The low seroprevalence of tick-transmitted agents of disease in dogs from
southern Ontario and Quebec
Abstract — Infectious diseases caused by pathogens transmitted by ticks and other insect vectors are an important
cause of morbidity and mortality in both dogs and humans throughout North America. The purpose of this study
was to determine the seroprevalence of selected vector-transmitted pathogens in southern Ontario and Quebec.
Samples submitted to the Vector Borne Disease Diagnostic Laboratory (VBDDL) at the North Carolina State
University College of Veterinary Medicine were evaluated for antibodies to Ehrlichia canis, Anaplasma phagocyto-
philum, Babesia canis, Bartonella henselae, Borrelia burgdorferi, Bartonella vinsonii subspecies berkhoffii, and Rickettsia
rickettsii. Information regarding breed and the city or province from which the sample originated was recorded;
however, travel history was unknown for the majority of dogs. Overall seroprevalence to these tick-borne pathogens
in southern Ontario and Quebec is low compared with most regions of the United States, suggesting that veteri-
narians in this region of Canada should pursue diagnostic evidence of infection in dogs with a travel history or
prior residence in areas endemic for exposure to tick-borne infections.
Résumé — Faible séroprévalence de certains agents infectieux transmis par les tiques chez les chiens du sud
de l’Ontario et du Québec. Les maladies infectieuses causées par des pathogènes transmis par les tiques et autres
insectes vecteurs sont une importante source de morbidité et de mortalité à la fois chez le chien et l’homme dans
toute l’Amérique du Nord. Le but de cette étude était de déterminer la séroprévalence de pathogènes particuliers,
transmis par vecteurs, dans le sud de l’Ontario et du Québec. Les échantillons ont été transmis au Vector Borne
Disease Diagnostic Laboratory (VBDDL) au North Carolina State University College of Veterinary Medicine pour
être soumis à une évaluation des anticorps contre Ehrlichia canis, Anaplasma phagocytophilum, Babesia canis,
Bartonella henselae, Borrelia burgdorferi, Bartonella vinsonii sous-espèce berkhoffii et Rickettsia rickettsii. Les
renseignements concernant les races et les villes ou provinces d’origine des échantillons ont été notés mais l’historique
du déplacement des chiens était inconnu dans la majorité des cas. La séroprévalence globale de ces pathogènes
transmis par les tiques dans le sud de l’Ontario et du Québec est faible comparé à celle de la majorité des régions
des États-Unis. Les vétérinaires de ces régions du Canada devraient être sensibilisés aux signes diagnostiques
d’infection chez les chien ayant voyagé ou résidé dans des endroits où l’exposition aux infections transmises par
les tiques est endémique.
(Traduit par Docteur André Blouin)
Can Vet J 2006;47:1194–1200
nfectious diseases caused by pathogens transmitted by ticks
and other vectors are an important cause of morbidity
and mortality in both humans and dogs throughout North
America. Notable etiologic agents in veterinary medicine include
Anaplasma phagocytophilum, Babesia canis, Bartonella, Borrelia
burgdorferi, Ehrlichia canis, and Rickettsia rickettsii. While
numerous studies have described the seroprevalence and geo-
graphic distribution of these vector-borne organisms throughout
the United States (1–7), little information is available regarding
the seroprevalence in Canada. Knowledge of the seroprevalence,
combined with the known distribution of vector ticks, will
aid the veterinarian in selecting appropriate diagnostic tests
and optimal treatment regimens, while awaiting test results.
Additionally, definitive documentation of vector-borne infec-
tions in dogs can provide important sentinel information for the
potential of human infection in a defined geographic location,
which has important public health implications (8,9).
