2009;73:125–131 The Canadian Journal of Veterinary Research 125
Foodborne gastrointestinal illness induced by bacterial infec-
tion affects millions of people in North America each year (1).
Salmonella spp., Esherichia coli O157:H, Campylobacter spp., and
Yersinia enterocolitica are important causes of gastrointestinal ill-
ness and are often found in production animal settings. There are
numerous routes by which these organisms can access the food
chain, including direct contamination of water for consumption as
well as contamination of water used at various points in the food
Transmission of foodborne zoonotic pathogens to riparian areas
by grazing sheep
Sara J. Sutherland, Jeffrey T. Gray, Paula I. Menzies, Sarah E. Hook, Suzanne T. Millman
The objective of this study was to determine if sheep grazing near riparian areas on pasture in Ontario are an important risk
factor for the contamination of water with specific foodborne pathogens. Ten Ontario sheep farms were visited weekly for
12 wk during the summer of 2005. Samples of feces, soil, and water were collected and analyzed for the presence of Escherichia
coli O157:H7, Salmonella spp., Campylobacter jejuni and C. coli, and Yersinia enterocolitica, by bacteriological identification and
polymerase chain reaction (PCR). The data was analyzed as repeated measures over time using mixed models. No samples
were positive for Salmonella, and no samples were confirmed positive for E. coli O157:H7 after PCR. Levels of Campylobacter
were highest in the soil, but did not differ between soil where sheep grazed or camped and roadside soil that had never been
grazed (P = 0.85). Levels of Yersinia were highest in water samples and were higher in soil where sheep had access (P = 0.01).
The prevalence of positive Campylobacter and Yersinia samples were not associated with locations where sheep spent more time
(Campylobacter P = 0.46, Yersinia P = 0.99). There was no effect of stocking density on the prevalence of Campylobacter (P = 0.30),
but as the stocking density increased the levels of Yersinia increased (P = 0.04). It was concluded that although sheep transmit
Yersinia to their environment, pastured sheep flocks are not major risk factors for the transmission of zoonotic pathogens into
Cette étude avait comme objectif de déterminer si des moutons broutant près de zones riveraines dans des pâturages en Ontario sont
d’importants facteurs de risque pour la contamination de l’eau avec des agents de toxi-infections alimentaires spécifiques. Dix fermes ovines
ontariennes ont été visitées à chaque semaine pour 12 semaines au cours de l’été 2005. Des échantillons de fèces, de sol et d’eau ont été prélevés
et analysés pour la présence d’Escherichia coli O157:H7, Salmonella spp., Campylobacter jejuni et C. coli, et Yersinia enterocolitica,
par culture et identification bactériologique ainsi que par réaction d’amplification en chaîne par la polymérase (PCR). Les résultats ont été
analysés comme des mesures répétées dans le temps à l’aide de modèles mixtes. Aucun échantillon ne s’est avéré positif pour Salmonella, et
aucun échantillon n’a été confirmé comme positif pour E. coli O157:H7 après PCR. Les quantités de Campylobacter étaient plus élevées
dans le sol, mais il n’y avait pas de différence entre les sols où les moutons avaient brouté ou séjourné et des sols routiers où aucun mouton
n’a pu paître (P = 0,85). Les quantités de Yersinia étaient maximales dans les échantillons d’eau et étaient plus élevées dans les sols où
les moutons avaient eu accès (P = 0,01). Les prévalences d’échantillons positifs pour Campylobacter et Yersinia n’étaient pas associées à
l’endroit où les moutons ont passé le plus de temps (Campylobacter P = 0,46; Yersinia P = 0,99). La densité animale n’avait pas d’effet
sur la prévalence de Campylobacter (P = 0,30), mais à mesure que la densité animale augmentait il en était de même pour la quantité de
Yersinia (P = 0,04). En conclusion, bien que les moutons transmettent Yersinia à leur environnement, les troupeaux de mouton au pâturage
ne sont pas un facteur de risque majeur pour la transmission d’agents zoonotiques dans l’eau.
(Traduit par Docteur Serge Messier)
Department of Population Medicine, University of Guelph, Guelph, Ontario N1G 2W1 (Sutherland, Menzies, Hook, Millman); Department of
Microbiology and Immunology, Des Moines University, 3200 Grand Avenue, Des Moines, Iowa 50312, USA (Gray).
