Browsing by Author "Goldsmith, Timothy"

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    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.
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    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, Emily
    In 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.
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    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, Jamie
    In 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.
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    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.