Department of Veterinary Medicine and Biological Sciences,
Colorado State University College of Veterinary Medicine,
300 West Drake, Ft. Collins, Colorado, 80523 USA (Gary);
Department of Clinical Studies, Ontario Veterinary College,
Guelph, Ontario N1G 2W1 (Webb); Department of Clinical
Sciences, North Carolina State University College of Veterinary
Medicine, 4700 Hillsborough Street, Raleigh, North Carolina,
27607 USA (Hegarty, Breitschwerdt).
Address all correspondence and reprint requests to Dr. Anthony
T. Gary; e-mail: email@example.com
The seroprevalence of many tick-transmitted pathogens is
directly correlated to the geographic distribution of the primary
vectors that transmit the organism (1,10,11). For instance,
the seroprevalence of B. burgdorferi, the etiologic agent of
Lyme borrelliosis, and A. phagocytophilum (formerly Ehrlichia
equi, E. phagocytophilum, or the agent of human granulocytic
ehrlichiosis) is directly related to the distribution of their shared
primary vectors, Ixodes scapularis and Ixodes pacificus in eastern
and western North America, respectively (1). Recent reports
have shown that I. scapularis, the blacklegged tick, is in numer-
ous locations throughout Canada and appears to be endemic in
several regions, including Rondeau Provincial Park, Long Point,
and Point Pelee National Park in southwestern Ontario (12–17).
Thus, the potentially expanding distribution of I. scapularis in
Canada may increase the likelihood that dogs and humans will
be infected with pathogens primarily transmitted by this vec-
tor. Other tick species that can be found throughout southern
Ontario and Quebec include Rhipicephalus sanguineus (18,19),
Dermacentor variabilis (12,19–22), Haemaphysalis leporispalustris
(19,22), Dermacentor albipictus (19,20,23), and Ixodes cookei
(24); however, based upon current knowledge, only the first
2 species are of immediate concern in small animal companion
animal medicine. Rhipicephalus sanguineus, the primary vector of
E. canis (25), Ba. canis and, possibly, Bartonella vinsonii (berkhof-
fii) (3), and possibly Anaplasma platys (formerly Ehrlichia platys)
(26), are closely associated with dog populations throughout
the world. All 3 stages of the R. sanguineus life cycle (larvae,
nymph, adult) feed preferentially on dogs, which results in
sustainable tick populations in homes or kennels wherever dogs
are present (27). Dermacentor variabilis, the primary vector
of Rickettsia rickettsii, the etiologic agent of Rocky Mountain
Spotted Fever (RMSF), is found east of 105º longitude and
south of 52º latitude in Canada, which includes portions of
Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick,
Prince Edward Island, and Nova Scotia, where large, expanding
populations have been described (20–22).
Based on the geographic distribution of various tick species,
transmission of vector-borne diseases in Canada could poten-
tially include ehrlichiosis, RMSF, babesiosis, bartonellosis,
anaplasmosis, and Lyme borrelliosis. Although primarily thought
to be limited to the warmer North American climates, the geo-
graphic distribution of many arthropod vectors is increasing as
a result of frequent, widespread human and pet travel, aerial
transport by adventitious birds, and changes in the environment,
including global warming, that allow tick populations to over-
winter (16,28,29). These factors, as well as the important role
of dogs as sentinel animals for detecting exposure to tick-borne
organisms, underscores the importance of periodic determina-
tion of the canine seroprevalence to tick-borne pathogens in
Canada. The purpose of this study was to determine the sero-
prevalence of selected vector-transmitted organisms in southern
Ontario and Quebec, based on samples submitted to the Vector
Borne Disease Diagnostic Laboratory (VBDDL) at the North
Carolina State University College of Veterinary Medicine.
Materials and methods
All available serum samples from dogs in southern Ontario and
Quebec submitted to the VBDDL between August 9, 2000, and
September 19, 2003, were included in the study. Samples were
submitted for diagnostic testing from clinics by the attending
veterinarian. Clinical data available from each dog were limited,
but they included breed and location (city and province) of
the veterinary hospital from which the sample was submitted.
Travel history and reason for submission were not available for
The specific tests performed on each sample at the VBDDL
were dependent on the tests requested by the submitting vet-
erinarian. A standard serological panel consisting of antibodies
to Bo. burgdorferi, Ba. canis, Bar. vinsonii (berkhoffii), E. canis,
and R. rickettsii might have been requested, as well as individual
serologic tests. In addition to the tests requested by the attend-
ing veterinarian, antibodies to A. phagocytophilum and Bar.
