Clinical and acquired immunologic responses to West Nile virus infection of domestic chickens (Gallus gallus domesticus).

Numerous bird species are highly susceptible to North American strains of West Nile virus (WNV), and although domestic chickens are relatively resistant to WNV-associated disease, this species currently represents the most practical avian model for immune responses to WNV infection. Knowledge of the immunomodulation of susceptibility to WNV in birds is important for understanding taxonomic differences in infection outcomes. While focusing on immunophenotyping of CD3(+), CD4(+), CD8(+), and CD45(+) lymphocyte subpopulations, we compared lymphocyte subpopulations, blood chemistries, cloacal temperatures, IgM and IgG antibody titers, and differential whole-blood cell counts of WNV-infected and uninfected hens. Total blood calcium and lymphocyte numbers were lower in WNV-infected chickens compared with uninfected chickens. The heterophil-to-lymphocyte ratio increased over time from 2 to 22 d postinoculation (DPI) in uninfected chickens and from 2 to 8 DPI in WNV-infected chickens, although levels declined from 8 to 22 DPI in the latter group. No significant differences were found in the remaining immunological and hematological variables of the WNV-infected and uninfected groups. Our results reaffirm that chickens are resistant to WNV infection, and demonstrated that the heterophil-to-lymphocyte ratio differed between groups, allowing for sorting of infection status. Similar patterns in immune responses over time in both infected and uninfected hens may be related to age (i.e., 10 wk) and associated immune development.