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Search Results: 1 - 10 of 1177 matches for " Willem Takken "
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Development of Metarhizium anisopliae and Beauveria bassiana formulations for control of malaria mosquito larvae
Tullu Bukhari, Willem Takken, Constantianus JM Koenraadt
Parasites & Vectors , 2011, DOI: 10.1186/1756-3305-4-23
Abstract: Laboratory bioassays were conducted to test the ability of aqueous (0.1% Tween 80), dry (organic and inorganic) and oil (mineral and synthetic) formulations to facilitate the spread of fungal spores over the water surface and improve the efficacy of formulated spores against anopheline larvae as well as improve spore survival after application. Field bioassays were then carried out to test the efficacy of the most promising formulation under field conditions in western Kenya.When formulated in a synthetic oil (ShellSol T), fungal spores of both Metarhizium anisopliae and Beauveria bassiana were easy to mix and apply to the water surface. This formulation was more effective against anopheline larvae than 0.1% Tween 80, dry powders or mineral oil formulations. ShellSol T also improved the persistence of fungal spores after application to the water. Under field conditions in Kenya, the percentage pupation of An. gambiae was significantly reduced by 39 - 50% by the ShellSol T-formulated Metarhizium anisopliae and Beauveria bassiana spores as compared to the effects of the application of unformulated spores.ShellSol T is an effective carrier for fungal spores when targeting anopheline larvae under both laboratory and field conditions. Entomopathogenic fungi formulated with a suitable carrier are a promising tool for control of larval populations of malaria mosquitoes. Additional studies are required to identify the best delivery method (where, when and how) to make use of the entomopathogenic potential of these fungi against anopheline larvae.Recently, theoretical and experimental studies have shown the potential of entomopathogenic fungi as next generation agents for the control of malaria mosquitoes [1-5] However, most of this work has focused on targeting adult mosquitoes. Larval control has a convincing history of malaria eradication and recent studies have also shown this approach to be highly effective [6-11]. It is, therefore, worthwhile to investigate the ability
Autodissemination of the entomopathogenic fungus Metarhizium anisopliae amongst adults of the malaria vector Anopheles gambiae s.s.
Ernst-Jan Scholte, Bart GJ Knols, Willem Takken
Malaria Journal , 2004, DOI: 10.1186/1475-2875-3-45
Abstract: Virgin female Anopheles gambiae sensu stricto were exposed to conidia whilst resting on fungus-impregnated paper. These females were then placed together for one hour with uncontaminated males in proportions of either 1:1 or 1:10 shortly before the onset of mating activity.Males that had acquired fungal infection after mating indicate that passive transfer of the pathogen from infected females does occur, with mean male infection rates between 10.7 ± 3.2% and 33.3 ± 3.8%. The infections caused by horizontal transmission did not result in overall differences in survival between males from test and control groups, but in one of the three experiments the infected males had significantly shorter life spans than uninfected males (P < 0.05).This study shows that autodissemination of fungal inoculum between An. gambiae s.s. mosquitoes during mating activity is possible under laboratory conditions. Field studies are required next, to assess the extent to which this phenomenon may augment the primary contamination pathway (i.e. direct contact with fungus-impregnated targets) of vector populations in the field.Control of the main African malaria vector Anopheles gambiae (Diptera: Culicidae) continues to rely heavily on application of residual insecticides, either for indoor residual house spraying [1] or bednet impregnation [2]. These approaches have been highly effective in reducing malaria morbidity and mortality [2], but associated problems regarding environmental pollution [3,4], acceptability and cost [5,6] and the now widespread and continuing development of resistance [7-10] underscore the need for alternative strategies, such as vector control with biological agents [1,11,12].Entomopathogenic fungi are among the biological control agents used against insect pests. Interest in using the hyphomycete Metarhizium anisopliae against adult African malaria vectors has recently increased [13]. The fungus has proven to be highly virulent for this vector, both in the laboratory
Host-specific cues cause differential attractiveness of Kenyan men to the African malaria vector Anopheles gambiae
