Emerging infectious diseases (EID) present significant threats to the conservation of global biodiversity (Daszak et al. 2000). Evaluating impacts (spatial, temporal and demographic) of EIDs on sensitive and declining wildlife populations is challenging because quantitative information is usually dependent on estimates rather than counts (Wobeser 2007) and mortality rates are seldom quantified with conventional monitoring (Naugle et al. 2005).
West Nile virus (WNv), a mosquito-borne Flavivirus (family Flaviviridae; Komar 2001), was discovered in northwest Uganda in 1937 (Smithburn et al. 1940). First encountered in the western hemisphere in New York in 1999 (Nash et al. 2001), WNv has become enzootic in all 48 contiguous states, and has been reported from 96% of counties to date (Centers for Disease Control and Prevention [CDC] 2013). West Nile virus has been detected in 65 species of mosquito in the United States (CDC 2012) and its ability to establish and persist across ecosystems and hosts is illustrated by its extensive distribution (CDC 2013). West Nile virus infection has been reported in 326 avian species (CDC 2013). Among a more scarcely occurring avian guild like the raptors, the CDC Arbornet Surveillance System (1999 to 2004) have documented infection in 36 species (Nemeth et al. 2006), approximately 70% of all raptor species occurring in North America

Datta, Shubham

Grovenburg, Troy W.

Inselman, Will M.

Jenks, Jonathan A.

Jensen, Kent C.

Knudsen, David E.

Swanson, Christopher C.