hensalae were tested for retrospectively by using stored serum
for all samples that were submitted for the standard serologic
Antibodies against E. canis, R. rickettsii, Ba. canis, Ba. gibsonii,
Bar. vinsonii, Bar. hensalae, and A. phagocytophilum were deter-
mined by the indirect fluorescent antibody (IFA) test, as previ-
ously described (1,7,8). Briefly, serum serially diluted to 1:32
was applied to multiple-well microscope slides that contained
the affixed antigen of interest. After incubation, washing, and
drying, fluorescein isothiocyanate (FITC)-labeled goat anti-
dog immunoglobulin (Kirkegaard and Perry Laboratories,
Gaithersburg, Maryland, USA) was applied to each well. For
positive samples, serial dilutions were used to determine the
antibody titer; reciprocal titers $ 64 were considered sero-
positive. Borrelia burgdorferi was tested serologically by using
a commercially available peptide C6 enzyme-linked immuno-
sorbent assay-based test kit (SNAP® 3Dx™; IDEXX Laboratories,
Westbrook, Maine, USA), according to the manufacturer’s
Polymerase chain reaction assay.
Ehrlichia-genus primers were used first to detect DNA from
Ehrlichia spp. and Anaplasma spp., as previously described (30).
Positive samples were then analyzed with primers specific for
E. canis, E. chaffeensis, E. ewingii, A. platys, and A. phagocyto-
A total of 288 samples were submitted to the VBDDL from
veterinarians in southern Ontario and Quebec throughout the
period of study. Antibodies to Ba. gibsonii, Ba. canis, Bar. hensa-
lae, R. rickettsii, and Bo. burgdorferi were found most frequently,
but there was little serologic evidence to support the presence of
A. phagocytophilum (0/53), Bar. vinsonii (berkhoffii) (0/59), and
E. canis (1/271 [0.37%]), as shown in Table 1. The polymerase
chain reaction (PCR) prevalence of E. canis was 7.3% (3/38),
while 2 of the PCR-positive samples were seronegative for
E. canis antigens by IFA testing (Table 2). Of the 288 samples,
139 (48%) were submitted for only E. canis serologic testing,
54 (18.8%) for the standard tick-borne disease serologic panel,
35 (12%) for Bo. burgdorferi and E. canis serologic testing,
14 (4.9%) for Ehrlichia genus PCR, 4 (1.4%) for E. canis, Ba.
canis, Ba. gibsonii, Bo. burgdorferi, and R. rickettsii serologic
testing, 4 (1.4%) for E. canis, Bo. burgdorferi, and R. rickettsii
serologic testing, 3 (1%) for E. canis and Ba. canis serologic test-
ing, 3 (1%) for E. canis and Bar. vinsonii (berkhoffii) serologic
testing, 3 (1%) for E. canis, Ba. canis, and Bo. burgdorferi sero-
logic testing, 3 (1%) for E. canis and Bar. vinsonii (berkhoffii)
serologic testing, 3 (1%) for E. canis and R. ricketsii serologic
testing, and 23 (8%) for individual serological or PCR tests.
The population of dogs consisted of 72 different breeds and
included the Labrador retriever (9%, 26/288), greyhound (6.3%,
18/288), golden retriever (6%, 16/288), cocker spaniel (4.9%,
14/288), and mixed breed (17%, 49/288). Age and gender were
not available for the majority of dogs. The breeds with positive
serologic or PCR results are described in Table 2.
Many of the samples submitted for analysis were from the
province of Ontario with the majority (n = 240) from the
city of Guelph, of which 235 (82%) were submitted from
the Animal Health Laboratory at the Ontario Veterinary College.
The remaining submissions were from the cities of Ottawa
(n = 27), Toronto (n = 12), and Blenheim (n = 4). Five samples
were from the cities of Montreal (n = 4) and St. Hyacinthe
Table 1. Serological?and?polymerase?chain?reaction?(PCR)?results?for?selected?tick-borne?organisms?in?samples?from?
Reciprocal antibody titer
Organism Titer negative 64–256 256–2048
. 2048 Prevalence
Bartonella vinsonii berkhoffii
Ehrlichia canis PCR
Peptide C6 ELISA-based kit positive = 2
Positive = 3
Table 2. Geographical,?historical,?serological,?and?polymerase?chain?reaction?(PCR)?results?for?dogs?PCR?positive?or?seropositive?for?select?
