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Malladi S, Ssematimba A, Bonney PJ, St Charles KM, Boyer T, Goldsmith T, Walz E, Cardona CJ, Culhane MR. Predicting the time to detect moderately virulent African swine fever virus in finisher swine herds using a stochastic disease transmission model. BMC Vet Res 2022; 18:84. [PMID: 35236347 PMCID: PMC8889644 DOI: 10.1186/s12917-022-03188-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2021] [Accepted: 02/24/2022] [Indexed: 11/10/2022] Open
Abstract
Background 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.
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Affiliation(s)
- Sasidhar Malladi
- Secure Food Systems Team, University of Minnesota, Saint Paul, MN, 55108, USA
| | - Amos Ssematimba
- Secure Food Systems Team, University of Minnesota, Saint Paul, MN, 55108, USA. .,Department of Mathematics, Faculty of Science, Gulu University, Gulu, Uganda.
| | - Peter J Bonney
- Secure Food Systems Team, University of Minnesota, Saint Paul, MN, 55108, USA
| | | | - Timothy Boyer
- Center for Epidemiology and Animal Health, Veterinary Services, Animal and Plant Health Inspection Service, United States Department of Agriculture, Fort Collins, Colorado, USA
| | - Timothy Goldsmith
- Secure Food Systems Team, University of Minnesota, Saint Paul, MN, 55108, USA
| | - Emily Walz
- Secure Food Systems Team, University of Minnesota, Saint Paul, MN, 55108, USA
| | - Carol J Cardona
- Secure Food Systems Team, University of Minnesota, Saint Paul, MN, 55108, USA
| | - Marie R Culhane
- Secure Food Systems Team, University of Minnesota, Saint Paul, MN, 55108, USA
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Ewing DA, Pooley CM, Gamado KM, Porphyre T, Marion G. Exact Bayesian inference of epidemiological parameters from mortality data: application to African swine fever virus. J R Soc Interface 2022; 19:20220013. [PMID: 35259955 PMCID: PMC8905154 DOI: 10.1098/rsif.2022.0013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Pathogens such as African swine fever virus (ASFV) are an increasing threat to global livestock production with implications for economic well-being and food security. Quantification of epidemiological parameters, such as transmission rates and latent and infectious periods, is critical to inform efficient disease control. Parameter estimation for livestock disease systems is often reliant upon transmission experiments, which provide valuable insights in the epidemiology of disease but which may also be unrepresentative of at-risk populations and incur economic and animal welfare costs. Routinely collected mortality data are a potential source of readily available and representative information regarding disease transmission early in outbreaks. We develop methodology to conduct exact Bayesian parameter inference from mortality data using reversible jump Markov chain Monte Carlo incorporating multiple routes of transmission (e.g. within-farm secondary and background transmission from external sources). We use this methodology to infer epidemiological parameters for ASFV using data from outbreaks on nine farms in the Russian Federation. This approach improves inference on transmission rates in comparison with previous methods based on approximate Bayesian computation, allows better estimation of time of introduction and could readily be applied to other outbreaks or pathogens.
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Affiliation(s)
- David A Ewing
- Biomathematics and Statistics Scotland, James Clerk Maxwell Building, The King's Buildings, Edinburgh, UK
| | - Christopher M Pooley
- Biomathematics and Statistics Scotland, James Clerk Maxwell Building, The King's Buildings, Edinburgh, UK
| | - Kokouvi M Gamado
- Biomathematics and Statistics Scotland, James Clerk Maxwell Building, The King's Buildings, Edinburgh, UK
| | - Thibaud Porphyre
- The Epidemiology, Economics and Risk Assessment (EERA) Group, The Roslin Institute, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Roslin, UK.,Université de Lyon, Université Lyon 1, CNRS, VetAgro Sup, Laboratoire de Biométrie et Biologie Evolutive, Marcy l'Étoile, France
| | - Glenn Marion
- Biomathematics and Statistics Scotland, James Clerk Maxwell Building, The King's Buildings, Edinburgh, UK
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Ryu HW, Tai JH. Object detection and tracking using a high-performance artificial intelligence-based 3D depth camera: towards early detection of African swine fever. J Vet Sci 2022; 23:e17. [PMID: 35088954 PMCID: PMC8799950 DOI: 10.4142/jvs.21252] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Revised: 11/22/2021] [Accepted: 11/24/2021] [Indexed: 11/20/2022] Open
Abstract
Background Objectives Methods Results Conclusions
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Affiliation(s)
- Harry Wooseuk Ryu
- Research Institute for Veterinary Science, College of Veterinary Medicine, Seoul National University, Seoul 08826, Korea
- Department of Computer Science, University of Toronto, Toronto, Ontario, M5S 1A1, Canada
| | - Joo Ho Tai
- Research Institute for Veterinary Science, College of Veterinary Medicine, Seoul National University, Seoul 08826, Korea
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Machado G, Farthing TS, Andraud M, Lopes FPN, Lanzas C. Modelling the role of mortality-based response triggers on the effectiveness of African swine fever control strategies. Transbound Emerg Dis 2021; 69:e532-e546. [PMID: 34590433 DOI: 10.1111/tbed.14334] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2021] [Revised: 09/15/2021] [Accepted: 09/17/2021] [Indexed: 01/26/2023]
Abstract
African swine fever (ASF) is considered the most impactful transboundary swine disease. In the absence of effective vaccines, control strategies are heavily dependent on mass depopulation and shipment restrictions. Here, we developed a nested multiscale model for the transmission of ASF, combining a spatially explicit network model of animal shipments with a deterministic compartmental model for the dynamics of two ASF strains within 3 km × 3 km pixels in one Brazilian state. The model outcomes are epidemic duration, number of secondary infected farms and pigs, and distance of ASF spread. The model also shows the spatial distribution of ASF epidemics. We analyzed quarantine-based control interventions in the context of mortality trigger thresholds for the deployment of control strategies. The mean epidemic duration of a moderately virulent strain was 11.2 days, assuming the first infection is detected (best-case scenario), and 15.9 days when detection is triggered at 10% mortality. For a highly virulent strain, the epidemic duration was 6.5 days and 13.1 days, respectively. The distance from the source to infected locations and the spatial distribution was not dependent on strain virulence. Under the best-case scenario, we projected an average number of infected farms of 23.77 farms and 18.8 farms for the moderate and highly virulent strains, respectively. At 10% mortality-trigger, the predicted number of infected farms was on average 46.27 farms and 42.96 farms, respectively. We also demonstrated that the establishment of ring quarantine zones regardless of size (i.e. 5 km, 15 km) was outperformed by backward animal movement tracking. The proposed modelling framework provides an evaluation of ASF epidemic potential, providing a ranking of quarantine-based control strategies that could assist animal health authorities in planning the national preparedness and response plan.
