Browsing by Author "Ssematimba, Amos"
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Item African Swine Fever Detection and Transmission Estimates Using Homogeneous Versus Heterogeneous Model Formulation in Stochastic Simulations Within Pig Premises(Research Square, 2022) Ssematimba, Amos; Malladi, Sasidhar; Bonney, Peter J.; Charles, Kaitlyn M. St.; Boyer, Timothy C.; Goldsmith, Timothy; Cardona, Carol J.; Corzo, Cesar A.; Culhane, Marie R.This study aimed to assess the impact on within-herd transmission dynamics of African swine fever (ASF) when the models used to simulate transmission assume there is homogeneous mixing of animals within a barn. Barn-level heterogeneity was explicitly captured using a stochastic, individual pig-based, heterogeneous transmission model that considers three types of infection transmission, 1) within-pen via nose-to-nose contact; 2) between-pen via nose-to-nose contact with pigs in adjacent pens; and 3) both between- and within-pen via distance independent mechanisms (e.g., via fomites). Predictions were compared between the heterogeneous and the homogeneous Gillespie models. Results showed that the predicted mean number of infectious pigs at specific time points differed greatly between the homogeneous and heterogeneous models for scenarios with low levels of between pen contacts via distance independent pathways and the differences between the two model predictions were more pronounced for the slow contact rate scenario. The heterogeneous transmission model results also showed that it may take significantly longer to detect ASF, particularly in large barns when transmission predominantly occurs via nose-to-nose contact between pigs in adjacent pens. The findings emphasize the need for completing preliminary explorations when working with homogeneous mixing models to ascertain their suitability to predict disease outcomes.Item Analysis of geographic location and pathways for influenza A virus infection of commercial upland game bird and conventional poultry farms in the United States of America(BMC veterinary research, 2019) Ssematimba, Amos; Charles, Kaitlyn M. St.; Bonney, Peter J.; Malladi, Sasidhar; Culhane, Marie; Goldsmith, Timothy J.; Halvorson, David A.; Cardona, Carol J.Avian influenza (AI) is an infectious viral disease that affects several species and has zoonotic potential. Due to its associated health and economic repercussions, minimizing AI outbreaks is important. However, most control measures are generic and mostly target pathways important for the conventional poultry farms producing chickens, turkeys, and eggs and may not target other pathways that may be specific to the upland game bird sector. The goal of this study is to provide evidence to support the development of novel strategies for sector-specific AI control by comparing and contrasting practices and potential pathways for spread in upland game bird farms with those for conventional poultry farms in the United States. Farm practices and processes, seasonality of activities, geographic location and inter-farm distance were analyzed across the sectors. All the identified differences were framed and discussed in the context of their associated pathways for virus introduction into the farm and subsequent between-farm spread. Results: Differences stemming from production systems and seasonality, inter-farm distance and farm densities were evident and these could influence both fomite-mediated and local-area spread risks. Upland game bird farms operate under a single, independent owner rather than being contracted with or owned by a company with other farms as is the case with conventional poultry. The seasonal marketing of upland game birds, largely driven by hunting seasons, implies that movements are seasonal and customer-vendor dynamics vary between industry groups. Farm location analysis revealed that, on average, an upland game bird premises was 15.42 km away from the nearest neighboring premises with birds compared to 3.74 km for turkey premises. Compared to turkey premises, the average poultry farm density in a radius of 10 km of an upland game bird premises was less than a half, and turkey premises were 3.8 times (43.5% compared with 11.5%) more likely to fall within a control area during the 2015 Minnesota outbreak. Conclusions: We conclude that the existing differences in the seasonality of production, isolated geographic location and epidemiological seclusion of farms influence AI spread dynamics and therefore disease control measures should be informed by these and other factors to achieve success.Item Assessment of replicate numbers for titrating avian influenza virus using dose-response models(Journal of Veterinary Diagnostic