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Distribution of Anopheles in Vietnam, with particular attention to malaria vectors of the Anopheles minimus complex
Claire Garros, Cam Van Nguyen, Ho Trung, Wim Van Bortel, Marc Coosemans, Sylvie Manguin
Malaria Journal , 2008, DOI: 10.1186/1475-2875-7-11
Abstract: Large entomological surveys based on cattle collections and molecular identifications of An. minimus s.l. were carried out in 23 sites throughout northern, central and south-eastern regions of Vietnam.Based on previous molecular works and our data, the distribution of anopheline species and the relative densities of An. minimus and An. harrisoni were mapped. It is noteworthy that there was a high specific biodiversity at each study site. Anopheles minimus s.l. and Anopheles sinensis were the main anopheline species in the northern region, whereas Anopheles aconitus and Anopheles vagus were the most frequent ones in the central region. The southern limit of An. harrisoni was increased to the latitude of 11°N. Sympatry between both sibling species has been extended to new provinces.Malaria transmission is still high in central Vietnam and along bordering countries. Therefore, it is important to know and map the precise distribution of the main and secondary malaria vectors in Vietnam for applying efficient vector control programmes. Moreover, these maps should be regularly updated and linked to environmental characteristics relative to disease epidemiology, and environmental and climatic changes occurring in southeast Asia.The main malaria vector Anopheles minimus s.l. (Myzomyia Series, Funestus Group) is composed of three sibling species, An. minimus (former species A), Anopheles harrisoni (former species C), and An. minimus species E [1]. Anopheles minimus and An. harrisoni can be sympatrically distributed over the southeast Asian mainland whereas species E is restricted to the Ishigaki Island in the Ryukyu Archipelago, Japan, a malaria free region [2,3]. Because the morphological identification of the two sympatric species is unreliable [4], accurate data on the distribution of An. minimus and An. harrisoni are missing [3]. Morphological misidentifications with the closely related sympatric species, such as Anopheles aconitus, Anopheles pampanai and Anopheles varun
Absence of knockdown resistance suggests metabolic resistance in the main malaria vectors of the Mekong region
Katrijn Verhaeghen, Wim Van Bortel, Ho Trung, Tho Sochantha, Marc Coosemans
Malaria Journal , 2009, DOI: 10.1186/1475-2875-8-84
Abstract: By use of molecular assays and biochemical assays the presence of the two major insecticide resistance mechanisms, knockdown and metabolic resistance, were assessed in the main malaria vectors of the Mekong region.Two FRET/MCA assays and one PCR-RFLP were developed to screen a large number of Anopheles populations from the Mekong region for the presence of knockdown resistance (kdr), but no kdr mutation was observed in any of the study species. Biochemical assays suggest an esterase mediated pyrethroid detoxification in An. epiroticus and An. subpictus of the Mekong delta. The DDT resistance in An. subpictus might be conferred to a high GST activity. The pyrethroid resistance in An. minimus s.l. is possibly associated with increased detoxification by esterases and P450 monooxygenases.As different metabolic enzyme systems might be responsible for the pyrethroid and DDT resistance in the main vectors, each species may have a different response to alternative insecticides, which might complicate the malaria vector control in the Mekong region.In the Mekong region, the malaria vector control relies on the use of insecticides for impregnation of bed nets and for indoor residual spraying and is mainly focussed on three vector species complexes: Anopheles dirus sensu stricto (s.s.) [1], Anopheles minimus sensu lato (s.l.) [2] and Anopheles sundaicus s.l. [3]. Hence, the emergence of insecticide resistance in vector species may have important implications for the effectiveness of insecticide based vector control measures. This is particularly true for the Mekong region, where vector control efforts have significantly contributed to decrease the malaria burden in recent years [4].WHO bioassays done in the framework of a three year survey (from March 2003 until July 2005) on insecticide resistance in the Mekong region (Vietnam, Laos, Cambodia and Thailand) have shown that different levels of pyrethroid and DDT resistance occur in the main malaria vectors of the Mekong region
Impact of insecticide-treated nets on wild pyrethroid resistant Anopheles epiroticus population from southern Vietnam tested in experimental huts
Wim Van Bortel, Vu Chinh, Dirk Berkvens, Niko Speybroeck, Ho Trung, Marc Coosemans
Malaria Journal , 2009, DOI: 10.1186/1475-2875-8-248
