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Israel Journal of Veterinary Medicine  Vol. 70 (3)  September 2015 Tirosh Levy, S. 32
Prevalence and Risk Factor Analysis of Equine Infestation with
Gastrointestinal Parasites in Israel
Tirosh Levy, S.,
1
Kaminiski-Perez, Y.
1
Horn Mandel, H.,
1
Sutton, G.A.,
1
Markovics, A.
2
and Steinman, A.
1
*
1
Koret School of Veterinary Medicine, Te Robert H. Smith Faculty of Agriculture, Food and Environment,
Te Hebrew University of Jerusalem, P.O.B. 12, Rehovot 76100, Israel.
2
Division of Parasitology, Kimron Veterinary Institute, P.O. Box 12, Bet Dagan 50250, Israel.
*
Corresponding Author: Dr. Amir Steinman, DVM, PhD, MHA., Tel: 972-54-8820516, Fax: 972-3-9604079. Email: amirst@savion.huji.ac.il
ABSTRACT
Te horse is a host for a large number of intestinal helminthic parasites. Tis study was designed as a survey
for the prevalence, species distribution and potential risk factors of equine intestinal helminth parasites among
horses in Israel. Fecal foatation and egg counts were performed on 485 fecal samples collected from 403
horses (mostly adults) at 30 farms across Israel. Strongyle eggs were found in 116/485 (24%) of the samples
from 18/30 (60%) farms, of which 44 (38% of positive samples, 9% of the total population) were highly
infested (over 500 eggs/gm feces). Ascarids were found in 26/485 (5%) samples from 10/30 (33%) farms,
7 (27% of positive samples, 1.4% of the total population) of which were highly infested. Singular fatworm
eggs (family Anoplocephala) were detected in two samples. Risk factors signifcantly (p<0.005) associated with
Strongyle infestation by the univariate statistical analysis were the farm, geographical location, age of the
horse and breed, and the time of last deworning treatment. Season, horse gender, horse age, and housing were
signifcantly associated with ascarid infestation.Infestation with gastrointestinal helminths in Israel appears
to be low, and resistance against anthelminthics in adult horses is probably uncommon. Tese fndings should
lead to re-investigation and re-evaluation of deworming regimes in Israel recommended for adult horses in
equine facilities in areas with low infestation rates.
Keywords: Equine; Helminth; Fecal Floatation; Small Strongyles; Ascarids; Parascaris equorum;
Risk Factors; Israel
INTRODUCTION
Te horse is a host for a large number of intestinal helminthic
parasites, including roundworms, fatworms and pinworms.
Infestation may range from asymptomaticto life threatening,
depending on the host, helminth species and parasite burden
(1). In the past, large Strongyles, and mainly Strongylus vul-
garis, were the main concern of horse owners and veterinar-
ians due to its high occurrence and resulting high mortality.
Tis encouraged most equine practitioners to advise routine
anthelminthic treatments for most horses.Te introduction
of these routine treatments has led over the past few decades
to changes in species distribution and to the emergence of
parasite resistance to some of the anthelminthic drugs (2).
In recent years small Strongyles, and mainly Cyathostomins
have been the most prevalent helminth species in adult
horses, with increasing reports of their clinical signifcance
and resistance to benzimidazole and tetrahydropyrimidine
drugs (2). Parascaris equorum is also a clinically important
species, especially in young horses, with reports of resistance
to macrocyclic lactones (2).
Israel has a climate ranging from Mediterranean to ex-
treme arid, with very few pasture areas for horses. Most horses
are stabled or turned out in small paddocks, a factor which
may afect the probability of being infected by helminth
Israel Journal of Veterinary Medicine  Vol. 70 (3)  September 2015 33 Gastrointestinal Equine Parasites in Israel
parasites. Te only survey that examined the distribution of
diferent gastro-intestinal helminth species in horses in Israel
was conducted three decades ago (3). Tat study revealed
that 48% of horses had positive egg fotations, and the most
prevalent species were small Strongyles (Trichonemma spp.,
in 78% of farms; Triodontophorus spp., in 22% of farms),
Parascaris equorum (in 44% of farms), Strongylus vulgaris and
Oxiuris equi (in 22% of farms respectively) (3). Since then,
most horse owners and veterinarians have been administering
periodic anthelminthic treatments. In recent years equine
practitioners in Israel have been under the impression that
they encounter more clinical cases of Parascaris infections
in foals that have been regularly dewormed which raised the
suspicion that resistance to treatment may have developed.