Wolfgang R Mukabana, Willem Takken, Richard Coe, Bart GJ Knols
Malaria Journal , 2002, DOI: 10.1186/1475-2875-1-17
Abstract: A new three-port olfactometer that accommodates complete human beings as sources of host-seeking stimuli was used to study behavioural responses of Anopheles gambiae Giles sensu stricto (hereafter An. gambiae) under semi-field conditions in western Kenya. Differential attractiveness of nine male Kenyans was assessed by simultaneously exposing the mosquitoes to (a mixture of) total body emanations of 3 people occupying separate tents. Controls (empty tents) were included and the effect of residual odours following tent occupation was also examined.Trap catches increased significantly (P < 0.001) when a tent was occupied. Based on 'competition' experiments, the nine persons were classified into least, medium and most attractive groups. There was no significant interaction between person and trap (P = 0.302) or person and test period (P = 0.223). Presence (P < 0.001) or absence (P = 0.949) of significant differences in the number of mosquitoes caught per trap when tents were simultaneously occupied by one person in each or left empty, respectively, demonstrated that residual odours following tent occupation did not affect behavioural responses of the mosquitoes.We provide evidence that in the vicinity of humans, when exposed to a blend of physical and olfactory signals from more than one host, An. gambiae can effectively and consistently express host-selection behaviour that results in non-random biting.Although there is evidence that some humans are more attractive to host-seeking African malaria mosquitoes than others [1-3] the reasons for this variability are not clearly understood [4]. Various studies have implicated some Anopheles species as preferring to feed on adults rather than children [5,6] and on men rather than women [6]. The preference for feeding on adults rather than children by An. gambiae s.l. [7-9] has been attributed to size [10] and surface area and weight [11]. In contrast, random feeding irrespective of age [12,13] and sex [10,11] by this mosquit
Circumstantial evidence for an increase in the total number and activity of borrelia-infected ixodes ricinus in the Netherlands
Sprong Hein,Hofhuis Agnetha,Gassner Fedor,Takken Willem
Parasites & Vectors , 2012, DOI: 10.1186/1756-3305-5-294
Abstract: Background Between 1994 and 2009, a threefold increase has been observed in consultations of general practitioners for tick bites and Lyme disease in The Netherlands. The objective of this study was to determine whether an increase in the number of questing ticks infected with B. burgdorferi sensu lato is a potential cause of the rise in Lyme disease incidence. Methods Historic data on land usage, temperature and wildlife populations were collected and analyzed together with data from two longitudinal field studies on density of questing ticks. Effective population sizes of Borrelia burgdorferi s.l. were calculated. Results Long-term trend analyses indicated that the length of the annual tick questing season increased as well as the surface area of tick-suitable habitats in The Netherlands. The overall abundances of feeding and reproductive hosts also increased. Mathematical analysis of the data from the field studies demonstrated an increase in mean densities/activities of questing ticks, particularly of larvae between 2006 and 2009. No increase in infection rate of ticks with Borrelia burgdorferi sensu lato was found. Population genetic analysis of the collected Borrelia species points to an increase in B. afzelii and B. garinii populations. Conclusions Together, these findings indicate an increase in the total number of Borrelia-infected ticks, providing circumstantial evidence for an increase in the risk of acquiring a bite of a tick infected with B. burgdorferi s.l. Due to the high spatiotemporal variation of tick densities/activities, long-term longitudinal studies on population dynamics of I. ricinus are necessary to observe significant trends.
Efficacy of Aquatain, a Monomolecular Film, for the Control of Malaria Vectors in Rice Paddies
Tullu Bukhari,Willem Takken,Andrew K. Githeko,Constantianus J. M. Koenraadt
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0021713
Abstract: Rice paddies harbour a large variety of organisms including larvae of malaria mosquitoes. These paddies are challenging for mosquito control because their large size, slurry and vegetation make it difficult to effectively apply a control agent. Aquatain, a monomolecular surface film, can be considered a suitable mosquito control agent for such breeding habitats due to its physical properties. The properties allow Aquatain to self-spread over a water surface and affect multiple stages of the mosquito life cycle.
