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Search Results: 1 - 10 of 248759 matches for " Tchouassi David P "
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Sheep Skin Odor Improves Trap Captures of Mosquito Vectors of Rift Valley Fever
David P. Tchouassi,Rosemary Sang,Catherine L. Sole,Armanda D. S. Bastos,Klaus Mithoefer,Baldwyn Torto
PLOS Neglected Tropical Diseases , 2012, DOI: 10.1371/journal.pntd.0001879
Abstract: In recent years, the East African region has seen an increase in arboviral diseases transmitted by blood-feeding arthropods. Effective surveillance to monitor and reduce incidence of these infections requires the use of appropriate vector sampling tools. Here, trapped skin volatiles on fur from sheep, a known preferred host of mosquito vectors of Rift Valley fever virus (RVFV), were used with a standard CDC light trap to improve catches of mosquito vectors. We tested the standard CDC light trap alone (L), and baited with (a) CO2 (LC), (b) animal volatiles (LF), and (c) CO2 plus animal volatiles (LCF) in two highly endemic areas for RVF in Kenya (Marigat and Ijara districts) from March–June and September–December 2010. The incidence rate ratios (IRR) that mosquito species chose traps baited with treatments (LCF, LC and LF) instead of the control (L) were estimated. Marigat was dominated by secondary vectors and host-seeking mosquitoes were 3–4 times more likely to enter LC and LCF traps [IRR = 3.1 and IRR = 3.8 respectively] than the L only trap. The LCF trap captured a greater number of mosquitoes than the LC trap (IRR = 1.23) although the difference was not significant. Analogous results were observed at Ijara, where species were dominated by key primary and primary RVFV vectors, with 1.6-, 6.5-, and 8.5-fold increases in trap captures recorded in LF, LC and LCF baited traps respectively, relative to the control. These catches all differed significantly from those trapped in L only. Further, there was a significant increase in trap captures in LCF compared to LC (IRR = 1.63). Mosquito species composition and trap counts differed between the RVF sites. However, within each site, catches differed in abundance only and no species preferences were noted in the different baited-traps. Identifying the attractive components present in these natural odors should lead to development of an effective odor-bait trapping system for population density-monitoring and result in improved RVF surveillance especially during the inter-epidemic period.
Characterization of malaria transmission by vector populations for improved interventions during the dry season in the Kpone-on-Sea area of coastal Ghana
Tchouassi David P,Quakyi Isabella A,Addison Ebenezer A,Bosompem Kwabena M
Parasites & Vectors , 2012, DOI: 10.1186/1756-3305-5-212
Abstract: Background Malaria is a major public health problem in Ghana. We present a site-specific entomological study of malaria vectors and transmission indices as part of an effort to develop a site for the testing of improved control strategies including possible vaccine trials. Methods Pyrethrum spray catches (PSC), and indoor and outdoor human landing collections of adult female anopheline mosquitoes were carried out over a six-month period (November 2005 - April 2006) at Kpone-on-Sea, a fishing village in southern Ghana. These were morphologically identified to species level and sibling species of the Anopheles gambiae complex further characterized by the polymerase chain reaction (PCR). Enzyme-linked immunosorbent assay was used to detect Plasmodium falciparum mosquito infectivity and host blood meal sources. Parity rate was examined based on dilatation of ovarian tracheoles following dissection. Results Of the 1233 Anopheles mosquitoes collected, An. gambiae s.l. was predominant (99.5%), followed by An. funestus (0.4%) and An. pharoensis (0.1%). All An. gambiae s.l. examined (480) were identified as An. gambiae s.s. with a majority of M molecular form (98.2%) and only 1.8% S form with no record of M/S hybrid. A significantly higher proportion of anophelines were observed outdoors relative to indoors (χ2 = 159.34, df = 1, p < 0.0000). Only An. gambiae M molecular form contributed to transmission with a high degree of anthropophily, parity rate and an estimated entomological inoculation rate (EIR) of 62.1 infective bites/person/year. The Majority of the infective bites occurred outdoors after 09.00 pm reaching peaks between 12.00-01.00 am and 03.00-04.00 am. Conclusion Anopheles gambiae M molecular form is responsible for maintaining the status quo of malaria in the surveyed site during the study period. The findings provide a baseline for evidence-based planning and implementation of improved malaria interventions. The plasticity observed in biting patterns especially the combined outdoor and early biting behavior of the vector may undermine the success of insecticide-based strategies using insecticide treated nets (ITN) and indoor residual spray (IRS). As such, novel or improved vector interventions should be informed by the local malaria epidemiology data as it relates to vector behavior.
