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Papers by Kip Bett
tropentag.de
Highly Pathogenic Avian Influenza (HPAI) is a major threat to the poultry industry worldwide. In ... more Highly Pathogenic Avian Influenza (HPAI) is a major threat to the poultry industry worldwide. In developing countries backyard poultry production is often an important livelihood activity for women who use the additional income for unexpected household expenses. The disease ...
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The Onderstepoort journal of veterinary research, 2002
Point prevalences and animal-level risk factors for Trypanosoma evansi infection were investigate... more Point prevalences and animal-level risk factors for Trypanosoma evansi infection were investigated in a cross-sectional study that involved 2227 camels from eastern and central parts of Kenya. The screening tests used were haematocrit centrifugation technique (HCT), mouse inoculation and latex agglutination (Suratex). All camels were screened with HCT, while 396 and 961 of them were, in addition, screened with mouse inoculation and Suratex tests, respectively. Parasitological and Suratex test results were used in parallel to determine the number of camels exposed to T. evansi infections. Statistical analyses were conducted using Statistical Analysis Systems. Parasitological and Suratex test results in parallel were dependent variables in multivariable logistic regression models that determined risk factors for T. evansi infection. Herd-level clustering was corrected with general estimation equations. The prevalences were 2.3% and 19.6%, using parasitological and Suratex tests, respe...
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Revue scientifique et technique (International Office of Epizootics)
The authors characterised sources of early warning messages about occurrences of Rift Valley feve... more The authors characterised sources of early warning messages about occurrences of Rift Valley fever (RVF) and examined the response measures that were used by the Department of Veterinary Services (DVS) to manage the 2006-2007 RVF outbreaks in Kenya. The study was conducted between November 2009 and March 2010 and it included national, provincial and district veterinary officers who were involved in the management of the outbreak. Structured questionnaires were used to collect the data. Although the majority of the respondents reported having limited capacity to implement response measures, they perceived that the measures implemented were effective. Vaccination, movement control and market closures were the main response measures implemented, particularly in districts that had cases in both livestock and humans. Vaccination, however, was implemented too late and the coverage achieved was too low to be effective. The authors suggest ways to improve the capacity of the DVS to respond ...
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Climate change has been stated as being one of the greatest challenges to global health in the cu... more Climate change has been stated as being one of the greatest challenges to global health in the current century. Climate change impacts on human health and the socio-economic and related poverty consequences are however still poorly understood. While epidemiological issues are strongly coupled with environmental and climatic parameters, the social and economic circumstances of populations might be of equal or even greater importance when trying to identify vulnerable populations and design appropriate and well-targeted adaptation measures. The inter-linkage between climate change, human health risk and socio-economic impacts remains an important - but largely outstanding - research field. We present an overview on how risk is traditionally being conceptualised in the human health domain and reflect critically on integrated approaches as being currently used in the climate change context. The presentation will also review existing approaches, and how they can be integrated towards ada...
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The risk of spread of HPAI in Nigeria was derived by using a compartmental model to outline endem... more The risk of spread of HPAI in Nigeria was derived by using a compartmental model to outline endemic and burn-out scenarios. Two paths, low and high mortality risks, were associated to each of the scenarios. The estimated risk parameters were then used to stochastically simulate the trajectory of the disease; without intervention and with an intervention. The intervention costs the country US$ 41 million obtained through a World Bank IDA loan of US$ 50million yearly disbursed over the 2006-2010 period. The key output variables (net social welfare gain – with incremental net benefits as proxy, disease cost, and benefit cost ratio) were estimated for each randomly drawn risk parameter. On average, the results show that such an intervention would make economic sense under the endemic scenario with high mortality. The discounted costs (12% discount rate) of the disease without intervention would have amounted to US$ 145 million in total over the 2006-2010 period. The model indicates that...