Tis study was designed to update the survey for the
prevalence and species distribution of equine intestinal
helminth parasites among adult horses in Israel, investigate
potential risk factors for infestation, and to draw conclusions
as to the probability of drug resistance.
MATERIAL AND METHODS
Sample collection
Between March 2012 and March 2013, 485 fresh fe-
cal samples were collected from 403 horses at 30 stables,
representing the distribution of farms across Israel. From
some horses, fecal samples were collected more than once, on
diferent collection dates. Fecal samples were collected from
the rectum or from freshly voided feces. Data was collected
regarding the management of the farm, the signalment of
each horse, the deworming regime used, and the details of
the last deworming treatment of each horse. After collection,
samples were kept refrigerated and were examined within
48 hours.
Fecal egg count
Egg counts were performed according to a Modifed
McMaster technique: Briefy, three grams of feces were sus-
pended in 42 ml water, fltered through a 100 mesh sieve, 15
ml were centrifuged at 1500 g for 5 minutes and the sediment
was resuspended in a saturated NaCl solution. Sampled were
examined microscopically, eggs were identifed morphologi-
cally and counted using the McMaster counting slide (3).
Infestation with specifc helminth species was defned as low
(<500 eggs per gram feces) or high (>500 eggs per gram
feces) based on its egg count.
Fecal cultures
Fecal cultures were performed by placing a moist sample in
an uncovered 35 mm diameter Petri dish which was placed
in a 90 mm diameter dish flled with water. After incubating
the sample at 27ºC for 7 days the fuid from the larger Petri
dish, which contained many of the larvae, was pipetted into a
conical centrifuge tube and centrifuged at 1500 g for 3 min.
Te supernatant was discarded and the larvae were examined
microscopically for identifcation (3).
Statistical analysis
Univariate and multivariate forward stepwise logistic re-
gressions were calculated using statistical software program
(SPSS® 19.0 for Windows®). Association between variables
was considered signifcant when p-values were less than 0.05.
All signifcant parameters in the univariate analysis were
included in the multivariate analysis.
RESULTS
Population
Geographic Distribution
Fecal samples were collected at 30 stables across Israel.
Between 1 and 47 samples were collected at each stable
(Figure 1). Two of the stables were located in the Golan
Heights (32 horses, 6.6%), 11 in the north (Galilee, Carmel,
Ramot Menashe, 223 horses, 46%), 9 in central Israel (111
horses, 22.9%), 4 around Jerusalem (63 horses, 13%), and 4 in
the Negev desert in the south (56 horses, 11.5%) (Figure 1).
Horse characteristics
A total of 485 fresh fecal samples were collected from
403 horses (some horses were sampled at more than one
occasion). About half of the horses were mares (192,
48.4%), and the rest were geldings (173, 43.6%) and
stallions (32, 8%). Most of the horses (158, 56.2%) were
local breed horses, and the rest were Quarter horses (71,
25.3%), Arabians (20, 7.2%), Appaloosas (14, 5%), Ponies
(11, 3.9%), Tennessee Walking horses (6, 2.1%) and one
Warmblood (0.3%). Most of the horses were adults, and
only 21 (4%) samples were collected from young horses
under three years of age.
Research Articles
Israel Journal of Veterinary Medicine  Vol. 70 (3)  September 2015 Tirosh Levy, S. 34
Stable interface
Approximately half of the samples (243, 50.1%) were collect-
ed from horses that were housed in stalls, and the remainder
from horses in either paddocks (86, 18%) or pastures (126,
26%). Information regarding the date of the last deworming
treatment was available for only 75% of the horses. Almost
half of the latter (174, 48%) were not treated against helmin-
thes over the previous 6 months. Drugs used for deworming
treatment were Ivermectin (208, 88.9%), Pyrantel (22, 9.4%)
or VermX (4, 1.7%).
