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DOI: 10.7589/2015-04-103 Journal of Wildlife Diseases, 52(3), 2016, pp. 000–000
ÓWildlife Disease Association 2016
EYEWORMS (OXYSPIRURA PETROWI) IN NORTHERN BOBWHITES
(COLINUS VIRGINIANUS) FROM THE ROLLING PLAINS ECOREGION
OF TEXAS AND OKLAHOMA, 20112013
Nicholas R. Dunham,
1
Andrea Bruno,
2
Sadia Almas,
3
Dale Rollins,
4
Alan M. Fedynich,
2
Steven
M. Presley,
3
and Ronald J. Kendall
1,5
1
The Wildlife Toxicology Laboratory, The Institute of Environmental and Human Health, Texas Tech University, Box
43290, Lubbock, Texas 79409-3290, USA
2
Caesar Kleberg Wildlife Research Institute, Texas A&M University–Kingsville, 700 University Blvd., Kingsville, Texas
78363, USA
3
The Institute of Environmental and Human Health, Texas Tech University, Box 41163, Lubbock, Texas 79409-1163,
USA
4
Rolling Plains Quail Research Ranch, 1262 US Highway 180 W., Rotan, Texas 79546, USA
5
Corresponding author (email: ron.kendall@ttu.edu)
ABSTRACT: The Northern Bobwhite (Colinus virginianus) has been steadily declining throughout much
of its historic range for decades. The Rolling Plains ecoregion of Texas and western Oklahoma,
historically rich with wild bobwhites and one of the last remaining quail strongholds, also has a declining
population. During August and October in 2011–2013, 348 Northern Bobwhites from the Rolling Plains
were examined for eyeworms (Oxyspirura petrowi). Of these 348 Northern Bobwhites, 144 (41.4%)
were infected with 1,018 total eyeworms. Eyeworm abundance (mean6SE) was 2.960.4 (range 0–64),
with an intensity (mean6SE) of 7.160.6. Eyeworm prevalence was significantly higher in adult
Northern Bobwhites (58.7%) than in juveniles (35.4%). Recent research suggests that eyeworms have
the potential to cause cellular tissue damage to the eye, but it is unknown how these worms affect host
survivability. This study further expands the regional distribution of O. petrowi in Northern Bobwhites
in the Rolling Plains ecoregion and assesses the prevalence and abundance of infection across host age,
host sex, and year. Further research is warranted on the life history of O. petrowi and assessing the
impacts of eyeworms on their definitive host at individual and population levels.
Key words:Colinus virginianus, eyeworm, Northern Bobwhite, Oklahoma, Oxyspirura petrowi,
quail, Rolling Plains ecoregion, Texas.
INTRODUCTION
The Northern Bobwhite (Colinus virgin-
ianus) has been declining throughout its
native range for decades (Brennan 1991).
This decline is especially apparent when it
comes to the Rolling Plains ecoregion of Texas
and western Oklahoma, which was once
regarded for its productive bobwhite habitat.
Over the past few decades, much of the focus
has been on the effects of habitat loss or
degradation due to changes in agriculture
practices or variable weather patterns on
Northern Bobwhite populations; however,
Northern Bobwhite populations continue to
decline (Brennan 1991; Bridges et al. 2001).
Quail in semiarid environments tend to follow
a‘‘boom or bust’’ population cycle because
they fluctuate drastically (Herna
´ndez et al.
2007). During summer 2010, a boom year was
expected due to above-average precipitation
in 2010 (National Oceanic and Atmospheric
Administration 2015) and a link between
precipitation and Northern Bobwhite popula-
tion cycle expectations (Bridges et al. 2001).
However, the expected Northern Bobwhite
population surge of 2010 never came. The
missed boom year sparked a research initiative
throughout the Rolling Plains of Texas and
Oklahoma that investigated disease, contami-
nants, viruses, and parasites in quail from
2011 to 2013. Early in the study, eyeworms,
(Oxyspirura petrowi) became the focus be-
cause of their spatial and temporal occurrence
throughout the Rolling Plains ecoregion.
Oxyspirura petrowi is a heteroxenous
parasitic nematode that can be found in the
orbital cavity (Addison and Anderson 1969),
Harderian and lacrimal glands (Bruno et al.
2015), the nasal sinuses (Dunham et al. 2014),
1
underneath the eyelids and nictitating mem-
brane (Saunders 1935; Jackson 1969), and
inside the lacrimal duct and gland (Robel et
al. 2003). Although the life cycle is not
completely known, O. petrowi has an indirect
life cycle and requires an arthropod interme-
diate host for development. Oxyspirura pet-
rowi has been found in many wild avian
species (Pence 1972), including the Scaled
Quail (Callipepla squamata; Landgrebe et al.