Dog Breeda City of origin Pathogen(s) Serology PCR Travel Clinical history
American Eskimo (3)
Golden retriever (16)
Belgian Malinois (1)
Nova Scotia duck
tolling retriever (5)
Labrador retriever (26) Guelph, ON
Bartonella hensalae $ 1:64
Bartonella hensalae 1:128
Bartonella hensalae 1:128
1:64, C6 peptide —
New Hampshire, Unknown
New Hampshire, Unknown
Ehrlichia PCR None
Ehrlichia PCR None
1:128 None Chronic renal failure
St. Hyacinthe, QC Ehrlichia canis
No clinical signs
Ehrlichia canis Unknown
Ehrlichia canis None
a Number in parenthesis is the total number of samples submitted for the identified breed
(n = 1) in Quebec. Overall, 16 different veterinary hospitals
submitted samples for analysis during the study period. A map
showing the origin of submitted samples is shown in Figure 1.
Samples with positive serologic or PCR test results were
submitted mainly from the Animal Health Laboratory at the
Ontario Veterinary College in Guelph. Other cities with posi-
tive samples included: Blenheim (n = 2), 1 seroreactive to Bar.
henselae ($ 1:64) and the other seroreactive to Bo. burgdorferi
and Ba. gibsonii (1:64) antigens; Ottawa (n = 1), antibodies to
R. rickettsii (1:128); and St Hyacinthe (n = 1) PCR positive for
E. canis (Figure 1).
Travel history was not available for the majority of cases and
direct questioning of owners was not possible. Follow-up ques-
tioning did determine that the 2 E. canis PCR-positive dogs with
negative IFA serologic results were native to Ontario and had
not traveled outside the province prior to evaluation; the travel
history of the additional dog with positive E. canis PCR results
was unknown. Travel to Africa was documented for the single
case seropositive for E. canis. Both Bo. burgdorferi seropositive
dogs (1 also PCR1 for Ehrlichia) had not traveled outside their
respective provinces. One dog that was R. rickettsii seroreactive
had traveled to Virginia, a state endemic for RMSF, 1–2 wk
prior to sample submission. Two Ixodes spp. ticks were found
on the dog at the time of examination and sample submission.
Acute and convalescent antibody titers (1:128 and 1:128,
respectively) to R. rickettsii failed to document seroconversion
consistent with a diagnosis of RMSF. Travel to the United States
was documented for an additional case seropositive for RMSF
(1:4096). Two of the 3 Bar. henselae seropositive dogs did not
travel outside Canada; travel history for the remaining Bar.
henselae-positive dog was unknown. All greyhounds seropositive
for Ba. canis were obtained from the United States. Travel and
clinical history are further summarized in Table 2.
The overall seroprevalence to a panel of tick-transmitted organ-
isms in dogs from southern Ontario and Quebec is low, based
on the findings of the current study. Previous studies of vec-
tor-borne disease in dogs from Canada include isolated case
reports (31,32) and a study of rural dogs that documented a
R. rickettsii seroprevalence of 2.5% in Alberta and Saskatchewan
(33). Because there is little serologic evidence of tick-transmitted
disease in southern Ontario and Quebec, veterinarians should
actively pursue the travel history of dogs with suspected tick-
borne illness to determine if the dog has visited geographic areas
that are endemic for various tick-borne pathogens.
Figure 1. Map?of?Ontario?and?Quebec?indicating?cities?from?which?positive?and?negative?serologic?
