Estimating the between-farm transmission rates for highly pathogenic avian influenza subtype H5N1 epidemics in Bangladesh between 2007 and 2013
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Date
2018
Journal Title
Journal ISSN
Volume Title
Publisher
Transboundary and emerging diseases
Abstract
Highly Pathogenic Avian Influenza (HPAI) is classified by the World Organization for
Animal Health as one of the notifiable diseases. Its occurrence is associated with severe
socio-economic impacts and is also zoonotic. Bangladesh HPAI epidemic data for
the period between 2007 and 2013 were obtained and split into epidemic waves
based on the time lag between outbreaks. By assuming the number of newly infected
farms to be binomially distributed, we fit a Generalized Linear Model to the data to
estimate between-farm transmission rates (b). These parameters are then used
together with the calculated infectious periods to estimate the respective basic reproduction
numbers (R0). The change in b and R0 with time during the course of each epidemic
wave was explored. Finally, sensitivity analyses of the effects of reducing the
delay in detecting infection on a farm as well as extended infectiousness of a farm
beyond the day of culling were assessed. The point estimates obtained for b ranged
from 0.08 (95% CI: 0.06–0.10) to 0.11 (95% CI: 0.08–0.20) per infectious farm per day
while R0 ranged from 0.85 (95% CI: 0.77–1.02) to 0.96 (95% CI: 0.72–1.20). Sensitivity
analyses reveal that the estimates are quite robust to changes in the assumptions
about the day in reporting infection and extended infectiousness. In the analysis
allowing for time-varying transmission parameters, the rising and declining phases
observed in the epidemic data were synchronized with the moments when R0 was
greater and less than one, respectively. From an epidemiological perspective, the consistency
of these estimates and their magnitude (R0 1) indicate that the effectiveness
of the deployed control measures was largely invariant between epidemic waves
and the trend of the time-varying R0 supports the hypothesis of sustained farm-tofarm
transmission that is possibly initiated by a few unique introductions.
Description
Keywords
Disease control, Transmission, Veterinary epidemiology, Zoonosis/zoonotics
Citation
Ssematimba, A., Okike, I., Ahmed, G. M., Yamage, M., Boender, G. J., Hagenaars, T. J., & Bett, B. (2018). Estimating the between‐farm transmission rates for highly pathogenic avian influenza subtype H5N1 epidemics in Bangladesh between 2007 and 2013. Transboundary and emerging diseases, 65(1), e127-e134. DOI: 10.1111/tbed.12692