Avian influenza and water supply to poultry farms

To understand and appreciate the risk that surface water poses to poultry it is necessary to understand the epidemiology of AI viruses in waterfowl (Arzey 2004; East, Hamilton, & Garner 2008; Khalenkov, Laver, & Webster R.G 2008; Leung et al. 2007; Senne 2003; Stallknecht et al. 1990b) and the ability of the viruses to persist in surface water and ambient conditions (De Benedictis, Beato, & Capua 2007; Doyle, Schultz-Cherry, &  Robach 2007; McFerran 1997; Ogata & Shibata 2008; Rice et al. 2007). Readers are referred to the various publications for further detail on these subjects.

Wild bird surveillance programs have detected LPAI viruses in the Australian wild water bird population.

While Australia is not in the high-risk migratory waterfowl pathways for H5N1 HPAI virus, there  is still a low risk of viruses being introduced from overseas where migrating shorebirds, waterfowl and commercial poultry share close proximity. There are  a few localities in Australia where such an association occurs (East, Hamilton, & Garner 2008). There is also a risk from Australian AI strains for poultry farms located close to water bodies that host wild waterfowl. The risk is through the potential for the supply of contaminated surface water,  physical association of these waterfowl or their fomites with commercial poultry, and possibly through other horizontal contacts.

Contaminated surface water and/or the presence of wild waterfowl have been implicated in previous AI outbreaks in Australia (East, Hamilton, & Garner 2008; Selleck et al. 2003; Senne 2003; Westbury 2003). The persistence of the AI virus in water is an important component of the epidemiology of the spread of AI virus from waterfowl  to commercial poultry via surface water. Low water temperatures combined with prolonged shedding  of virus by waterfowl can result in particular strains of AI virus persisting in the environment for up to 200 days. This may account for the generational cycling of the virus in ducks  returning to water habitats for breeding purposes (Stallknecht, Shane, Kearney, & Zwank 1990b; Stallknecht  2003).

AI viruses have also demonstrated tolerance and stability at a pH range from neutral to 8.5, with infectivity declining below a pH of 6.0. Under saline conditions, infectivity is inversely related to salt concentration (Stallknecht et  al. 1990a).