Journal of Wildlife Diseases, 44(3), 2008, pp. 760–765
#Wildlife Disease Association 2008
Ocelots on Barro Colorado Island Are Infected with Feline
Immunodeficiency Virus but Not Other Common Feline and
Samuel P. Franklin,1,4Roland W. Kays,2Ricardo Moreno,3Julie A. TerWee,1Jennifer L. Troyer,1and
Sue VandeWoude1 1Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort
Collins, Colorado 80523, USA;2New York State Museum and Science Services, Albany, New York 12230, USA;
3Smithsonian Tropical Research Institute, Apartado Postal 0843-03092, Balboa, Ancon, Republic of Panama;
4Corresponding author (email: email@example.com)
domestic animals to wildlife populations (spill-
over) has precipitated local wildlife extinctions
in multiple geographic locations. Identifying
such events before they cause population
declines requires differentiating spillover from
endemic disease, a challenge complicated by a
lack of baseline data from wildlife populations
that are isolated from domestic animals. We
tested sera collected from 12 ocelots (Leopar-
dus pardalis) native to Barro Colorado Island,
Panama, which is free of domestic animals, for
antibodies to feline herpes virus, feline calici-
virus, feline corona virus, feline panleukopenia
virus, canine distemper virus, and feline
immunodeficiency virus (FIV), typically a
species-specific infection. Samples also were
tested for feline leukemia virus antigens.
Positive tests results were only observed for
FIV; 50% of the ocelots were positive. We
hypothesize that isolation of this population has
prevented introduction of pathogens typically
attributed to contact with domestic animals.
The high density of ocelots on Barro Colorado
Island may contribute to a high prevalence of
FIV infection, as would be expected with
increased contact rates among conspecifics in
a geographically restricted population.
Barro Colorado Island, FIV,
Leopardus, ocelot, serology.
Transmission of pathogens from
The spillover of pathogens from do-
mestic animal species has been a source
of numerous outbreaks in wildlife pop-
ulations with disastrous consequences
(Daszak et al., 2000). Evaluating the risk
of spillover in wildlife populations is
complicated by a lack of baseline data
from populations isolated from domestic
animals (Munson and Karesh, 2002). Most
surveys are performed in populations
in proximity to human settlements and
domestic animals because the threat of
adventitial disease is presumed to be
greater in such locations. However,
without appropriate baseline data, it is
difficult to determine whether the pres-
ence of a pathogen represents an intro-
duction from domestic animals, signify-
ing a potential threat to the wildlife
population, or whether the pathogen has
been historically present in the wild
Exposure to multiple pathogens typical-
ly considered to reside in domestic animal
reservoirs have been documented in
ocelots (Leopardus pardalis), including
feline herpes virus (FHV), feline calici-
virus (FCV), feline corona virus (FCoV),
feline panleukopenia virus (FPV), feline
leukemia virus (FeLV), and canine dis-
temper virus (CDV; Schmitt et al., 2003;
de Carvalho Ruthner Batista et al., 2005;
Filoni et al., 2006; Fiorello et al., 2007).
Fiorello et al. (2007) reported that from a
sample of 10 ocelots sampled in Kyaa-Iya
del Gran Chaco National Park (Bolivia)
and the adjacent area, seven and 10 had
antibodies to CDV and FCV, respectively.
Although this national park is approxi-
mately 40 km from human settlement,
villagers frequently hunt in areas adjacent
to the national park with dogs (Canis
familiaris). This makes it difficult to
determine whether the exposure of these
ocelots to CDV and FCV represents the
presence of an endemic wildlife disease,
or whether it occurs as a result of direct or
indirect contact with domestic animals in
areas adjacent to the national park.
Unlike the aforementioned diseases,
wild felid infection with feline immuno-
deficiency viruses (FIV; family Retrovir-
idae, genus Lentivirus) is not suggestive of
cross-species transmission. Domestic cat
(Felis catus) FIV has been identified in a
wild felid only once (Nishimura et al.,
1999), and transmission of different strains
of FIV among captive or free-ranging
nondomestic felids has been documented
on few occasions (Carpenter et al., 1996;
Troyer et al., 2005; Franklin et al., 2007a).
Rather, species-specific FIV strains have
been identified in almost all cases of
nondomestic cat infections where FIV
genotype analyses were performed; this
relationship has been demonstrated with a
virus that was isolated from an ocelot
(Troyer et al., 2005).
We tested 12 ocelots from an estimated
total population of 30 animals (Ziegler,
2002) from Barro Colorado Island (BCI),
Panama, for antibodies to FHV, FCV,
FCoV, FPV, CDV, and FIV. Samples also
were tested for FeLV antigen. Our objec-
tive was to acquire baseline antibody
prevalence data from a population of
ocelots isolated from domestic animals.