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Rift Valley fever virus (RVFv) is a mosquito-borne pathogen of livestock, wildlife and humans tha... more Rift Valley fever virus (RVFv) is a mosquito-borne pathogen of livestock, wildlife and humans that causes severe outbreaks in intervals of several years. One of the open questions is how the virus persists between outbreaks. We developed a spatially-explicit, individual-based simulation model of the RVFv transmission dynamics to investigate this question. The model, is based on livestock and mosquito population dynamics. Spatial aspects are explicitly represented by a set of grid cells that represent mosquito breeding sites. A grid cell measures 500 by 500m and the model considers a grid of 100 by 100 grid cells; the model thus operates on the regional scale of 2500km2. Livestock herds move between grid cells, and provide connectivity between the cells. The model is used to explore the spatio-temporal dynamics of RVFv persistence in absence of a wildlife reservoir in an east African semi-arid context. Specifically, the model assesses the importance of local virus persistence in mosq...
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Historical data on Rift Valley Fever (RVF) outbreaks in Kenya covering the period 1951 - 2010 wer... more Historical data on Rift Valley Fever (RVF) outbreaks in Kenya covering the period 1951 - 2010 were analyzed using a logistic regression model to identify factors associated with RVF occurrence. The analysis used a division, an administrative unit below a district, as the unit of analysis. The infection status of each division was defined on a monthly time scale and used as a dependent variable. Predictors investigated include: monthly precipitation (minimum, maximum and total), normalized difference vegetation index, altitude, agro-ecological zone, presence of game, livestock and human population densities, the number of times a division has had an outbreak before and time interval in months between successive outbreaks (used as a proxy for immunity). Both univariable and multivariable analyses were conducted. The models used incorporated an auto-regressive correlation matrix to account for clustering of observations in time, while dummy variables were fitted in the multivariable mo...
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This is a case study on using PE to characterize Type A H5N1 highly pathogenic avian influenza (H... more This is a case study on using PE to characterize Type A H5N1 highly pathogenic avian influenza (HPAI) outbreaks, and using similar methods to understand diseases in other settings. In Indonesia, a list of all outbreaks of HPAI that were diagnosed in the past year was derived. 1-3 outbreaks per district were randomly selected for investigation. An infection tree reconstruction approach was used to trace chickens and households in outbreak neighborhoods. Investigations started with a checklist guided focus group interview. Mapping was used to document all households, poultry kept in each, and households and species affected by the outbreak. Spread through the neighborhood was recorded. The index, 2nd affected and closest unaffected households were geo-referenced. Risk factors were discussed. Individual interviews were held with up to five heads of affected households. Timelines were used to determine morbidity, mortality, slaughter and sales rates. Transect walks were used to triangul...
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Epidemiology and Infection, 2014
SUMMARYA large-scale mass vaccination campaign was carried out in Java, Indonesia in an attempt t... more SUMMARYA large-scale mass vaccination campaign was carried out in Java, Indonesia in an attempt to control outbreaks of highly pathogenic avian influenza (HPAI) in backyard flocks and commercial smallholder poultry. Sero-monitoring was conducted in mass vaccination and control areas to assess the proportion of the target population with antibodies against HPAI and Newcastle disease (ND). There were four rounds of vaccination, and samples were collected after each round resulting in a total of 27 293 samples. Sampling was performed irrespective of vaccination status. In the mass vaccination areas, 20–45% of poultry sampled had a positive titre to H5 after each round of vaccination, compared to 2–3% in the control group. In the HPAI + ND vaccination group, 12–25% of the population had positive ND titres, compared to 5–13% in the areas without ND vaccination. The level of seropositivity varied by district, age of the bird, and species (ducksvs.chickens).
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Transboundary and Emerging Diseases, 2014
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Transboundary and Emerging Diseases, 2013
The spread of H5N1 avian influenza continues to pose an economic burden and a public health risk ... more The spread of H5N1 avian influenza continues to pose an economic burden and a public health risk worldwide. Despite this, estimates of the transmissibility of infection exist in only a handful of settings and vary considerably. Using final size methods and flock-level infection data from a field trial of mass vaccination, we obtained the first estimates of the transmissibility of infection between and within flocks in Indonesia. We also found that outbreaks in areas designated as vaccination zones were less transmissible than in non-vaccination zones. However, this reduction is only comparable with a limited degree of protective vaccination coverage. Quantifying the overall effect of vaccination in these zones remains challenging. However, this result would appear to imply that, although the interventions applied in vaccination zones were not sufficient to completely prevent transmission in all areas, when outbreaks occur, they are less transmissible than those in areas where vaccination was not applied. This could be either a direct or an indirect effect of vaccination. Given the dynamism of small-scale poultry production in Indonesia, more regular vaccination may be required to ensure that infection is fully controlled in vaccination zones.