Address all correspondence to Dr. Suzanne Millman; telephone: (515) 294-2817; fax: (515) 294-1072; e-mail: email@example.com
Dr. Millman’s current address is Veterinary Diagnostic and Production Animal Medicine, Lloyd Veterinary Medical Center 2424, Iowa State
University, 1600 South 16th Street, Ames, Iowa 50011, USA.
Funding for this research was received from the Ontario Ministry of Agriculture and Food and the Natural Sciences and Engineering Research
Council of Canada.
This research comprised a component of a Masters thesis by Sara Sutherland.
Received June 22, 2007. Accepted April 11, 2008.
126 The Canadian Journal of Veterinary Research 2000;64:0–00
chain. Each of these organisms can be carried and shed by sheep,
and can be transmitted to humans through water. However, there
is a paucity of information regarding the risks of sheep production
to nearby water supplies.
The World Health Organization estimates that 2 million deaths per
year result from drinking water that is contaminated with bacterial
pathogens (2). Pathogens from livestock feces are the source of some
of the water contamination. After direct feces deposition by grazing
animals or manure application on farm fields, pathogens can move
from manure to waterways or riparian areas (3). In Canada, a study
has shown that 32% of farm wells in Ontario exceed the maximum
acceptable concentrations of coliforms (4).
Mead et al (5) estimated that 0.5% of all foodborne infections and
3% of deaths from foodborne infections in the United States were due
to E. coli O157:H7. The main reservoir species for E. coli O157:H7 are
ruminants, such as cattle and sheep (6). Pollution of groundwater
with livestock manure can be an important cause of E. coli O157:H7
outbreaks (7); however, the risk from sheep production is unclear.
Estimates of overall prevalence of E. coli O157:H7 in sheep range
from 0 to 60% (8,9), with differences stemming from animal age,
production type, and season.
Salmonella is thought to be responsible for the highest cost per case
of foodborne gastroenteritis in Canada and the US (1). A study in the
United States estimated that 9.7% of foodborne infections and 31%
of deaths were due to nontyphoidal Salmonella (5). There has been
no study on the prevalence of Salmonella in sheep in Canada. A sur-
vey in Great Britain by Davies et al (10) found a fecal prevalence
of Salmonella in sheep of only 0.1%. However, Hutchinson et al (11)
found that 8% to 11% of sheep manure samples contained Salmonella.
Contamination of the environment by manure outflow may lead to
significant levels of this pathogen in surface water. Johnson et al
(12) found that 6.2% of river water samples in Alberta, Canada were
positive for Salmonella.
Campylobacter, particularly C. jejuni and C. coli, is the most com-
mon foodborne pathogen in the developed world. These organisms
cause gastroenteritis, but this is usually not fatal (13). The main
reservoirs of these bacteria are poultry and wild birds (14,15), but
they are commonly found in ruminants and other production ani-
mal species. A study of sheep on pasture in the UK found that the
prevalence of shedding of Campylobacter varied from 0 to 100%, with
the highest prevalence following lambing and very low shedding
during other times (16). There has been no study on the prevalence
of Campylobacter in sheep in Canada. Commonly transmitted by
water, Campylobacter has been found in 50% of river water samples
in New Zealand (17). Contamination of streams, rivers, ponds, and
groundwater is strongly associated with upstream agricultural loca-
tions, or sewage contamination (15).
There is a much higher prevalence of Y. enterocolitica in pigs than
in ruminants, and serotypes associated with human disease are more
likely to be isolated from pigs (18). Estimates of the prevalence of
Yersinia infection in humans in Canada are not available. There has
been no study on the prevalence of Yersinia in sheep from Canada.
In the UK, McNally et al (18) found 10.7% of samples from slaughter
sheep feces were positive for Yersinia enterocolitica. Yersinia survives
well in spring, river, or groundwater (19), and is often isolated from
According to recent figures (21), there are 230 000 sheep in Ontario,
which comprises 27% of the national flock. There is increasing con-
cern in Ontario and elsewhere regarding the health risks of livestock
grazing near waterways and riparian areas. This is partly due to
large outbreaks of human disease associated with cattle manure (22).
