tetano
Editor, Senior Moderator
Both high and low pathogenic subtype A avian influenza remain ongoing threats to the commercialpoultry industry globally. The emergence of a novel low pathogenic H7N9 lineage in China presentsitself as a new concern to both human and animal health and may necessitate additional surveillancein commercial poultry operations in affected regions.
Methods: Sampling data was simulated using a mechanistic model of H7N9 influenza transmission within commercialpoultry barns together with a stochastic observation process.
Parameters were estimated usingmaximum likelihood. We assessed the probability of detecting an outbreak at time of slaughter usingboth real-time polymerase chain reaction (rt-PCR) and a hemagglutinin inhibition assay (HI assay)before considering more intense sampling prior to slaughter.
The day of virus introduction and R0were estimated jointly from weekly flock sampling data. For scenarios where R0 was known, weestimated the day of virus introduction into a barn under different sampling frequencies.
Results: If birds were tested at time of slaughter, there was a higher probability of detecting evidence of an outbreakusing an HI assay compared to rt-PCR, except when the virus was introduced <2 weeks beforetime of slaughter.
Prior to the initial detection of infection Nsample = 50 (1%) of birds were sampledon a weekly basis once, but after infection was detected, Nsample = 2000 birds (40%) were sampledto estimate both parameters. We accurately estimated the day of virus introduction in isolation withweekly and 2-weekly sampling.
Conclusions: A strong sampling effort would be required to infer both the day of virus introduction and R0.
Sucha sampling effort would not be required to estimate the day of virus introduction alone once R0 wasknown, and sampling Nsample = 50 of birds in the flock on a weekly or 2 weekly basis would besufficient.
Author: Amy PinsentIsobel M BlakeMichael T WhiteSteven Riley
Credits/Source: BMC Infectious Diseases 2014, 14:427
http://7thspace.com/headlines/47772...nd_estimation_of_virus_introduction_time.html
Methods: Sampling data was simulated using a mechanistic model of H7N9 influenza transmission within commercialpoultry barns together with a stochastic observation process.
Parameters were estimated usingmaximum likelihood. We assessed the probability of detecting an outbreak at time of slaughter usingboth real-time polymerase chain reaction (rt-PCR) and a hemagglutinin inhibition assay (HI assay)before considering more intense sampling prior to slaughter.
The day of virus introduction and R0were estimated jointly from weekly flock sampling data. For scenarios where R0 was known, weestimated the day of virus introduction into a barn under different sampling frequencies.
Results: If birds were tested at time of slaughter, there was a higher probability of detecting evidence of an outbreakusing an HI assay compared to rt-PCR, except when the virus was introduced <2 weeks beforetime of slaughter.
Prior to the initial detection of infection Nsample = 50 (1%) of birds were sampledon a weekly basis once, but after infection was detected, Nsample = 2000 birds (40%) were sampledto estimate both parameters. We accurately estimated the day of virus introduction in isolation withweekly and 2-weekly sampling.
Conclusions: A strong sampling effort would be required to infer both the day of virus introduction and R0.
Sucha sampling effort would not be required to estimate the day of virus introduction alone once R0 wasknown, and sampling Nsample = 50 of birds in the flock on a weekly or 2 weekly basis would besufficient.
Author: Amy PinsentIsobel M BlakeMichael T WhiteSteven Riley
Credits/Source: BMC Infectious Diseases 2014, 14:427
http://7thspace.com/headlines/47772...nd_estimation_of_virus_introduction_time.html