Pathogenicity of West Nile Virus Lineage 1 to German Poultry

Abstract

West Nile virus (WNV) is a mosquito-borne virus that originates from Africa and at present causes neurological disease in birds, horses, and humans all around the globe. As West Nile fever is an important zoonosis, the role of free-ranging domestic poultry as a source of infection for humans should be evaluated. This study examined the pathogenicity of an Italian WNV lineage 1 strain for domestic poultry (chickens, ducks, and geese) held in Germany. All three species were subcutaneously injected with WNV, and the most susceptible species was also inoculated via mosquito bite. All species developed various degrees of viremia, viral shedding (oropharyngeal and cloacal), virus accumulation, and pathomorphological lesions. Geese were most susceptible, displaying the highest viremia levels. The tested waterfowl, geese, and especially ducks proved to be ideal sentinel species for WNV due to their high antibody levels and relatively low blood viral loads. None of the three poultry species can function as a reservoir/amplifying host for WNV, as their viremia levels most likely do not suffice to infect feeding mosquitoes. Due to the recent appearance of WNV in Germany, future pathogenicity studies should also include local virus strains.

Keywords: Culex pipiens; West Nile virus; arbovirus; chickens; ducks; experimental infection; geese; pathogenesis; poultry; sentinel.

Figure 1

Viremia in chickens (in blue), ducks (in red), and geese (in green) after subcutaneous injection (s.c.) with WNV or the bite of WNV-infected mosquitoes (m.b.).

Figure 2

Viral shedding of chickens (C), ducks (D), and geese (G) after subcutaneous injection with WNV or the bite of WNV-infected mosquitoes. Numbers indicate the viral copies/µL of total RNA of positive or inconclusive oropharyngeal (PS in dark or light red) and cloacal (CS in dark or light blue) swabs. Asterisk indicates one duck (D 07) that succumbed early after infection, so that swab samples could only be taken one and two days post infection. NA stands for not applicable. Ct stands for cycle threshold.

Figure 3

Seroconversion of chickens (in blue), ducks (in red), and geese (in green) after inoculation with WNV via subcutaneous injection (s.c.) or the bite of WNV-infected mosquitoes (m.b.; G 13 – G 16). (A) Antibody titers determined by a virus neutralization test (VNT) and (B) antibody titers determined by a commercial competition ELISA. Data are presented in a box-and-whisker plot, where the ends of the whiskers represent the minimum and maximum values. Outliers are represented by an x instead of the whisker-ends. The box includes 50% of the values of each group and the line in the middle of each group represents the median value.

Figure 4

Selected organ samples of chickens (in blue), ducks (in red), and geese (in green) infected with WNV via subcutaneous injection (s.c.) or the bite of WNV-infected mosquitoes (m.b.). Brain samples depicted as filled circles and spleen samples as filled triangles. All birds were euthanized 19, 20, or 21 dpi, except for one duck (D 07) that succumbed 2 dpi.

Figure 5

Histopathological findings in WNV-infected geese. (A) Liver of G 01, showing vacuolar degeneration (*), acute hemorrhages (arrowheads), and multifocal subacute non-suppurative hepatitis (arrows). (B,C) Variability of pathomorphological lesions in the spleen with (B) focal acute necrotizing splenitis of G 03 and (C) focal mild subacute non-suppurative arteritis with distinct intima hyperplasia (arrow) in the vessel wall of G 13. (D-F) Multifocal acute to subacute non-suppurative encephalitis (D) in the brain stem of G 02 with glia nodules (arrow) and mild lymphohistiocytic perivascular cuffing (arrowheads). (E) Cerebrum of G 06 with necrotic foci consisting of mild lymphoplasmacellular perivascular cuffing, migrating mononuclear cells, small glia nodules, and scattered single cell necrosis (neurons, glia cells, and leucocytes). (F) Cerebrum of G 06 with leucocytic degeneration (arrowheads) within the mononuclear perivascular cuffing (lymphocytes, histiocytes, and plasma cells). Bars: A–E 50 µm, F 20 µm.