Susceptibility of Carrion Crows to Experimental Infection with Lineage 1 and 2 West Nile Viruses

Abstract

West Nile virus (WNV) outbreaks in North America have been characterized by substantial die-offs of American crows (Corvus brachyrhynchos). In contrast, a low incidence of bird deaths has been observed during WNV epidemic activity in Europe. To examine the susceptibility of the western European counterpart of American crows, we inoculated carrion crows (Corvus corone) with WNV strains isolated in Greece (Gr-10), Italy (FIN and Ita09), and Hungary (578/10) and with the highly virulent North American genotype strain (NY99). We also inoculated American crows with a selection of these strains to examine the strains' virulence in a highly susceptible bird species. Infection with all strains, except WNV FIN, resulted in high rates of death and high-level viremia in both bird species and virus dissemination to several organs. These results suggest that carrion crows are highly susceptible to WNV and may potentially be useful as part of dead bird surveillance for early warning of WNV activity in Europe.

Keywords: Corvus corone; Europe; WNV; West Nile virus; carrion crow; corvid; experimental infection; sentinel; surveillance; susceptibility; virulence; viruses.

Figure 1

Survival rate for West Nile virus (WNV)–infected carrion crows after inoculation with 2,000 50% tissue culture infectious doses of WNV; each group (n = 6) was inoculated with a different strain. Crows were monitored daily for signs of disease through postinoculation day 14.

Figure 2

Viral RNA copy numbers for West Nile virus (WNV)–infected carrion crows after inoculation with 2,000 50% tissue culture infectious doses of WNV; each group (n = 6) was inoculated with a different strain. RNA copy numbers are represented as log-transformed medians. The assay had a detection limit of 9 (1.0 log₁₀) RNA copies/mL of serum.

Figure 3

Infectious virus titer profiles for West Nile virus (WNV)–infected carrion crows after inoculation with 2,000 50% tissue culture infectious doses (TCID₅₀) of WNV; each group (n = 6) was inoculated with a different strain. Infectious virus titers were determined by TCID₅₀ titration and are represented as log-transformed medians; error bars indicate range. The assay had a detection limit of 1.8 TCID₅₀/mL.

Figure 4

Viral RNA copy numbers in organs from 10 carrion crows (2 per group) euthanized 4 days after being experimentally infected with 1 of 5 different West Nile virus strains (n = 6, per group). Virus titers are represented as log-transformed medians; error bars indicate range. The assay had a detection limit of 9 (1.0 log₁₀) RNA copies/g of tissue. H, heart; L, liver; S, spleen; K, kidney; Bo, bone marrow; Br, brain.

Figure 5

Viral RNA copy numbers in organs from 22 carrion crows euthanized because of illness after being experimentally infected with 1 of 4 different West Nile virus strains (n = 6, per group). Copy numbers are represented as log-transformed medians; error bars indicate range. The assay had a detection limit of 9 (1.0 log₁₀) RNA copies/g of tissue. H, heart; L, liver; S, spleen; K, kidney; Bo, bone marrow; Br, brain.