The animal-human interface and infectious disease in industrial food animal production: rethinking biosecurity and biocontainment

Abstract

Understanding interactions between animals and humans is critical in preventing outbreaks of zoonotic disease. This is particularly important for avian influenza. Food animal production has been transformed since the 1918 influenza pandemic. Poultry and swine production have changed from small-scale methods to industrial-scale operations. There is substantial evidence of pathogen movement between and among these industrial facilities, release to the external environment, and exposure to farm workers, which challenges the assumption that modern poultry production is more biosecure and biocontained as compared with backyard or small holder operations in preventing introduction and release of pathogens. An analysis of data from the Thai government investigation in 2004 indicates that the odds of H5N1 outbreaks and infections were significantly higher in large-scale commercial poultry operations as compared with backyard flocks. These data suggest that successful strategies to prevent or mitigate the emergence of pandemic avian influenza must consider risk factors specific to modern industrialized food animal production.

Figure 1a

Dot density maps of swine and broiler production in the U.S. in 2002^a

Figure 1b

Density distribution maps of swine and poultry in Asia estimated for 1998–2000^a

Figure 2

Temporal trends in the number of hog operations and number of hogs per operation in the U.S., 1965–2003^a

Figure 3

Chicken catchers at work in a poultry concentrated animal feeding operation, U.S., 1999^a

Figure 4

A schematic representation (not to scale) of multiple potential pathways for exposure to and transfer of pathogens within the environs of concentrated animal feeding operations^a

Figure 5

Percentage of poultry workers seropositive for H5 antibody by number of poultry-related tasks performed^a

Figure 6

Contribution of different flock types to total domestic poultry population (approximately 280 million birds) in Thailand in 2004^a

Figure 7

Contribution of different flock types to total number of flocks (approximately 2.9 million flocks) in Thailand in 2004^a

Figure 8

Spatial distribution of poultry population counts at district level in Thailand in 2003

Figure 9

Risk of infection (percent) with HPAI in Thailand in 2004 by flock type