatrically, which, combined with the occurrence of a high number of species complexes and suspected species complexes, and behavioural plasticity of many of these major vectors, adds a level of entomological complexity not comparable elsewhere globally. To try and untangle the intricacy of the vectors of this region and to increase the effectiveness of vector control interventions, an understanding of the contemporary distribution of each species, combined with a synthesis of the current knowledge of their behaviour and ecology is needed.

RESULTS

Expert opinion (EO) range maps, created with the most up-to-date expert knowledge of each DVS distribution, were combined with a contemporary database of occurrence data and a suite of open access, environmental and climatic variables. Using the Boosted Regression Tree (BRT) modelling method, distribution maps of each DVS were produced. The occurrence data were abstracted from the formal, published literature, plus other relevant sources, resulting in the collation of DVS occurrence at 10116 locations across 31 countries, of which 8853 were successfully geo-referenced and 7430 were resolved to spatial areas that could be included in the BRT model. A detailed summary of the information on the bionomics of each species and species complex is also presented.

CONCLUSIONS

This article concludes a project aimed to establish the contemporary global distribution of the DVS of malaria. The three articles produced are intended as a detailed reference for scientists continuing research into the aspects of taxonomy, biology and ecology relevant to species-specific vector control. This research is particularly relevant to help unravel the complicated taxonomic status, ecology and epidemiology of the vectors of the Asia-Pacific region. All the occurrence data, predictive maps and EO-shape files generated during the production of these publications will be made available in the public domain. We hope that this will encourage data sharing to improve future iterations of the distribution maps.