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Affiliation(s)
- Gustavo Machado
- Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA
| | - Trevor S Farthing
- Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA
| | - Mathieu Andraud
- Anses, French Agency for Food, Environmental and Occupational Health & Safety, Ploufragan-Plouzané-Niort Laboratory, Epidemiology, Health and Welfare Research Unit, Ploufragan, France
| | - Francisco Paulo Nunes Lopes
- Departamento de Defesa Agropecuária, Secretaria da Agricultura, Pecuária e Desenvolvimento Rural, Porto Alegre, Brazil
| | - Cristina Lanzas
- Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA
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Hayes BH, Andraud M, Salazar LG, Rose N, Vergne T. Mechanistic modelling of African swine fever: A systematic review. Prev Vet Med 2021; 191:105358. [PMID: 33930624 DOI: 10.1016/j.prevetmed.2021.105358] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Revised: 04/06/2021] [Accepted: 04/13/2021] [Indexed: 12/11/2022]
Abstract
The spread of African swine fever (ASF) poses a grave threat to the global swine industry. Without an available vaccine, understanding transmission dynamics is essential for designing effective prevention, surveillance, and intervention strategies. These dynamics can often be unraveled through mechanistic modelling. To examine the assumptions on transmission and objectives of the mechanistic models of ASF, a systematic review of the scientific literature was conducted. Articles were examined across multiple epidemiological and model characteristics, with filiation between models determined through the creation of a neighbor-joined tree using phylogenetic software. Thirty-four articles qualified for inclusion, with four main modelling objectives identified: estimating transmission parameters (11 studies), assessing determinants of transmission (7), examining consequences of hypothetical outbreaks (5), assessing alternative control strategies (11). Population-based (17), metapopulation (5), and individual-based (12) model frameworks were represented, with population-based and metapopulation models predominantly used among domestic pigs, and individual-based models predominantly represented among wild boar. The majority of models (25) were parameterized to the genotype II isolates currently circulating in Europe and Asia. Estimated transmission parameters varied widely among ASFV strains, locations, and transmission scale. Similarly, parameter assumptions between models varied extensively. Uncertainties on epidemiological and ecological parameters were usually accounted for to assess the impact of parameter values on the modelled infection trajectory. To date, almost all models are host specific, being developed for either domestic pigs or wild boar despite the fact that spillover events between domestic pigs and wild boar are evidenced to play an important role in ASF outbreaks. Consequently, the development of more models incorporating such transmission routes is crucial. A variety of codified and hypothetical control strategies were compared however they were all a priori defined interventions. Future models, built to identify the optimal contributions across many control methods for achieving specific outcomes should provide more useful information for policy-makers. Further, control strategies were examined in competition with each other, which is opposed to how they would actually be synergistically implemented. While comparing strategies is beneficial for identifying a rank-order efficacy of control methods, this structure does not necessarily determine the most effective combination of all available strategies. In order for ASFV models to effectively support decision-making in controlling ASFV globally, these modelling limitations need to be addressed.
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Affiliation(s)
- Brandon H Hayes
- UMR ENVT-INRAE IHAP, National Veterinary School of Toulouse, 31000, Toulouse, France; Epidemiology Health and Welfare Department, Ploufragan-Plouzané-Niort Laboratory, French Agency for Food, Environmental and Occupational Health & Safety (ANSES), 22440, Ploufragan, France.
| | - Mathieu Andraud
- Epidemiology Health and Welfare Department, Ploufragan-Plouzané-Niort Laboratory, French Agency for Food, Environmental and Occupational Health & Safety (ANSES), 22440, Ploufragan, France
| | - Luis G Salazar
- Epidemiology Health and Welfare Department, Ploufragan-Plouzané-Niort Laboratory, French Agency for Food, Environmental and Occupational Health & Safety (ANSES), 22440, Ploufragan, France
| | - Nicolas Rose
- Epidemiology Health and Welfare Department, Ploufragan-Plouzané-Niort Laboratory, French Agency for Food, Environmental and Occupational Health & Safety (ANSES), 22440, Ploufragan, France
| | - Timothée Vergne
- UMR ENVT-INRAE IHAP, National Veterinary School of Toulouse, 31000, Toulouse, France
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