# Intrinsic Factors Influencing the Infection by Helminth Parasites in Horses under an Oceanic Climate Area (NW Spain)

Authors: I. Francisco; M. Arias; F. J. Cortiñas; R. Francisco; E. Mochales; V. Dacal; J. L. Suárez; J. Uriarte; P. Morrondo; R. Sánchez-Andrade; P. Díez-Baños; A. Paz-Silva
Journal: Journal of Parasitology Research
 (2009)

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## Abstract

A coprological survey to determine the influence of some intrinsic factors (breed, age, and sex) on the infection by helminth parasites in equine livestock (n=418) under an oceanic climate area (NW Spain) was conducted. Faecal samples were individually collected and analyzed by the coprological techniques. The main strongylid genera identified were Trichonema and Cyalocephalus spp (small strongyles) and Strongylus and Triodontophorus (large strongyles). The prevalence of gastrointestinal nematode was 89% (95% CI 86, 92) and 1% cestoda (0, 2). The percentage of horses with strongyloid parasites was 89% (86, 92), 11% (8, 14) for Parascaris, and 3% (1, 5) for Oxyuris. The highest prevalence for ascariosis was observed in the youngest horses (<3 years), for oxyurosis in the >10 years animals, and for strongylosis in the 3–10 years ones. Females were significantly more parasitized than males. A negative correlation between the age and the egg-excretion of ascarids and strongyles was recorded. The autochthonous and the English Pure Blood horses were the most parasitized. We concluded that the infections by helminths, especially the strongyloids, are significantly common in the region, so that greater importance should be given to this situation.


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## Body

## 1. Introduction

The horse  industry  is increasing because of its diversity, and involves
business, sport, gaming, entertainment, or recreation. The raising of horses
plays a significant role, due to the high number of animals for leisure, which
has generated several direct jobs, such as those needed for handling and the
sanity of the animals.Nowadays, horses are being used in wild pastures and countries for the
forest management, utilizing unwanted vegetation for production. For this
reason, this industry deserves the attention of the general public and the
governments also. This new situation requires more information about the
sanitary status of these animals, and the appropriate measures for ensuring the
horses are in an adequate fitness condition. Among the diseases affecting
horses, helminth infections are much extended [1].An
oceanic climate (also called marine west coast climate and maritime climate) is
the climate typically found along the west coasts at the middle latitudes of
all the world's continents and in southeastern Australia. Oceanic climates are
characterized by a narrower annual range of temperatures than are encountered
in other places at a comparable latitude and do not have the extremely dry
summers of Mediterranean climates. Under those conditions, survival of
parasitology resistant forms is enhanced, enabling thus the possibility for
infection throughout the year.Several
investigations have shown the effect of some factors on the infection by
parasites in horses. Osterman Lind et al.
[2] and Larsen et al. [3] observed
the highest output of strongyle eggs in animals aged 2-3 years from Sweden.
Bucknell et al. [4] reported that
in Australia
cyathostomes were more prevalent in young horses, and P. equorum was found exclusively in horses less than 2 years of age,
and the highest mean intensity of infection for Anoplocephala perfoliata was in those horses. Lyons et al. [5] obtained similar results in
equids from Kentucky (USA). Nevertheless, there is a lack of knowledge about
the influence of breed or sex on the infection by helminth parasites in horses
from oceanic climate areas.This
study reports the effect of various intrinsic factors (breed,
age, sex) on the equine infection by helminth parasites. Fecal samples were
individually collected form 418 horses in an oceanic climate area (NW Spain) and
analyzed by the coprological flotation, sedimentation, and migration techniques.
Coprocultures were also done to identify the main strongylid genera affecting
the horses.