Investigation, 2019) Spackman, Erica; Malladi, Sasidhar; Ssematimba, Amos; Stephens, Christopher B.Embryonating chicken eggs (ECEs) are among the most sensitive laboratory host systems for avian influenza virus (AIV) titration, but ECEs are expensive and require space for storage and incubation. Therefore, reducing ECE use would conserve resources. We utilized statistical modeling to evaluate the accuracy and precision of AIV titration with 3 instead of 5 ECEs for each dilution by the Reed–Muench method for 50% endpoint calculation. Beta-Poisson and exponential doseresponse models were used in a simulation study to evaluate observations from actual titration data from 18 AIV isolates. The reproducibility among replicates of a titration was evaluated with one AIV isolate titrated in 3 replicates with the beta-Poisson, exponential, and Weibull dose-response models. The standard deviation (SD) of the error between input and estimated virus titers was estimated with Monte Carlo simulations using the fitted dose-response models. Good fit was observed with all models that were utilized. Reducing the number of ECEs per dilution from 5 to 3 resulted in the width of the 95% confidence interval increasing from ±0.64 to ±0.75 log 10 50% ECE infectious doses (EID 50 ) and the SD of the error increased by 0.03 log 10 EID 50 . Our study suggests that using fewer ECEs per dilution is a viable approach that will allow laboratories to reduce costs and improve efficiency.Item An Assessment of the Risk Associated with the Movement Broilers to Market Into, Within, and Out of a Control Area During a Highly Pathogenic Avian Influenza Outbreak in the United States(University of Minnesota Center for Secure Food Systems, 2018) Cardona, Carol; Alexander, Carie; Bonney, Peter; Contadini, Francesca; Culhane, Marie; Goldsmith, Timothy; Halvorson, David; Linskens, Eric; Malladi, Sasidhar; Ssematimba, Amos; Umber, Jamie; Weaver, Todd; Walz, EmilyIn the event of a highly pathogenic avian influenza (HPAI) outbreak in the United States, poultry industry, local, State, and Federal authorities will implement a foreign animal disease emergency response. In these circumstances, permit requests to move poultry and poultry products must be supported by risk assessments which demonstrate that the risk of HPAI spread associated with the movement is acceptable. Performing the risk assessments prior to an HPAI outbreak can enhance emergency response and facilitate timely movement permitting decisions during an outbreak. This document assesses the risk that the movement of market-age broilers to processing (i.e., broilers to market), during an HPAI outbreak, from a premises located within the Control Area, will result in HPAI virus spread to a virus-free poultry premises. This risk assessment is a joint effort of the Secure Broiler Supply (SBS) Working Group, which is made up of representatives from the broiler industry, academia, State Animal Health Officials (SAHOs), and the United States Department of Agriculture Animal and Plant Health Inspection Service (USDA:APHIS), to support permits for the terminal movement of broilers to processing during an HPAI outbreak. This assessment is applicable to intensively raised commercial or contract grow-out broiler premises that do not have other poultry on the premises and practice an all-in, all-out single-age growing system. These broiler facilities must participate in the USDA APHIS National Poultry Improvement Plan (NPIP) and follow the SBS Plan in the event of an HPAI outbreak. The SBS Plan contains science-based outbreak measures developed by the SBS working group to mitigate the risk of HPAI spread associated with the terminal movement of live birds to market.Item An Assessment of the Risk Associated with the Movement Turkeys to Market Into, Within, and Out of a Control Area During a Highly Pathogenic Avian Influenza Outbreak in the United States(University of Minnesota Center for Secure Food Systems, 2018) Cardona, Carol; Alexander, Carie; Bergeron, Justin; Bonney, Peter; Culhane, Marie; Goldsmith, Timothy; Halvorson, David; Linskens, Eric; Malladi, Sasidhar; Ssematimba, Amos; Walz, Emily; Weaver, Todd; Umber, JamieIn the event of a highly pathogenic avian influenza (HPAI) outbreak in the United States, poultry industry, local, state, and federal authorities will implement a foreign animal disease emergency response. In these circumstances, permit requests to move poultry and poultry products must be supported by risk assessments which demonstrate that the risk of HPAI spread associated with the movement is acceptable. Performing the risk assessments prior to an HPAI outbreak can enhance emergency response and facilitate timely movement permitting