However, it is known that sheep and cattle exhibit different behav-
ior patterns on pasture (23). Combined with the lack of foodborne
pathogen data associated with sheep, it has been difficult to estimate
the risk of transmission of zoonotic pathogens from sheep.
The objective of this study was to determine whether sheep
pastured near riparian areas are an important risk factor for the
contamination of water with foodborne zoonotic pathogens.
Materials and methods
Study design and sample collection
Written surveys were mailed to all producers in the Ontario Sheep
Marketing Agency District 5 to determine the existence of riparian
areas on sheep farms (24). Ten farms were selected to participate in
the study, based on proximity to laboratory facilities, presence of a
suitable waterway, and willingness to participate. From the period
of May 30th until August 19th, 2005, each of the 10 farms was vis-
ited weekly. Order of visits was formally randomized for day of the
week and time of day (morning or afternoon). Over the course of
this study period, each farm received 5 morning visits (07:30–11:30)
and 5 afternoon visits (15:30–19:30), during which time behavioral
observations were taken for an associated study.
Soil, water, and fecal samples were collected each day after the
end of the morning behavioral observations. Water samples (50 mL)
were collected within 30 cm of the water’s edge, in open water,
using a sterile conical tube. Because of their strong flocking behav-
ior, sheep typically access water sources from particular locations.
Hence, water samples were collected from 3 different locations,
1 taken at the location where sheep access the stream (access),
1 taken 10 m upstream from the access point (upstream), and 1 taken
10 m downstream from the access point (downstream). If the sheep
were contaminating the water source, pathogen levels would be
higher at the access and downstream locations than at the upstream
Soil samples were collected from 5 locations, and a minimum of
1 cm3 of soil, free of vegetation, was collected using a sterile scupula.
One sample was taken at the edge of the water at the sheep access
point (Access), 1 in the open field where the sheep were observed to
graze (field), and 1 from the road edge where sheep had never had
access (roadside). The behavior of pastured sheep includes grazing
bouts interspersed with camping bouts where sheep congregate to
lie down, ruminate, and rest. Therefore, 2 samples were collected
from each camping area. On farms where sheep had barn access,
camping tended to occur in the barn with a 2nd camping site located
in the pasture.
Two fecal samples of approximately 5–10 g each were collected
from the ground at the sheep camping site. Where possible, feces
were collected immediately after excretion. If the sheep were not on
the camping site at the end of the observation period, the freshest
feces were collected.
2000;64:0–00 The Canadian Journal of Veterinary Research 127
All fecal and soil samples were placed in Whirl-pak plastic bags
(Nasco; Fort Atkinson, Wisconsin, USA), and transported to the
laboratory within 1 h of collection.
Methods were approved by the University of Guelph Animal
Care and Use Committee in concordance with the Canadian Council
for Animal Care (CCAC) guidelines (AUP#05R093, “Risks of water
borne pathogens from pastured sheep”).
During each farm visit, the air temperature, relative humidity
and black-globe temperature were recorded hourly. Air tempera-
ture data were collected using a thermometer (VWR International,
Mississauga, Ontario), black globe temperature using an identical
thermometer located inside a black globe (10 cm-diameter copper
sphere painted matt black) (25), and relative humidity data were
collected using an electronic thermohygrometer (Mannix Testing
and Measurement, Lynbrook, New York, USA). The equipment was
always situated in direct sunlight, in or beside the field containing
the sheep. The black globe humidity index (BGHI) was calculated
using the equation:
(0.8 3 T) 1 [RH 3 (T - 14.3)/100] 1 46.3
where: T = the temperature on the black globe, and
RH = the relative humidity (26).
Samples were enriched as previously described (27) with appropri-
ate sample size modifications. Briefly, 2 g (1/- 0.5 g) of each of the
soil and fecal samples were weighed and individually placed into
20 mL of Brilliant Green Bile Broth 2% (Fisher Scientific, Hampton,
New Hampshire, USA). Five mL of each of the water samples was
pipetted into 45 mL of Brilliant Green Bile Broth 2%. All samples
were enriched for 18 h at 37°C.
