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Search Results: 1 - 10 of 401417 matches for " Loyce M Okedi "
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The population structure of Glossina fuscipes fuscipes in the Lake Victoria basin in Uganda: implications for vector control
Hyseni Chaz,Kato Agapitus B,Okedi Loyce M,Masembe Charles
Parasites & Vectors , 2012, DOI: 10.1186/1756-3305-5-222
Abstract: Background Glossina fuscipes fuscipes is the primary vector of trypanosomiasis in humans and livestock in Uganda. The Lake Victoria basin has been targeted for tsetse eradication using a rolling carpet initiative, from west to east, with four operational blocks (3 in Uganda and 1 in Kenya), under a Pan-African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC). We screened tsetse flies from the three Ugandan PATTEC blocks for genetic diversity at 15 microsatellite loci from continental and offshore populations to provide empirical data to support this initiative. Methods We collected tsetse samples from 11 sites across the Lake Victoria basin in Uganda. We performed genetic analyses on 409 of the collected tsetse flies and added data collected for 278 individuals in a previous study. The flies were screened across 15 microsatellite loci and the resulting data were used to assess the temporal stability of populations, to analyze patterns of genetic exchange and structuring, to estimate dispersal rates and evaluate the sex bias in dispersal, as well as to estimate demographic parameters (NE and NC). Results We found that tsetse populations in this region were stable over 4-16 generations and belong to 4 genetic clusters. Two genetic clusters (1 and 2) corresponded approximately to PATTEC blocks 1 and 2, while the other two (3 and 4) fell within PATTEC block 3. Island populations grouped into the same genetic clusters as neighboring mainland sites, suggesting presence of gene flow between these sites. There was no evidence of the stretch of water separating islands from the mainland forming a significant barrier to dispersal. Dispersal rates ranged from 2.5 km per generation in cluster 1 to 14 km per generation in clusters 3 and 4. We found evidence of male-biased dispersal. Few breeders are successfully dispersing over large distances. Effective population size estimates were low (33–310 individuals), while census size estimates ranged from 1200 (cluster 1) to 4100 (clusters 3 and 4). We present here a novel technique that adapts an existing census size estimation method to sampling without replacement, the scheme used in sampling tsetse flies. Conclusion Our study suggests that different control strategies should be implemented for the three PATTEC blocks and that, given the high potential for re-invasion from island sites, mainland and offshore sites in each block should be targeted at the same time.
Pyrethroid Resistance in an Anopheles funestus Population from Uganda
John C. Morgan,Helen Irving,Loyce M. Okedi,Andrew Steven,Charles S. Wondji
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0011872
Abstract: The susceptibility status of Anopheles funestus to insecticides remains largely unknown in most parts of Africa because of the difficulty in rearing field-caught mosquitoes of this malaria vector. Here we report the susceptibility status of the An. funestus population from Tororo district in Uganda and a preliminary characterisation of the putative resistance mechanisms involved.