## 2. Material and Methods

### 2.1. Horses

Between April and September 2007,
fecal samples from the rectum of 418 horses from NW Spain were collected. According
to the breed, four groups were established (Table1): Spanish Sport Horse
(SSH), Spanish Pure Breed (SPB), English Pure Breed (EPB) and the autochthonous
Pura Raza Galega (PRG). By considering the age, horses were divided into three
groups: G-1 (<3 years old), G-2
(3–10), and G-3 (>10) (Table 1).Table 1
Distribution of the
fecal samples from horses under an oceanic climate area (NW Spain) according
to their breed, sex, and age.
FemaleMaleTotalBreedAge (years)<33–10>10Total<33–10>10TotalCDE48719342928PRE165123251022PSI15402075350883PRG40129552241637861285Total601838733025481588418


### 2.2. Study Design

Although some interesting information about
horses management as hygienic conditions, treatment history, and so forth would be
helpful to explain the results, it was not possible to achieve in many
cases, so we decided not to include it in the current paper. Many samples were
collected from horses under an extensive management, and ask those
questions to the owners was not possible.For
that reason, the impossibility for ensuring the collection of all data
belonging to the total population limited us to the analysis of the factors
possibly involved in the infection of equines by helminth parasites. The
factors we analyzed corresponded to parameters which can be observed and
measured for us in all cases.The influence of climatic conditions on the dynamics
of egg expulsion has been reported [6]. Nevertheless, by considering that the main goal in the current
work was to gain more information about the presence of helminth infection in
horses and the difficulty in taking more than one fecal sample from each
animal in several cases, the data presented here must be comprehended as a
coprological survey.


### 2.3. Coprological Analysis

The observation of parasitic forms in the feces of the horses was
evaluated by using the coprological flotation, sedimentation, and migration
techniques [7]. Five
grams of each fecal sample were processed (in duplicate) by the flotation,
sedimentation, and migratory techniques [8], with a sensitivity of 10
eggs per gram of feces (EPG).The laboratory technician conducting the
microscope analysis was also blinded to the study design of the selection of
the stool specimens.


### 2.4. Genera Identification

Since it is not possible to distinguish strongyle eggs of different
species morphologically, fecal samples are cultured for 10–14 days at 20–25°C to allow the development
of L3s, which may be collected by means of the Baermann procedure [6, 9]. Genera
were identified according to Lichtenfels [10].


### 2.5. Statistical Analysis

By taking account that the egg elimination is not normally distributed,
statistical analysis was done by means of the nonparametric Kruskal-Wallis and
Mann-WhitneyU two-sided tests (α = 0.05), and significant differences were considered when p<.05. The
descriptive parameters were the EPG quartiles 1, 2, and 3. All tests were done using SPSS for Windows (14.1).Prevalences were expressed as the percentage
and the 95% Confidence Interval (CI).The
existence of correlation among the different parameters was assessed by using
nonparametric Spearman’s rank correlation test.


## 2.1. Horses

Between April and September 2007,
fecal samples from the rectum of 418 horses from NW Spain were collected. According
to the breed, four groups were established (Table1): Spanish Sport Horse
(SSH), Spanish Pure Breed (SPB), English Pure Breed (EPB) and the autochthonous
Pura Raza Galega (PRG). By considering the age, horses were divided into three
groups: G-1 (<3 years old), G-2
(3–10), and G-3 (>10) (Table 1).Table 1
Distribution of the
fecal samples from horses under an oceanic climate area (NW Spain) according
to their breed, sex, and age.
FemaleMaleTotalBreedAge (years)<33–10>10Total<33–10>10TotalCDE48719342928PRE165123251022PSI15402075350883PRG40129552241637861285Total601838733025481588418


## 2.2. Study Design

Although some interesting information about
horses management as hygienic conditions, treatment history, and so forth would be
helpful to explain the results, it was not possible to achieve in many
cases, so we decided not to include it in the current paper. Many samples were
collected from horses under an extensive management, and ask those
questions to the owners was not possible.For
that reason, the impossibility for ensuring the collection of all data
belonging to the total population limited us to the analysis of the factors
possibly involved in the infection of equines by helminth parasites. The
factors we analyzed corresponded to parameters which can be observed and
measured for us in all cases.The influence of climatic conditions on the dynamics
of egg expulsion has been reported [6]. Nevertheless, by considering that the main goal in the current
work was to gain more information about the presence of helminth infection in
horses and the difficulty in taking more than one fecal sample from each
animal in several cases, the data presented here must be comprehended as a
coprological survey.