2007), Ring-necked Pheasant (Phasianus col-
chicus; McClure 1949), Lesser Prairie-chick-
en (Tympanuchus pallidicinctus; Robel et al.
2003), and Ruffed Grouse (Bonasa umbellus;
Erickson et al. 1949).
The genus Oxyspirura was first document-
ed from 11 counties in the Rolling Plains of
Texas from 1961 to 1964 (Jackson and Green
1965). During that study, Oxyspirura syg-
moides (¼O. petrowi) was found in 44.1% of
605 Northern Bobwhites and prevalence of
infection in adults ranged from 61% to 79%
(Jackson and Green 1965). Jackson (1969)
speculated on the potentially negative impact
of eyeworms on Northern Bobwhite vision.
Villarreal et al. (2012) reported similar eye-
worm occurrence (57%) over a 3-yr period in
Fisher County (Rolling Plains). Oxyspirura
petrowi was also found in Mitchell County
(Rolling Plains) in both the Northern Mock-
ingbird (Mimus polyglottos) and Curve-billed
Thrasher (Toxostoma curvirostre)andat
‘‘elevated’’ levels in Northern Bobwhites and
Scaled Quail (Dunham and Kendall 2014;
Dunham et al. 2014).
Considering the importance of Northern
Bobwhites to the Rolling Plains ecoregion, we
provide recent data on the prevalence,
abundance, and intensity of O. petrowi in
Northern Bobwhites; assess prevalence, and
abundance across host age, host sex, and year
of study; and further evaluate the regional
distribution of O. petrowi in Northern Bob-
whites.
MATERIALS AND METHODS
Study area
In August and October 2011, 2012, and 2013,
Northern Bobwhites were trapped in 29 counties
throughout the Rolling Plains of Texas and
Oklahoma (Fig. 1). Each of the designated
trapping teams spent 2.5 d on each of the study
ranches or wildlife management areas trapping
quail. The Rolling Plains ecoregion is dominated
with mesquite (Prosopis glandulosa) savannas,
junipers (Juniperus pinchotii), prickly pear
(Opuntia spp.), woody species such as lotebrush
(Ziziphus obtusifolia) and sand shinery oak
(Quercus havardii), and the grassland species
silver bluestem (Bothriochloa saccharoides) and
buffalo grass (Buchloe dactyloides; Rollins 2007).
Rangelands comprise about 65% of the Rolling
Plains, with croplands making up an additional
30% (Rollins 2007). This ecoregion averages
55.876.2 cm of rain annually, and the average
temperature is 1518 C (Texas Parks and Wildlife
2013).
Trapping
Northern Bobwhites were trapped under Texas
Parks and Wildlife Scientific Research permits
SRP 1098-984 and SRP-0690-152. Northern
Bobwhites were handled consistent with Texas
A&M University Acceptable Use Policy (2011-
193), Texas Tech University Animal Care and Use
Committee (11049-07), Texas A&M University-
Kingsville (TAMUK) Institutional Animal Care
and Use Committee (2009-09-21A), and TAMUK
Institutional Biosafety Committee (IBC-ID 009-
2011). Twenty galvanized, welded-wire walk-in
funnel traps (25.4391.4361 cm) were placed near
minimally travelled ranch roads on respective trap
sites. All traps were covered with vegetation or
burlap cloth to provide cover, and each trap was
baited using milo (Sorghum bicolor) for 2 wk
before trapping. Traps were monitored daily at 2
FIGURE 1. Counties in the Rolling Plains ecoregion
of Texas and western Oklahoma, USA, sampled for
Northern Bobwhites (Colinus virginianus), 20112013.
2 JOURNAL OF WILDLIFE DISEASES, VOL. 52, NO. 3, JULY 2016
h after sunrise and 1 h before or at sunset.
Northern Bobwhites were euthanized in the field
by cervical dislocation and placed in a cooler with
dry ice and transported to either The Institute of
Environmental and Human Health (TIEHH)
central receiving laboratory or Buddy Temple
Wildlife Pathology and Diagnostic Laboratory at
TAMUK.
Eyeworm examination
The eyelids, nictitating membrane, and associ-
ated ocular tissue of Northern Bobwhites were
thoroughly examined for eyeworms under 1–403
magnification. After the surface of the eyelids and
nictitating membrane were examined, the eyelids
were removed and the eyeball and its associated
ducts and tissues were detached from the orbital
cavity and placed into a Petri dish. The Harderian
gland, lacrimal gland, and lacrimal duct were
removed from the eyeball and teased apart. In
addition, 188 heads were individually floated in a
jar of 10% physiological saline solution (at room
temperature), thereby causing any eyeworms that
were still attached to the eye socket area to release
and fall to the bottom of the jar. Eyeworms
recovered from Northern Bobwhites necropsied
at TIEHH (n¼188) were placed in saline holding
media within a 32 C isotemp CO
2
incubator and
used for additional studies. Eyeworms recovered
from Northern Bobwhites necropsied at TAMUK
(n¼161) were fixed in glacial acetic acid and
preserved in 70% ethanol and 8% glycerol.