Escherichia coli O157:H7
Following enrichment, samples were processed for E. coli O157:H7
as described previously (27) with appropriate sample size modi-
fications. Briefly, 1 mL aliquots were removed and added to a
suspension of E. coli O157 antibody coated immunomagnetic beads
(Dynal, Oslo, Norway). The resulting suspensions were processed by
immunomagnetic separation (IMS) according to the manufacturer’s
instructions. Fifty mL of the resuspended bead-bacteria complexes
were plated onto sorbitol MacConkey (SMAC; Difco, Becton Dickson,
Sparks, Maryland, USA) supplemented with cefixime/tellurite
(CT-SMAC; SMAC Media Cefixime-Tellurite Supplement, Oxoid,
Nepean, Ontario) and incubated overnight at 37°C. Nonsorbital
fermenting colonies on CT-SMAC agars were tested for the presence
of b-glucuronidase and the ability to ferment lactose using E. coli
broth containing 4-methylumbelliferyl-b-D-glucuronide (MUG)
and MacConkey agar, respectively. Lactose-fermenting and MUG
negative isolates were tested for the presence of the E. coli O157
antigen gene locus, rfbEO157, using PCR as previously described
(28). Isolates positive for rfbEO157 were also tested for the presence
of genes encoding for the H7 flagellum (fliC-H7), by PCR analysis as
previously described (29).
Following enrichment, Salmonella spp. were cultured, detected,
and confirmed as described previously (30). A 1-mL aliquot was
placed in tetrathionate broth (Difco; Becton Dickson) for 48 h at
37°C using a ratio of 1 mL of sample to 10 mL of media. After 48 h of
incubation, 100 mL of tetrathionate media was transferred to 10 mL
Rappaports broth (Difco; Becton Dickson) and incubated at 37°C
for 24 h. Subsequently, the broth was streaked to XLT4 agar (Difco;
Becton Dickson) and incubated as described previously. Suspect colo-
nies were tested on TSI and LIA agar slants (Difco; Becton Dickson)
for reactions typical of Salmonella spp.
Following enrichment, the presence of Campylobacter spp. was
evaluated by plating the sample onto Blood-free Karmali plates
(Oxoid). Plates were incubated at 42°C for 48 h in a microaerophilic
atmosphere generated by Campypak with catalyst (Fisher Scientific,
Fort Atkinson, Wisconsin, USA). Plates were subsequently examined
for the presence of typical Campylobacter colonies. All suspect colo-
nies were selected and subjected to identification and processed for
PCR confirmation. Isolates were confirmed using methods described
by Persson and Olsen (31) for identification of Campylobacter spp. and
differentiation of C. coli and C. jejuni. Primers were directed towards
the following loci: a universal 16S rDNA gene sequence serving as
an internal positive control for Campylobacter with a 1062 kb product,
the hippuricase gene (hipO) with a 344 kb product characteristic
of C. jejuni, and a sequence partly covering an aspartokinase gene
characteristic of C. coli with a 500 kb product.
For detection of Yersinia spp. following enrichment, each sample
was streaked onto CIN agar (Oxoid) and incubated at 25°C for 48 h.
Suspect colonies were further tested for lactose fermentation on
MacConkey agar plates. Nonlactose-fermenting colonies were evalu-
ated for Rhamnose (10 g rhamnose/L) fermentation using Rhamnose
MacConkey (Fisher Scientific) agar at 25°C for 18 h. Nonrhamnose-
fermenting colonies were selected and subjected to PCR. Isolates
were confirmed using methods described by Wannet (32) for iden-
tification of Yersinia enterocolitica. The ail gene was identified with a
PCR product size of 454 kb which identifies a large proportion of the
Y. enterocolitica which are considered to be pathogenic.
In order to test if differences exist between prevalence of patho-
gens in soil, feces and water, a Fisher’s exact test was used, SAS proc
freq (33). Where there was significance, a mixed model (SAS proc
glimmix) was used to estimate the probability of finding a posi-
tive sample in different sample types. The model used test results
(positive and negative coded as 1 and 0) as the response, with farm,
date, and sample type (feces, soil, or water) as class statements. A
model was also used to determine if there were differences between
prevalence of positive samples in different soil sample and water
A model was used (SAS proc glimmix) to test whether temperature
or stocking density affected the prevalence of organisms recovered.
