Stochastic risk model of highly pathogenic avian influenza spread and impact of biosecurity protocols
Dorea, Fernanda Cetrangolo
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The potential spread of HPAI between commercial broiler farms in Georgia (USA) was mathematically modeled in order to evaluate the impact of different biosecurity measures in reducing the risk of disease spread. Compliance to standard biosecurity protocols by broiler growers in the state was investigated in a survey. Scenarios of biosecurity adoption were defined based on the results of the survey for two different areas of the state with different density of poultry farms, and which are facing different disease risks. Additional scenarios evaluated the impact of increasing attention to biosecurity. Off farm spread of virus for the different scenarios was estimated stochastically for periods of one day, and then modeled through days using geographical information to explicitly account for the effect of density on secondary spread. Results showed that in case of introduction of HPAI viruses in the state immediate detection is crucial, as the epidemic would start growing exponentially in the same day detection of mortality by the grower in the first affected farm is expected to occur (fifth day). The adoption of biosecurity measures was shown to delay the phase of exponential growth for the epidemic and slow spread, increasing the chances of outbreak control. Farms in North Georgia are under higher risk of disease spread due to higher farm density. The current level of biosecurity compliance in that region, where disease awareness among growers is higher in response to an ongoing outbreak of infectious laryngotracheitis, represents a small reduction in the risk of disease spread when compared to the frequency of biosecurity adoption in the South. Measures to prevent contamination spread through vehicles have the highest potential to reduce the current risk of disease outbreaks in the state.