English

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University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
The Prairie Naturalist Great Plains Natural Science Society 
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WEST NILE VIRUS AND FERRUGINOUS HAWKS (BUTEO REGALIS) 
IN THE NORTHERN GREAT PLAINS 
Shubham Datta 
Jonathan A. Jenks 
David E. Knudsen 
Kent C. Jensen 
Will M. Inselman 
See next page for additional authors 
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 Part of the Biodiversity Commons, Botany Commons, Ecology and Evolutionary Biology Commons, 
Natural Resources and Conservation Commons, Systems Biology Commons, and the Weed Science 
Commons 
This Article is brought to you for free and open access by the Great Plains Natural Science Society at 
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Authors 
Shubham Datta, Jonathan A. Jenks, David E. Knudsen, Kent C. Jensen, Will M. Inselman, Christopher C. 
Swanson, and Troy W. Grovenburg 
The Prairie Naturalist 47:38–40; 2015
WEST NILE VIRUS AND FERRUGINOUS HAWKS 
(BUTEO REGALIS) IN THE NORTHERN GREAT 
PLAINS—Emerging infectious diseases (EID) present sig-
nificant	 threats	 to	 the	 conservation	 of	 global	 biodiversity	
(Daszak et al. 2000).  Evaluating impacts (spatial, temporal 
and demographic) of EIDs on sensitive and declining wild-
life populations is challenging because quantitative infor-
mation is usually dependent on estimates rather than counts 
(Wobeser	 2007)	 and	mortality	 rates	 are	 seldom	quantified	
with conventional monitoring (Naugle et al. 2005).
West Nile virus (WNv), a mosquito-borne Flavivirus 
(family Flaviviridae; Komar 2001), was discovered in north-
west Uganda in 1937 (Smithburn et al. 1940).  First encoun-
tered in the western hemisphere in New York in 1999 (Nash 
et al. 2001), WNv has become enzootic in all 48 contiguous 
states,	and	has	been	reported	from	96%	of	counties	 to	date	
(Centers for Disease Control and Prevention [CDC] 2013). 
West Nile virus has been detected in 65 species of mosquito 
in the United States (CDC 2012) and its ability to establish 
and persist across ecosystems and hosts is illustrated by its 
extensive distribution (CDC 2013).  West Nile virus infection 
has been reported in 326 avian species (CDC 2013).  Among 
a more scarcely occurring avian guild like the raptors, the 
CDC Arbornet Surveillance System (1999 to 2004) have 
documented infection in 36 species (Nemeth et al. 2006), 
approximately	70%	of	all	raptor	species	occurring	in	North	
America.  
In free-ranging raptors, WNv can be transmitted by a vec-
tor (e.g., mosquito), through oral exposure (infected food; af-
ter Root 2013), or direct contact with infected animals (e.g., 
in a nest; Komar et al. 2003).  In in situ and controlled ex-
periments, most passerines infected with WNv developed ab-
normal behavior, including neurologic signs such as lethargy, 
ataxia, disorientation, and weight loss (Komar et al. 2003). 
Clinical signs of adult raptors infected with WNv ranged 
from	absent,	mild	and	nonspecific,	to	acute	and	varied	among	
species (Nemeth et al. 2006, 2008).  Most adult raptors ex-
perimentally exposed to WNv were found to develop vire-
mia	within	five	days	post-inoculation	 (Nemeth	et	 al.	2006)	
and once seroconverted, WNv-induced humoral antibodies 
were found to persist throughout life (>4 years; Nemeth et 
al. 2008).  Population and ecosystem-level impacts of WNv 
infection on declining populations of grassland obligate rap-
tors (e.g., ferruginous hawk [Buteo regalis]) have not been 
documented.      
In July 2013, while monitoring active ferruginous hawk 
nests in McPherson County, South Dakota (14T 5071049 N, 
493014	W),	we	recovered	five	dead	ferruginous	hawk	fledg-
lings with estimated ages of 25 (n = 3) and 40 (n = 2) days 
from two tree nests.  Remote camera footage indicated dis-
orientation	and	ataxia	in	fledglings	approximately	three	days	
prior to death.  Carcasses were submitted to the Animal Dis-
ease Research and Diagnostic Laboratory at South Dakota 
State University, Brookings, South Dakota, for examination. 
All recovered carcasses underwent necropsy and microscop-
ic	examination	of	routine	tissues	by	histopathology.	All	five	
birds had histologic evidence of subacute multifocal nonsup-
purative	encephalitis,	with	mononuclear	cell	cuffing	around	
vessels	 (Fig.	 1A)	 and	diffuse	nonsuppurative	 inflammatory	
infiltrates	 throughout	 the	parenchyma.	 	Occasional	microg-
lial gitter cells surrounded neuronal cell bodies.  Immunohis-
tochemistry (Smedley et al. 2007) revealed WNv antigen in 
numerous	cerebral	neurons	(Fig.	1B).		To	confirm	histologic	
findings,	frozen	brain	samples	were	pooled	within	nests	and	
submitted (National Veterinary Service Laboratory, Ames, 
IA) for reverse transcriptase polymerase chain reaction (RT-
PCR; Shi 2001); WNv RNA was detected in both samples. 
Concurrent acute heterophilic myocarditis was present in 