Barro Colorado Island (1,600 ha; 9u99N,
79u519W) is a hilltop that was isolated
from the mainland in 1914 when the
Chagres River was dammed to create
Lake Gatun as part of the Panama Canal.
The minimum distance between the island
and the mainland is 200 m, although small
islands break up this interval in some
places. There are no domestic animals
permitted on BCI, and poaching of native
fauna is limited or nonexistent because the
island is heavily guarded (Wright et al.,
2000). The area of BCI was not well
developed before the creation of the canal,
and it is unlikely that there were any
domestic animals at this site before 1913.
Movement of ocelots between the island
and the mainland has not been studied in
detail, although a low level of ocelot
emigration from BCI has been document-
ed in that one radiocollared BCI ocelot
was tracked to the mainland. Other
predators may likely limit cross-water
movement of ocelots as evidenced by the
killing of another radiocollared BCI ocelot
by a crocodile. Additional felid species
residing on BCI include margay (Leopar-
dus wiedii) and jaguarundi (Herpailurus
yagouaroundi). Puma (Puma concolor) are
detected regularly, and jaguars (Panthera
onca) rarely; neither of these species
reside permanently on the island (Moreno
et al., 2006).
Ocelots were trapped with metal and
wooden box-traps from January 2001 to
May 2004 and sedated with either a
tiletamine and zolezapam premixture (Tel-
azolH, Fort Dodge Animal Health, Fort
Dodge, Iowa, USA) or ketamine hydro-
chloride and xylazine. Whole blood sam-
ples were collected in untreated serum
tubes. Samples were spun at 25 3 G for
10 min, and the serum was separated from
the coagulated cells. Samples were stored
at 270 C or 220 C until serology was
performed with serum for five common
feline and canine viruses at the Colorado
State University Diagnostic Laboratory
(see Table 1 for a list of pathogens and
A triple chemiluminescent immunoblot
with antigen preparations from three
distinct strains of feline lentivirus (domes-
tic cat FIV; puma lentivirus, PLV; and
African lion lentivirus) was used to test for
antibodies to FIV (Franklin et al., 2007a).
Use of this multi-antigen-based immuno-
blot has been shown to enhance sensitivity
without loss of specificity in the detection
of wild felid FIV (Franklin et al., 2007b). A
commercial enzyme-linked immunosor-
bent assay (ELISA) (FIV/FeLV Combo
SNAPTMtest; Idexx Inc., Westbrook,
Maine, USA) was used as a comparison
to FIV immunoblot and for detection of
FeLV antigen. Deoxyribonucleic acid was
extracted using a standard phenol chloro-
form protocol (Sambrook and Russell,
2001) using the coagulated blood cell
volume (,2 ml). Nested PCR was per-
formed using degenerate primers de-
signed from the conserved reverse tran-
GenBank sequences of FIV (accession
nos. M25381 and U11820), PLV (acces-
sion no. U03982), and FIV-Oma (Otoco-
lobus manul; accession no. U56928)
(Troyer et al., 2005). Positive and negative
-negative laboratory domestic cats and
FIV-positive pumas, bobcats, and African
lions (Panthera leo) were run concurrent-
ly. The immunoblot, ELISA, DNA extrac-
tion techniques, and PCR protocols and
the relative sensitivity and specificity of
each are discussed in detail in Franklin et
Except for FIV, all test results were
negative (Table 1). These negative results
are inconsistent with previous studies in
which exposure to all six viruses other than
FIV is reported (Schmitt et al., 2003; de
Carvalho Ruthner Batista et al., 2005;
Filoni et al., 2006; Fiorello et al., 2007).
We do not believe that this disparity
between studies can be attributed to small
sample size, because with one exception
our sample size was larger than these
previous studies. In addition, very high
antibody prevalence rates for some of
these pathogens have been reported,
including a 70% and 100% antibody
prevalence rate for CDV and FCV,
respectively, in ocelots from Bolivia (Fior-
ello et al., 2007). Moreover, the diagnostic
tests used in our study and these previous
studies also were similar.
These findings support the hypothesis
that these pathogens are not endemic to
BCI. The absence of these pathogens may
be the result of isolation from domestic
animals. Alternatively, the BCI ocelot
population, and that of other sympatric
felids, may be too small to ensure
persistence of these viruses. Sampling of
additional ocelots on BCI, and sampling of
ocelots and sympatric domestic animals on
the mainland, is needed to further inves-
tigate these possibilities. Unlike the other
viruses we investigated, the prevalence of
FIV was higher in our sample than
reported previously for ocelots from other
studies. Six of the 12 BCI ocelots tested
were positive (50%) compared with 0%
for 38 captive ocelots from Brazil (Filoni
et al., 2003), 0% for 10 wild ocelots in
Bolivia (Fiorello et al., 2007), and 6% for
90 free-ranging, wild-born, and captive
ocelots (Troyer et al., 2005). These previ-
ous studies used a virtually identical
immunoblot protocol or the same com-
mercial ELISA test used in this study.