## 2.3. Coprological Analysis

The observation of parasitic forms in the feces of the horses was
evaluated by using the coprological flotation, sedimentation, and migration
techniques [7]. Five
grams of each fecal sample were processed (in duplicate) by the flotation,
sedimentation, and migratory techniques [8], with a sensitivity of 10
eggs per gram of feces (EPG).The laboratory technician conducting the
microscope analysis was also blinded to the study design of the selection of
the stool specimens.


## 2.4. Genera Identification

Since it is not possible to distinguish strongyle eggs of different
species morphologically, fecal samples are cultured for 10–14 days at 20–25°C to allow the development
of L3s, which may be collected by means of the Baermann procedure [6, 9]. Genera
were identified according to Lichtenfels [10].


## 2.5. Statistical Analysis

By taking account that the egg elimination is not normally distributed,
statistical analysis was done by means of the nonparametric Kruskal-Wallis and
Mann-WhitneyU two-sided tests (α = 0.05), and significant differences were considered when p<.05. The
descriptive parameters were the EPG quartiles 1, 2, and 3. All tests were done using SPSS for Windows (14.1).Prevalences were expressed as the percentage
and the 95% Confidence Interval (CI).The
existence of correlation among the different parameters was assessed by using
nonparametric Spearman’s rank correlation test.


## 3. Results

### 3.1. Identification of Helminth Parasites

Eggs from gastrointestinal nematoda and cestoda were observed in the
feces of the horses. No eggs from trematoda or lungworm larvae were obtained.The analysis of the gastrointestinal eggs showed that the horses were
parasitized byParascaris equorum,
Strongyles, and Oxyuris equi. By means
of the coprocultures, we identified Cyathostominea and Gyalocephalus spp (small
strongyles) and Strongylus and Triodontophorus (large strongyles).No differences in the genera of strongyles identified according to breed,
age, or sex were recorded.


### 3.2. Prevalence of Helminth Parasites

Eighty nine percent (95% CI 86, 92) of the samples had gastrointestinal
eggs and 1% (0, 2) cestoda. The prevalence of horses passingParascaris eggs by feces was 11% (8,
14), 88% (85, 91) strongyles, and 3% (1, 5) oxyurids.As drawn in Table2, the highest prevalence of parascariosis was
obtained in the youngest animals, English Pure Blood horses and females. No Parascaris eggs were observed in Sport
Spanish Horse animals. Significant differences were obtained by considering the
age, breed, and sex of the animals.Table 2
Prevalences of helminth
parasites in 418 horses from an oceanic climate area (NW Spain). Results are
expressed as the percentage and the 95% Confidence Interval (CI). Spanish Sport Horse (SSH), Spanish
Pure Breed (SPB), English Pure Breed (EPB), autochthonous Pura Raza Galega
(PRG).
AscaridsStrongylesOxyuridsCestodaAge<3229310(18, 26)(90, 96)(0, 2)3–1069122(4, 8)(88, 94)(1, 3)(1, 3)>10128161(9, 15)(77, 85)(4, 8)(0, 2)χ215.8428.7325.5842.228p0.0010.00130.0610.328BreedSSH0000SPB51900(3, 7)(15, 23)EPB349851(29, 39)(97, 99)(3, 7)(0, 2)PRG510022(3, 7)(1, 3)(1, 3)χ264.960366.9362.870.976p0.0010.0010.4120.807SexMale129032(9, 15)(87, 93)(1, 5)(1, 3)Female28400(1, 3)(80, 88)χ27.2443.3332.7991.508p0.0070.0680.0940.219The prevalence of strongyles was higher in G-1 and G-2, horses belonging
to the autochthonous PRG breed and females. No positive cases were recorded in
the Sport Spanish horses. Significant differences were observed by taking into
account the age and the breed of the animals.Table2 reflects that the greatest percentage of horses with oxyurids
corresponded to the oldest animals (G-3), English Pure Blood, and females. No
eggs were observed in males or in SSH animals.Finally, the highest prevalence of horses passing cestode eggs by feces
was obtained in the equids from the G-2 (3–10 years), autochthonous (PRG), and
females, although these differences were not significant.Spearman’s rank test  showed a statistical negative correlation
between the age of the horses and the prevalence of ascarids and strongyles (r=−0.141, p=0.005 and r=−0.143, p=0.004, resp.). Likewise, a
weak and positive correlation between age and prevalence of pinworms was matched
(r=0.113, 0.023).