Temporal stability of Glossina fuscipes fuscipes populations in Uganda
Richard Echodu, Jon S Beadell, Loyce M Okedi, Chaz Hyseni, Serap Aksoy, Adalgisa Caccone
Parasites & Vectors , 2011, DOI: 10.1186/1756-3305-4-19
Abstract: Results of an AMOVA indicated that time of sampling did not explain a significant proportion of the variance in allele frequencies observed across all samples. Estimates of differentiation between samples from a single population ranged from approximately 0 to 0.019, using Jost's DEST. Effective population size estimates using momentum-based and likelihood methods were generally large. We observed significant change in mitochondrial haplotype frequencies in just one population, located along the zone of contact. The change in haplotypes was not accompanied by changes in microsatellite frequencies, raising the possibility of asymmetric mating compatibility in this zone.Our results suggest that populations of G. f. fuscipes were stable over the 8-12 generations studied. Future studies should aim to reconcile these data with observed seasonal fluctuations in the apparent density of tsetse.Tsetse flies, Glossina spp (Diptera: Glossinidae) transmit several species of pathogenic trypanosomes causing Human African Trypanosomiasis (HAT) and African Animal Trypanosomiasis (AAT). HAT affects human welfare directly through the chronic and acute forms of the disease caused by Trypanosoma brucei gambiense and T. b. rhodesiense respectively. AAT, on the other hand, stands as a major obstacle to the development of more efficient and sustainable livestock production systems in tsetse-infested areas [1]. A major challenge to controlling HAT is lack of suitable prophylactic drugs and vaccines against trypanosomiasis. Furthermore, chemotherapeutic agents for treatment of HAT are expensive, difficult to administer in remote areas and exhibit poor safety profiles. Consequently, vector control remains a viable alternative for large-scale control of trypanosomiasis.Understanding tsetse population dynamics is critical for determining which control strategy is most appropriate (e.g., suppression, eradication), for choosing the best method for enacting that strategy (e.g., traps, insecticide
Genetic diversity and population structure of Glossina pallidipes in Uganda and western Kenya
Johnson O Ouma, Jon S Beadell, Chaz Hyseni, Loyce M Okedi, Elliot S Krafsur, Serap Aksoy, Adalgisa Caccone
Parasites & Vectors , 2011, DOI: 10.1186/1756-3305-4-122
Abstract: AMOVA indicated that differences among sampling sites explained a significant proportion of the genetic variation. Principal component analysis and Bayesian assignment of microsatellite genotypes identified three distinct clusters: western Uganda, southeastern Uganda/Lambwe Valley, and Nguruman in central-southern Kenya. Analyses of mtDNA confirmed the results of microsatellite analysis, except in western Uganda, where Kabunkanga and Murchison Falls populations exhibited haplotypes that differed despite homogeneous microsatellite signatures. To better understand possible causes of the contrast between mitochondrial and nuclear markers we tested for sex-biased dispersal. Mean pairwise relatedness was significantly higher in females than in males within populations, while mean genetic distance was lower and relatedness higher in males than females in between-population comparisons. Two populations sampled on the Kenya/Uganda border, exhibited the lowest levels of genetic diversity. Microsatellite alleles and mtDNA haplotypes in these two populations were a subset of those found in neighboring Lambwe Valley, suggesting that Lambwe was the source population for flies in southeastern Uganda. The relatively high genetic diversity of G. pallidipes in Lambwe Valley suggest large relict populations remained even after repeated control efforts.Our research demonstrated that G. pallidipes populations in Kenya and Uganda do not form a contiguous tsetse belt. While Lambwe Valley appears to be a source population for flies colonizing southeastern Uganda, this dispersal does not extend to western Uganda. The complicated phylogeography of G. pallidipes warrants further efforts to distinguish the role of historical and modern gene flow and possible sex-biased dispersal in structuring populations.Glossina pallidipes is a major vector of animal African trypanosomiasis. The vector has also been implicated in the transmission of Human African Trypanosomiasis (HAT). For example, the expa
Phylogeography and Population Structure of Glossina fuscipes fuscipes in Uganda: Implications for Control of Tsetse
Jon S. Beadell ,Chaz Hyseni,Patrick P. Abila,Rogers Azabo,John C. K. Enyaru,Johnson O. Ouma,Yassir O. Mohammed,Loyce M. Okedi,Serap Aksoy,Adalgisa Caccone
PLOS Neglected Tropical Diseases , 2010, DOI: 10.1371/journal.pntd.0000636
Abstract: Background Glossina fuscipes fuscipes, a riverine species of tsetse, is the main vector of both human and animal trypanosomiasis in Uganda. Successful implementation of vector control will require establishing an appropriate geographical scale for these activities. Population genetics can help to resolve this issue by characterizing the extent of linkage among apparently isolated groups of tsetse. Methodology/Principal Findings We conducted genetic analyses on mitochondrial and microsatellite data accumulated from approximately 1000 individual tsetse captured in Uganda and neighboring regions of Kenya and Sudan. Phylogeographic analyses suggested that the largest scale genetic structure in G. f. fuscipes arose from an historical event that divided two divergent mitochondrial lineages. These lineages are currently partitioned to northern and southern Uganda and co-occur only in a narrow zone of contact extending across central Uganda. Bayesian assignment tests, which provided evidence for admixture between northern and southern flies at the zone of contact and evidence for northerly gene flow across the zone of contact, indicated that this structure may be impermanent. On the other hand, microsatellite structure within the southern lineage indicated that gene flow is currently limited between populations in western and southeastern Uganda. Within regions, the average FST between populations separated by less than 100 km was less than ~0.1. Significant tests of isolation by distance suggested that gene flow is ongoing between neighboring populations and that island populations are not uniformly more isolated than mainland populations. Conclusions/Significance Despite the presence of population structure arising from historical colonization events, our results have revealed strong signals of current gene flow within regions that should be accounted for when planning tsetse control in Uganda. Populations in southeastern Uganda appeared to receive little gene flow from populations in western or northern Uganda, supporting the feasibility of area wide control in the Lake Victoria region by the Pan African Tsetse and Trypanosomiasis Eradication Campaign.