decisions during an outbreak. This document assesses the risk that the movement of market-age turkeys to processing (i.e., turkeys to market), during an HPAI outbreak, from a premises located within the Control Area, will result in HPAI virus spread to a virus-free commercial poultry population (e.g., another poultry farm or birds remaining on a multi-age premises). The purpose of this assessment is to provide regulators with an objective and defensible method of assessing the disease risk associated with the movement of live turkeys (for meat) to slaughter.Item Avian Influenza in the U.S. Commercial Upland Game Bird Industry: An Analysis of Selected Practices as Potential Exposure Pathways and Surveillance System Data Reporting(Avian diseases, 2018) Charles, Kaitlyn M. St.; Ssematimba, Amos; Malladi, Sasidhar; Bonney, Peter J.; Linskens, Eric; Culhane, Marie; Goldsmith, Timothy J.; Halvorson, David A.; Cardona, Carol J.Producing a smaller yield of higher-value birds compared to conventional poultry production, the U.S. commercial upland game bird industry deals primarily in the sale of live birds for recreational hunting. In this study, our aims were to gain insights into the occurrence of avian influenza (AI) in the U.S. commercial upland game bird industry in comparison to other poultry sectors, to identify the presence of the specific AI risk factors in the practices of raising ducks on site and having connections to live bird markets (LBMs), and to assess how AI surveillance systems may have played a role in the reporting of the presence of exposure pathway–related information. We found that 23 AI epizootics involving upland game bird premises were reported, compared to 485 epizootics in the other poultry industries, and 86% of epizootics involving upland game birds were limited to only one premises. Regarding specific AI risk factors, 70% of upland game bird epizootics involved one of the two examined practices. In assessing the impact of surveillance systems, data framed around the implementation of surveillance systems revealed that the introduction of active surveillance coincided with the more thorough reporting of both the raising of ducks on site and premises having connections to LBMs. Our results suggest the need for more thorough data collection during epizootics and the need to assess additional exposure pathways specific to the commercial raise-for-release upland game bird industry.Item Estimating epidemiological parameters using diagnostic testing data from low pathogenicity avian influenza infected turkey houses(Scientific reports, 2021) Bonney, Peter J.; Malladi, Sasidhar; Ssematimba, Amos; Spackman, Erica; Torchetti, Mia Kim; Culhane, Marie; Cardona, Carol J.Limiting spread of low pathogenicity avian influenza (LPAI) during an outbreak is critical to reduce the negative impact on poultry producers and local economies. Mathematical models of disease transmission can support outbreak control efforts by estimating relevant epidemiological parameters. In this article, diagnostic testing data from each house on a premises infected during a LPAI H5N2 outbreak in the state of Minnesota in the United States in 2018 was used to estimate the time of virus introduction and adequate contact rate, which determines the rate of disease spread. A well-defined most likely time of virus introduction, and upper and lower 95% credibility intervals were estimated for each house. The length of the 95% credibility intervals ranged from 11 to 22 with a mean of 17 days. In some houses the contact rate estimates were also well-defined; however, the estimated upper 95% credibility interval bound for the contact rate was occasionally dependent on the upper bound of the prior distribution. The estimated modes ranged from 0.5 to 6.0 with a mean of 2.8 contacts per day. These estimates can be improved with early detection, increased testing of monitored premises, and combining the results of multiple barns that possess similar production systems.Item Estimating the Basic Reproductive Number (R0) for African Swine Fever Virus (ASFV) Transmission between Pig Herds in Uganda(PLoS ONE, 2015) Barongo, Mike B.; Ståhl, Karl; Bett, Bernard; Bishop, Richard P.; Fèvre, Eric M.; Aliro, Tony; Okoth, Edward; Masembe, Charles; Knobel, Darryn; Ssematimba, AmosAfrican swine fever (ASF) is a highly contagious, lethal and economically devastating haemorrhagic disease of domestic pigs. Insights into the dynamics and scale of virus transmission can be obtained from estimates of the basic reproduction number (R0). We estimate R0 for ASF virus in small holder, free-range pig production system in Gulu, Uganda. The estimation was based on data collected from outbreaks that affected 43 villages (out of the 289 villages with an overall pig population of 26,570) between April 2010 and November 2011. A total of 211 outbreaks met the criteria for inclusion in the study. Three methods were used, specifically; (i) GIS- based identification of the nearest infectious neighbour based on the Euclidean distance between outbreaks, (ii) epidemic doubling time, and (iii) a compartmental susceptible-infectious (SI) model. For implementation of the SI model, three approaches were used namely; curve fitting (CF), a linear regression model (LRM) and the SI/ N proportion. The R0 estimates from the nearest infectious neighbour and epidemic doubling time methods were 3.24 and 1.63 respectively. Estimates from the SI-based method were 1.58 for the CF approach, 1.90 for the LRM, and 1.77 for the SI/N proportion. Since all these values were above one, they predict the observed persistence of the virus in the population. We hypothesize that the observed variation in the estimates is a consequence of the data used. Higher resolution and temporally better defined data would likely reduce this variation. This is the first estimate of R0 for ASFV in a free range smallholder pig keeping system in sub-Saharan Africa and highlights the requirement for more efficient application of available disease control measures.Item Estimating the Per-Contact Probability of Infection by Highly Pathogenic Avian Influenza (H7N7) Virus during the 2003 Epidemic in The Netherlands(PLoS ONE, 2012) Ssematimba, Amos; Elbers, Armin R. W.; Hagenaars, Thomas J.; de Jong, Mart C. M.Estimates of the per-contact probability of transmission between farms of Highly Pathogenic Avian Influenza virus of H7N7 subtype during the 2003 epidemic in the Netherlands are important for the design of better control and biosecurity strategies. We used standardized data collected during the epidemic and a model to extract data for untraced contacts based on the daily number of infectious farms within a given distance of a susceptible farm. With these data, we used a maximum likelihood estimation approach to estimate the transmission probabilities by the individual contact types, both traced and untraced. The estimated conditional probabilities, conditional on the contact originating from an infectious farm, of virus transmission were: 0.000057 per infectious farm within 1 km per day, 0.000413 per infectious farm between 1 and 3 km per day, 0.0000895 per infectious farm between 3 and 10 km per day, 0.0011 per crisis organisation contact, 0.0414 per feed delivery contact, 0.308 per egg transport contact, 0.133 per other-professional contact and, 0.246 per rendering contact. We validate these outcomes against literature data on virus genetic sequences for outbreak farms. These estimates can be used to inform further studies on the role that improved biosecurity between contacts and/or contact frequency reduction can play in eliminating between-farm spread of the virus during future epidemics. The findings also highlight the need to; 1) understand the routes underlying the infections without traced contacts and, 2) to review whether the contacttracing protocol is exhaustive in relation to all the farm’s day-to-day activities and practices.Item A Mathematical Model that Simulates Control Options for African Swine Fever Virus (ASFV)(PLoS ONE, 2016) Barongo, Mike B.; Bishop, Richard P.; Fèvre, Eric M.; Knobel, Darryn L.; Ssematimba, AmosA stochastic model designed to simulate transmission dynamics of African swine fever virus (ASFV) in a free-ranging pig population under various intervention scenarios is presented. The model was used to assess the relative impact of the timing of the implementation of different control strategies on disease-related mortality. The implementation of biosecurity measures was simulated through incorporation of a decay function on the transmission rate. The model predicts that biosecurity measures implemented within 14 days of the onset of an epidemic can avert up to 74% of pig deaths due to ASF while hypothetical vaccines that confer 70% immunity when deployed prior to day 14 of the epidemic could avert 65% of pig deaths. When the two control measures are combined, the model predicts that 91% of the pigs that would have otherwise succumbed to the disease if no intervention was implemented would be saved. However, if the combined interventions are delayed (defined as implementation from > 60 days) only 30% of ASF-related deaths would be averted. In the absence of vaccines against ASF, we recommend early implementation of enhanced biosecurity measures. Active surveillance and use of pen-side diagnostic assays, preferably linked to rapid dissemination of this data to veterinary authorities through