We were unable to amplify genomic
FIV sequences from any of the seroposi-
tive animals using degenerate PCR prim-
ers for FIV. These negative results are
consistent with reported difficulties in
attempts to amplify and sequence virus
from ocelots (Troyer et al., 2005) and
other nondomestic cat species. PCR am-
plification of FIV sequences from nondo-
mestic cats is not sensitive because se-
degenerate primers that do not bind viral
sequence efficiently (Troyer et al., 2005;
Brennan et al., 2006; Franklin et al.,
2007b). Furthermore, proviral load may
TABLE 1.Results of serologic testing of 12 Barro Colorado Island ocelots.
Feline calicivirus (FCV)
Canine distemper virus (CDV)
Feline herpes virus (FHV)
Feline corona virus (FCoV)
Feline panleukopenia (FPV)
Feline leukemia virus (FeLV)
Serum Neutralization (SN)
Hemagglutination Inhibition (HI)
Immunofluorescent Antibody (IFA)
aNA 5 not applicable.
bFIV/FeLV Combo SNAP test (Idexx).
762JOURNAL OF WILDLIFE DISEASES, VOL. 44, NO. 3, JULY 2008
be low, thus decreasing the probability of
adequate binding between sufficient num-
bers of primer and target sequences
(Brennan et al., 2006). Successful ampli-
fication of proviral sequences from puma,
bobcat, and domestic cat samples run in
parallel to the DNA samples from BCI
ocelots suggest that there were not inher-
ent problems with our PCR assay and that
antibody-positive ocelots were not infect-
ed with a FIV strain associated with other
hosts, most notably domestic cats. Because
cross-species transmission of FIV strains is
rare, we suspect that the virus in our study
animals is most likely an ocelot-specific
virus and that our assay lacked the
sensitivity to detect it due to the afore-
The high density of ocelots on BCI may
promote more frequent contact among
individuals and enhance FIV transmission,
explaining the high antibody prevalence
observed in this study. The BCI popula-
tion has been estimated at 30 ocelots
based on camera-trapping surveys (Zieg-
ler, 2002), and because BCI is only
1,600 ha, this represents a higher density
(,2 individuals/km2) than reported from
other locations where densities range from
0.077 to approximately 0.8 ocelots/km2
(Emmons, 1988; Trolle and Kery, 2003;
Maffei et al., 2005; Trolle and Kery, 2005;
Di Bitetti et al., 2006). Density-related
transmission is supported by the finding
that African lion densities are positively
correlated with FIV prevalence (Winter-
bach et al., 2006). Interestingly, only one
of five (20%) male BCI ocelots was
positive for FIV infection, whereas five
or six of the seven females (71–86%) were
FIV immunoblot positive (P.0.05). No
FIV gender bias has been previously
reported, but this possibility should be
further evaluated because it may provide
insight into the mode of FIV transmission
within this population.
The implications of FIV infection in the
BCI ocelot population are unknown.
Although studies have not detected clini-
cal affects of FIV in naturally occurring
infections in wild pumas (Biek et al., 2003,
2006a, b), other reports of captive, or in
one study free-ranging animals, have
detected end-stage or subclinical immu-
nologic dyscrasias (Poli et al., 1995; Bull et
al., 2003; Brennan et al., 2006; Roelke et
al., 2006). The PCR amplification and
sequencing are needed to characterize the
virus infecting the BCI ocelots as is
further evaluation of its pathogenicity.
Development of a primer set from the
ocelot sequence reported by Troyer et al.
(2005) would be a possible strategy to
increase sensitivity of this assay.
In summary, we hypothesize that isola-
tion from domestic animals has protected
this population from pathogens that are
normally present in domestic animal
reservoirs, whereas a high density of
ocelots on BCI may have increased
transmission of a species-specific FIV.
Further study of BCI ocelots and of
ocelots and domestic animals on the
adjacent mainland is warranted to test
We thank B. Powers and the CSU
FHV, FCV, FCoV, FPV, and CDV assays,
and M. Lappin for assistance with ELISA
testing. D. Bogan, R. Mares, C. Fiorello,
and M. Wikelski were instrumental in
ocelot sampling. Capture of animals was
approved by the Animal Care and Use
Committee at the Smithsonian Tropical
Research Institute. Funding was provided
by the Peninsula Foundation, the National
Geographic Society, The National Science
Foundation, a Merck Merial summer
research fellowship, and a College of
Veterinary Medicine and Biomedical Sci-
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Received for publication 23 February 2007.