Unexpected High Losses of Anopheles gambiae Larvae Due to Rainfall
Krijn P. Paaijmans, Moses O. Wandago, Andrew K. Githeko, Willem Takken
PLOS ONE , 2007, DOI: 10.1371/journal.pone.0001146
Abstract: Background Immature stages of the malaria mosquito Anopheles gambiae experience high mortality, but its cause is poorly understood. Here we study the impact of rainfall, one of the abiotic factors to which the immatures are frequently exposed, on their mortality. Methodology/Principal Findings We show that rainfall significantly affected larval mosquitoes by flushing them out of their aquatic habitat and killing them. Outdoor experiments under natural conditions in Kenya revealed that the additional nightly loss of larvae caused by rainfall was on average 17.5% for the youngest (L1) larvae and 4.8% for the oldest (L4) larvae; an additional 10.5% (increase from 0.9 to 11.4%) of the L1 larvae and 3.3% (from 0.1 to 3.4%) of the L4 larvae were flushed away and larval mortality increased by 6.9% (from 4.6 to 11.5%) and 1.5% (from 4.1 to 5.6%) for L1 and L4 larvae, respectively, compared to nights without rain. On rainy nights, 1.3% and 0.7% of L1 and L4 larvae, respectively, were lost due to ejection from the breeding site. Conclusions/Significance This study demonstrates that immature populations of malaria mosquitoes suffer high losses during rainfall events. As these populations are likely to experience several rain showers during their lifespan, rainfall will have a profound effect on the productivity of mosquito breeding sites and, as a result, on the transmission of malaria. These findings are discussed in the light of malaria risk and changing rainfall patterns in response to climate change.
Identifying the most productive breeding sites for malaria mosquitoes in The Gambia
Ulrike Fillinger, Heleen Sombroek, Silas Majambere, Emiel van Loon, Willem Takken, Steven W Lindsay
Malaria Journal , 2009, DOI: 10.1186/1475-2875-8-62
Abstract: A case-control design was used to identify characteristics of sites with or without mosquitoes. Sites were surveyed for their physical water properties and invertebrate fauna. The characteristics of 83 sites with anopheline larvae (cases) and 75 sites without (controls) were collected between June and November 2005. Weekly adult productivity was estimated with emergence traps in water-bodies commonly containing larvae.The presence of anopheline larvae was associated with high invertebrate diversity (Odds Ratio, OR 11.69, 95% CI 5.61–24.34, p < 0.001), the presence of emergent vegetation (OR 2.83, 95% CI 1.35–5.95, p = 0.006), and algae (at borderline significance; OR 1.87, 95% CI 0.96–3.618, p = 0.065). The density of larvae was reduced in sites that were larger than 100 m in perimeter (OR 0.151; 95% CI 0.060–0.381, p < 0.001), where water was tidal (OR 0.232; 95% CI 0.101–0.533, p = 0.001), vegetation shaded over 25% of the habitat (OR 0.352; 95% CI 0.136–0.911, p = 0.031) and water conductivity was above 2,000 μS/cm (OR 0.458; 95% CI 0.220–0.990, p = 0.048). Pools produced the highest numbers of Anopheles gambiae adults compared with rice fields, floodwater areas close to the edge of the floodplain or close to the river, and stream fringes. Pools were characterized by high water temperature and turbidity, low conductivity, increased presence of algae, and absence of tidal water.There are few breeding sites that produce a high number of adult vectors in the middle reaches of the river in The Gambia, whereas those with low productivity are larger in area and can be found throughout the rainy season. Even though risk factors could be identified for the presence and density of larvae and productivity of habitats, the results indicate that anti-larval interventions in this area of The Gambia cannot be targeted in space or time during the rainy season.Larval source management (LSM), a strategy which includes larviciding and source reduction (environmental manipulation,
Novel strategies lead to pre-elimination of malaria in previously high-risk areas in Suriname, South America
Hélène Hiwat, Loretta S Hardjopawiro, Willem Takken, Leopoldo Villegas
Malaria Journal , 2012, DOI: 10.1186/1475-2875-11-10
Abstract: The interventions of the MM-MP included new strategies for prevention, vector control, case management, behavioral change communication (BCC)/information, education and communication (IEC), and strengthening of the health system (surveillance, monitoring and evaluation and epidemic detection system). After a slow first year with non-satisfying scores for the performance indicators, the MM-MP truly engaged in its intervention activities in 2006 and kept its performance up until the end of 2009. A total of 69,994 long-lasting insecticide-treated nets were distributed and more than 15,000 nets re-impregnated. In high-risk areas, this was complemented with residual spraying of insecticides. Over 10,000 people were screened with active case detection in outbreak and high-risk areas. Additional notification points were established and the national health system was strengthened.In the current paper, the MM-MP is evaluated both on account of the targets established within the programme and on account of its impact on the malaria situation in Suriname. Malaria vector populations, monitored in sentinel sites, collapsed after 2006 and concurrently the number of national malaria cases decreased from 8,618 in 2005 to 1,509 in 2009. Malaria transmission risk shifted from the stabile village communities to the mobile gold mining communities, especially those along the French Guiana border.The novel strategies for malaria control introduced in Suriname within the MM-MP have led to a significant decrease in the national malaria burden. The challenge is to further reduce malaria using the available strategies as appropriate in the affected areas and populations. Elimination of malaria in the country will require a thorough understanding of transmission dynamics and a dedicated investment in key effective interventions.The Amazon basin harbors 95% of the total malaria burden in the region and 98% of the Plasmodium falciparum infections of the Americas [1,2]. The Guyanan Shield area (
