Contact structure and potential risk factors for avian influenza transmission among open-sided chicken farms in Kamalia, an important poultry rearing area of Pakistan

Since 1994, the domestic poultry in Pakistan has experienced several outbreaks due to avian influenza viruses of subtypes H7N3, H5N1, and H9N2. This paper reveals horizontal contacts and potential risk factors for the spread of avian influenza infection between open-sided chicken farms in Kamalia, a sub-district of Punjab province. Between April and June 2009, an interview-based questionnaire was administered to a sample of 78 growers. The survey identified the following potential biosecurity risks for outbreak propagation: i) short buffer distances between farms, ii) disposal of carcasses and other organic wastes into the environment, iii) entry of feral birds into poultry sheds, iv) visits of poultry farmers to possible cross-contamination sites, v) absence of boundary walls, vi) incomplete biosecurity on high-risk visitors (i. e. those going inside the poultry houses), essential vehicles and equipment used by vaccination crews vii) visits of intermediaries and service providers and, viii) sharing of egg trays between farms at production. For most of the variables, there was no significant difference between the broiler and layer type of farms (p < or = 0.05). The risk of an extensive outbreak in Kamalia was concluded to be due to its high poultry density, ubiquitous small-scale, market-oriented poultry production with medium to low biosecurity, and the affiliation of the farmers to multiple service providers. To reduce the risk of having an outbreak, farm-specific biosecurity gaps should be identified and appropriate action taken to close these gaps. Improvement in biosecurity and targeted surveillance are therefore considered critical to limit the spread of infection should an outbreak occur.