Immunogenicity and Serological Cross-Reactivity of Saliva Proteins among Different Tsetse Species
Xin Zhao?,Thiago Luiz Alves e Silva?,Laura Cronin?,Amy F. Savage?,Michelle O’Neill?,Barbara Nerima?,Loyce M. Okedi,Serap Aksoy
PLOS Neglected Tropical Diseases , 2015, DOI: 10.1371/journal.pntd.0004038
Abstract: Tsetse are vectors of pathogenic trypanosomes, agents of human and animal trypanosomiasis in Africa. Components of tsetse saliva (sialome) are introduced into the mammalian host bite site during the blood feeding process and are important for tsetse’s ability to feed efficiently, but can also influence disease transmission and serve as biomarkers for host exposure. We compared the sialome components from four tsetse species in two subgenera: subgenus Morsitans: Glossina morsitans morsitans (Gmm) and Glossina pallidipes (Gpd), and subgenus Palpalis: Glossina palpalis gambiensis (Gpg) and Glossina fuscipes fuscipes (Gff), and evaluated their immunogenicity and serological cross reactivity by an immunoblot approach utilizing antibodies from experimental mice challenged with uninfected flies. The protein and immune profiles of sialome components varied with fly species in the same subgenus displaying greater similarity and cross reactivity. Sera obtained from cattle from disease endemic areas of Africa displayed an immunogenicity profile reflective of tsetse species distribution. We analyzed the sialome fractions of Gmm by LC-MS/MS, and identified TAg5, Tsal1/Tsal2, and Sgp3 as major immunogenic proteins, and the 5'-nucleotidase family as well as four members of the Adenosine Deaminase Growth Factor (ADGF) family as the major non-immunogenic proteins. Within the ADGF family, we identified four closely related proteins (TSGF-1, TSGF-2, ADGF-3 and ADGF-4), all of which are expressed in tsetse salivary glands. We describe the tsetse species-specific expression profiles and genomic localization of these proteins. Using a passive-immunity approach, we evaluated the effects of rec-TSGF (TSGF-1 and TSGF-2) polyclonal antibodies on tsetse fitness parameters. Limited exposure of tsetse to mice with circulating anti-TSGF antibodies resulted in a slight detriment to their blood feeding ability as reflected by compromised digestion, lower weight gain and less total lipid reserves although these results were not statistically significant. Long-term exposure studies of tsetse flies to antibodies corresponding to the ADGF family of proteins are warranted to evaluate the role of this conserved family in fly biology.
