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Search Results: 1 - 10 of 144534 matches for " Gerry F Killeen "
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The potential of a new larviciding method for the control of malaria vectors
Gregor J Devine, Gerry F Killeen
Malaria Journal , 2010, DOI: 10.1186/1475-2875-9-142
Abstract: The basic tools for malaria vector control are the insecticide-treated bed net (ITN) and indoor residual spraying (IRS). These have a considerable impact on malaria transmission [1,2] by exposing female, host-seeking mosquitoes to insecticide-treated surfaces every time they enter a house to take a blood meal. Repeated contacts over the life cycle amplify the impact of these tools on transmission, even though their effect on mosquito density may remain limited [3]. However, fundamental limitations regarding the coverage of houses or sleeping spaces [3,4] ensure that ITNs and IRS alone may not stop malaria transmission in intensely endemic regions [5]. Moreover, these tools will not be optimally effective in areas where mosquitoes exhibit outdoor resting and biting behaviours, or where the widespread use of ITNs and IRS has controlled endophillic mosquitoes, but left a smaller, more intractable population of exophillic and exophagic mosquitoes behind (e.g. the appearance of Anopheles arabiensis as the most abundant vector in areas once dominated by An. gambiae and An. funestus [6,7]). The sustainability of IRS and ITNs is further threatened by the appearance of pyrethroid resistance in some mosquito populations [8]. All of these factors require that novel but complementary control methods are developed, that use novel insecticide classes that are not yet resisted.Targeting the aquatic habitat is one obvious additional strategy. This is an increasingly valued approach in many African settings [9] but larvicides, unlike IRS and ITNs, act on a single, non-transmitting stage in the mosquito lifecycle and can only impact disease by reducing vector abundance [10]. The myriad and cryptic nature of aquatic habitats and the difficulty in identifying and targeting the most productive of these [10] makes maximizing that impact very challenging.A recent field trial with the dengue vector, Aedes aegypti, exploited the obligate behaviours of adult mosquitoes to transfer a potent l
Target product profiles for protecting against outdoor malaria transmission
Gerry F Killeen, Sarah J Moore
Malaria Journal , 2012, DOI: 10.1186/1475-2875-11-17
Abstract: For any assumed level of indoor coverage and personal protective efficacy with insecticidal products, process-explicit malaria transmission models suggest that insecticides that repel mosquitoes will achieve less impact upon transmission than those that kill them outright. Here such models are extended to explore how outdoor use of products containing either contact toxins or spatial repellents might augment or attenuate impact of high indoor coverage of LLINs relying primarily upon contact toxicity.LLIN impact could be dramatically enhanced by high coverage with spatial repellents conferring near-complete personal protection, but only if combined indoor use of both measures can be avoided where vectors persist that prefer feeding indoors upon humans. While very high levels of coverage and efficacy will be required for spatial repellents to substantially augment the impact of LLINs or IRS, these ambitious targets may well be at least as practically achievable as the lower requirements for equivalent impact using contact insecticides.Vapour-phase repellents may be more acceptable, practical and effective than contact insecticides for preventing outdoor malaria transmission because they need not be applied to skin or clothing and may protect multiple occupants of spaces outside of treatable structures such as nets or houses.Long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) have dramatically reduced malaria transmission by indoor-feeding (endophagic) mosquito populations in recent years [1-4]. However, elimination of transmission is not currently considered possible without cost-effective new technologies that protect against the persistent outdoor-biting (exophagic) vectors that continue to mediate self-sustaining residual transmission [4-6] because they are less vulnerable to insecticides applied to indoor surfaces [7-9]. Now that LLINs and IRS are being successfully scaled up in many countries across the tropics [10], it is timely to consider
Advantages of larval control for African malaria vectors: Low mobility and behavioural responsiveness of immature mosquito stages allow high effective coverage
Gerry F Killeen, Ulrike Fillinger, Bart GJ Knols
Malaria Journal , 2002, DOI: 10.1186/1475-2875-1-8