Prevalence of diferent helminth species
Two major helminth families (Strongylidea and Ascaridea)
were detected by fecal fotation examination (Figure 2).
Strongyle eggs were found in 116/485 (24%) of the samples,
44 of which were highly infested with over 500 eggs/gr fe-
ces (38% of positive samples, 9% of the total population).
Parascaris equorum eggs were found in 26/485 (5%) samples,
7 of which were highly infested (27% of positive samples,
1.4% of the total population). In two samples a low number
of Anoplocephala eggs were detected.
Both Strongyle and Ascarid eggs were detected in 7/30
farms (23.3%). Eleven farms (36.6%) were infested only with
Strongyles, while 3 farms (10%) were infested only with
Ascarids. In 9 farms (30%), no parasites were detected.
A sample of 10 specimens positive for Strongyles were
cultured to identify their species, and were all classifed as
small Strongyles.
Risk factors associated with infestation with diferent
helminth species
Strongyles
Te data from all horses was analysed to detect potential
risk factors for Strongyle infestation. Univariate analysis
showed that the stable, geographical location, horse age and
breed and the time of last deworming treatment were sig-
nifcantly (p<0.005) associated with low or high infestation
with Strongyles (Table 1). Similar analysis were conducted
for Strongyle infestation as a binary parameter (i.e. whether
Figure 1: Geographic distribution of the farms sampled. Te number
of fecal samples collected in each ranch is represented by the size and
color of each mark.
Figure 2: Prevalence of the presence of helminth eggs in equine fecal
samples (n=486), from the families Strongylidae, Ascaridea or both.
Research Articles
Israel Journal of Veterinary Medicine  Vol. 70 (3)  September 2015 35 Gastrointestinal Equine Parasites in Israel
Table 1: Univariate analysis of risk factors considered to be associated with low (under 500 eggs/gr feces) or high (over 500 eggs/gr feces)
infestetion of Strongyles. P values under 0.05 were considered signifcant, and appears in bold
Variable Category (n)
Number of carriers/ n in category (%)
P-value (χ
2
)
0 <500 >500
Ranch Beer Sheva 15/29 (52%) 10/29 (34%) 4/29 (14%) <0.0001
Beit Dagan 3/3 (100%) 0 0
Beit Oren 21/39 (54%) 11/39 (28%) 7/39 (18%)
Beit Yehoshua 10/11 (91%) 1/11 (9%) 0
Binyamina 23/47 (49%) 8/47 (17%) 16/47 (34%)
Ein Dor 4/5 (80%) 1/5 (20%) 0
Ein Harod 10/10 (100%) 0 0
Ein Yahav 9/9 (100%) 0 0
Givaat Koah 12/12 (100%) 0 0
Harei Yehuda 8/8 (100%) 0 0
Hulda 3/6 (50%) 3/6 (50%) 0
Kanot 12/12 (100%) 0 0
Kefar Bialik 9/11 (82%) 2/11 (18%) 0
Kerem Maharal 16/22 (73%) 4/22 (18%) 2/22 (9%)
Mevo Hama 6/21 (29%) 6/21 (29%) 9/21 (43%)
Michmoret 25/32 (78%) 6/32 (19%) 1/32 (3%)