Polyandry Is a Common Event in Wild Populations of the Tsetse Fly Glossina fuscipes fuscipes and May Impact Population Reduction Measures
Angelica Bonomi,Federico Bassetti,Paolo Gabrieli,Jon Beadell,Marco Falchetto,Francesca Scolari,Ludvik M. Gomulski,Eugenio Regazzini,Johnson O. Ouma,Adalgisa Caccone,Loyce M. Okedi,Geoffrey M. Attardo,Carmela R. Guglielmino,Serap Aksoy,Anna R. Malacrida
PLOS Neglected Tropical Diseases , 2011, DOI: 10.1371/journal.pntd.0001190
Abstract: Background Glossina fuscipes fuscipes is the main vector of human and animal trypanosomiasis in Africa, particularly in Uganda. Attempts to control/eradicate this species using biological methods require knowledge of its reproductive biology. An important aspect is the number of times a female mates in the wild as this influences the effective population size and may constitute a critical factor in determining the success of control methods. To date, polyandry in G.f. fuscipes has not been investigated in the laboratory or in the wild. Interest in assessing the presence of remating in Ugandan populations is driven by the fact that eradication of this species is at the planning stage in this country. Methodology/Principal Findings Two well established populations, Kabukanga in the West and Buvuma Island in Lake Victoria, were sampled to assess the presence and frequency of female remating. Six informative microsatellite loci were used to estimate the number of matings per female by genotyping sperm preserved in the female spermathecae. The direct count of the minimum number of males that transferred sperm to the spermathecae was compared to Maximum Likelihood and Bayesian probability estimates. The three estimates provided evidence that remating is common in the populations but the frequency is substantially different: 57% in Kabukanga and 33% in Buvuma. Conclusions/Significance The presence of remating, with females maintaining sperm from different mates, may constitute a critical factor in cases of re-infestation of cleared areas and/or of residual populations. Remating may enhance the reproductive potential of re-invading propagules in terms of their effective population size. We suggest that population age structure may influence remating frequency. Considering the seasonal demographic changes that this fly undergoes during the dry and wet seasons, control programmes based on SIT should release large numbers of sterile males, even in residual surviving target populations, in the dry season.
Cryptic Diversity within the Major Trypanosomiasis Vector Glossina fuscipes Revealed by Molecular Markers
Naomi A. Dyer equal contributor,Sophie Ravel equal contributor,Kwang-Shik Choi,Alistair C. Darby,Sandrine Causse,Berisha Kapitano,Martin J. R. Hall,Keith Steen,Pascal Lutumba,Joules Madinga,Steve J. Torr,Loyce M. Okedi,Michael J. Lehane,Martin J. Donnelly
PLOS Neglected Tropical Diseases , 2011, DOI: 10.1371/journal.pntd.0001266
Abstract: Background The tsetse fly Glossina fuscipes s.l. is responsible for the transmission of approximately 90% of cases of human African trypanosomiasis (HAT) or sleeping sickness. Three G. fuscipes subspecies have been described, primarily based upon subtle differences in the morphology of their genitalia. Here we describe a study conducted across the range of this important vector to determine whether molecular evidence generated from nuclear DNA (microsatellites and gene sequence information), mitochondrial DNA and symbiont DNA support the existence of these taxa as discrete taxonomic units. Principal Findings The nuclear ribosomal Internal transcribed spacer 1 (ITS1) provided support for the three subspecies. However nuclear and mitochondrial sequence data did not support the monophyly of the morphological subspecies G. f. fuscipes or G. f. quanzensis. Instead, the most strongly supported monophyletic group was comprised of flies sampled from Ethiopia. Maternally inherited loci (mtDNA and symbiont) also suggested monophyly of a group from Lake Victoria basin and Tanzania, but this group was not supported by nuclear loci, suggesting different histories of these markers. Microsatellite data confirmed strong structuring across the range of G. fuscipes s.l., and was useful for deriving the interrelationship of closely related populations. Conclusion/Significance We propose that the morphological classification alone is not used to classify populations of G. fuscipes for control purposes. The Ethiopian population, which is scheduled to be the target of a sterile insect release (SIT) programme, was notably discrete. From a programmatic perspective this may be both positive, given that it may reflect limited migration into the area or negative if the high levels of differentiation are also reflected in reproductive isolation between this population and the flies to be used in the release programme.