Abstract: We hypothesize that the control of adult but not immature mosquitoes is compromised by their ability to avoid interventions such as excito-repellant insecticides.We apply a simple model of intervention avoidance by mosquitoes and demonstrate that this can substantially reduce effective coverage, in terms of the proportion of the vector population that is covered, and overall impact on malaria transmission. We review historical evidence that larval control of African malaria vectors can be effective and conclude that the only limitations to the effective coverage of larval control are practical rather than fundamental.Larval control strategies against the vectors of malaria in sub-Saharan Africa could be highly effective, complementary to adult control interventions, and should be prioritized for further development, evaluation and implementation as an integral part of Rolling Back Malaria.Domestic insecticide interventions such as pyrethroid-treated bednets can substantially lower morbidity and mortality [1] and remain the most commonly advocated methods for malaria prevention. Bednets have revitalized interest in vector control of malaria in sub-Saharan Africa where high transmission levels result in extremely stable malaria prevalence, incidence and clinical burden [2-4]. Insecticide-treated nets protect their occupants by diverting host-seeking vectors to look for a blood meal elsewhere and by killing those that attempt to feed [5,6]. Treated nets can therefore also prevent malaria in unprotected individuals by suppressing vector numbers [7-9], survival [7-9], human blood indices [10,11] and feeding frequency [11] in local populations. However, the results of individual studies often differ and although some trials with African vectors have demonstrated substantial reductions of vector density, survival and sporozoite prevalence [7-9], others have found little or no effects on the vector population as a whole [12-14]. These instances where bednets appear to have
The Importance of Drains for the Larval Development of Lymphatic Filariasis and Malaria Vectors in Dar es Salaam, United Republic of Tanzania
Marcia C. Castro ,Shogo Kanamori,Khadija Kannady,Sigsbert Mkude,Gerry F. Killeen,Ulrike Fillinger
PLOS Neglected Tropical Diseases , 2010, DOI: 10.1371/journal.pntd.0000693
Abstract: Background Dar es Salaam has an extensive drain network, mostly with inadequate water flow, blocked by waste, causing flooding after rainfall. The presence of Anopheles and Culex larvae is common, which is likely to impact the transmission of lymphatic filariasis and malaria by the resulting adult mosquito populations. However, the importance of drains as larval habitats remains unknown. Methodology Data on mosquito larval habitats routinely collected by the Urban Malaria Control Program (UMCP) and a special drain survey conducted in 2006 were used to obtain a typology of habitats. Focusing on drains, logistic regression was used to evaluate potential factors impacting the presence of mosquito larvae. Spatial variation in the proportion of habitats that contained larvae was assessed through the local Moran's I indicator of spatial association. Principal Findings More than 70% of larval habitats in Dar es Salaam were human-made. Aquatic habitats associated with agriculture had the highest proportion of Anopheles larvae presence and the second highest of Culex larvae presence. However, the majority of aquatic habitats were drains (42%), and therefore, 43% (1,364/3,149) of all culicine and 33% (320/976) of all anopheline positive habitats were drains. Compared with drains where water was flowing at normal velocity, the odds of finding Anopheles and Culex larvae were 8.8 and 6.3 (p<0.001) times larger, respectively, in drains with stagnant water. There was a positive association between vegetation and the presence of mosquito larvae (p<0.001). The proportion of habitats with mosquito larvae was spatially correlated. Conclusion Restoring and maintaining drains in Dar es Salaam has the potential to eliminate more than 40% of all potential mosquito larval habitats that are currently treated with larvicides by the UMCP. The importance of human-made larval habitats for both lymphatic filariasis and malaria vectors underscores the need for a synergy between on-going control efforts of those diseases.
Potential Benefits, Limitations and Target Product-Profiles of Odor-Baited Mosquito Traps for Malaria Control in Africa
Fredros O. Okumu,Nicodem J. Govella,Sarah J. Moore,Nakul Chitnis,Gerry F. Killeen
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0011573
Abstract: Traps baited with synthetic human odors have been proposed as suitable technologies for controlling malaria and other mosquito-borne diseases. We investigated the potential benefits of such traps for preventing malaria transmission in Africa and the essential characteristics that they should possess so as to be effective.