Trapping of the malaria vector Anopheles gambiae with odour-baited MM-X traps in semi-field conditions in western Kenya
Basilio N Njiru, Wolfgang R Mukabana, Willem Takken, Bart GJ Knols
Malaria Journal , 2006, DOI: 10.1186/1475-2875-5-39
Abstract: The response of 3–5 day old female An. gambiae towards odour-baited counterflow geometry traps (MM-X model; American Biophysics Corp., RI) was studied in semi-field (screen house) conditions in western Kenya. Traps were baited with human foot odour (collected on socks), carbon dioxide (CO2, 500 ml min-1), ammonia (NH3), 1-octen-3-ol, or various combinations thereof. Trap catches were log (x+1) transformed and subjected to Latin square analysis of variance procedures.Apart from 1-octen-3-ol, all odour baits caused significant (P < 0.05) increases in trap catches over non-baited traps. Foot odour remained behaviourally active for at least 8 days after collection on nylon or cotton sock fabric. A synergistic response (P < 0.001) was observed towards the combination of foot odour and CO2, which increased catches of these odours alone by 3.8 and 2.7 times, respectively.These results are the first to report behavioural responses of an African malaria vector to human foot odour outside the laboratory, and further investigation of fractions and/or individual chemical components of this odour complex are called for. Semi-field systems offer the prospect of high-throughput screening of candidate kairomones, which may expedite the development of efficient trap-bait systems for this and other African mosquito species.Development of odour-baited trapping devices for biting insects remains a challenge for many important species, including African malaria vectors [1,2]. Such traps may find application in mosquito surveillance [3], risk assessment and forecasting [4], and/or be used en masse for population suppression and disease transmission reduction similar to trap-bait systems developed for tsetse flies [5-7]. There are three important components of trap development, namely the 'attractant', the physical trap design, and trapping mechanism used. A fourth set of essentials follows, namely the cost, applicability and acceptance of such devices by end-users in anticipated market s
Pyrethroid resistance in Anopheles gambiae leads to increased susceptibility to the entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana
Annabel FV Howard, Constantianus JM Koenraadt, Marit Farenhorst, Bart GJ Knols, Willem Takken
Malaria Journal , 2010, DOI: 10.1186/1475-2875-9-168
Abstract: Pieces of white polyester netting were dipped in Metarhizium anisopliae ICIPE-30 or Beauveria bassiana IMI391510 mineral oil suspensions. These were kept at 27 ± 1°C, 80 ± 10% RH and the viability of the fungal conidia was recorded at different time points. Tube bioassays were used to infect insecticide-resistant (VKPER) and insecticide-susceptible (SKK) strains of An. gambiae s.s., and survival analysis was used to determine effects of mosquito strain, fungus species or time since fungal treatment of the net.The resistant VKPER strain was significantly more susceptible to fungal infection than the insecticide-susceptible SKK strain. Furthermore, B. bassiana was significantly more virulent than M. anisopliae for both mosquito strains, although this may be linked to the different viabilities of these fungal species. The viability of both fungal species decreased significantly one day after application onto polyester netting when compared to the viability of conidia remaining in suspension.The insecticide-resistant mosquito strain was susceptible to both species of fungus indicating that entomopathogenic fungi can be used in resistance management and integrated vector management programmes to target insecticide-resistant mosquitoes. Although fungal viability significantly decreased when applied to the netting, the effectiveness of the fungal treatment at killing mosquitoes did not significantly deteriorate. Field trials over a longer trial period need to be carried out to verify whether polyester netting is a good candidate for operational use, and to see if wild insecticide-resistant mosquitoes are as susceptible to fungal infection as the VKPER strain.It is estimated that in 2008 there were 243 million cases of malaria and 863,000 deaths [1]. Clearly, mosquito-borne diseases are still a major health risk, particularly in developing countries. Current mosquito control strategies depend heavily on insecticides but mosquito populations in various disease-endemic countr
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