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Transboundary and Emerging Diseases, 2013
We conducted an operational research study involving backyard and semicommercial farms on Java Is... more We conducted an operational research study involving backyard and semicommercial farms on Java Island, Indonesia, between April 2008 and September 2009 to evaluate the effectiveness of two preventive mass vaccination strategies against highly pathogenic avian influenza (HPAI). One regimen used Legok 2003 H5N1 vaccine, while the other used both Legok 2003 H5N1 and HB1 Newcastle disease (ND) vaccine. A total of 16 districts were involved in the study. The sample size was estimated using a formal power calculation technique that assumed a detectable effect of treatment as a 50% reduction in the baseline number of HPAI-compatible outbreaks. Within each district, candidate treatment blocks with village poultry populations ranging from 80 000 to 120 000 were created along subdistrict boundary lines. Subsequently, four of these blocks were randomly selected and assigned one treatment from a list that comprised control, vaccination against HPAI, vaccination against HPAI + ND. Four rounds of vaccination were administered at quarterly intervals beginning in July 2008. A vaccination campaign involved vaccinating 100 000 birds in a treatment block, followed by another 100 000 vaccinations 3 weeks later as a booster dose. Data on disease incidence and vaccination coverage were also collected at quarterly intervals using participatory epidemiological techniques. Compared with the unvaccinated (control) group, the incidence of HPAI-compatible events declined by 32% (P = 0.24) in the HPAI-vaccinated group and by 73% (P = 0.00) in the HPAI- and ND-vaccinated group. The effect of treatment did not vary with time or district. Similarly, an analysis of secondary data from the participatory disease and response (PDSR) database revealed that the incidence of HPAI declined by 12% in the HPAI-vaccinated group and by 24% in the HPAI + ND-vaccinated group. The results suggest that the HPAI + ND vaccination significantly reduced the incidence of HPAI-compatible events in mixed populations of semicommercial and backyard poultry.
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Preventive Veterinary Medicine, 2010
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Preventive Veterinary Medicine, 2013
The primary objective of this study was to assess the impact of Rhipicephalus appendiculatus tick... more The primary objective of this study was to assess the impact of Rhipicephalus appendiculatus tick presence (exposure variable) on Theileria parva infection seroprevalence (outcome variable) in a group of cattle belonging to a farm using population attributable fractions (PAF). The analyses were based on a representative sample of 80 traditional smallholder mixed farms. The farms were selected by first stratifying the population administratively and implementing a multistage random sampling in Mbeere district in Kenya. The PAFs were estimated using the stratified, Bruzzi, and sequential partitioned PAF approaches. A secondary objective was, thus, to evaluate the impact of the approaches on the PAF estimates. The stratified and Bruzzi approaches estimated proportion of T. parva infection cases directly attributable to the exposure after controlling for confounding by agro-ecological zone (AEZ). The sequential partitioned PAF approach estimated a PAF associated with exposure after adjusting for any effect that the AEZ may have had by influencing the prevalence of the exposure. All analyses were carried out at the farm level where a farm was classified as infested if the tick was found on cattle on a farm, and infected if at least one animal on a farm was positive for T. parva antibodies. Variance estimation for PAFs was implemented using 'delete-a-group' jackknife re-sampling method. The stratified PAF (26.7% [95% CI: 9.0%, 44.4%]) and Bruzzi PAF (26.4% [95% CI: 9.6%, 43.2%]) were consistent in estimating a relatively low impact of farm vector tick presence with a relatively high level of uncertainty. The partitioned PAF (15.5% [95% CI: 1.5%, 29.6%]) suggested that part of the impacts estimated using the stratified PAF and Bruzzi approaches was driven by AEZ effects. Overall, the results suggested that under endemic instability in Mbeere district, (1) presence of R. appendiculatus was not a good indicator of T. parva infection occurrence on a farm; (2) ecological variation could play a role in determining infection impacts. This study provides a preliminary basis for evaluating the potential value and utility of estimating PAFs for variables amenable to control in tick-borne diseases (TBDs) epidemiological studies.