Abstract: An experimental station, based on the model of West Africa and adapted to the behaviour of the target species, was built in southern Vietnam. The study design was adapted from the WHO phase 2 guidelines. The study arms included a conventionally treated polyester net (CTN) with deltamethrin washed just before exhaustion, the WHO recommended long-lasting insecticidal net (LLIN) PermaNet 2.0? unwashed and 20 times washed and PermaNet 3.0?, designed for the control of pyrethroid resistant vectors, unwashed and 20 times washed.The nets still provided personal protection against the resistant An. epiroticus population. The personal protection ranged from 67% for deltamethrin CTN to 85% for unwashed PermaNet 3.0. Insecticide resistance in the An. epiroticus mosquitoes did not seem to alter the deterrent effect of pyrethroids. A significant higher mortality was still observed among the treatment arms despite the fact that the An. epiroticus population is resistant against the tested insecticides.This study shows that CTN and LLINs still protect individuals against a pyrethroid resistant malaria vector from the Mekong region, where insecticide resistance is caused by a metabolic mechanism. In the light of a possible elimination of malaria from the Mekong region these insights in operational consequences of the insecticide resistance on control tools is of upmost importance.Insecticide resistance has been demonstrated in many African and Asian malaria vectors [1,2]. The impact of the observed resistance on the applied control tools will depend on the mechanism(s) conferring resistance, the biology of the vector and the control method applied. Evidence exists that resistance reduces the efficacy of indoor residual spraying (IRS). In South Africa, for example, increased levels of mixed function oxidases in Anopheles funestus was associated with malaria control failure [3]. On the island Bioko, Equatorial Guinea, IRS with pyrethroids failed to reduce the pyrethroid resistant Ano
Detection of the East and West African kdr mutation in Anopheles gambiae and Anopheles arabiensis from Uganda using a new assay based on FRET/Melt Curve analysis
Katrijn Verhaeghen, Wim Van Bortel, Patricia Roelants, Thierry Backeljau, Marc Coosemans
Malaria Journal , 2006, DOI: 10.1186/1475-2875-5-16
Abstract: Here, a new assay for the detection of knockdown resistance in An. gambiae s.s. and An. arabiensis based on Fluorescence Resonance Energy Transfer/Melt Curve analysis (FRET/MCA) is presented and compared with the existing assays.The new FRET/MCA method has the important advantage of detecting both kdr alleles in one assay. Moreover, results show that the FRET/MCA is more reliable and more sensitive than the existing AS-PCR assays and is able to detect new genotypes. By using this technique, the presence of the East African kdr mutation (L1014S) is shown for the first time in An. arabiensis specimens from Uganda. In addition, a new kdr genotype is reported in An. gambiae s.s. from Uganda, where four An. gambiae s.s. mosquitoes possess both, the West (L1014F) and East (L1014S) African kdr allele, simultaneously.The presence of both kdr mutations in the same geographical region shows the necessity of a reliable assay that enables to detect both mutations in one single assay. Hence, this new assay based on FRET/MCA will improve the screening of the kdr frequencies in An. gambiae s.s. and An. arabiensis.Malaria vector control strategies rely on the use of insecticides for the impregnation of bed nets and for indoor residual spraying. Increasing resistance of malaria vectors may have important implications for the vector control programmes, especially considering the scaling up of insecticide treated bed nets (ITNs). Hence, knowledge on changing trends in insecticide resistance is a basic requirement to guide the use of insecticides in the malaria control programmes.Pyrethroids are the most commonly used insecticides in the fight against malaria. These insecticides modify the gating kinetics of the para-type sodium channels by slowing both the activation and the inactivation of the channels [1]. An important resistance mechanism against pyrethroids and DDT, known as knockdown resistance (kdr), has been linked to a single mutation in the para-type sodium channel gene in se
Knockdown resistance in Anopheles vagus, An. sinensis, An. paraliae and An. peditaeniatus populations of the Mekong region
Katrijn Verhaeghen, Wim Van Bortel, Ho Trung, Tho Sochantha, Kalouna Keokenchanh, Marc Coosemans
Parasites & Vectors , 2010, DOI: 10.1186/1756-3305-3-59
Abstract: Bioassays were performed on field collected unfed female mosquitoes using the standard WHO susceptibility tests. In addition, the DIIS6 region of the para-type sodium channel gene was amplified and sequenced and four allele-specific PCR assays were developed to assess the kdr frequencies.In Southern Vietnam all species were DDT and pyrethroid resistant, which might suggest the presence of a kdr resistance mechanism. Sequence-analysis of the DIIS6 region of the para-type sodium channel gene revealed the presence of a L1014S kdr mutation in An. vagus, An. sinensis and An. paraliae. In An. peditaeniatus, a low frequency L1014S kdr mutation was found in combination with a high frequency L1014F kdr mutation. For pyrethroids and DDT, no genotypic differentiation was found between survivors and non-survivors for any of these species. In the two widespread species, An. vagus and An. sinensis, kdr was found only in southern Vietnam and in Cambodia near the Vietnamese border.Different levels of resistance were measured in Laos, Cambodia and Vietnam. The kdr mutation in