Motsa 8/8 (100%) 0 0
Nahal Alexander 7/8 (87%) 1/8 (12%) 0
Nov 2/11 (18%) 5/11 (45%) 4/11 (36%)
Ora 36/37 (97%) 1/37 (3%) 0
Pardes Hanna 30/34 (88%) 4/34 (12%) 0
Ramat Gan 11/11 (100%) 0 0
Ramat HaSharon 5/10 (50%) 4/10 (40%) 1/10 (10%)
Ramot Menashe 8/9 (89%) 1/9 (11%) 0
Rishpon 19/19 (100%) 0 0
Shavei Zion 1/1 (100%) 0 0
Urim 6/6 (100%) 0 0
Vered HaGalil 32/32 (100%) 0 0
Yassur 9/12 (75%) 3/12 (25%) 0
Zur Hadassa 9/10 (90%) 1/10 (10%) 0
Geographical area Golan Heights 8/32 (25%) 11/32 (34%) 13/32 (41%) <0.0001
North 164/223 (73%) 34/223 (15%) 25/223 (11%)
Center 94/111 (85%) 15/111 (13%) 2/111 (2%)
Jerusalem 61/63 (97%) 2/63 (3%) 0
South 42/56 (75%) 10/56 (18%) 4/56 (7%)
Season Spring (Apr-Jun) 26/39 (67%) 9/39 (23%) 4/39 (10%) 0.31
Summer ( Jul-Sep) 37/57 (65%) 11/57 (19%) 9/57 (16%)
Autumn (Oct-Dec) 103/138 (75%) 23/138 (17%) 12/138 (9%)
Winter ( Jan-Mar) 168/215 (78%) 28/215 (13%) 19/215 (9%)
Research Articles
Israel Journal of Veterinary Medicine  Vol. 70 (3)  September 2015 Tirosh Levy, S. 36
or not eggs were detected), and led to similar (slightly more
signifcant) results (data not shown).
Te prevalence of Strongyles in diferent stables ranged
from zero (in several stables) to 82% (in Nov), and when
grouped to geographic provinces it ranged from 15% around
Jerusalem to 75% in the Golan Heights. Both stable and
geographic location were found to be factors signifcantly
associated with infestation, with the stables in Nov and Mevo
Hama, both located in the Golan heights, with higher risk
of infestation. Horse breed was found to be signifcantly as-
sociated with infestation, with Tennessee Walking horses
more prone to infestation. Horses that did not receive an-
thelminthic treatment at least 6 month prior to sampling
were found to have a signifcantly higher risk for infestation
with Strongyles.
Te stable was the only factor found signifcant in mul-
tivariate statistical analysis, and the stables of Mevo Hama
(32°44’15.6”N 35°39’19.3”E, p=0.01) and Nov (32°49’56.3”N
35°47’01.3”E, p=0.037) had highest risk of infestation.
Te relative risk of infestation in Nov was 87 times higher
(p<0.001, 95% CI: 4.26-1793) than in Ramat Gan (a stable
located in central Israel, with similar number of horses).
Ascarids
Univariate statistical analysis was performed to detect risk
factors associated with low or high Ascarid egg counts.
Season (spring), horse gender (stallion), horse age and
farm interface (paddock) were signifcantly associated with
Ascarid infestation. When evaluating infestation as a binary
parameter farm geographical location and the drug used in
the last deworming were also found to be signifcant (Table
2). Multivariate analysis did not reveal any signifcant risk
factors.