Voucher specimens of O. petrowi (107283) from
TIEHH were deposited in the US National
Parasite Collection, Beltsville, Maryland. Voucher
specimens from TAMUK were deposited in the
Sam Houston State University Parasite Museum
(SHSUP), Sam Houston State University, Hunts-
ville, Texas (SHSUP 000,366–000,381; 131299,
130404, 130644, 130356, 131983, 131479, 131382,
130380, 131461, and 131431).
Data analysis and terminology
Prevalence, mean abundance, mean intensity,
and the range of eyeworms within all quail
sampled were calculated. Prevalence refers to
the number of Northern Bobwhites infected with
O. petrowi in the sample divided by total quail
examined in the sample and mean abundance is
the number of O. petrowi found in the total
sample divided by the total number of quail
examined (Bush et al. 1997). Mean intensity is
defined as the average number of eyeworms in
infected Northern Bobwhites sampled.
Chi-square analysis was conducted to compare
prevalence of eyeworms between host sex, host
age class, and year sampled (R Development Core
Team 2015). Oxyspirura petrowi infection data
were aggregated toward 0, with a few birds
containing most of the parasites, indicating non-
normality. To account for nonnormality, data were
fitted with a negative binomial distribution and
analyzed using a generalized linear mixed model
procedure (PROC GLIMMIX) in SAS 9.3 soft-
ware (SAS Institute Inc., Cary, North Carolina,
USA). Models were created to explain variation in
abundance of O. petrowi by using independent
variables of host age, host sex, and year and their
two-way interactions (age3sex, age3year, sex3-
year). We used backward selection based on type
III effects Ftests to eliminate terms that did not
describe an adequate amount of variation in the
response (i.e., parameters that where P.0.05).
Type III Ftests calculate the significance of each
parameter after variation attributable to all other
parameters in the model has been taken into
account. Least-squares mean separation was
generated to compare significant effects among
the levels of categorical variables (i.e., host age,
host sex, and year) and considered means
statistically different if P0.05. Due to the skewed
distribution of the data, our analyses were based
on a log (countþ1) analysis of variance of a general
linear model; back-transformed means and asym-
metric SE are presented and referred to as the
estimated mean6SE (Sokal and Rohlf 2011).
Significance was determined at P0.05, and all
means are reported as mean6SE.
RESULTS
The eyes, nictitating membrane, and all
associated ocular tissue of 348 Northern
Bobwhites (97 adults, 251 juveniles; 183
males, 145 females, 20 unknown) were
examined for eyeworms. One hundred forty-
four (41.4%) were collectively infected with
1,018 eyeworms. Prevalence was similar
among male and female Northern Bobwhites
(v
21
¼0.12, P¼0.73; Table 1); however, preva-
lence was higher in adults than juveniles
(v
22
¼15.74, P,0.0001). Prevalence also was
significantly different (v
22
¼11.6, P¼0.002)
among years (Table 1).
Host age, year, and a host age3year
interaction best explained O. petrowi abun-
dance in Northern Bobwhites. The effect of
year was not significant on its own (P¼0.640),
but it was included in the model because of
the host age3year interaction. The effect of
host age on abundance of O. petrowi depend-
ed on year (Fig. 2). In 2011 and 2012, the
DUNHAM ET AL.—OXYSPIRURA PETROWI INFECTION IN NORTHERN BOBWHITES 3
estimated mean O. petrowi was significantly
(P¼0.012 and P,0.0001, respectively) higher
in adults (n¼29; 6.262.4 and n¼10; 13.168.8,
respectively) compared to juveniles (n¼12;
0.860.6 and n¼46; 0.360.1, respectively)
(Fig 2). However, the estimated mean abun-
dance was similar (P¼0.275) in 2013 between
adults (n¼58; 3.361.0) and juveniles (n¼191;
2.360.4; Fig. 2).
Within adults, there was no difference in
estimated mean abundance O. petrowi be-
tween 2011 and 2012 (P¼0.341), 2011 and
2013 (P¼0.214), and 2012 and 2013 (P¼0.064;
Fig. 2). The estimated mean of adults in 2012
(13.168.8) and 2013 (3.361.0) seemed sig-
nificantly different; however, when tested in
SAS (ESTIMATE) the estimated difference
on the back-transformed scale was 3.962.8
(95% confidence interval 3.2 to 10). Since
the 95% confidence interval includes 0, we
accept the null hypothesis of no difference.