Community-owned resource persons for malaria vector control: enabling factors and challenges in an operational programme in Dar es Salaam, United Republic of Tanzania
Prosper P Chaki, Stefan Dongus, Ulrike Fillinger, Ann Kelly, Gerry F Killeen
Human Resources for Health , 2011, DOI: 10.1186/1478-4491-9-21
Abstract: A mixed method, cross-sectional survey assessed the ability of CORPs to detect mosquito breeding sites and larvae, and investigated demographic characteristics of the CORPs, their reasons for participating in the UMCP, and their work performance. Detection coverage was estimated as the proportion of wet habitats found by the investigator which had been reported by CORP. Detection sensitivity was estimated as the proportion of wet habitats found by the CORPS which the investigator found to contain Anopheles larvae that were also reported to be occupied by the CORP.The CORPs themselves perceived their role as professional rather than voluntary, with participation being a de facto form of employment. Habitat detection coverage was lower among CORPs that were recruited through the program administrative staff, compared to CORPs recruited by local government officials or health committees (Odds Ratio = 0.660, 95% confidence interval = [0.438, 0.995], P = 0.047). Staff living within their areas of responsibility had > 70% higher detection sensitivity for both Anopheline (P = 0.016) and Culicine (P = 0.012): positive habitats compared to those living outside those same areas.Improved employment conditions as well as involving the local health committees in recruiting individual program staff, communication and community engagement skills are required to optimize achieving effective community participation, particularly to improve access to fenced compounds. A simpler, more direct, less extensive community-based surveillance system in the hands of a few, less burdened, better paid and maintained program personnel may improve performance and data quality.Cities and large towns are regarded as some of the most favourable environments for sustainable public health development programs because of their relatively well educated, readily accessible populations, with access to information, governance and social infrastructure [1,2]. Nevertheless, many vertically-organized public h
Target product profile choices for intra-domiciliary malaria vector control pesticide products: repel or kill?
Gerry F Killeen, Nakul Chitnis, Sarah J Moore, Fredros O Okumu
Malaria Journal , 2011, DOI: 10.1186/1475-2875-10-207
Abstract: A process-explicit model of malaria transmission is described which captures the sequential interaction between deterrent and toxic actions of vector control pesticides and accounts for the distinctive impacts of toxic activities which kill mosquitoes before or after they have fed upon the occupant of a covered house or sleeping space.Increasing deterrency increases personal protection but consistently reduces communal protection because deterrent sub-lethal exposure inevitably reduces the proportion subsequently exposed to higher lethal doses. If the high coverage targets of the World Health Organization are achieved, purely toxic products with no deterrence are predicted to generally provide superior protection to non-users and even users, especially where vectors feed exclusively on humans and a substantial amount of transmission occurs outdoors. Remarkably, this is even the case if that product confers no personal protection and only kills mosquitoes after they have fed.Products with purely mosquito-toxic profiles may, therefore, be preferable for programmes with universal coverage targets, rather than those with equivalent toxicity but which also have higher deterrence. However, if purely mosquito-toxic products confer little personal protection because they do not deter mosquitoes and only kill them after they have fed, then they will require aggressive "catch up" campaigns, with behaviour change communication strategies that emphasize the communal nature of protection, to achieve high coverage rapidly.The most important front line vector control strategies for malaria prevention rely on killing mosquitoes that enter human houses by delivering insecticidal products to these domestic targets in the form of indoor residual spray (IRS) or long-lasting insecticidal nets (LLINs) [1,2]. The common rationale underpinning these strategies is based on two well-established biological phenomena: 1) that the most important malaria vectors prefer to feed on humans and rest
Limitation of using synthetic human odours to test mosquito repellents
Fredros O Okumu, Emmanuel Titus, Edgar Mbeyela, Gerry F Killeen, Sarah J Moore
Malaria Journal , 2009, DOI: 10.1186/1475-2875-8-150
Abstract: This paper reports on a semi-field evaluation of repellents using a synthetic blend of human derived attractants for the malaria vector, Anopheles gambiae sensu stricto Different concentrations of known repellents, N, N diethyl-3-methylbenzamide (deet) and Para-methane-3, 8, diol (PMD) were added into traps baited with the synthetic blend, and resulting changes in mosquito catches were measured.All test concentrations of deet (0.001% to 100%) reduced the attractiveness of the synthetic blend. However, PMD was repellent only at 0.25%. Above this concentration, it significantly increased the attractiveness of the blend. There was no relationship between the repellent concentrations and the change in mosquito catches when either deet (r2 = 0.033, P = 0.302) or PMD (r2 = 0.020, P = 0.578) was used.It is concluded that while some repellents may reduce the attractiveness of synthetic human odours, others may instead increase their