128 The Canadian Journal of Veterinary Research 2000;64:0–00
The final model included type of sample, BGHI (or dry temperature)
and stocking density. Farm was included as a random effect, with
farm, date and sample type as class statements.
Contrasts were used to test for differences between farms that
had ponds and those farms that had streams, and for differences
between farms where the waterway was inside or on the edge of
Flock size for the 10 farms used in this study varied from 12 to
250 sheep. The stocking density varied from approximately 0.75
to 167 sheep per acre (Table I). Four of the farms had ponds, 5 had
streams and 1 farm rotated sheep between different pastures of
which 2 had pond access and 2 had stream access.
A total of 542 samples were collected over the course of the study,
279 of which were soil samples, 143 were water samples, and 102
were fecal samples. Soil samples could be subdivided by location
of collection into 51 from field soil, 49 from roadside soil, 57 from
sheep access soil, and 122 from camping soil. Of the camping soil
samples, 64 were from inside barns, 20 from field camping sites,
and the remaining 38 from camping areas on farms where the sheep
did not have barn access. The 143 water samples could be further
subdivided into 52 from the site where the sheep had water access,
24 from upstream of this site, and 23 downstream. The remaining
44 water samples were from pond water to one side or the other of
the sheep access point. All fecal samples were collected from camp-
ing areas, with 64 samples from barn camping areas, 8 from field
camping areas, and 30 from “near barn” camping areas on farms
where the sheep did not have barn access.
No Salmonella spp. were recovered from the samples collected in
this study. Preliminary confirmation classified 54 out of 524 (10.3%)
of the samples as positive for E. coli O157:H7. However, none of the
samples were confirmed as true E. coli O157:H7, since they were
lacking one or more genotypic traits.
There were 92 out of 524 (17.6%) samples positive for Campylobacter
spp. The sample type most commonly positive for Campylobacter was
soil (22.3%), compared with water (14.7%), and feces (8.7%). There
was a significant difference in the prevalence of Campylobacter
between types of sample (P = 0.0063), with higher levels in the soil
than feces (P = 0.0034) and a tendency towards being higher in soil
than water (P = 0.0677), but not significantly different between feces
and water (P = 0.1553) (Figure 1). The overall difference between soil
locations was not quite significant (P = 0.068). There was a signifi-
cantly higher level of Campylobacter recovered from access soil than
from field soil (P = 0.0140), but none of the other sample location
comparisons were significantly different (camping soil versus field
soil P = 0.0835; camping soil versus roadside soil P = 0.8395; camp-
ing soil versus access soil P = 0.1958; field soil versus roadside soil
P = 0.2088; access soil versus roadside soil P = 0.1877). There was no
difference between levels of Campylobacter in samples from different
water locations (P = 0.2588).
There were 97 out of 524 (18.5%) samples positive for Yersinia
spp. There was a significant difference in levels of Yersinia between
Table I. Description of the 10 farms used in this study. Note: Farm D rotated the sheep between 4 different
pastures. On some of these pastures strip grazing was practiced, with the result that the stocking density
varied between visits
(sheep per acre)
Edge of pasture
Edge of pasture
Edge of pasture
Edge of pasture
Edge of pasture
Edge of pasture
Edge of pasture
Edge of pasture
Figure 1. Proportion of positive samples of Campylobacter from different
sample types. Samples from soil were significantly more likely to be positive
for Campylobacter than samples from feces or water (P , 0.05).
% positive samples
Feces Soil Water
2000;64:0–00 The Canadian Journal of Veterinary Research 129
different types of samples (P = 0.0122), with higher levels found in
water samples than in feces (P = 0.0164), but not significantly higher
in soil than feces (P = 0.0689) or in soil than water (P = 0.3384). When
the soil samples were examined by collection location (camping,
field, access, and roadside), Fisher’s exact test indicated a significant
difference in prevalence of Yersinia between soil types (P = 0.0047).
Samples from the roadside soil were lower in Yersinia compared with
camping (P = 0.0161), field (P = 0.0165), and access (P = 0.0007) soils.
None of the other differences were significant (camping versus field
soils P = 0.8968; camping versus access soils P = 0.1078; field versus
access soils P = 0.1772) (Figure 2).