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Transboundary and emerging diseases, 2012
Outbreaks of highly pathogenic avian influenza (HPAI) H5N1 occurred in Nigeria between December 2... more Outbreaks of highly pathogenic avian influenza (HPAI) H5N1 occurred in Nigeria between December 2005 and July 2008. We describe temporal and spatial characteristics of these outbreaks at State and Local Government Area (LGA) levels. A total of 25 of 37 States (67.6%; Exact 95% CI: 50.2-82.0%) and 81 of 774 LGAs (10.5%; Exact 95% CI: 8.4-12.8%) were affected by HPAI outbreaks over the period from 2005 to 2008. The incidence risk of HPAI outbreak occurrence at the State level was 5.6% (0.7-18.7%) for 2005, 50.0% (30.7-69.4%) for 2006, 54.5% (29.9-80.3%) for 2007 and 0% for 2008. Only very few LGAs experienced HPAI outbreaks within the affected States. The incidence risk of HPAI outbreak occurrence on a LGA level was 0.3% (0.0-0.9%) for 2005, 6.6% (4.9-8.6%) for 2006, 4.2% (2.9-6.0%) for 2007 and 0% for 2008. The mean period between farmers noticing HPAI outbreaks and reporting them to veterinary authorities, and between reporting HPAI outbreaks and the depopulation of infected premise...
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Preventive veterinary …, 2004
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Veterinary parasitology, 2004
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Veterinary parasitology, 2003
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Encouraging learners to avoid exams irregularities
tropentag.de
Highly Pathogenic Avian Influenza (HPAI) is a major threat to the poultry industry worldwide. In ... more Highly Pathogenic Avian Influenza (HPAI) is a major threat to the poultry industry worldwide. In developing countries backyard poultry production is often an important livelihood activity for women who use the additional income for unexpected household expenses. The disease ...
Bookmarks Related papers MentionsView impact
The Onderstepoort journal of veterinary research, 2002
Point prevalences and animal-level risk factors for Trypanosoma evansi infection were investigate... more Point prevalences and animal-level risk factors for Trypanosoma evansi infection were investigated in a cross-sectional study that involved 2227 camels from eastern and central parts of Kenya. The screening tests used were haematocrit centrifugation technique (HCT), mouse inoculation and latex agglutination (Suratex). All camels were screened with HCT, while 396 and 961 of them were, in addition, screened with mouse inoculation and Suratex tests, respectively. Parasitological and Suratex test results were used in parallel to determine the number of camels exposed to T. evansi infections. Statistical analyses were conducted using Statistical Analysis Systems. Parasitological and Suratex test results in parallel were dependent variables in multivariable logistic regression models that determined risk factors for T. evansi infection. Herd-level clustering was corrected with general estimation equations. The prevalences were 2.3% and 19.6%, using parasitological and Suratex tests, respe...
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Revue scientifique et technique (International Office of Epizootics)
The authors characterised sources of early warning messages about occurrences of Rift Valley feve... more The authors characterised sources of early warning messages about occurrences of Rift Valley fever (RVF) and examined the response measures that were used by the Department of Veterinary Services (DVS) to manage the 2006-2007 RVF outbreaks in Kenya. The study was conducted between November 2009 and March 2010 and it included national, provincial and district veterinary officers who were involved in the management of the outbreak. Structured questionnaires were used to collect the data. Although the majority of the respondents reported having limited capacity to implement response measures, they perceived that the measures implemented were effective. Vaccination, movement control and market closures were the main response measures implemented, particularly in districts that had cases in both livestock and humans. Vaccination, however, was implemented too late and the coverage achieved was too low to be effective. The authors suggest ways to improve the capacity of the DVS to respond ...
