Clinical, pathological, and immunohistochemical findings in bald eagles (Haliaeetus leucocephalus) and golden eagles (Aquila chrysaetos) naturally infected with West Nile virus

Abstract

Fifteen bald eagles (Haliaeetus leucocephalus) and 3 golden eagles (Aquila chrysaetos) were diagnosed with West Nile disease based on 1) presence of lesions in brain, eyes, and heart, 2) viral antigen detection in brain, eyes, heart, kidney, and/or liver by immunohistochemical staining, 3) detection of viral RNA in tissue samples and/or cerebrospinal fluid (CSF) by polymerase chain reaction, and/or 4) detection of West Nile virus (WNV)-specific antibodies in CSF by serum neutralization assay. West Nile virus-associated gross lesions included cerebral pan-necrosis with hydrocephalus ex vacuo (7/15 bald eagles), fibrin exudation into the fundus in 1 golden eagle, retinal scarring in 1 bald eagle, and myocardial pallor and rounded heart apex in 4 bald eagles. Histologic lesions included lymphoplasmacytic encephalitis, most prominently in the cerebrum (17 eagles), lymphoplasmacytic pectenitis and choroiditis (15 and 8 eagles, respectively), and myocarditis (12 eagles). West Nile virus antigen was detected in the majority of the eagles in neurons of the brain (cerebrum and cerebellum), and less commonly present in neurons of the retina, tubular epithelial cells of the kidney, and cardiomyocytes. West Nile disease was diagnosed in 2 bald eagles based on the presence of cerebral pan-necrosis and WNV-specific antibodies in the CSF despite lacking viral antigen and RNA. In conclusion, WNV infection causes a fatal disease in bald and golden eagles. A variety of gross and histologic lesions are highly suggestive of WN disease in most eagles. A combination of detection of viral antigen and/or RNA or virus-specific antibodies proved useful in confirming the diagnosis.

Comparative Pathology of West Nile Virus in Humans and Non-Human Animals

“…This chart has been modified to include the most recent literature as well as pathologic findings in birds experimentally infected with WNV (Table 1) [106][107][108][109][110][111][112][113][114][115][116]. Ocular lesions are seen in raptors (red-tailed hawks, Cooper s hawks, bald eagles, golden eagles, goshawks) and owls (great horned owls, barred owls) and range from lymphoplasmacytic pectenitis and chorioretinal inflammation and scarring to generalized endophthalmitis [110,[116][117][118][119]. Vasculitis has occasionally been noted within multiple organs in a variety of affected avian species [103,120,121].…”

Multidecade Mortality and a Homolog of Hepatitis C Virus in Bald Eagles (Haliaeetus leucocephalus), the National Bird of the USA

“…Infections of bald eagles have been documented since the early 1900s but (with the possible exception of West Nile virus 14,15 ) have generally been considered sporadic and incidental 10,12,16,17 . Among 2,980 bald eagle carcasses submitted to the U.S. Geological Survey National Wildlife Health Center (NWHC) in Madison, Wisconsin, USA, between 1982 and 2013, only 5.2% of deaths were attributed to infectious diseases 12 .…”

“…Among 2,980 bald eagle carcasses submitted to the U.S. Geological Survey National Wildlife Health Center (NWHC) in Madison, Wisconsin, USA, between 1982 and 2013, only 5.2% of deaths were attributed to infectious diseases 12 . Documented infectious diseases of bald eagles include: ectoparasitoses 18,19 , helminthoses 20–24 , aspergillosis 25 , coccidiosis 26 , toxoplasmosis 27–29 , sarcocystosis 30–32 , leucocytozoonosis 33 , avian malaria 34–36 , avian cholera 37 , mycobacteriosis 38,39 , trichomoniasis 40 , other bacterioses 41–43 , avian pox 44 , herpes 45 , avian influenza 46,47 , Newcastle disease 48 , eastern equine encephalitis 49 , and West Nile encephalitis 15 . However, many of these infections are known from only single cases or case clusters and affected birds often present with comorbidities, such that the importance of infection for bald eagle population health remains unclear.…”

“…Given the known susceptibility of raptors to viral encephalitides (e.g. West Nile encephalitis 15 ) and the observation of neurologic signs and hepatic pathology in affected eagles, we investigated potential viral causes. Our analyses led to the identification of a novel hepacivirus-like virus ( Flaviviridae : Hepacivirus ), the type-virus of which is the globally important human pathogen hepatitis C virus (HCV) 51 .…”

DNA vaccines encoding the envelope protein of West Nile virus lineages 1 or 2 administered intramuscularly, via electroporation and with recombinant virus protein induce partial protection in large falcons (Falco spp.)

“…Besides asymptomatic courses, WNV infections may lead to severe morbidity and mortality in different avian species, especially in raptors, crows and domestic geese [ 18 - 27 ], which seemed to be particularly vulnerable to WNV. In raptors, natural WNV infections have been described in hawks [ 20 , 21 , 28 - 30 ], eagles [ 24 - 26 , 31 - 33 ], condors [ 34 ] and different falcon species, such as peregrine falcons ( Falco peregrinus ), gyrfalcons ( F. rusticolus ), prairie falcons ( F. mexicanus ), merlins ( F. columbarius ) and American kestrels ( F. sparverius ) [ 27 , 30 ]. Experimental WNV infection studies have been performed in single raptor species [ 27 , 35 - 37 ], demonstrating that falcons can act as amplifying hosts, developing viremia, virus shedding, and subclinical to fatal diseases.…”