The Pattern Method for Incorporating Tidal Uncertainty Into Probabilistic Tsunami Hazard Assessment (PTHA)
Loyce M. Adams,Randall J. LeVeque,Frank I. González
Physics , 2014,
Abstract: In this paper we describe a general framework for incorporating tidal uncertainty into probabilistic tsunami hazard assessment and propose the Pattern Method and a simpler special case called the $\Delta t$ Method as effective approaches. The general framework also covers the method developed by Mofjeld et.al in 2007 that was used for the 2009 Seaside, Oregon probabilistic study by Gonzalez et.al. We show the Pattern Method is superior to past approaches because it takes advantage of our ability to run the tsunami simulation at multiple tide stages and uses the time history of flow depth at strategic gauge locations to infer the temporal pattern of waves that is unique to each tsunami source. Combining these patterns with knowledge of the tide cycle at a particular location improves the ability to estimate the probability that a wave will arrive at a time when the tidal stage is sufficiently large that a quantity of interest such as the maximum flow depth exceeds a specified level.
Epidemiological Overview of African Swine Fever in Uganda (2001–2012)
David Kalenzi Atuhaire,Sylvester Ochwo,Mathias Afayoa,Frank Norbert Mwiine,Ikwap Kokas,Eugene Arinaitwe,Rose Anna Ademun-Okurut,Julius Boniface Okuni,Ann Nanteza,Christosom Ayebazibwe,Loyce Okedi,William Olaho-Mukani,Lonzy Ojok
Journal of Veterinary Medicine , 2013, DOI: 10.1155/2013/949638
Abstract: African swine fever (ASF) is a contagious viral disease, which can cause up to 100% mortality among domestic pigs. In Uganda there is paucity of information on the epidemiology of the disease, hence a study was carried out to elucidate the patterns of ASF outbreaks. Spatial and temporal analyses were performed with data collected monthly by the district veterinary officers (DVOs) and sent to the central administration at MAAIF from 2001 to 2012. Additionally, risk factors and the associated characteristics related to the disease were assessed based on semistructured questionnaires sent to the DVOs. A total of 388 ASF outbreaks were reported in 59 districts. Of these outbreaks, 201 (51.8%) were reported in districts adjacent to the national parks while 80 (20.6%) were adjacent to international borders. The number of reported ASF outbreaks changed over time and by geographical regions; however, no outbreak was reported in the North-Eastern region. ASF was ranked as second most important disease of pigs, and it occurred mostly during the dry season ( ). Pig movements due to trade (OR 15.5, CI 4.9–49.1) and restocking (OR 6.6, CI 2.5–17.3) were the major risk factors. ASF control strategies should focus on limiting pig movements in Uganda. 1. Introduction African swine fever (ASF) is a highly fatal disease of domestic pigs and can cause mortality of up to 100% of affected pigs [1]. The disease is caused by double-stranded DNA virus with an icosahedral symmetry that belongs to genus Asfivirus and family Asfarviridae [2]. Since its first description in Kenya in the early 1920s [3], the disease has been reported in several countries around the world, remaining endemic in Sardinia, and in 2007 outbreaks was reported in Georgia, Russia, and neighbouring countries [4]. The epidemiology of ASF is complex, transmission is direct and vector-borne, and the disease has well-recognized sylvatic and domestic cycles. In sub-Saharan Africa, ASFV is maintained by long-term, inapparent infection of wildlife hosts such as bush pigs (Potamochoerus porcus) and warthogs (Phacochoerus africanus) which are infected via tick bites of the argasid tick vector (Ornithodoros complex) [5]. ASF is highly contagious and is transmitted by direct contact between infected pigs and susceptible ones or by contact with or ingestion of infectious secretions/excretions. The virus is highly resistant in tissues and the environment, contributing to its transmission over long distances through swill feeding and fomites (e.g., contaminated material, vehicles, or visitors to pig premises) [6]. In
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