different Anopheles species seems to occur in the same geographical area. These species breed in open agricultural lands where malaria endemicity is low or absent and vector control programs less intensive. It is therefore likely that the selection pressure occurred on the larval stages by insecticides used for agricultural purposes.Insecticide resistance may jeopardize the enormous malaria control efforts which have resulted in a significant decrease in the malaria burden in the Mekong region [1]. Insects may survive the toxic effect of insecticides by different resistance mechanisms. The major mechanisms involve either mutations within the target site of the insecticide or an alteration in the rate of insecticide detoxification. The para-type sodium channel is the target for both pyrethroids and DDT and mutations in this gene have been linked to knockdown resistance (kdr) in several insects [2]. In the malari
Invasive Process and Repeated Cross-Sectional Surveys of the Mosquito Aedes japonicus japonicus Establishment in Belgium
David Damiens, Audrey Ayrinhac, Wim Van Bortel, Veerle Versteirt, Wouter Dekoninck, Thierry Hance
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0089358
Abstract: When accidentally introduced in a new location, a species does not necessarily readily become invasive, but it usually needs several years to adapt to its new environment. In 2009, a national mosquito survey (MODIRISK) reported the introduction and possible establishment of an invasive mosquito species, Aedes j. japonicus, in Belgium. First collected in 2002 in the village of Natoye from a second-hand tire company, then sampled in 2003 and 2004, the presence of adults and larvae was confirmed in 2007 and 2008. A repeated cross-sectional survey of Ae. j. japonicus was then conducted in 2009 in Natoye to study the phenology of the species on two different sites using three kinds of traps: Mosquito Magnet Liberty Plus traps, BG sentinel traps and CDC Gravid traps. An analysis of the blood meals was done on females to assess the epidemiological risks. Five species of mosquitos were caught using the different kind of traps: Culex pipiens, Cx torrentium, Anopheles claviger, Aedes geniculatus and Ae. j. japonicus, Cx pipiens being the most abundant. The CDC gravid traps gave the best results. Surprisingly Ae. j. japonicus was only found on one site although both sites seem similar and are only distant of 2.5 km. Its population peak was reached in July. Most of the engorged mosquitoes tested acquired blood meals from humans (60%). No avian blood meals were unambiguously identified. Larvae were also collected, mostly from tires but also from buckets and from one tree hole. Only one larva was found in a puddle at 100 m of the tire storage. A first local treatment of Ae. j. japonicus larvae population was done in May 2012 using Bacillus thuringiensis subsp. israelensis (Bti) and was followed by preventive actions and public information. A monitoring is also presently implemented.
Ranking Malaria Risk Factors to Guide Malaria Control Efforts in African Highlands
Natacha Protopopoff,Wim Van Bortel,Niko Speybroeck,Jean-Pierre Van Geertruyden,Dismas Baza,Umberto D'Alessandro,Marc Coosemans
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0008022
Abstract: Malaria is re-emerging in most of the African highlands exposing the non immune population to deadly epidemics. A better understanding of the factors impacting transmission in the highlands is crucial to improve well targeted malaria control strategies.
Vector control in a malaria epidemic occurring within a complex emergency situation in Burundi: a case study
Natacha Protopopoff, Michel Van Herp, Peter Maes, Tony Reid, Dismas Baza, Umberto D'Alessandro, Wim Van Bortel, Marc Coosemans
Malaria Journal , 2007, DOI: 10.1186/1475-2875-6-93
Abstract: Twenty nine hills (administrative areas) were selected in collaboration with the provincial health authorities for the vector control interventions combining indoor residual spraying with deltamethrin and insecticide-treated nets. Impact was evaluated by entomological and parasitological surveys. Almost all houses (99%) were sprayed and nets use varied between 48% and 63%. Anopheles indoor resting density was significantly lower in treated as compared to untreated hills, the latter taken as controls. Despite this impact on the vector, malaria prevalence was not significantly lower in treated hills except for people sleeping under a net.Indoor spraying was feasible and resulted in high coverage despite being a logistically complex intervention in the Burundian context (scattered houses and emergency situation). However, it had little impact on the prevalence of malaria infection, possibly because it was implemented after the epidemic's peak. Nevertheless, after this outbreak the Ministry of Health improved the surveillance system, changed its policy with introduction of effective drugs and implementation of vector control to prevent new malaria epidemics.In the absence of effective drugs and sufficient preparedness, present study failed to demonstrate any impact of vector control activities upon the course of a short-duration malaria epidemic. However, the experience gained lead to increased preparedness and demonstrated the feasibility of vector control measures in this specific context.Malaria epidemics are a growing problem in the African highlands with devastating effects on their immunologically naive population [1,2]. When occurring during complex emergency situations their control is even more difficult. According to WHO [3] "a complex emergency is a situation that affects large civilian populations with war or civil strife, food shortages and population displacement, resulting in excess mortality and morbidity". The approach to malaria control in the acute ph