mobile phone technology platforms are essential for rapid detection and confirmation of ASF outbreaks. This prediction, although it may seem intuitive, rationally confirms the importance of early intervention in managing ASF epidemics. The modelling approach is particularly valuable in that it determines an optimal timing for implementation of interventions in controlling ASF outbreaks.Item Mathematical Modelling of the Population Dynamics of Two- Prey and One- Predator Systems at the Human-Livestock-Wildlife Interface(EC Veterinary Sciencem, 2019) Ssematimba, Amos; Kinyera, Joel; Okello, Atila; Akena, Richard; Nsamba, Samuel; Canpwonyi, Sam; Abola, Benard; Kayanja, Andrew; Kikawa, Cliff RUnderstanding the population dynamics at the human-livestock-wildlife interface is key to managing zoonotic and cross-species diseases as well as maintaining ecosystem biodiversity at this interface. This necessitates elucidation of the effects of within and between species interactions and human activities such as farming and animal harvesting among others. Keywords: Prey-Predator Systems; Predation; Population Dynamics; Ecological Modelling; Harvesting Threshold In this study, a mathematical model was developed and analyzed to study the dynamics of two- prey (Uganda-kobs (kobus kob thomasi) and the buffaloes (Syncerus caffer)) and one-predator (the lions (Panthera leo)) system at the human-livestock-wildlife interface. The model was analysed qualitatively for equilibrium points and their stability and, upon parametrization based on data in literature, numerical simulations were performed. Our findings re-echoed/re-emphasized that, for co-existence of the three species, the rate of human harvesting of kobus kob thomasi needed to be maintained below the species’ intrinsic growth rate. Existence of such a critical harvesting threshold was demonstrated and any harvesting rate exceeding that threshold would lead to ultimate extinction of both the kobus kob thomasi and the Panthera leo. Our findings further revealed that, for their long-term survival, the predator needs not to focus only on the easy-to-catch prey but use a balanced approach to ensure continued survival of both prey species. We conclude that, given the field data limitations, our findings are rather preliminary and more of a basis for future studies geared towards improving management of ecosystems involving interacting species. Most importantly, this study demonstrates that mathematical models can play a significant role in tackling complex system dynamics to generate useful information to guide policy decisions.Item Mathematical Modelling of the Transmission Dynamics of Contagious Bovine Pleuropneumonia Reveals Minimal Target Profiles for Improved Vaccines and Diagnostic Assays(PLoS One, 2015) Ssematimba, Amos; Jores, Joerg; Mariner, Jeffrey C.Contagious bovine pleuropneumonia (CBPP) is a cattle disease that has hampered the development of the livestock sector in sub-Saharan Africa. Currently, vaccination with a live vaccine strain is its recommended control measure although unofficial antimicrobial use is widely practiced. Here, modelling techniques are used to assess the potential impact of early elimination of infected cattle via accurate diagnosis on CBPP dynamics. A herd-level stochastic epidemiological model explicitly incorporating test sensitivity and specificity is developed. Interventions by annual vaccination, annual testing and elimination and a combination of both are implemented in a stepwise manner and their effectiveness compared by running 1000 simulations per intervention over ten years. The model predicts that among the simulated interventions, the ones likely to eliminate the disease from an isolated herd all involved annual vaccination of more than 75% of the animals with a vaccine that protects for at least 18 months combined with annual testing (and elimination of positive reactors) of 75% of the animals every six months after vaccination. The highest probability of disease elimination was 97.5%and this could occur within a median of 2.3 years. Generally, our model predicts that regular testing and elimination of positive reactors using improved tests will play a significant role in minimizing CBPP burden especially in the current situation where improved vaccines are yet to be developed.Item Predicting the time to detect moderately virulent African swine fever virus in finisher swine herds using a stochastic disease transmission model(BMC Veterinary Research, 2022) Malladi, Sasidhar; Ssematimba, Amos; Bonney, Peter J.; Charles, Kaitlyn M. St.; Boyer, Timothy; Goldsmith, Timothy; Walz, Emily; Cardona, Carol J.; Culhane, Marie R.African swine fever (ASF) is a highly contagious and