Following PCR confirmation, 26 of 524 samples were confirmed
positive for Yersinia enterocolitica specifically. The sample type most
commonly positive for Yersinia enterocolitica was water (6.3%), com-
pared to soil (4.7%), and feces (3.9%). There was no significant dif-
ference in Y. enterocolitica levels between different types of samples
(P = 0.8775). There was also no difference in levels of Y. enterocolitica
between different soil sample location (P = 0.4159), or different water
sample location (P = 0.8223). None of the samples tested positive by
PCR for the presence of the Y. enterocolitica ail gene associated with
Farm level factors
The prevalence of positive Campylobacter samples recovered per
farm varied between 6% and 32%. The results of the mixed model
indicate that there was no effect of stocking density on the prevalence
of Campylobacter (P = 0.1772). There was no difference in likelihood
of recovering Campylobacter from farms with waterways inside the
pasture (so that the sheep could access all sides) (P = 0.8911) or on
the edge of the pasture (so that sheep could only access one side),
or between farms with ponds or streams (P = 0.2770).
The prevalence of Y. enterocolitica recovered per farm varied
between 0 and 12% of samples. As the stocking density increased,
the probability of recovering Yersinia increased (P = 0.0358), but
the probability of recovering Yersinia enterocolitica did not change
(P = 0.7807). There was no difference in likelihood of recovering
Yersinia from farms with different types of waterway (P = 0.99) loca-
tion of waterway in the pasture (P = 0.99).
Over the 12-week study period, the average dry temperature
ranged from 12°C to 38°C, with an average of 25°C. The relative
humidity ranged from 25% to 100% and the temperature in the black
globe ranged from 13°C to 47°C, corresponding to a BGHI range from
52.70 to 109.70, with an average BGHI of 81.9 (Figure 3).
There was a significant effect of temperature on the probability
of recovering Yersinia enterocolitica (P = 0.0025). With each increase
in one degree Celsius on the day of the observation, the odds of
recovering Yersinia enterocolitica decreased by 0.21. There was also
a significant effect of temperature on the probability of recovering
Campylobacter (P = 0.0022). With each increase in one degree Celsius
on the day of the observation, the odds of recovering Campylobacter
decreased by 0.17. The BGHI also was associated with pathogens
recovered in this study. With each increase in one unit of BGHI,
the odds of recovering Yersinia enterocolitica decreased by 0.096
(P = 0.0005). For each increase in one unit of BGHI, the odds of
recovering Campylobacter decreased by 0.049 (P = 0.0139).
Under certain circumstances cattle can cause negative effects on
natural water sources by shedding zoonotic pathogens into the envi-
ronment (34). Being ruminants, sheep carry and shed many of the
same zoonotic organisms as cattle including E. coli O157:H7 (8,35),
Salmonella spp. (10), Campylobacter spp. (16), and Yersinia enterocolitica
(36). One of the factors that make cattle a risk for transmission of
pathogens into water sources is how they use riparian areas and their
behavior in and around water sources (37). Even though sheep may
pose similar risks, there are few data available on the impact of sheep
production on natural water sources, and to the authors’ knowledge
there have been no previous studies on how sheep behavior may
affect zoonotic pathogen load in surface water and riparian areas.
Ruminants, particularly cattle, are considered the main reservoirs
for E. coli O157:H7. In the present study, no E. coli O157:H7 was
recovered from the water, the soil or the sheep feces. Reliance on
biochemical tests alone to identify and differentiate E. coli O157:H7
from other organisms and E. coli types would have resulted in a
number of false positives. However, further confirmation with PCR
eliminated all suspects. The objective of this study was to determine
Figure 3. Variation in temperature () and % relative humidity () over
the course of the 12-week study period (May 30 to August 19, 2005).