attractiveness. Such inconsistencies indicate that even though the synthetic attractants may provide exposure-free and consistent test media for repellents, careful selection and multiple-repellent tests are necessary to ascertain their suitability for use in repellent screening. The synthetic odour blend tested here is not yet sufficiently refined to serve as replacement for humans in repellent testing, but may be developed further and evaluated in different formats for exposure free repellent testing purposes.Personal protection with insect repellents is a popular method for preventing contact with arthropod disease vectors. While their modes of action may vary, repellents generally prevent host seeking vectors from landing on or biting the user. The vectors, which under normal circumstances would be attracted to the person, are either diverted away or disoriented in such a way that they fail to bite the host [1]. These are the most important determinants of effectiveness of any repellent, though there are certainly other essential factors suc
Habitat characterization and spatial distribution of Anopheles sp. mosquito larvae in Dar es Salaam (Tanzania) during an extended dry period
Michael A Sattler, Deo Mtasiwa, Michael Kiama, Zul Premji, Marcel Tanner, Gerry F Killeen, Christian Lengeler
Malaria Journal , 2005, DOI: 10.1186/1475-2875-4-4
Abstract: In total 151 km2 of central Dar es Salaam, the biggest city of Tanzania, were systematically searched for open mosquito breeding sites. Ecologic parameters, mosquito larvae density and geographic location were recorded for each site. Logistic regression analysis was used to determine the key ecological factors explaining the different densities of mosquito larvae.A total of 405 potential open breeding sites were examined. Large drains, swamps and puddles were associated with no or low Anopheles sp. larvae density. The probability of Anopheles sp. larvae to be present was reduced when water was identified as "turbid". Small breeding sites were more commonly colonized by Anopheles sp. larvae. Further, Anopheles gambiae s.l. larvae were found in highly organically polluted habitats.Clear ecological characteristics of the breeding requirements of Anopheles sp. larvae could not be identified in this setting. Hence, every stagnant open water body, including very polluted ones, have to be considered as potential malaria vector breeding sites.Urbanization is progressing fast worldwide. By the year 2030, more than 50% of the African population will live in urban areas [1]. It is anticipated that infectious disease problems including vector-borne diseases such as malaria might also increase in urban areas [2]. Keiser et al. [3] estimated that 24.8–103.2 million clinical malaria episodes occur annually in urban settings endemic for malaria. Urban malaria is generally characterized by: low transmission intensity, lack of immunity in the population and higher mortality rates in older age groups [4]. The distribution pattern of malaria transmission intensity is dependent on the degree of urbanization and on the distance from vector breeding sites [5,6]. Consequently, a high heterogeneity of transmission intensity is characteristic for urban malaria [7]. Increasing urban agriculture is thought to play a major role in increasing malaria in urban areas. However, this is not yet demo
An exploratory study of community factors relevant for participatory malaria control on Rusinga Island, western Kenya
Pamela Opiyo, W Richard Mukabana, Ibrahim Kiche, Evan Mathenge, Gerry F Killeen, Ulrike Fillinger
Malaria Journal , 2007, DOI: 10.1186/1475-2875-6-48
Abstract: Focus group discussions and semi-structured individual interviews were carried out in 1,451 households to determine (1) demographics of respondent and household; (2) socio-economic status of the household; (3) knowledge and beliefs about malaria (symptoms, prevention methods, mosquito life cycle); (4) typical practices used for malaria prevention; (5) the treatment-seeking behaviour and household expenditure for malaria treatment; and (6) the willingness to prepare and implement community-based vector control.Malaria was considered a major threat to life but relevant knowledge was a chimera of scientific knowledge and traditional beliefs, which combined with socio-economic circumstances, leads to ineffective malaria prevention. The actual malaria prevention behaviour practiced by community members differed significantly from methods known to the respondents. Beside bednet use, the major interventions implemented were bush clearing and various hygienic measures, even though these are ineffective for malaria prevention. Encouragingly, most respondents believed malaria could be controlled and were willing to contribute to a community-based malaria control program but felt they needed outside assistance.Culturally sensitive but evidence-based education interventions, utilizing participatory tools, are urgently required which consider traditional beliefs and enable understanding of causal connections between mosquito ecology, parasite transmission and the diagnosis, treatment and prevention of disease. Community-based organizations and schools need to be equipped with knowledge through partnerships with national and international research and tertiary education institutions so that evidence-based research can be applied at the grassroots level.Malaria imposes a huge burden upon the health and economic development of tropical nations [1-3] and has been identified as a major obstacle towards achieving several of the health-related Millennium Development Goals [3,4]. The di
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