Trapping of Rift Valley Fever (RVF) vectors using Light Emitting Diode (LED) CDC traps in two arboviral disease hot spots in Kenya
David P Tchouassi, Rosemary C Sang, Catherine L Sole, Armanda DS Bastos, Lee W Cohnstaedt, Baldwyn Torto
Parasites & Vectors , 2012, DOI: 10.1186/1756-3305-5-94
Abstract: The efficiency of selected colored LED CDC light traps (red, green, blue, violet, combination of blue-green-red (BGR)) to sample RVF vectors was evaluated relative to incandescent light (as control) in a CDC light trap in two RVF hotspots (Marigat and Ijara districts) in Kenya. In field experiments, traps were baited with dry ice and captures evaluated for Aedes tricholabis, Ae. mcintoshi, Ae. ochraceus, Mansonia uniformis, Mn. africana and Culex pipiens, following Latin square design with days as replicates. Daily mosquito counts per treatment were analyzed using a generalized linear model with Negative Binomial error structure and log link using R. The incidence rate ratios (IRR) that mosquito species chose other treatments instead of the control, were estimated.Seasonal preference of Ae.mcintoshi and Ae. ochraceus at Ijara was evident with a bias towards BGR and blue traps respectively in one trapping period but this pattern waned during another period at same site with significantly low numbers recorded in all colored traps except blue relative to the control. Overall results showed that higher captures of all species were recorded in control traps compared to the other LED traps (IRR?<?1) although only significantly different from red and violet.Based on our trapping design and color, none of the LEDs outcompeted the standard incandescent light. The data however provides preliminary evidence that a preference might exist for some of these mosquito species based on observed differential attraction to these light colors requiring future studies to compare reflected versus transmitted light and the incorporation of colored light of varying intensities.
Common Host-Derived Chemicals Increase Catches of Disease-Transmitting Mosquitoes and Can Improve Early Warning Systems for Rift Valley Fever Virus
David P. Tchouassi,Rosemary Sang,Catherine L. Sole,Armanda D. S. Bastos,Peter E. A. Teal,Christian Borgemeister,Baldwyn Torto
PLOS Neglected Tropical Diseases , 2013, DOI: 10.1371/journal.pntd.0002007
Abstract: Rift Valley fever (RVF), a mosquito-borne zoonosis, is a major public health and veterinary problem in sub-Saharan Africa. Surveillance to monitor mosquito populations during the inter-epidemic period (IEP) and viral activity in these vectors is critical to informing public health decisions for early warning and control of the disease. Using a combination of field bioassays, electrophysiological and chemical analyses we demonstrated that skin-derived aldehydes (heptanal, octanal, nonanal, decanal) common to RVF virus (RVFV) hosts including sheep, cow, donkey, goat and human serve as potent attractants for RVFV mosquito vectors. Furthermore, a blend formulated from the four aldehydes and combined with CO2-baited CDC trap without a light bulb doubled to tripled trap captures compared to control traps baited with CO2 alone. Our results reveal that (a) because of the commonality of the host chemical signature required for attraction, the host-vector interaction appears to favor the mosquito vector allowing it to find and opportunistically feed on a wide range of mammalian hosts of the disease, and (b) the sensitivity, specificity and superiority of this trapping system offers the potential for its wider use in surveillance programs for RVFV mosquito vectors especially during the IEP.
Development and Assessment of Plant-Based Synthetic Odor Baits for Surveillance and Control of Malaria Vectors
Vincent O. Nyasembe, David P. Tchouassi, Hillary K. Kirwa, Woodbridge A. Foster, Peter E. A. Teal, Christian Borgemeister, Baldwyn Torto
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0089818
Abstract: Background Recent malaria vector control measures have considerably reduced indoor biting mosquito populations. However, reducing the outdoor biting populations remains a challenge because of the unavailability of appropriate lures to achieve this. This study sought to test the efficacy of plant-based synthetic odor baits in trapping outdoor populations of malaria vectors. Methodology and Principal Finding Three plant-based lures ((E)-linalool oxide [LO], (E)-linalool oxide and (E)-β-ocimene [LO + OC], and a six-component blend comprising (E)-linalool oxide, (E)-β-ocimene, hexanal, β-pinene, limonene, and (E)-β-farnesene [Blend C]), were tested alongside an animal/human-based synthetic lure (comprising heptanal, octanal, nonanal, and decanal [Blend F]) and worn socks in a malaria endemic zone in the western part of Kenya. Mosquito Magnet-X (MM-X) and lightless Centre for Disease Control (CDC) light traps were used. Odor-baited traps were compared with traps baited with either solvent alone or solvent + carbon dioxide (controls) for 18 days in a series of randomized incomplete-block designs of days × sites × treatments. The interactive effect of plant and animal/human odor was also tested by combining LO with either Blend F or worn socks. Our results show that irrespective of trap type, traps baited with synthetic plant odors compared favorably to the same traps baited with synthetic animal odors and worn socks in trapping malaria vectors, relative to the controls. Combining LO and worn socks enhanced trap captures of Anopheles species while LO + Blend F recorded reduced trap capture. Carbon dioxide enhanced total trap capture of both plant- and animal/human-derived odors. However, significantly higher proportions of male and engorged female Anopheles gambiae s.l. were caught when the odor treatments did not include carbon dioxide. Conclusion and Significance The results highlight the potential of plant-based odors and specifically linalool oxide, with or without carbon dioxide, for surveillance and mass trapping of malaria vectors.
