http://www.cdc.gov/eid/content/14/3/ICEID2008.pdf (board 262 pg 206)
Background:
Outbreaks of avian influenza in the commercial poultry industry are associated with mass culling of birds and significant economic losses. Rapid detection of infected flocks is critical to limiting the financial impact of avian influenza outbreaks, but poor knowledge of the most likely mechanism of inter-farm spread limits the success of surveillance efforts early in the outbreak. In 2005 a survey of poultry growers in two Georgia counties assessed the number and type of farm visitors in the previous 7 days, and the probability of bird contact of each visitor. The results of this survey were used to model the risk of farm infection with avian influenza associated with human movement between farms.
Methods:
A compartmental epidemic (SEIR) model was used to estimate the time to grower detection of infection following the introduction of a highly pathogenic avian influenza (HPAI) virus. Using the results of the on farm epidemic model, off farm spread of disease was stochastically modeled for the time period between disease introduction and the estimated day of grower detection of infection. Off farm spread of influenza was based upon the probability distributions of the following: the daily likelihood of each farm visitor, the risk that the visit was associated infectious material contact and the daily number of farms visited by each visitor.
Results:
The results of the on farm model estimated that the introduction of HPAI virus strains into commercial poultry will likely be detected by the grower within 5 days. The off-farm disease spread model estimated the number of farms potentially infected by the index farm in the days prior to grower detection ranged from 0-5, depending upon the density of susceptible farms in the county.
Conclusions:
According to this stochastic model of HPAI spread, a sudden introduction of HPAI virus may take up to 5 days to be detected by the poultry grower. During this time the movement of people between farms plays a major role in the off-farm spread. The number of exposed farms was most influenced by the relative frequencies of different farm visitors and the probability of contact with infectious materials while on the farm. The likelihood that the exposed (contact) farms become infected is highly dependent upon the
attention to biosecurity.
Background:
Outbreaks of avian influenza in the commercial poultry industry are associated with mass culling of birds and significant economic losses. Rapid detection of infected flocks is critical to limiting the financial impact of avian influenza outbreaks, but poor knowledge of the most likely mechanism of inter-farm spread limits the success of surveillance efforts early in the outbreak. In 2005 a survey of poultry growers in two Georgia counties assessed the number and type of farm visitors in the previous 7 days, and the probability of bird contact of each visitor. The results of this survey were used to model the risk of farm infection with avian influenza associated with human movement between farms.
Methods:
A compartmental epidemic (SEIR) model was used to estimate the time to grower detection of infection following the introduction of a highly pathogenic avian influenza (HPAI) virus. Using the results of the on farm epidemic model, off farm spread of disease was stochastically modeled for the time period between disease introduction and the estimated day of grower detection of infection. Off farm spread of influenza was based upon the probability distributions of the following: the daily likelihood of each farm visitor, the risk that the visit was associated infectious material contact and the daily number of farms visited by each visitor.
Results:
The results of the on farm model estimated that the introduction of HPAI virus strains into commercial poultry will likely be detected by the grower within 5 days. The off-farm disease spread model estimated the number of farms potentially infected by the index farm in the days prior to grower detection ranged from 0-5, depending upon the density of susceptible farms in the county.
Conclusions:
According to this stochastic model of HPAI spread, a sudden introduction of HPAI virus may take up to 5 days to be detected by the poultry grower. During this time the movement of people between farms plays a major role in the off-farm spread. The number of exposed farms was most influenced by the relative frequencies of different farm visitors and the probability of contact with infectious materials while on the farm. The likelihood that the exposed (contact) farms become infected is highly dependent upon the
attention to biosecurity.