Bird Flu :: Tracking the spread of bird flu between farms

A new way of understanding how highly pathogenic avian influenza (HPAI) spreads among farm birds is published today in PLoS ONE. The study could help analyse the success of different control measures in the event of future outbreaks.

The study, carried out by mathematical modellers from Imperial College London and the London School of Hygiene and Tropical Medicine, focuses on how H7N3, H7N7 and H7N1 strains of the virus were transmitted between different farms in three recent outbreaks.

The scientists used these case studies to devise a numerical measure for how fast the virus spreads, giving the team an important insight into the overall transmissibility of the virus. This can be used to determine whether an outbreak will turn into a self-sustaining epidemic, in which the virus spreads from each infected farm to at least one other farm. The team hopes that their method, which can be used to assess the effectiveness of control measures used to counter any outbreak, will be useful for future planning to stop the transmission of highly pathogenic avian influenza between birds.

Focusing on outbreaks in Italy, the Netherlands and Canada in recent years, the researchers tracked the rate of the virus’ transmission at different stages of each outbreak ? both before and after measures were brought in to control it. All of the investigated outbreaks occurred in extremely dense poultry farming areas, which increases the chances of transmission and therefore poses particular problems for control. Their findings showed that although the spread of the disease between farms was slowed by the introduction of control measures such as enhanced bio-security, movement restrictions and culling on infected farms, the rate of transmissibility remained close to the threshold point at which the outbreak would become a self-sustaining epidemic.

Dr Tini Garske, from Imperial College London’s Institute for Mathematical Sciences says: “Our analyses suggest that in the event of an outbreak of highly pathogenic avian flu in a very dense poultry farming area, additional measures may be needed in order to halt the epidemic. In the case studies we looked at we found that pre-emptive culling and de-population of nearby at-risk areas succeeded in containing the outbreak, where other less drastic measures had failed.”

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