Within juveniles, there was no difference in
the estimated mean between 2011 and 2012
(P¼0.180) and between 2011 and 2013
(P¼0.146); however, the estimated mean was
significantly (P,0.0001) higher in 2013 com-
pared to 2012 (Fig. 2).
DISCUSSION
Eyeworms were previously documented in
11 counties throughout the Rolling Plains of
Texas (Jackson and Green 1965), and the
current study expands the survey region to 29
counties throughout the Rolling Plains ecor-
egion of Texas and Oklahoma. Given the
eyeworm occurrence throughout this ecor-
egion in the early 1960s and with similar
distribution in the current study, our study
confirms that O. petrowi has been persis-
tently enzootic in Northern Bobwhite
throughout the region for decades. Baseline
studies are needed to determine its presence
in other regions of North America, coupled
with monitoring to determine whether this
nematode spreads to regions where it is
absent.
The distribution of eyeworms, although
being broad spatially, is disproportionately
distributed within age classes of Northern
Bobwhites. Two recent studies, both limited
to a single county within the Rolling Plains
ecoregion, also support our findings that adult
Northern Bobwhites have a higher prevalence
Table 1. Prevalence, abundance (mean6SE), intensity (mean6SE), and range of Oxyspirura petrowi in
Northern Bobwhites (Colinus virginianus) in the Rolling Plains ecoregion of Texas and western Oklahoma, USA,
20112013.
Overall Adult Juvenile Male Female Unknown 2011 2012 2013
Sample size 348 97 251 183 145 20 41 56 251
Prevalence (%) 41.4 58.7 35.4 40.4 42.1 45 51 21.4 44.2
Abundance 2.960.4 5.261.1 2.060.4 3.160.6 2.560.6 4.4611.9 4.661.6 2.661.2 2.760.5
Intensity 7.160.6 8.861.3 5.860.7 7.860.9 5.860.9 9.663.6 9.062.0 12.062.3 6.260.7
Range 0–64 0–61 0–64 0–61 0–64 0–54 0–46 0–61 0–64
FIGURE 2. Estimated abundance (mean6SE) of
Oxyspirura petrowi by host age3year predicted by a
negative binomial model from 348 Northern Bob-
whites (Colinus virginianus) collected during August
and October 20112013 within the Rolling Plains
ecoregion of Texas and western Oklahoma, USA.
4 JOURNAL OF WILDLIFE DISEASES, VOL. 52, NO. 3, JULY 2016
and abundance of O. petrowi than juveniles
(Villarreal et al. 2012; Dunham et al. 2014). In
addition, Jackson and Green (1965) found
substantially higher prevalence (61–79%) in
adult Northern Bobwhites compared to juve-
niles (16–33%). Prevalence and abundance of
parasites can be higher in adults than
juveniles due to longer exposure times to
infected intermediate hosts (Davidson et al.
1980). In two of 3 yr of our study, we also
found differences in abundance due to host
age. It is possible that no differences by host
age in 2013 may be related to increased
rainfall during summer 2013. Peak transmis-
sion of many heteroxenous life cycle nema-
todes typically coincides with the wet season
when intermediate hosts are most plentiful
(Davidson et al. 1980). We speculate that
increased precipitation from 2012 to 2013
triggered an increase in vegetation, facilitating
intermediate host survival and increasing
transmission potential to the definitive host.
Within age classes, we saw little difference in
infection across years, indicating that preva-
lence of infection among adults remains
consistent temporally. Drought conditions
persisting in 2012 may have affected host
and parasite recruitment and survival during
breeding season, resulting in lower eyeworm
prevalence in juveniles in 2012.
Due to the microhabitats where adult O.
petrowi occurs, we speculate that infections
have the potential to impair respiratory
function, cause visual obstruction, increase
energy expenditure, and reduce flight and
forage ability. Additional research is needed
to understand the impact, if any, O. petrowi
has on the survivability of Northern Bob-
whites at the population level before drawing
conclusions on the status of this nematode as
a potential factor in quail decline. The results
of this study provide recent information on
the spatial, temporal, and demographic
distribution of O. petrowi in Northern
Bobwhites from the Rolling Plains ecoregion.
In addition, this research identifies O.
petrowi as a common and frequently occur-
ring helminth of Northern Bobwhites within
the study area.
ACKNOWLEDGMENTS
Funding for this research was provided by the
Rolling Plains Quail Research Foundation. We
thank Texas A&M University at College Station
and the Oklahoma Department of Wildlife and
Conservation for assistance in trapping and field
processing and the Central Receiving Laboratory
at TIEHH for their field and laboratory assis-
tance. We also thank all of the landowners that
graciously provided access to their study ranches
and housed our trapping teams.
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6 JOURNAL OF WILDLIFE DISEASES, VOL. 52, NO. 3, JULY 2016