Infection with Ehrlichia spp. may cause a variety of clinical
signs, ranging from fever, polyarthritis, and thrombocytopenia
to asymptomatic infections. Previous seroprevalence rates for
E. canis of 2.4%, 2.9%, and 6.4% have been found in recent
studies conducted in Rhode Island, North Carolina, Virginia,
Maryland, and Pennsylvania (1,4,9). The low prevalence of
0.37% in the current study may be explained by several factors,
including the absence of E. canis in ticks from southern Ontario
and Quebec, infrequent exposure of pet dogs to R. sanguineus,
or inefficient transmission of E. canis by R. sanguineus in colder
climates. While there is evidence that E. canis, E. chaffeensis, and,
to a lesser extent, E. ewingii and A. phagocytophilum cross-react
serologically (4,26,30), there is also evidence that antibodies to
1 strain of E. canis may not react similarly to other strains of
E. canis (30). Thus, if the current study utilized E. canis anti-
gens that differed from the endemic strain in a given geo-
graphic area, the seroprevalence might be falsely low. Of addi-
tional interest is a recent report that describes the presence of
E. canis-like infection in 3 cats, 2 of which were from southern
Ontario (34). Antibodies to available E. canis antigens were
not detected by IFA testing, but identical ehrlichial DNA was
amplified from all 3 cats (100% homologous to 16S rDNA
sequences in GenBank). In the current study, the dramatic dif-
ference between serologic and PCR prevalence may be related
to the presence of a different strain or an Ehrlichia sp. that
is present in Canada but does not cross-react with currently
available E. canis antigens. It remains possible, however, that
acute infections were documented prior to the development
of antibodies to E. canis. Based on the discrepancy between
E. canis serologic and PCR results, the prevalence of ehrlichial or
ehrlichial-like infection in dogs in southern Ontario and Quebec
may be underestimated, using serologic tests alone. Further
research is necessary to determine the significance of the current
The R. rickettsii seroprevalence in RMSF endemic areas in
the United States has been reported in several studies and ranges
from 12.5% to 69% of the dog sera tested (1,7,9). However,
antibodies to pathogenic spotted fever group Rickettsia spp.
cross-react with nonpathogenic Rickettsia, which may result in
the prevalence of disease caused by Rickettsia spp. in a given
geographic region being overestimated (7,35). In a previous
serosurvey, for instance, the prevalence of RMSF was markedly
reduced to an overall prevalence of 5% from 17% to 69% in
various geographic locations in North Carolina, after adjusting
for cross-reactive antibodies (7). It is likely that the R. rickettsii
seroprevalence of 4.4% in the current study overestimates the
true prevalence of RMSF in southern Ontario and Quebec.
Although 1 dog with travel history to Virginia was R. rickettsii
seroreactive, it did not develop a 4-fold rise in titer in the conva-
lescent sample, which would have been expected after a primary
infection; thus, it remains possible that exposure to a Rickettsia
sp. occurred in Canada, predating travel to Virginia. Because
the known vector (D. variabilis) is present east of 105° longi-
tude in Canada, the potential for R. rickettsii infection exists,
and human cases, although infrequent, have been reported in
this region (36). Additionally, isolates of R. rickettsii have been
found in D. variabilis from Ontario and Nova Scotia, further
emphasizing the potential for human or canine RMSF in this
Antibodies to Ba. canis were detected only in greyhounds, a
breed in which the disease is endemic in the southeastern United
States (37,38). Previous studies documented overall seropreva-
lences of 3.8% for Ba. canis and 5.6% for Babesia spp. (39,40).
Because many Babesia spp. infections are subclinical, transporta-
tion of dogs is common, and transmission occurs transovarially
in the primary vector (R. sanguineus), establishment of babesiosis
in southern Ontario and Quebec is possible, although the cur-
rent study does not provide serological evidence of Ba. canis
infection outside the greyhound population (18,37).
The Bo. burgdorferi (1.85%) and A. phagocytophilum
(0%) seroprevalences in the current study are low compared
with those in areas of the northeastern United States, where
I. scapularis, the shared primary vector, is endemic. For instance,
in a report from Rhode Island, where testing was performed
by the VBDDL, the seroprevalence of Bo. burgdorferi and
A. phagocytophilum in dogs was 52% and 14.4%, respectively
(1). Importantly, the C6 peptide serologic assay (SNAP® 3Dx™,
IDEXX Laboratories) for Bo. burgdorferi used in the current
study is not affected by vaccination (41). Thus, the seroposi-
tive samples represent natural exposure to Bo. burgdorferi. The
lack of travel history of Bo. burgdorferi-seropositive dogs and
low seroprevalence suggest that disease transmission may be
inefficient in this region, possibly secondary to climate or other
environmental factors, despite the presence of the vector and
organism. However, there is evidence that Bo. burgdorferi can
be transmitted by I. scapularis, the primary vector in southern
Ontario and Quebec (13–16). Of the I. scapularis ticks collected
from dogs across southern Ontario with no history of travel,
Bo. burgdorferi DNA was amplified from 7/121 (5.8%) ticks,
and 9/9 dogs tested were seroreactive to Bo. burgdorferi antigens
by IFA and western blotting (12). In addition, A. phagocytophi-
lum DNA was amplified from I. scapularis ticks collected from
an endemic region of southern Ontario, providing further evi-
dence that both organisms are present in southern Ontario and
Quebec and remain closely associated with I. scapularis (42).