Variable Category (n)
Number of carriers/ n in category (%)
P-value (χ
2
)
0 <500 >500
Horse gender Gelding 136/173 (79%) 25/173 (14%) 12/173 (7%) 0.063
Stallion 20/32 (62%) 5/32 (16%) 7/32 (22%)
Mare 133/192 (69%) 35/192 (18%) 24/192 (12%)
Horse age <3 years 12/21 (57%) 2/21 (9%) 7/21 (33%) 0.012
3-15 years 181/258 (70%) 50/258 (19%) 27/258 (10%)
>15 years 49/59 (83%) 6/59 (10%) 4/59 (7%)
Horse breed Appaloosa 8/14 (57%) 3/14 (21%) 3/14 (21%) 0.027
Arabian 13/20 (65%) 5/20 (25%) 2/20 (10%)
Grade 113/158 (71%) 29/158 (18%) 16/158 (10%)
Pony 7/11 (64%) 3/11 (27%) 1/11 (9%)
Quarter Horse 62/71 (87%) 7/71 (10%) 2/71 (3%)
Tennessee Walking
Horse 2/6 (33%) 2/6 (33%) 2/6 (33%)
Warmblood 1/1 (100%) 0 0
Farm interface Stall 193/243 (79%) 33/243 (14%) 17/234 (7%) 0.001
Paddock 69/86 (80%) 12/86 (14%) 5/86 (6%)
Pasture 78/126 (62%) 26/126 (21%) 22/126 (17%)
Last deworming under 2 months 46/54 (85%) 4/54 (7%) 4/54 (7%) <0.0001
2-4 months 52/61 (85%) 7/61 (11%) 2/61 (3%)
4-6 months 58/70 (83%) 11/70 (16%) 1/70 (1%)
over 6 months 105/174 (60%) 36/174 (21%) 33/174 (19%)
Drug used for last
deworming
Ivermectin 158/208 (76%) 32/208 (15%) 18/208 (9%) 0.347
Pyrantel 17/22 (77%) 2/22 (9%) 3/22 (14%)
VermX 2/4 (50%) 1/4 (25%) 1/4 (25%)
Research Articles
Israel Journal of Veterinary Medicine  Vol. 70 (3)  September 2015 37 Gastrointestinal Equine Parasites in Israel
Table 2: Univariate analysis of risk factors considered to be associated with low (under 500 eggs/gr feces) or high (over 500 eggs/gr feces)
infestetion of Ascarides. P values under 0.05 were considered signifcant, and appears in bold. Parameters that were signifcant when examined
as binary (ascarid eggs present or not) are starred
Variable Category (n)
Number of carriers/ n in category (%)
P-value (χ
2
)
0 <500 >500
Ranch Beer Sheva 22/29 (76%) 5/29 (17%) 2/29 (7%) -
Beit Dagan 3/3 (100%) 0 0
Beit Oren 37/39 (95%) 2/39 (5%) 0
Beit Yehoshua 10/11 (91%) 0 1/11 (9%)
Binyamina 38/47 (81%) 7/47 (15%) 2/47 (4%)
Ein Dor 5/5 (100%) 0 0
Ein Harod 9/10 (90%) 0 1/10 (10%)
Ein Yahav 9/9 (100%) 0 0
Givaat Koah 11/12 (92%) 1/12 (8%) 0
Harei Yehuda 8/8 (100%) 0 0
Hulda 6/6 (100%) 0 0
Kanot 12/12 (100%) 0 0
Kefar Bialik 10/11 (91%) 0 1/11 (9%)
Kerem Maharal 22/22 (100%) 0 0
Mevo Hama 21/21 (100%) 0 0
Michmoret 30/32 (94%) 2/32 (6%) 0
Motsa 8/8 (100%) 0 0
Nahal Alexander 8/8 (100%) 0 0
Nov 11/11 (100%) 0 0
Ora 37/37 (100%) 0 0
Pardes Hanna 34/34 (100%) 0 0
Ramat Gan 11/11 (100%) 0 0
Ramat HaSharon 10/10 (100%) 0 0
Ramot Menashe 9/9 (100%) 0 0
Rishpon 19/19 (100%) 0 0
Shavei Zion 1/1 (100%) 0 0
Urim 6/6 (100%) 0 0
Vered HaGalil 31/32 (97%) 1/32 (3%) 0
Yassur 11/12 (92%) 1/12 (8%) 0
Zur Hadassa 10/10 (100%) 0 0
Geographical area Golan Heights 32/32 (100%) 0 0 0.148
North 208/223 (93%) 11/223 (5%) 4/223 (2%) *0.013
Center 107/111 (96%) 3/111 (3%) 1/111 (1%)
Jerusalem 63/63 (100%) 0 0
South 49/56 (87%) 5/56 (9%) 2/56 (4%)
Season Spring (Apr-Jun) 32/39 (82%) 5/39 (13%) 2/39 (5%) 0.001
Summer ( Jul-Sep) 54/57 (95%) 2/57 (3%) 1/57 (2%)
Autumn (Oct-Dec) 127/138 (92%) 9/138 (6%) 2/138 (1%)
Winter ( Jan-Mar) 211/215 (98%) 2/215 (1%) 2/215 (1%)
Horse gender Gelding 170/173 (98%) 3/173 (2%) 0 0.002
Stallion 27/32 (84%) 2/32 (6%) 3/32 (9%)
Mare 177/192 (92%) 11/192 (6%) 4/192 (2%)
Research Articles
Israel Journal of Veterinary Medicine  Vol. 70 (3)  September 2015 Tirosh Levy, S. 38
Age was a signifcant risk factor for both helminth spe-
cies, with young horses more prone to infestation, and with
a higher chance of high infestation (over 500 eggs/gr feces).