Bookmarks Related papers MentionsView impact
Climate change has been stated as being one of the greatest challenges to global health in the cu... more Climate change has been stated as being one of the greatest challenges to global health in the current century. Climate change impacts on human health and the socio-economic and related poverty consequences are however still poorly understood. While epidemiological issues are strongly coupled with environmental and climatic parameters, the social and economic circumstances of populations might be of equal or even greater importance when trying to identify vulnerable populations and design appropriate and well-targeted adaptation measures. The inter-linkage between climate change, human health risk and socio-economic impacts remains an important - but largely outstanding - research field. We present an overview on how risk is traditionally being conceptualised in the human health domain and reflect critically on integrated approaches as being currently used in the climate change context. The presentation will also review existing approaches, and how they can be integrated towards ada...
Bookmarks Related papers MentionsView impact
The risk of spread of HPAI in Nigeria was derived by using a compartmental model to outline endem... more The risk of spread of HPAI in Nigeria was derived by using a compartmental model to outline endemic and burn-out scenarios. Two paths, low and high mortality risks, were associated to each of the scenarios. The estimated risk parameters were then used to stochastically simulate the trajectory of the disease; without intervention and with an intervention. The intervention costs the country US$ 41 million obtained through a World Bank IDA loan of US$ 50million yearly disbursed over the 2006-2010 period. The key output variables (net social welfare gain – with incremental net benefits as proxy, disease cost, and benefit cost ratio) were estimated for each randomly drawn risk parameter. On average, the results show that such an intervention would make economic sense under the endemic scenario with high mortality. The discounted costs (12% discount rate) of the disease without intervention would have amounted to US$ 145 million in total over the 2006-2010 period. The model indicates that...
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Rift Valley fever virus (RVFv) is a mosquito-borne pathogen of livestock, wildlife and humans tha... more Rift Valley fever virus (RVFv) is a mosquito-borne pathogen of livestock, wildlife and humans that causes severe outbreaks in intervals of several years. One of the open questions is how the virus persists between outbreaks. We developed a spatially-explicit, individual-based simulation model of the RVFv transmission dynamics to investigate this question. The model, is based on livestock and mosquito population dynamics. Spatial aspects are explicitly represented by a set of grid cells that represent mosquito breeding sites. A grid cell measures 500 by 500m and the model considers a grid of 100 by 100 grid cells; the model thus operates on the regional scale of 2500km2. Livestock herds move between grid cells, and provide connectivity between the cells. The model is used to explore the spatio-temporal dynamics of RVFv persistence in absence of a wildlife reservoir in an east African semi-arid context. Specifically, the model assesses the importance of local virus persistence in mosq...
Bookmarks Related papers MentionsView impact
Historical data on Rift Valley Fever (RVF) outbreaks in Kenya covering the period 1951 - 2010 wer... more Historical data on Rift Valley Fever (RVF) outbreaks in Kenya covering the period 1951 - 2010 were analyzed using a logistic regression model to identify factors associated with RVF occurrence. The analysis used a division, an administrative unit below a district, as the unit of analysis. The infection status of each division was defined on a monthly time scale and used as a dependent variable. Predictors investigated include: monthly precipitation (minimum, maximum and total), normalized difference vegetation index, altitude, agro-ecological zone, presence of game, livestock and human population densities, the number of times a division has had an outbreak before and time interval in months between successive outbreaks (used as a proxy for immunity). Both univariable and multivariable analyses were conducted. The models used incorporated an auto-regressive correlation matrix to account for clustering of observations in time, while dummy variables were fitted in the multivariable mo...
Bookmarks Related papers MentionsView impact
This is a case study on using PE to characterize Type A H5N1 highly pathogenic avian influenza (H... more This is a case study on using PE to characterize Type A H5N1 highly pathogenic avian influenza (HPAI) outbreaks, and using similar methods to understand diseases in other settings. In Indonesia, a list of all outbreaks of HPAI that were diagnosed in the past year was derived. 1-3 outbreaks per district were randomly selected for investigation. An infection tree reconstruction approach was used to trace chickens and households in outbreak neighborhoods. Investigations started with a checklist guided focus group interview. Mapping was used to document all households, poultry kept in each, and households and species affected by the outbreak. Spread through the neighborhood was recorded. The index, 2nd affected and closest unaffected households were geo-referenced. Risk factors were discussed. Individual interviews were held with up to five heads of affected households. Timelines were used to determine morbidity, mortality, slaughter and sales rates. Transect walks were used to triangul...