younger	 fledglings	 (n	 =	 3),	 while	 older	 fledglings	 (n = 2) 
from the second nest had concurrent lesions in multiple tis-
sues related to Escherichia coli septicemia, as well as enteric 
coccidiosis.  No other gross or histologic lesions were noted. 
Old world data indicate that susceptibility to fatal infec-
tion with WNv varies markedly for birds, with high death 
rates in juveniles and incidence of circulating antibodies in 
adults (Work et al. 1955, Hull et al. 2006).  Innate immunity 
is believed to play a role in protection against primary infec-
tion; however, humoral immunity is an essential component 
of immune control over primary infection and protection 
against subsequent infections (Diamond et al. 2003).  Hahn 
et al. (2006) showed evidence of passive transfer of antibod-
ies from seropositive females to nestlings; however, observed 
susceptibility	of	fledglings	 to	WNv	infection	 in	 the	present	
scenario indicates a lack of adequate immune response (ef-
fective levels of neutralizing antibody) irrespective of the 
protective mechanism.  Why clinical manifestation of WNv 
infection might occur in a small percentage of infected in-
dividuals is not well understood but has been attributed to 
host-dependent genetic factors like point mutation-dependent 
susceptibility (Mashimo et al. 2002).  Ability of virus strains 
to modify virulence through mutation makes it even more 
capricious	and	difficult	to	control,	rendering	these	already	de-
clining grassland populations highly vulnerable to infection 
and mortality.  Antibody duration in WNv pre-exposed adult 
raptors might contribute to long-term survival and reproduc-
tive	output	(Nemeth	et	al.	2008)	but	fledgling	susceptibility	
to WNv infection is detrimental to recruitment and nesting 
success. 
Ferruginous hawks are a grassland/shrubland obligate 
nesting	 raptor	 (Woffinden	and	Murphy	1989)	and	prefer	 to	
nest in lightly grazed pasture or idle areas (Lokemoen and 
Duebbert 1976, Blair 1978, Blair and Schitoskey 1982).  In 
the Great Plains, breeding range, local abundance, and pro-
ductivity of several populations of ferruginous hawk have de-
clined	(Woffinden	and	Murphy	1989,	Houston	and	Schmutz	
1999); they have vacated close to half of their reproductive 
range on the northern prairies (Houston and Bechard 1984, 
Schmutz 1984, Houston and Schmutz 1999). Within the 
NOTES 39
northern	prairie,	landscapes	with	≥50%	agricultural	crop	pro-
duction are only marginally suitable for ferruginous hawks 
(Schmutz 1987, 1989), which has been attributed to the avail-
ability of Sciurid prey (Schumtz 1989, Zelenak and Rotella 
1997).	 	 Impacts	of	anthropogenic	habitat	modifications	and	
reduced prey availability on ferruginous hawks are com-
pounded by WNv-caused mortality; an EID that demands 
coordinated long-term surveillance, monitoring, and research 
examining the prevalence and ecology of the virus among 
reservoir hosts (Naugle et al. 2005).  Though susceptibility 
and reservoir competence decreases with increasing accumu-
lation of adult survivors of WNv infection in a population 
(Nemeth et al. 2008), evidence and understanding of passive 
transfer of protective antibodies to nestlings is limited.  
We thank D. Naugle for reviewing an earlier draft of this 
manuscript.  We thank S. Kempema and R. Johnson for tech-
nical assistance.  Our study was supported by State Wildlife 
Grant (SD #T-58-R-1) administered through South Dakota 
Department of Game, Fish and Parks.  We appreciated the 
support provided by the Department of Natural Resource 
Management and the Agricultural Experiment Station at 
South	Dakota	State	University.		The	findings	and	conclusions	
in this article are those of the author(s) and do not necessarily 
represent the views of the U.S. Fish and Wildlife Service.—
Shubham Datta1, 4, Jonathan A. Jenks1, David E. Knudsen2, 
Kent. C. Jensen1, Will M. Inselman1, Christopher C. Swan-
son3, and Troy. W. Grovenburg1.  1 Department of Natural 
Resource Management, South Dakota State University, Box 
2140B SNP 138, Brookings, SD 57007, USA;  2Animal Dis-
ease Research & Diagnostic Lab, South Dakota State Uni-
versity, Brookings, SD 57007, USA;  3 U.S. Fish and Wildlife 
Service, 1 First Street SW, Kulm, ND 58546, USA;  4 Cor-
responding author e-mail address: shubham.datta@sdstate.
edu. 
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Figure	1.		Photomicrographs	of	brain	tissue	from	ferruginous	hawk	fledgling	with	West	Nile	virus	infection.		A)	Cerebrum,	Mono-
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Immunohistochemical demonstration of WNV antigen within cerebral neurons. Toluidine blue.  Bar = 100 µm.


WEST NILE VIRUS AND FERRUGINOUS HAWKS (BUTEO REGALIS) IN THE NORTHERN GREAT PLAINS

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WEST NILE VIRUS AND FERRUGINOUS HAWKS (BUTEO REGALIS) IN THE NORTHERN GREAT PLAINS

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