Te distribution of the presence of both helminths in relation
to age is depicted in Figure 3.
DISCUSSION
Tis study was designed to re-investigate the prevalence and
species distribution of intestinal helminths in horses in Israel.
Te overall helminth prevalence appears to be low, with only
24% of horses positive for Strongyle eggs, 5% positive for
Ascarid eggs and less than 1% positive for Anoplocephala
eggs in their faeces.
At present, small Strongyles is the most common
helminth family known to infest horses worldwide, with
prevalence ranging from 61-100% of horses, and 98-100% of
stables in most European countries (1, 4, 5, 6, 7, 8, 9). Te low
prevalence we found (24% of horses) is similar to the fndings
of the 2009 survey from Greece, that found Strongyle eggs
in 25.6% of horses (8). Te last survey of the Israeli horse
population was conducted in 1986 (3). Here, small Strongyle
eggs were found in 60% (18/30) of the farms, which is less
than the 78% prevalence that was found in the 1986 survey
(3). In this time period, routine deworming programs were
introduced to most of the horse population. Although the
decline in prevalence was not statistically signifcant, it
may suggest a trend. Tis concurs with another study from
Louisiana conducted over similar time scale, which demon-
strated a decrease in the infestation of most helminth species,
and a shift in species distribution of small strongyles (10). In
the current survey, most of the horses sampled were adults
that had not received anthelminthic treatment for at least
two months prior to sampling.
Current recommendations for deworming strategies are
for targeted deworming, since most studies show that about
10% of horses are responsible for over 80% of helminth egg
contamination on a specifc farm (1, 11). However, our study
found that ten of eighteen farms infested with Strongyles had
only horses with low infestation (fewer than 500 eggs per
gram feces). In farms with higher infestation, the prevalence
of high shedding horses (over 500 eggs per gram feces) were
9-43% (9% of the study population) of the horses, and 14-
Variable Category (n)
Number of carriers/ n in category (%)
P-value (χ
2
)
0 <500 >500
Horse age <3 years 11/21 (52%) 5/21 (24%) 5/21 (24%) <0.0001
3-15 years 247/258 (96%) 10/258 (4%) 1/258 (0.5%)
>15 years 59/59 (100%) 0 0
Horse breed Appaloosa 14/14 (100%) 0 0 0.146
Arabian 19/20 (95%) 1/20 (5%) 0
Grade 151/158 (96%) 5/158 (3%) 2/158 (1%)
Pony 11/11 (100%) 0 0
Quarter Horse 69/71 (97%) 1/71 (1%) 1/71 (1%)
Tennessee Walking
Horse
4/6 (67%) 0 2/6 (33%)
Warmblood 1/1 (100%) 0 0
Farm interface Stall 232/243 (95%) 7/243 (3%) 4/243 (2%) 0.016
Paddock 75/86 (87%) 8/86 (9%) 3/86 (3%)
Pasture 123/126 (98%) 3/126 (2%) 0
Last deworming under 2 months 48/54 (89%) 5/54 (9%) 1/54 (2%) 0.2
2-4 months 60/61 (98%) 0 1/61 (2%)
4-6 months 67/70 (96%) 2/70 (3%) 1/70 (1%)
over 6 months 166/174 (95%) 6/174 (3%) 2/174 (1%)
Drug used for last
deworming
Ivermectin 200/208 (96%) 7/208 (3%) 1/208 (0.5%) 0.068
Pyrantel 18/22 (82%) 4/22 (18%) 0 *0.042
VermX 4/4 (100%) 0 0
Research Articles
Israel Journal of Veterinary Medicine  Vol. 70 (3)  September 2015 39 Gastrointestinal Equine Parasites in Israel
66% (38% of the study population) of shedding horses, much
higher than reported elsewhere.