### 3.3. Intensity of Infection

The results of the egg-excretion are summarized in Table3. The highest number
of Parascaris eggs was observed in
the foals, autochthonous horses (PRG), and males. The Kruskal-Wallis test showed
significant differences according to the age of the animals.Table 3
Helminth eggs per gram of feces (EPG) in 418 horses from
an oceanic climate area (NW Spain). Spanish Sport Horse (SSH), Spanish
Pure Breed (SPB), English Pure Breed (EPB); autochthonous Pura Raza Galega
(PRG). Results are expressed as EPG quartiles 1, 2, and 3 (Q1, Q2, and Q3,
resp.).
StatisticsAscaridsStrongylesOxyuridsCestodaAge<3Q10100350Q250400350Q31377753503–10Q1010011250Q2038015050Q3507503225150>10Q1010010050Q2020010050Q35050032550χ214.78110.5001.5600.2p0.0010.0050.4580.655BreedSSHQ1Q2Q3SPBQ125Q250Q3725EPBQ1041310050Q2065015050Q350127515050PRGQ1010010050Q2030022550Q31007001362150χ23.450148.8410.1650.2p0.3270.0010.6840.655SexMaleQ150Q2150Q3600MareQ1010010050Q2035115050Q350750375100χ20.3647.942p0.5460.005As drawing in Table3, there were reached differences in the
egg excretion of small strongyles regarding the breed and sex of the horses.
The greatest numbers were observed in the English Pure Blood animals and in females,
whereas no elimination was observed in Spanish Sport Horses.No differences were obtained in the egg elimination of oxyurids and
cestoda by considering the age, breed, or sex of the horses.By means of Spearman’s rank test, a statistical negative correlation
between the age of the horses and the elimination of ascarids and strongyles
eggs was proved (r=−0.445, p=0.001 and r=−0.167, p=0.001,
resp.).


## 3.1. Identification of Helminth Parasites

Eggs from gastrointestinal nematoda and cestoda were observed in the
feces of the horses. No eggs from trematoda or lungworm larvae were obtained.The analysis of the gastrointestinal eggs showed that the horses were
parasitized byParascaris equorum,
Strongyles, and Oxyuris equi. By means
of the coprocultures, we identified Cyathostominea and Gyalocephalus spp (small
strongyles) and Strongylus and Triodontophorus (large strongyles).No differences in the genera of strongyles identified according to breed,
age, or sex were recorded.


