Humoral immunity to West Nile virus is long-lasting and protective in the house sparrow (Passer domesticus)

Abstract

The house sparrow (Passer domesticus) is a common and abundant amplifying host of West Nile virus (WNV) and many survive infection and develop humoral immunity. We experimentally inoculated house sparrows with WNV and monitored duration and protection of resulting antibodies. Neutralizing antibody titers remained relatively constant for >or= 36 months (N = 42) and provided sterilizing immunity for up to 36 months post-inoculation in 98.6% of individuals (N = 72). These results imply that immune house sparrows are protected from WNV infection for multiple transmission seasons. Additionally, individuals experiencing WNV-associated mortality reached significantly higher peak viremia titers than survivors, and mortality during acute infection was significantly higher in caged versus free-flight sparrows. A better understanding of the long-term immunity and mortality rates in birds is valuable in interpreting serosurveillance and diagnostic data and modeling transmission and disease dynamics.

Figure 1

Timeline of West Nile virus experimental inoculation of three experimental groups of house sparrows. * Antibody (Ab) titer indicates when serum samples were titrated to determine WNV PRNT₉₀ antibody titers. † All birds were bled at 1 month post-inoculation to confirm seroconversion and assess antibody titers.

Figure 2

Average daily viremia titers among house sparrows experimentally inoculated with West Nile virus that succumbed and those that survived infection. Standard error bars are provided for 1–6 days post-inoculation.