Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2008
Publication Date: 9/1/2008
Citation: Swayne, D.E., Slemons, R.D. 2008. Using mean infectious dose of wild duck-and poultry-origin high and low pathogenicity avian influenza viruses as one measure of infectivity and adaptation to poultry. Avian Diseases. 52:455-460. Interpretive Summary: The quantity of avian influenza virus (AIV) needed to produce an infection in poultry is dependent upon both the bird species and virus strain. We propose a laboratory developed test, the intranasal chicken mean infectious dose (CID50), could serve as a predictor for which strains of AIV, could be the cause of a current, or future, AI outbreak in poultry. Most AIV that were infectious for chickens had CID50 of 3log10 or less, while low infectivity was observed for viruses with 4.7log10 CID50. However, chickens were not easily infected with most wild bird AIV, but domestic ducks and turkeys were easily infected and they could serve as key bridging species for waterfowl-origin AIV crossing into domestic poultry. Furthermore, these data suggest mixing of poultry species during raising and using outdoor production systems is a major risk factor for transmission of AIVs from wild birds to domestic poultry.
Technical Abstract: The mean infectious doses of selected avian influenza virus (AIV) isolates, determined in domestic poultry under experimental conditions, were shown to be both host and virus dependent and could be considered one measure of the infectivity and adaptation to a specific host. As such, the mean infectious dose could serve as a quantitative predictor for which strains of AIV, given the right conditions, would more likely be transmitted to and maintained in a given species and/or subsequently cause an AI outbreak in the given species. The intranasal (IN) mean bird infectious doses (BID50) were determined for 11 turkey- and chicken-origin, high pathogenicity AIV (HPAIV) isolates for White Leghorn (WL) chickens, and one chicken- and two wild mallard-origin, low pathogenicity AIV (LPAIV) isolates for turkeys, WL and White Plymouth Rock (WPR) chickens, domestic ducks and geese, and Japanese quail. The BID50 for HPAIV isolates for WL chickens ranged from 1.2-4.7log10 mean embryo infectious dose (EID50) (median = 2.9log109). For chicken-origin HPAIV isolates, the BID50 in WL chickens ranged from 1.2-3.0log10 EID50 (median = 2.6log10) while with turkey-origin HPAIV isolates, the BID50 in WL chickens were higher, ranging from 2.8-4.7log10 EID50 (median = 3.9log10). The BID50 of 4.7log10 was for a turkey-origin HPAIV virus that was not transmitted to chickens on the same farm suggesting that, under the specific conditions present on that farm, there was insufficient infectivity, adaptation or exposure to that virus population for sustained chicken transmission. Although the upper limit for BID50 to predict infectivity and sustainable transmissibility for a specific species is unknown, a BID50 <4.7log10 was suggestive of such transmissibility. For the LPAIVs, there was a trend for domestic ducks and geese, and Japanese quail to have the greatest susceptible and WL chickens to be most resistant, but turkeys were susceptible to all three LPAIV tested when used at moderate challenge doses. This suggests domestic ducks and geese, turkeys and Japanese quail could serve as bridging species for LPAIVs from wild waterfowl to chickens and other gallinaceous poultry. These data do provide support for the commonly held and intuitive belief that mixing of poultry species during rearing and in outdoor production systems is a major risk factor for interspecies transmission of AIVs and the emergence of new AIV stains capable of causing AI outbreaks as these situations present a more diverse host population to circumvent the natural host dependency or host range of naturally circulating viruses.