## 3.2. Prevalence of Helminth Parasites

Eighty nine percent (95% CI 86, 92) of the samples had gastrointestinal
eggs and 1% (0, 2) cestoda. The prevalence of horses passingParascaris eggs by feces was 11% (8,
14), 88% (85, 91) strongyles, and 3% (1, 5) oxyurids.As drawn in Table2, the highest prevalence of parascariosis was
obtained in the youngest animals, English Pure Blood horses and females. No Parascaris eggs were observed in Sport
Spanish Horse animals. Significant differences were obtained by considering the
age, breed, and sex of the animals.Table 2
Prevalences of helminth
parasites in 418 horses from an oceanic climate area (NW Spain). Results are
expressed as the percentage and the 95% Confidence Interval (CI). Spanish Sport Horse (SSH), Spanish
Pure Breed (SPB), English Pure Breed (EPB), autochthonous Pura Raza Galega
(PRG).
AscaridsStrongylesOxyuridsCestodaAge<3229310(18, 26)(90, 96)(0, 2)3–1069122(4, 8)(88, 94)(1, 3)(1, 3)>10128161(9, 15)(77, 85)(4, 8)(0, 2)χ215.8428.7325.5842.228p0.0010.00130.0610.328BreedSSH0000SPB51900(3, 7)(15, 23)EPB349851(29, 39)(97, 99)(3, 7)(0, 2)PRG510022(3, 7)(1, 3)(1, 3)χ264.960366.9362.870.976p0.0010.0010.4120.807SexMale129032(9, 15)(87, 93)(1, 5)(1, 3)Female28400(1, 3)(80, 88)χ27.2443.3332.7991.508p0.0070.0680.0940.219The prevalence of strongyles was higher in G-1 and G-2, horses belonging
to the autochthonous PRG breed and females. No positive cases were recorded in
the Sport Spanish horses. Significant differences were observed by taking into
account the age and the breed of the animals.Table2 reflects that the greatest percentage of horses with oxyurids
corresponded to the oldest animals (G-3), English Pure Blood, and females. No
eggs were observed in males or in SSH animals.Finally, the highest prevalence of horses passing cestode eggs by feces
was obtained in the equids from the G-2 (3–10 years), autochthonous (PRG), and
females, although these differences were not significant.Spearman’s rank test  showed a statistical negative correlation
between the age of the horses and the prevalence of ascarids and strongyles (r=−0.141, p=0.005 and r=−0.143, p=0.004, resp.). Likewise, a
weak and positive correlation between age and prevalence of pinworms was matched
(r=0.113, 0.023).


## 3.3. Intensity of Infection

The results of the egg-excretion are summarized in Table3. The highest number
of Parascaris eggs was observed in
the foals, autochthonous horses (PRG), and males. The Kruskal-Wallis test showed
significant differences according to the age of the animals.Table 3
Helminth eggs per gram of feces (EPG) in 418 horses from
an oceanic climate area (NW Spain). Spanish Sport Horse (SSH), Spanish
Pure Breed (SPB), English Pure Breed (EPB); autochthonous Pura Raza Galega
(PRG). Results are expressed as EPG quartiles 1, 2, and 3 (Q1, Q2, and Q3,
resp.).
StatisticsAscaridsStrongylesOxyuridsCestodaAge<3Q10100350Q250400350Q31377753503–10Q1010011250Q2038015050Q3507503225150>10Q1010010050Q2020010050Q35050032550χ214.78110.5001.5600.2p0.0010.0050.4580.655BreedSSHQ1Q2Q3SPBQ125Q250Q3725EPBQ1041310050Q2065015050Q350127515050PRGQ1010010050Q2030022550Q31007001362150χ23.450148.8410.1650.2p0.3270.0010.6840.655SexMaleQ150Q2150Q3600MareQ1010010050Q2035115050Q350750375100χ20.3647.942p0.5460.005As drawing in Table3, there were reached differences in the
egg excretion of small strongyles regarding the breed and sex of the horses.
The greatest numbers were observed in the English Pure Blood animals and in females,
whereas no elimination was observed in Spanish Sport Horses.No differences were obtained in the egg elimination of oxyurids and
cestoda by considering the age, breed, or sex of the horses.By means of Spearman’s rank test, a statistical negative correlation
between the age of the horses and the elimination of ascarids and strongyles
eggs was proved (r=−0.445, p=0.001 and r=−0.167, p=0.001,
resp.).


