Susceptibility of European jackdaws (Corvus monedula) to experimental infection with lineage 1 and 2 West Nile viruses

Abstract

Mass bird mortality has been observed in North America after the introduction of West Nile virus (WNV), most notably massive die-offs of American crows (Corvus brachyrhynchos). In contrast, WNV epidemic activity in Europe has been characterized by very low incidences of bird mortality. As the general susceptibility of European corvids to strains of WNV remains in question, European jackdaws (Corvus monedula) were inoculated with WNV strains circulating currently in Greece (Greece-10), Italy (FIN and Ita09) and Hungary (578/10), as well as a North American (NY99) genotype with a demonstrated corvid virulence phenotype. Infection with all strains except WNV-FIN resulted in mortality. Viraemia was observed for birds inoculated with all strains and virus was detected in a series of organs upon necropsy. These results suggested that jackdaws could potentially function as a sentinel for following WNV transmission in Europe; however, elicited viraemia levels might be too low to allow for efficient transmission of virus to mosquitoes.

Fig. 1

Survival of five or six European jackdaws, each inoculated with 2000 TCID₅₀ WNV strains NY99, Greece-10, FIN, Ita09 or 578/10. Jackdaws were monitored daily for signs of disease up to 14 days p.i.

Fig. 2

Serum viraemia profiles for WNV-infected European jackdaws after inoculation with 2000 TCID₅₀ NY99 (n=5), Greece-10 (n=6), FIN (n=5), Ita09 (n=5) or 578/10 (n=5). Viral titres were determined by RNA copy numbers and are represented as geometric mean±SD. A detection limit of 0.95 log₁₀RNA copies ml⁻¹ was determined.

Fig. 3

Tissue viral load, as determined by RNA copy numbers, in organs harvested from birds experimentally infected with different WNV strains and euthanized on day 4 p.i. (two per group). Viral titres are represented as geometric mean±SD. A detection limit of 0.95 log₁₀RNA copies g⁻¹ was determined.

Fig. 4

Tissue viral load, as determined by RNA copy numbers, in organs harvested from birds experimentally infected with different WNV strains and euthanized due to morbidity. NY99 (n=3): one bird euthanized on day 5 p.i., two birds on day 7 p.i.; Greece-10 (n=3): one bird euthanized on day 6 p.i., one bird on day 8 p.i. and one bird on day 9 p.i.; Ita09 (n=3): three birds euthanized on day 7 p.i.; and 578/10 (n=2): one bird euthanized on day 6 p.i. and one bird on day 8 p.i. Viral titres are represented as geometric mean±SD. A detection limit of 0.95 log₁₀RNA copies g⁻¹ was determined.

Fig. 5

Tissue viral load, as determined by RNA copy numbers, in organs harvested from birds experimentally infected with different WNV strains and euthanized on day 14 p.i. NY99, two birds euthanized; Greece-10, three birds; FIN, five birds; Ita09, two birds; and 578/10, three birds. Viral titres are represented as geometric mean±SD. A detection limit of 0.95 log₁₀RNA copies g⁻¹ was determined.