Natural Bagaza virus infection in game birds in southern Spain

Abstract

In late summer 2010 a mosquito born flavivirus not previously reported in Europe called Bagaza virus (BAGV) caused high mortality in red-legged partridges (Alectoris rufa) and ring-necked pheasants (Phasianus colchicus). We studied clinical findings, lesions and viral antigen distribution in naturally BAGV infected game birds in order to understand the apparently higher impact on red-legged partridges. The disease induced neurologic signs in the two galliform species and, to a lesser extent, in common wood pigeons (Columba palumbus). In red-legged partridges infection by BAGV caused severe haemosiderosis in the liver and spleen that was absent in pheasants and less evident in common wood pigeons. Also, BAGV antigen was present in vascular endothelium in multiple organs in red-legged partridges, and in the spleen in common wood pigeons, while in ring-necked pheasants it was only detected in neurons and glial cells in the brain. These findings indicate tropism of BAGV for endothelial cells and a severe haemolytic process in red-legged partridges in addition to the central nervous lesions that were found in all three species.

Figure 1

Microscopic lesions in the brain of BAGV infected game birds. Cerebrum, ring-necked pheasant. Neuronal necrosis and lymphoplasmacytic perivascular infiltrates. HE, ×100.

Figure 2

Microscopic lesions in the brain of BAGV infected game birds. Cerebellum, ring-necked pheasant. Purkinje cell necrosis and glial nodule. HE, ×200.

Figure 3

Microscopic lesions in the brain of BAGV infected game birds. Cerebrum, red-legged partridge. Neuronal necrosis and gliosis. HE, ×200.

Figure 4

Microscopic lesions in the brain of BAGV infected game birds. Cerebellum, red-legged partridge. Purkinje cell necrosis and phagocitosis and endothelial cell swelling (4a). HE, ×100.

Figure 5

Lesions and BAGV antigen distribution in the heart of BAGV infected red-legged partridges. Severe myocarditis with presence of BAGV antigen labeling in myofibres and capillary endothelial cells (5a). HE, ×100; immunohistochemistry for detection of flavivirus antigen, ×400.

Figure 6

Lesions and BAGV antigen distribution in the kidney of BAGV infected red- legged partridges. Focal necrosis and BAGV antigen labelling in capillary endothelial cells of the glomerular mesangium (6a). HE, ×100, immunohistochemistry for detection of flavivirus antigen, ×400.

Figure 7

Haemosiderosis in spleen section of red-legged partridges infected with BAGV. HE ×100.

Figure 8

Haemosiderosis in spleen section of red-legged partridges infected with BAGV. Perls’ stain, ×100.

Figure 9

Haemosiderosis in liver section of red-legged partridges infected with BAGV. HE, ×100.

Figure 10

Haemosiderosis in liver section of red-legged partridges infected with BAGV. Perls’ stain, ×100

Figure 11

Distribution of positive flavivirus (presumptive BAGV) immunostaining in naturally BAGV infected red-legged partridges, ring-necked pheasants and common wood pigeons. Each column represents the percentage of individuals that showed positive immunostaining in each organ and “n” is the number of individuals in which each tissue was tested.

Figure 12

Viral antigen distribution in the brain of BAGV infected game birds. Cerebrum, ring-necked pheasant. Labeling of BAGV antigen in the cytoplasm of neurons. Immunohistochemistry for detection of flavivirus antigen, ×100.

Figure 13

Viral antigen distribution in the brain of BAGV infected game birds. Cerebellum, ring-necked pheasant. Labeling of BAGV antigen in the cytoplasm of Purkinje cells (13a). Immunohistochemistry for detection of flavivirus antigen, ×200; ×400 (13a).

Figure 14

Viral antigen distribution in the brain of BAGV infected game birds. Cerebrum, red-legged partridge. Labeling of BAGV antigen in the cytoplasm of neurons and capillary endothelial cells. Immunohistochemistry for detection of flavivirus antigen, ×200.

Figure 15

Viral antigen distribution in the brain of BAGV infected game birds. Cerebellum, red-legged partridge. Labeling of BAGV antigen in the capillary endothelial cells (15a) and cytoplasm of Purkinje cells (15b). Immunohistochemistry for detection of flavivirus antigen, ×100; ×400 (15a and b).