Factors that were signifcantly associated with Strongyle
egg shedding in univariate analysis were the stable, geograph-
ical location, horse age and breed and the time of the last
deworming treatment. Te only factor that was signifcantly
associated with infestation with Strongyles in multivariate
analysis was the stable. Te two stables with signifcantly
higher infestation are located in the Golan Heights, where
the horses are turned out in pastures, and are not routinely
treated against helminthes. Te fact that young horses are
more susceptible to Strongyle infestation has been established
in many diferent surveys (1, 6, 7). In this study the popula-
tion consisted of mostly adult horses, which may partially
explain the low prevalence. Other risk factors that have been
previously demonstrated to infuence Strongyle infection
are breed, gender, farm interface, deworming regime, season
and precipitation. Of these factors only pasture (without
rotation) was consistent in most studies (1, 4, 6, 7, 9). Our
fndings concur with some of these risk factors, although it
is hard to rule out confounders, since many of the examined
factors were not distributed normally and might be linked
(for example, management, breed and geographical area, as
demonstrated before).
Te time of the last deworming was linked to Strongyle
egg shedding. Tis was not unexpected, although the only
group of horses with signifcantly higher shedding was the
group that had not been treated for at least 6 months. Te life
cycle of diferent Strongyle species varies from six to twelve
weeks. Tis fact led to regular and intensive anthelmintic
treatments (11). Our fndings suggest that owners that still
treat horses periodically should re-examine the necessary
time interval between treatments in adult horses. Te low
shedding rates in all treated horses may imply that anthel-
minthic resistance of Strongyle species in Israel is probably
low.
Parascaris equorum is a common parasite in young horses
worldwide, and its prevalence ranges between 0.4 and 76% of
horses in diferent surveys (1, 5, 6, 7, 8, 9, 12). In this study,
only one third of the farms had horses infested with Parascaris
equorum, which was even lower than the prevalence that was
found in the previous survey which was 44.4% (3), although
this diference was not statistically signifcant. Te low preva-
lence found in this study may refect the fact that our study
population consisted mostly of adult horses. Te signifcance of
risk factor analysis for Parascaris egg shedding was limited, due
to the low number of positive samples. Te only factor that was
consistently found to infuence infestation with Parascaris in
other surveys was young age (1, 7, 9). Many recent publications
indicate high levels of drug resistance in Parascaris equorum,
mostly to macrocyclic lactones (2). Many equine practitioners
in Israel suspect that they encounter an increasing number
of cases caused by Parascaris infestation in young horses that
have been regularly treated against helminths, and relate this
phenomenon to drug resistance. In this survey we did not fnd
an indication of such resistance, but in order to explore this
possibility a survey of younger horses is necessary.
Tapeworm eggs were only found in two cases. Tis may
suggest a low prevalence, but may be an underestimation,
since egg fotation is not the preferred detection method for
fatworms (13).
CONCLUSIONS
Tis work examined the prevalence and risk factors for infes-
tation with gastrointestinal helminths in Israel. Te overall
prevalence appeared to be low, and has declined over the last
20 years. Small Strongyles were the most common species
(24% of horses, 60% of farms) and Parascaris equorum was
found in small numbers (5% of horses, 33% of farms). Te
Figure 3: Age distribution of helminth carriage. Each mark represents
the number of Strongyle (circle) or Ascarid (rhombus) eggs per gram
feces of one horse of a certain age.
Research Articles
Israel Journal of Veterinary Medicine  Vol. 70 (3)  September 2015 Tirosh Levy, S. 40
distribution of egg shedding in infested farms appears to be
diferent than previously described. Anthelminthic resistance
was probably low. Tese fndings should lead to a further
investigation of infestation patterns in younger horses and
re-examination of parasite control strategies in adult horses.
REFERENCES
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Research Articles