|Ssematimba, Amos - University Of Minnesota|
|Malladi, Sasidhar - University Of Minnesota|
|Hagenaars, Thomas - Waneningen University|
|Bonney, Peter - University Of Minnesota|
|Weaver, Joseph Todd - Animal And Plant Health Inspection Service (APHIS)|
|Patyk, Kelly - Animal And Plant Health Inspection Service (APHIS)|
|Halvorson, Dave - University Of Minnesota|
|Cardona, Carol - University Of Minnesota|
Submitted to: Epidemiology and Infection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2019
Publication Date: 4/22/2019
Citation: Ssematimba, A., Malladi, S., Hagenaars, T., Bonney, P., Weaver, J., Patyk, K., Spackman, E., Halvorson, D., Cardona, C. 2019. Estimating within-flock transmission rate parameter for H5N2 highly pathogenic avian influenza virus in Minnesota turkey flocks during the 2015 epizootic. Epidemiology and Infection. 147:e179,1-8. https://doi.org/10.1017/S0950268819000633.
DOI: https://doi.org/10.1017/S0950268819000633 Interpretive Summary: In order to better control bird flu we need to understand how quickly the virus can transmit between birds that share the same house. Mathematical models have been previously developed to understand transmission efficiency for diseases. Here a well established model called "SEIR" was applied to turkeys using data from the 2015 bird flu outbreak in the U.S. It was found that, although there was some variation among flocks, the rate of virus spread was comparable to estimates with other diseases. The rate seems to be related to duration between when a turkey is infected and when it starts to get sick. This also demonstrates that using precise retrospective data in such a model system can provide accurate information on transmission efficiency of bird flu in poultry.
Technical Abstract: Better control of highly pathogenic avian influenza (HPAI) outbreaks requires deeper understanding of within-flock virus transmission dynamics. For such fatal diseases, daily mortality provides a proxy for disease incidence. We used the daily mortality data collected during the 2015 H5N2 HPAI outbreak in Minnesota turkey flocks to estimate the within-flock transmission rate parameter (ß). The number of birds in Susceptible, Exposed, Infectious and Recovered compartments was inferred from the data and used in a generalised linear mixed model (GLMM) to estimate the parameters. Novel here was the correction of these data for normal mortality before use in the fitting process. We also used mortality threshold to determine HPAI-like mortality to improve the accuracy of estimates from the back-calculation approach. The estimated ß was 3.2 (95% confidence interval (CI) 2.3–4.3) per day with a basic reproduction number of 12.8 (95% CI 9.2–17.2). Although flock-level estimates varied, the overall estimate was comparable to those from other studies. Sensitivity analyses demonstrated that the estimated ß was highly sensitive to the bird-level latent period, emphasizing the need for its precise estimation. In all, for fatal poultry diseases, the back-calculation approach provides a computationally efficient means to obtain reasonable transmission parameter estimates from mortality data.