devastating pig disease that has caused extensive global economic losses. Understanding ASF virus (ASFV) transmission dynamics within a herd is necessary in order to prepare for and respond to an outbreak in the United States. Although the transmission parameters for the highly virulent ASF strains have been estimated in several articles, there are relatively few studies focused on moderately virulent strains. Using an approximate Bayesian computation algorithm in conjunction with Monte Carlo simulation, we have estimated the adequate contact rate for moderately virulent ASFV strains and determined the statistical distributions for the durations of mild and severe clinical signs using individual, pig-level data. A discrete individual based disease transmission model was then used to estimate the time to detect ASF infection based on increased mild clinical signs, severe clinical signs, or daily mortality. Results: Our results indicate that it may take two weeks or longer to detect ASF in a finisher swine herd via mild clinical signs or increased mortality beyond levels expected in routine production. A key factor contributing to the extended time to detect ASF in a herd is the fairly long latently infected period for an individual pig (mean 4.5, 95% P.I., 2.4 - 7.2 days). Conclusion: These transmission model parameter estimates and estimated time to detection via clinical signs provide valuable information that can be used not only to support emergency preparedness but also to inform other simulation models of evaluating regional disease spread.Item Preparing for a Foreign Animal Disease Outbreak Using a Novel Tabletop Exercise(Prehospital and Disaster Medicine, 2018) Linskens, Eric J.; Neu, Abby E.; Walz, Emily J.; Charles, Kaitlyn M. St.; Culhane, Marie R.; Ssematimba, Amos; Goldsmith, Timothy J.; Halvorson, David A.; Cardona, Carol J.Foreign animal disease (FAD) outbreaks can have devastating impacts, but they occur infrequently in any specific sector anywhere in the United States (US). Training to proactively discuss implementation of control and prevention strategies are beneficial in that they provide stakeholders with the practical information and educational experience they will need to respond effectively to an FAD. Such proactive approaches are the mission of the Secure Food System (SFS; University of Minnesota; St. Paul, Minnesota USA). Methods: The SFS exercises were designed as educational activities based on avian influenza (AI) outbreaks in commercial poultry scenarios. These scenarios were created by subject matter experts and were based on epidemiology reports, risk pathway analyses, local industry practices, and site-specific circumstances. Target audiences of an exercise were the groups involved in FAD control: animal agriculture industry members; animal health regulators; and diagnosticians. Groups of industry participants seated together at tables represented fictional poultry premises and were guided by a moderator to respond to an onfarm situation within a simulated outbreak. The impact of SFS exercises was evaluated through interviews with randomized industry participants and selected table moderators. Descriptive statistics and qualitative analyses were performed on interview feedback. Results: Eleven SFS exercises occurred from December 2016 through October 2017 in multiple regions of the US. Exercises were conducted as company-wide, state-wide, or regional trainings. Nine were based on highly pathogenic avian influenza (HPAI) outbreaks and two focused on outbreaks of co-circulating HPAI and low pathogenicity avian influenza (LPAI). Poultry industry participants interviewed generally found attending an SFS exercise to be useful. The most commonly identified benefits of participation were its value to people without prior outbreak experience and knowledge gained about Continuity of Business (COB)-permitted movement. After completing an exercise, most participants evaluated their preparedness to respond to an outbreak as somewhat to very ready, and more than one-half reported their respective company or farms had discussions or changed actions due to participation. Conclusion: Evaluation feedback suggests the SFS exercises were an effective training method to supplement preparedness efforts for an AI outbreak. The concept of using multi-faceted scenarios and multiple education strategies during a tabletop exercise may be translatable to other emergency preparedness needs.Item Quantifying the effect of swab pool size on the detection of influenza A viruses in broiler chickens and its implications for surveillance(BMC veterinary research, 2018) Ssematimba, Amos; Malladi, Sasidhar; Bonney, Peter J.; Flores-Figueroa, Cristian; Muñoz-Aguayo, Jeannette; Halvorson, David