## 4. Discussion

Worldwide, horses are exposed to helminth parasites from different
groups resulting in significant morbidity and mortality [11]. The
most common helminths of horses include the small and large strongyles, along
with tapeworms, ascarids, pinworms, and the lungworms [12]. In the current study, we proved the existence of infection by ascarids,
strongyles (small and large) and pinworms in horses from NW Spain, which agrees
with data reported by Bucknell et al.
[4] in Australia, Romaniuk et al. [13] in Polonia, and Pereira and Vianna [1]
in Brazil, in horses housed under differing management schemes.The main helminth parasites observed were strongyles, in agreement with previous
investigations in areas with a similar weather [1, 14, 15]. Likewise, a low prevalence was obtained for
tapeworms, although the low sensitivity of the fecal examination techniques in
detecting cestode eggs could be the explanation to our results [16]. Meana et al. [17]
pointed that the coprological methods have a lower likelihood of diagnosing
cestode infection when horses have less than 100 tapeworms.The lack of flukes and coccidia in the current study provides evidence
to back up the rarity of infection by this class of parasite [1, 13].To get more knowledge about the factors influencing infections by helminths
in horses, the coprological data were examined by considering the age, breed,
and sex of the animals. OnlyP. equorum and strongyles showed any age effect. The values of prevalence and elimination of P. equi-eggs were significantly
the highest in horses less than 3 years old, which agrees with Mfitilodze and
Hutchinson [18] and Bucknell et al.
[4].The percentage of infection by strongyles was significantly greater in
the horses less than 10 years old. It has been proved that age does not
influence the cyathostome burdens [19], and Klei and Chapman [20] reported that the
naturally acquired immunity against small strongyles slowly develops with age,
but remains incomplete. This could be the explanation to the finding of a
negative correlation between the age and the infection by ascarids and
strongyles.The conditions of housing and management are usually related to the
horse breed. This explains why the autochthonous Pura Raza Galega horses, maintained
under extensive forest conditions and receiving an inadequate keeping, attained
the highest prevalence of infection by ascarids and strongyles. In addition, no
helminth parasites were observed in the fecal samples from Spanish Sport
horses, and the Spanish Pure Blood ones were few parasitized. Several studies
did not match the influence of the horse breed on the helminthosis [18, 21].It has been shown that helminth infection is ubiquitous in horses with
access to pasture. The absence of positive results in the Sport Spanish horses
seems to be attributable to a reduced possibility for pasturing and thus to
contact to the infective phases (larval 3rd stages for the
gastrointestinal nematoda) or to intermediate hosts (oribatids in the case of
tapeworms). Another possible explanation could be that these are economically
valuable horses, maintained under appropriate hygienic conditions, and
receiving periodical veterinary attention. Moreover, the observation of
elevated prevalences for gastrointestinal worms in the English Pure Blood and
in the Spanish Pure Blood equids was an unexpected result, because of their
economic value and the conditions of housing and keeping, similar to the
Sport Spanish horses.Our results showed that sex had influence on the prevalence of ascarids
and strongyles, being the females more infected than the males, in agreement
with Fikru et al. [21].This is the first study about the effect of several intrinsic factors on
the helminth parasites affecting horses from NW Spain, so the lack of
coprological surveys makes more difficult the discussion of the results
obtained in the current investigation. It must be taken into account that the presence
of seasonal dynamics of egg
expulsion influences the results for the intensity of parasitization [6].The development of coprological surveys provides a very interesting and indispensable
tool for knowing the main helminth parasites infecting the horses. In the light
of our results we consider that the infections caused by helminths, especially
the strongyles, are significantly common in the region of study, so that
greater importance should be given to this situation. The elevated prevalence
in the English Pure Blood and autochthonous horses underlines the need for the
application of appropriate measure to the control of helminth parasites. More
information is needed to know the applied ways for the control of parasites in
equids, in particular that related to chemoprophylaxis.



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*Source: 616173-2009-04-08.xml*