Bartonellosis in dogs may be caused by several different
Bartonella spp. with Bar. vinsonii (berkhoffii) presumably hav-
ing a primary pathogenic role. Previous studies have found
seroprevalence rates for Bar. vinsonii (berkhoffii) of 3.6% and
4.7% for sick dogs in North Carolina and Virginia (3,43).
Additionally, in a study utilizing military working dogs with
frequent tick exposure from across the United States, an overall
prevalence of 8.7% was found (44). Importantly, in the military
working dog study, the seroprevalence was significantly different
among geographic regions, with the southern and northeastern
states having higher seropositive rates than the Midwest and the
mountain states, which had no seroreactive samples. Possible
reasons for the differences include the presence of multiple
vectors or a single vector affected by environmental or geo-
graphic differences (44). The low seroprevalence of Bar. vinsonii
(berkhoffii) (0%) in the current study may be related to similar
factors, including the effects of the environment or the absence
of the vector in southern Ontario and Quebec, which, as yet, is
not clearly established.
The seroprevalence (5.45%) for Bar. henselae in the current
study is similar to previously published rates in Hawaii (6.5%)
(45), Japan (7.7%) (46), and the United Kingdom (3%) (47),
but lower than the prevalence in sick dogs from North Carolina
(27%) (43). The presence of antibodies reactive to Bar. hense-
lae antigens was associated with R. rickettsii and Bar. vinsonii
(berkhoffii) seroreactivity in a previous study (43); however, the
current study does not provide evidence for this association,
possibly because of the low overall Bartonella spp. seropreva-
lence. Although the current study provides evidence that dogs
in southern Ontario and Quebec can have antibodies to Bar.
henselae, the clinical significance of this finding is unknown.
There are several recent studies documenting the distribu-
tion of tick vectors in Canada (12–16,18,21,24). Because
the geographic range and distribution of arthropod vectors
is likely to change over time through changes in the environ-
ment, migrating birds, and travel, the distribution of diseases
caused by pathogens transmitted primarily by tick vectors may
also change. For example, there is evidence that migratory
birds are important in dispersing tick vectors and their associ-
ated diseases throughout various geographic areas, including
Canada (16,28,29). Amblyoma americanum ticks, a species
predominantly found in the southeastern United States and the
principle vector of human and canine monocytic ehrlichiosis
(E. chaffeensis), have been removed from birds throughout
various locations in Canada (16). Additionally, this tick species
has also been recovered from dogs and cats in Ontario with
no history of travel (16). Thus, diseases caused by pathogens
transmitted primarily by A. americanum, while likely uncom-
mon, may occur in new geographic regions, because transient
or sustainable populations with their associated pathogens may
develop far outside the natural host range (48).
Several important limitations should be considered when
examining the results of the current study. Because serum
samples were submitted from a proportionally small number of
veterinary hospitals from a limited geographic range, the sample
population is not representative of the general dog population
of southern Ontario and Quebec. The lack of available travel
history for some of the test-positive samples may also confound
the results, the possibility that tick-exposure occurred in areas
other than southern Ontario and Quebec cannot be ruled out.
Additionally, samples from animals with a travel history may
have been preferentially submitted for evaluation of vector-borne
disease by attending veterinarians. The findings of the current
study, however, may be used to provide an approximation of
the prevalence of selected vector-borne pathogens in southern
Ontario and Quebec.
Veterinarians should actively pursue the travel history of dogs
with infections suspected of having been caused by tick-borne
pathogens while attempting to determine the potential for
exposure to tick-borne organisms that are endemic in specific
geographic regions. Many tick-borne organisms can induce
chronic infections in dogs for months to years before disease
manifestations develop. Researchers should also consider the
potential that novel tick-borne pathogens may be transmitted
by tick species in colder climates that will not be detectable by
using currently available serological tests. Widespread serological
and molecular-based studies are needed to definitively determine
the prevalence of tick-borne organisms throughout Canada.
Furthermore, periodic studies that investigate prevalence and
distribution of arthropod vectors in Canada are necessary to
assess the dynamics associated with the risk disease caused by
tick-borne organisms in dogs and humans.
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