A.; Cardona, Carol J.Timely diagnosis of influenza A virus infections is critical for outbreak control. Due to their rapidity and other logistical advantages, lateral flow immunoassays can support influenza A virus surveillance programs and here, their field performance was proactively assessed. The performance of real-time polymerase chain reaction and two lateral flow immunoassay kits (FluDETECT and VetScan) in detecting low pathogenicity influenza A virus in oropharyngeal swab samples from experimentally inoculated broiler chickens was evaluated and at a flock-level, different testing scenarios were analyzed. Results: For real-time polymerase chain reaction positive individual-swabs, FluDETECT respectively detected 37% and 58% for the H5 and H7 LPAIV compared to 28% and 42% for VetScan. The mean virus titer in H7 samples was higher than for H5 samples. For real-time polymerase chain reaction positive pooled swabs (containing one positive), detections by FluDETECT were significantly higher in the combined 5- and 6-swab samples compared to 11-swab samples. FluDETECT detected 58%, 55.1% and 44.9% for the H7 subtype and 28.3%, 34.0% and 24.6% for the H5 in pools of 5, 6 and 11 respectively. In our testing scenario analysis, at low flock-level LPAIV infection prevalence, testing pools of 11 detected slightly more infections while at higher prevalence, testing pools of 5 or 6 performed better. For highly pathogenic avian influenza virus, testing pools of 11 (versus 5 or 6) detected up to 5% more infections under the assumption of similar sensitivity across pools and detected less by 3% when its sensitivity was assumed to be lower. Conclusions: Much as pooling a bigger number of swab samples increases the chances of having a positive swab included in the sample to be tested, this study’s outcomes indicate that this practice may actually reduce the chances of detecting the virus since it may result into lowering the virus titer of the pooled sample. Further analysis on whether having more than one positive swab in a pooled sample would result in increased sensitivity for low pathogenicity avian influenza virus is needed.Item Simulated Flock-Level Shedding Characteristics of Turkeys in Ten Thousand Bird Houses Infected with H7 Low Pathogenicity Avian Influenza Virus Strains(2021) Bonney, Peter J.; Malladi, Sasidhar; Ssematimba, Amos; Charles, Kaitlyn M. St.; Walz, Emily; Culhane, Marie R.; Halvorson, David A.; Cardona, Carol J.pathogenicity avian influenza virus (LPAIV) over time can help inform the type and timing of activities performed in response to a confirmed LPAIV-positive premises. To this end, we developed a mathematical model which allows us to estimate viral shedding by 10,000 turkey toms raised in commercial turkey production in the United States, and infected by H7 LPAIV strains. We simulated the amount of virus shed orally and from the cloaca over time, as well as the amount of virus in manure. In addition, we simulated the threshold cycle value (Ct) of pooled oropharyngeal swabs from birds in the infected flock tested by real-time reverse transcription polymerase chain reaction. The simulation model predicted that little to no shedding would occur once the highest threshold of seroconversion was reached. Substantial amounts of virus in manure (median 1.5 108 and 5.8 109; 50% egg infectious dose) were predicted at the peak. Lastly, the model results suggested that higher Ct values, indicating less viral shedding, are more likely to be observed later in the infection process as the flock approaches recovery.Item Small distances can keep bacteria at bay for days(National Academy of Sciences, 2014) Bunnika, Bram A. D. van; Ssematimba, Amos; Hagenaars, Thomas J.; Nodelijk, Gonnie; Haverkate, Manon R.; Bonten, Marc J. M.; Hayden, Mary K.; Weinstein, Robert A.; Bootsma, Martin C. J.; De Jong, Mart C. M.Transmission of pathogens between spatially separated hosts, i.e., indirect transmission, is a commonly encountered phenomenon important for epidemic pathogen spread. The routes of indirect transmission often remain untraced, making it difficult to develop control strategies. Here we used a tailor-made design to study indirect transmission experimentally, using two different zoonotic bacteria in broilers. Previous experiments using a single bacterial species yielded a delay in the onset of transmission, which we hypothesized to result from the interplay between diffusive motion of infectious material and decay of infectivity in the environment. Indeed, a mathematical model of diffusive pathogen transfer predicts a delay in transmission that depends both on the distance between hosts and on the magnitude of the pathogen