Bookmarks Related papers MentionsView impact
Epidemiology and Infection, 2014
SUMMARYA large-scale mass vaccination campaign was carried out in Java, Indonesia in an attempt t... more SUMMARYA large-scale mass vaccination campaign was carried out in Java, Indonesia in an attempt to control outbreaks of highly pathogenic avian influenza (HPAI) in backyard flocks and commercial smallholder poultry. Sero-monitoring was conducted in mass vaccination and control areas to assess the proportion of the target population with antibodies against HPAI and Newcastle disease (ND). There were four rounds of vaccination, and samples were collected after each round resulting in a total of 27 293 samples. Sampling was performed irrespective of vaccination status. In the mass vaccination areas, 20–45% of poultry sampled had a positive titre to H5 after each round of vaccination, compared to 2–3% in the control group. In the HPAI + ND vaccination group, 12–25% of the population had positive ND titres, compared to 5–13% in the areas without ND vaccination. The level of seropositivity varied by district, age of the bird, and species (ducksvs.chickens).
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Transboundary and Emerging Diseases, 2014
Bookmarks Related papers MentionsView impact
Transboundary and Emerging Diseases, 2013
The spread of H5N1 avian influenza continues to pose an economic burden and a public health risk ... more The spread of H5N1 avian influenza continues to pose an economic burden and a public health risk worldwide. Despite this, estimates of the transmissibility of infection exist in only a handful of settings and vary considerably. Using final size methods and flock-level infection data from a field trial of mass vaccination, we obtained the first estimates of the transmissibility of infection between and within flocks in Indonesia. We also found that outbreaks in areas designated as vaccination zones were less transmissible than in non-vaccination zones. However, this reduction is only comparable with a limited degree of protective vaccination coverage. Quantifying the overall effect of vaccination in these zones remains challenging. However, this result would appear to imply that, although the interventions applied in vaccination zones were not sufficient to completely prevent transmission in all areas, when outbreaks occur, they are less transmissible than those in areas where vaccination was not applied. This could be either a direct or an indirect effect of vaccination. Given the dynamism of small-scale poultry production in Indonesia, more regular vaccination may be required to ensure that infection is fully controlled in vaccination zones.
Bookmarks Related papers MentionsView impact
Transboundary and Emerging Diseases, 2013
We conducted an operational research study involving backyard and semicommercial farms on Java Is... more We conducted an operational research study involving backyard and semicommercial farms on Java Island, Indonesia, between April 2008 and September 2009 to evaluate the effectiveness of two preventive mass vaccination strategies against highly pathogenic avian influenza (HPAI). One regimen used Legok 2003 H5N1 vaccine, while the other used both Legok 2003 H5N1 and HB1 Newcastle disease (ND) vaccine. A total of 16 districts were involved in the study. The sample size was estimated using a formal power calculation technique that assumed a detectable effect of treatment as a 50% reduction in the baseline number of HPAI-compatible outbreaks. Within each district, candidate treatment blocks with village poultry populations ranging from 80 000 to 120 000 were created along subdistrict boundary lines. Subsequently, four of these blocks were randomly selected and assigned one treatment from a list that comprised control, vaccination against HPAI, vaccination against HPAI + ND. Four rounds of vaccination were administered at quarterly intervals beginning in July 2008. A vaccination campaign involved vaccinating 100 000 birds in a treatment block, followed by another 100 000 vaccinations 3 weeks later as a booster dose. Data on disease incidence and vaccination coverage were also collected at quarterly intervals using participatory epidemiological techniques. Compared with the unvaccinated (control) group, the incidence of HPAI-compatible events declined by 32% (P = 0.24) in the HPAI-vaccinated group and by 73% (P = 0.00) in the HPAI- and ND-vaccinated group. The effect of treatment did not vary with time or district. Similarly, an analysis of secondary data from the participatory disease and response (PDSR) database revealed that the incidence of HPAI declined by 12% in the HPAI-vaccinated group and by 24% in the HPAI + ND-vaccinated group. The results suggest that the HPAI + ND vaccination significantly reduced the incidence of HPAI-compatible events in mixed populations of semicommercial and backyard poultry.