Spatial targeted vector control in the highlands of Burundi and its impact on malaria transmission
Natacha Protopopoff, Wim Van Bortel, Tanguy Marcotty, Michel Van Herp, Peter Maes, Dismas Baza, Umberto D'Alessandro, Marc Coosemans
Malaria Journal , 2007, DOI: 10.1186/1475-2875-6-158
Abstract: In Karuzi, in 2002–2005, vector control activities combining indoor residual spraying and long-lasting insecticidal nets were implemented. The interventions were done before the expected malaria transmission period and targeted the valleys between hills, with the expectation that this would also protect the populations living at higher altitudes. The impact on the Anopheles population and on malaria transmission was determined by nine cross-sectional surveys carried out at regular intervals throughout the study period.Anopheles gambiae s.l. and Anopheles funestus represented 95% of the collected anopheline species. In the valleys, where the vector control activities were implemented, Anopheles density was reduced by 82% (95% CI: 69–90). Similarly, transmission was decreased by 90% (95% CI: 63%–97%, p = 0.001). In the sprayed valleys, Anopheles density was further reduced by 79.5% (95% CI: 51.7–91.3, p < 0.001) in the houses with nets as compared to houses without them. No significant impact on vector density and malaria transmission was observed in the hill tops. However, the intervention focused on the high risk areas near the valley floor, where 93% of the vectors are found and 90% of the transmission occurs.Spatial targeted vector control effectively reduced Anopheles density and transmission in this highland district. Bed nets have an additional effect on Anopheles density though this did not translate in an additional impact on transmission. Though no impact was observed in the hilltops, the programme successfully covered the areas most at risk. Such a targeted strategy could prevent the emergence and spread of an epidemic from these high risk foci.Malaria epidemics occur frequently in the African highlands [1-3]. Their control is a priority and a specific plan of action was adopted by the African leaders during the 2000 Abuja summit [4]. An early warning system to increase malaria epidemic preparedness and prevention has been promoted, based on climate data, p
False positive circumsporozoite protein ELISA: a challenge for the estimation of the entomological inoculation rate of malaria and for vector incrimination
Lies Durnez, Wim Van Bortel, Leen Denis, Patricia Roelants, Aurélie Veracx, Ho Dinh Trung, Tho Sochantha, Marc Coosemans
Malaria Journal , 2011, DOI: 10.1186/1475-2875-10-195
Abstract: Mosquitoes collected in Cambodia and Vietnam were identified and tested for the presence of sporozoites in head and thorax by using CSP-ELISA. ELISA positive samples were confirmed by a Plasmodium specific PCR. False positive mosquitoes were checked by PCR for the presence of parasites belonging to the Haemosporidia, Trypanosomatidae, Piroplasmida, and Haemogregarines. The heat-stability and the presence of the cross-reacting antigen in the abdomen of the mosquitoes were also checked.Specimens (N = 16,160) of seven anopheline species were tested by CSP-ELISA for Plasmodium falciparum and Plasmodium vivax (Pv210 and Pv247). Two new vector species were identified for the region: Anopheles pampanai (P. vivax) and Anopheles barbirostris (Plasmodium malariae). In 88% (155/176) of the mosquitoes found positive with the P. falciparum CSP-ELISA, the presence of Plasmodium sporozoites could not be confirmed by PCR. This percentage was much lower (28% or 5/18) for P. vivax CSP-ELISAs. False positive CSP-ELISA results were associated with zoophilic mosquito species. None of the targeted parasites could be detected in these CSP-ELISA false positive mosquitoes. The ELISA reacting antigen of P. falciparum was heat-stable in CSP-ELISA true positive specimens, but not in the false positives. The heat-unstable cross-reacting antigen is mainly present in head and thorax and almost absent in the abdomens (4 out of 147) of the false positive specimens.The CSP-ELISA can considerably overestimate the EIR, particularly for P. falciparum and for zoophilic species. The heat-unstable cross-reacting antigen in false positives remains unknown. Therefore it is highly recommended to confirm all positive CSP-ELISA results, either by re-analysing the heated ELISA lysate (100°C, 10 min), or by performing Plasmodium specific PCR followed if possible by sequencing of the amplicons for Plasmodium species determination.The entomological inoculation rate (EIR) is an important indicator in estimating mal
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