Each point is the average of the measures taken on farms visited during
% relative humidity
Week of study
Figure 2. Proportion of soil samples from different locations that tested
positive for Yersinia spp. Samples from the roadside soil (negative control)
were less likely to be positive for Yersinia than samples from camping soil
(P = 0.0161), open field soil (P = 0.0165), or soil from the sheep access
to water point (P = 0.0007)
% positive samples
130 The Canadian Journal of Veterinary Research 2000;64:0–00
which organisms sheep are contributing to their environment, rather
than to measure the prevalence of zoonotic organisms in the sheep
per se. Therefore, the flocks studied may have been colonized with
E. coli O157:H7, but at levels not detected in this study.
Other factors that have been shown to contribute to shedding of
E. coli O157:H7 by ruminants are sudden changes in diet, environ-
ment, or antimicrobial therapy (6,35). These factors were not present
in any of the flocks studied. Furthermore, levels of E. coli O157:H7
are lower in feces from sheep and cattle fed forage rather than con-
centrate diet (6,11), which is typical of pastured sheep production
in general and of the flocks studied here specifically. Hence, results
from the present study support the hypothesis that the amount of
E. coli O157:H7 contributed to the environment by pastured sheep
No Salmonella was detected in this experiment; again this is likely
a function of study design, sample type, and the low prevalence
expected in pastured sheep. Similar to E. coli and Campylobacter,
animals fed a pasture or forage-based diet shed less Salmonella
in their feces than those fed concentrate based diets (11). Further
study on the epidemiology of Salmonella in sheep would be
useful for determining how to manage this pathogen in sheep
Campylobacter were recovered in this study from sheep feces,
water, and soil samples. Campylobacter spp. are found frequently
in all animals including wild birds and poultry (14,15), which may
contribute to environmental levels of Campylobacter. One study
found that 42% of wild geese and other waterfowl feces were con-
taminated with Campylobacter jejuni (38). In the present study, wild
geese were observed near the water sources on each of the farms.
The hypothesis that wildfowl are at least partly responsible for the
environmental contamination is supported by the fact that there
was no significant difference in levels of Campylobacter between soil
that had never been grazed by sheep (the roadside control) and soil
where sheep grazed and camped. Therefore it would seem likely the
Campylobacter recovered from the soil and water was not exclusively
from ovine sources. Again, stress such as lambing or calving, moving
animals, weaning, transport or changing feed can cause an increase
in the shedding of Campylobacter (15,39). None of these were factors
in the study herein.
In the present study, more Yersinia spp. was recovered from soils
where the sheep had access than from roadside soil; however, there
were no differences in levels of Yersinia enterocolitica from the dif-
ferent soil locations. This suggests that sheep are at least partially
responsible for contaminating the environment and the water, but
serotypes of Yersinia that were shed are unlikely to cause disease in
humans. There has been little or no research on the effect of feeding
and management in the shedding of Yersinia from ruminants, and
therefore it is not clear how management affects Yersinia prevalence,
if at all.
The lack of association between amount of time that sheep spent
in one location and the levels of pathogens in samples from that
location was not expected. This lack of association was also found in
the related behavioral component to our study (24). To the authors’
knowledge, no other studies have examined these parameters with
regards to sheep production. Soils where sheep camp receive higher
levels of feces relative to noncamp areas (40) and, therefore, would
be expected to have higher levels of pathogens. Also higher levels
of pathogens would be expected in the water on farms where the
sheep spent more time near the water compared with farms where
the sheep were never seen near the water. These results indicate that
under the management conditions observed, sheep do not have a
significant impact on foodborne zoonotic pathogen levels in riparian
areas and surface waters. This result is likely due to a combination
of the organisms and levels that sheep typically shed, the behavior
patterns specific to sheep, and the typical management of sheep in
In conclusion, sheep on pasture in Ontario do not appear to be
an important source of water contamination with Escherichia coli
O157:H7 or Salmonella. Although in this study Campylobacter and
Yersinia were recovered from samples of sheep feces, soil, and water;
there was insufficient evidence to implicate sheep as an important
cause of environmental contamination with these pathogens. The
lack of association between prevalence of these pathogens and
behavior of sheep supports the hypothesis that grazing sheep are
not a major risk factor in the transmission of foodborne zoonotic
pathogens to water sources.
The authors gratefully acknowledge the funding support for this
project from the Ontario Ministry of Agriculture, Food and Rural
Affairs and Natural Sciences and Engineering Research Council of
Canada, and assistance from the Ontario Sheep Marketing Agency.
William Sears kindly provided statistical advice, and Charlotte
Friendship provided technical assistance for collection and process-
ing of samples.
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