Population Genetics of Two Key Mosquito Vectors of Rift Valley Fever Virus Reveals New Insights into the Changing Disease Outbreak Patterns in Kenya
David P. Tchouassi,Armanda D. S. Bastos,Catherine L. Sole,Mawlouth Diallo,Joel Lutomiah,James Mutisya,Francis Mulwa,Christian Borgemeister,Rosemary Sang,Baldwyn Torto
PLOS Neglected Tropical Diseases , 2014, DOI: 10.1371/journal.pntd.0003364
Abstract: Rift Valley fever (RVF) outbreaks in Kenya have increased in frequency and range to include northeastern Kenya where viruses are increasingly being isolated from known (Aedes mcintoshi) and newly-associated (Ae. ochraceus) vectors. The factors contributing to these changing outbreak patterns are unclear and the population genetic structure of key vectors and/or specific virus-vector associations, in particular, are under-studied. By conducting mitochondrial and nuclear DNA analyses on >220 Kenyan specimens of Ae. mcintoshi and Ae. ochraceus, we uncovered high levels of vector complexity which may partly explain the disease outbreak pattern. Results indicate that Ae. mcintoshi consists of a species complex with one of the member species being unique to the newly-established RVF outbreak-prone northeastern region of Kenya, whereas Ae. ochraceus is a homogeneous population that appears to be undergoing expansion. Characterization of specimens from a RVF-prone site in Senegal, where Ae. ochraceus is a primary vector, revealed direct genetic links between the two Ae. ochraceus populations from both countries. Our data strongly suggest that unlike Ae. mcintoshi, Ae. ochraceus appears to be a relatively recent, single 'introduction' into Kenya. These results, together with increasing isolations from this vector, indicate that Ae. ochraceus will likely be of greater epidemiological importance in future RVF outbreaks in Kenya. Furthermore, the overall vector complexity calls into question the feasibility of mosquito population control approaches reliant on genetic modification.
Genre et commerce équitable au Cameroun
G Tchouassi
Africa Development , 2007,
Abstract: The article seeks, through an analysis of literature on gender, to illustrate how basic principles of fair trade can permit the reading of the position of women in international exchange or their access to world trade. Using the hypothesis that women are the main creators of fair trade enterprises in Cameroon, the paper employs a socio-economic approach to analyse relevant data on Cameroon. In conclusion, the paper highlights certain basic principles to be respected in order to secure gender equality in fair trade. The distribution channel permits the setting up of a ‘Fair Price’ for goods produced that take into account ethics and the real costs of production, rather than simply coming under the influence of multinationals and big distributors present in the various sectors of production.
Does Gender Equality work for Sustainable Development in Central Africa Countries? Some Empirical Lessons
Gérard Tchouassi
European Journal of Sustainable Development , 2012,
Abstract: It is commonly argued that Central Africa countries need economic growth andgender equality to ensure economic well-being and improve the living standards ofthe population. This paper, based on the Kuznets curve associated toenvironmental analysis, aims to analyze the relationship between gender equalityand sustainable development. The cross-sectional analysis, with data from 11countries in Central Africa in 2010, was used. Results find a positive correlationbetween gender equality and sustainable development. When the Multidimensionalpoverty index increases, environmental problems reduce, translating the role ofgender in sustainable development in all Central Africa countries.
Women in Informal Cross-border Trade: Empirical Evidence from Cameroon
Ousmanou Njikam,Gérard Tchouassi
International Journal of Economics and Finance , 2011, DOI: 10.5539/ijef.v3n3p202
Abstract: What are the opportunities offered through informal cross-border trade-ICBT? What are the business and institutional constraints hindering the achievement of these opportunities? What are the coping mechanisms and do they differ with gender? These issues are addressed in this paper using the survey data covering three border sites in Cameroon e.g. Cameroon-Gabon-Equatorial Guinea, Cameroon-Chad-Nigeria, and Cameroon-Nigeria. A number of clear patterns emerge from the analysis. First, we find significant differences in the male-female socio-economic characteristics. Second, opportunities related to ICBT range from the strengthening of regional integration, involvement of women in the decision-making process within households, to the fulfilment of basic needs. Third, negative aspects of ICBT include violence-both physical and psychological and poor childrearing. We finally find gender differentials not only in the constraints faced, but in the coping strategies as well.
Altruistic Preferences as Motivation for Migrants in the Diaspora to Remit to Home Communities
Gérard TCHOUASSI,Fondo SIKOD
Research in Applied Economics , 2010, DOI: 10.5296/rae.v2i1.404
Abstract: The purpose of this article is to analyse what motivates the migrants from the Central African Region who are in the diaspora, to remit part of their earnings to target development within their region of origin. This contribution is based on the hypothesis that the remittances of the migrants living abroad are organized and motivated by altruism to contribute to the improvement of the social welfare. We have used a utility function, and an altruistic preference function to show that altruism is the main driving force for diasporans to continue supporting various development projects in their countries of origin. The main result is that, altruistic diasporans are the key strategic agents that make the nexus between migration and development a reality.
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