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Preventive Veterinary Medicine, 2010
Bookmarks Related papers MentionsView impact
Preventive Veterinary Medicine, 2013
The primary objective of this study was to assess the impact of Rhipicephalus appendiculatus tick... more The primary objective of this study was to assess the impact of Rhipicephalus appendiculatus tick presence (exposure variable) on Theileria parva infection seroprevalence (outcome variable) in a group of cattle belonging to a farm using population attributable fractions (PAF). The analyses were based on a representative sample of 80 traditional smallholder mixed farms. The farms were selected by first stratifying the population administratively and implementing a multistage random sampling in Mbeere district in Kenya. The PAFs were estimated using the stratified, Bruzzi, and sequential partitioned PAF approaches. A secondary objective was, thus, to evaluate the impact of the approaches on the PAF estimates. The stratified and Bruzzi approaches estimated proportion of T. parva infection cases directly attributable to the exposure after controlling for confounding by agro-ecological zone (AEZ). The sequential partitioned PAF approach estimated a PAF associated with exposure after adjusting for any effect that the AEZ may have had by influencing the prevalence of the exposure. All analyses were carried out at the farm level where a farm was classified as infested if the tick was found on cattle on a farm, and infected if at least one animal on a farm was positive for T. parva antibodies. Variance estimation for PAFs was implemented using 'delete-a-group' jackknife re-sampling method. The stratified PAF (26.7% [95% CI: 9.0%, 44.4%]) and Bruzzi PAF (26.4% [95% CI: 9.6%, 43.2%]) were consistent in estimating a relatively low impact of farm vector tick presence with a relatively high level of uncertainty. The partitioned PAF (15.5% [95% CI: 1.5%, 29.6%]) suggested that part of the impacts estimated using the stratified PAF and Bruzzi approaches was driven by AEZ effects. Overall, the results suggested that under endemic instability in Mbeere district, (1) presence of R. appendiculatus was not a good indicator of T. parva infection occurrence on a farm; (2) ecological variation could play a role in determining infection impacts. This study provides a preliminary basis for evaluating the potential value and utility of estimating PAFs for variables amenable to control in tick-borne diseases (TBDs) epidemiological studies.
Bookmarks Related papers MentionsView impact
Transboundary and emerging diseases, 2012
Outbreaks of highly pathogenic avian influenza (HPAI) H5N1 occurred in Nigeria between December 2... more Outbreaks of highly pathogenic avian influenza (HPAI) H5N1 occurred in Nigeria between December 2005 and July 2008. We describe temporal and spatial characteristics of these outbreaks at State and Local Government Area (LGA) levels. A total of 25 of 37 States (67.6%; Exact 95% CI: 50.2-82.0%) and 81 of 774 LGAs (10.5%; Exact 95% CI: 8.4-12.8%) were affected by HPAI outbreaks over the period from 2005 to 2008. The incidence risk of HPAI outbreak occurrence at the State level was 5.6% (0.7-18.7%) for 2005, 50.0% (30.7-69.4%) for 2006, 54.5% (29.9-80.3%) for 2007 and 0% for 2008. Only very few LGAs experienced HPAI outbreaks within the affected States. The incidence risk of HPAI outbreak occurrence on a LGA level was 0.3% (0.0-0.9%) for 2005, 6.6% (4.9-8.6%) for 2006, 4.2% (2.9-6.0%) for 2007 and 0% for 2008. The mean period between farmers noticing HPAI outbreaks and reporting them to veterinary authorities, and between reporting HPAI outbreaks and the depopulation of infected premise...
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Preventive veterinary …, 2004
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Veterinary parasitology, 2004
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Veterinary parasitology, 2003
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HPAI Research Brief, 2009
HPAI disease-transmission pathways are linked to the economic incentives that chain actors face. ... more HPAI disease-transmission pathways are linked to the economic incentives that chain actors face. Disease transmission risk is strongly related to commercial practices and trade in poultry and poultry products. Consumer influences are insufficient to change governance and ...
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