decay rate. Our experiments, carried out with two bacterial species with very different decay rates in the environment, confirm the difference in transmission delay predicted by the model. These results imply that for control of an infectious agent, the time between the distant exposure and the infection event is important. To illustrate how this can work we analyzed data observed on the spread of vancomycin-resistant Enterococcus in an intensive care unit. Indeed, a delayed vancomycin-resistant Enterococcus transmission component was identified in these data, and this component disappeared in a study period in which the environment was thoroughly cleaned. Therefore, we suggest that the impact of control strategies against indirect transmission can be assessed using our model by estimating the control measures’ effects on the diffusion coefficient and the pathogen decay rate.Item Social Media Marketing for Small and Medium Enterprise Performance in Uganda: A Structural Equation Model(Sustainability, 2022) Kikawa, Cliff R.; Kiconco, Charity; Agaba, Moses; Ntirampeba, Dimas; Ssematimba, Amos; Kalema, Billy M.Thanks to the ongoing expansion of internet access and, most recently, the movement restrictions that were put in place globally to stop COVID-19 spread, many small and medium enterprises (SMEs) are prepared to use social media platforms to market their products as a way to improve their business performance in emerging economies. Businesses at all levels that use social media marketing (SMM) see a considerable increase in their output. This study’s objective is to identify the factors that significantly help Ugandan SMEs implement SMM techniques to enhance their commercial performance. Here, statistical models are utilized to analyze how the age and gender of SMEs owners as moderating variables affect the adoption and performance of SMEs in Uganda. A theoretical model that is based on the Technology Acceptance Model (TAM) and Innovation Diffusion Theory (IDT) theories has been put out as part of a specific conceptual framework. The following indicators are used to evaluate the performance of SMEs: sales, customer engagement, awareness of customers’ needs, low operation costs, and brand modification by staff. Empirical model validation has been performed using 152 business units (observation units) corresponding to the number of respondents (units of analysis), and the ensuing analyses have been done using structural equation modelling (SEM). The results indicate that compatibility and perceived ease of use have a positive impact on SMEs to adopt SMM, while perceived usefulness has a negative impact on SMEs to adopt SMM. Age and gender as moderating variables all have a positive moderating effect. With limited studies available on the subject, this research contributes to already existing literature by combining two components of the TAM model and one component of the IDT to explain the impact of SMM on SMEs when moderated by both age and gender in a developing economy.Item Spatial transmission of H5N2 highly pathogenic avian influenza between Minnesota poultry premises during the 2015 outbreak(PLoS ONE, 2018) Bonney, Peter J.; Malladi, Sasidhar; Jan Boender, Gert; Weaver, J. Todd; Ssematimba, Amos; Halvorson, David A.; Cardona, Carol J.The spatial spread of highly pathogenic avian influenza (HPAI) H5N2 during the 2015 outbreak in the U.S. state of Minnesota was analyzed through the estimation of a spatial transmission kernel, which quantifies the infection hazard an infectious premises poses to an uninfected premises some given distance away. Parameters were estimated using a maximum likelihood method for the entire outbreak as well as for two phases defined by the daily number of newly detected HPAI-positive premises. The results indicate both a strong dependence of the likelihood of transmission on distance and a significant distance-independent component of outbreak spread for the overall outbreak. The results further suggest that HPAI spread differed during the later phase of the outbreak. The estimated spatial transmission kernel was used to compare the Minnesota outbreak with previous HPAI outbreaks in the Netherlands and Italy to contextualize the Minnesota transmission kernel results and make additional inferences about HPAI transmission during the Minnesota outbreak. Lastly, the spatial transmission kernel was used to identify high risk areas for HPAI spread in Minnesota. Risk maps were also used to evaluate the potential impact of an early marketing strategy implemented by poultry producers in a county in Minnesota during the outbreak, with results providing evidence that the strategy was successful in reducing the potential for HPAI spread.