ISRAEL JOURNAL OF
VETERINARY MEDICINE
VOLUME 54 (1), 1999
TITLE: EFFICACY OF GARLIC AS AN ANTHELMINTIC IN DONKEYS
AUTHOR: G. Abells Sutton and R. Haik
Koret School of Veterinary Medicine
Hebrew University of Jerusalem, P.O.B. 12, 76100 Rehovot
Summary
Garlic was ineffective in decreasing fecal Strongyl ova counts in donkeys two
weeks after treatment. Either was garlic simply not effective or was the
extraction method or the dose inappropriate. Alternatively, garlic may function
by stimulaing the immune system. This aspect was not evaluated in this
study.
Introduction
Garlic (Allium sativum) has been used medicinally worldwide for many
centuries (1,2,3). In Chinese herbal medicine, it is used to prevent influenza,
relieve toxicities and kill parasites such as roundworms and tapeworms (4).
Today, garlic is used as a home remedy for diverse health problems such as
head cold, toothache, earache, nausea, high blood pressure and for treatment
of cancer and other chronic diseases (5). Recent evidence of its current use
by lay persons in Israel is available through reports recently published on
treatment of burns caused by the use of garlic compresses (6).
Empirical evidence in favor of the use of garlic has been accumulating since
the 1970s. Garlic and garlic extracts have been under investigation for
specific roles such as antibacterial activity (2), lipid-lowering effects (1,2,7),
anti-platelet activity (2,3) and anti-carcinogenic effects (2,8,9,10). Some of
the results have been encouraging.
Strongylidae are intestinal nematodes of horses and donkeys (11,13) which
can be extremely pathogenic. In horses, they commonly cause anemia but
occasionally cause diarrhea, severe emaciation and even fatal colic.
Parasitism in the equine is universally controlled by the use of commercially
available anthelmintics with proven efficacy administered at regular intervals
(13,14).
In Israel, many horse and donkey owners consider garlic as a viable
alternative to commercial anthelmintics. It is readily available, appears to
improve the health of the animals and is perceived to cost less than
commercial preparations. There is some evidence to support this practice.
Garlic has been reportedly successful in reducing parasitism by Capillaria
spp. in carp (15) and as a mosquito larvacide (16).
Efficacy of a parasite control program can be evaluated by documenting
reduction in the herd average fecal egg counts one to two weeks after
treatment. This is carried out on populations of individuals since the variation
in fecal egg counts in an individual can vary greatly (13,17,23,24).
The main objective of this study was to determine whether a garlic treatment
method commonly used in Israel to treat horses and donkeys is efficacious as
an anthelmintic against Stongylidae in donkeys.
Materials and Methods
Thirty six donkeys from one farm were included in the study. The donkeys
were not on a commercial anthelmintic program. Their ages were estimated
by descriptions of dental wear and growth (11). Their weights were estimated
by the use of a formula which incorporates the height and chest
circumference of each individual (12). The donkeys were randomly divided
into three groups of twelve. Most of the donkeys were females. Seven
donkeys were under 2 years of age. These were randomized separately as a
block to ensure equal distribution among the groups. One group was left
untreated as a negative control. A second group was treated with a standard
anthelmintic as a positive control. The third group was treated with garlic.
Fecal ova counts
The Cornell-McMaster dilution egg count technique was used (13). Fecal
samples were taken directly from the rectum of each animal. The fecal
counting was carried out in a blind fashion; the group of origin was unknown
at the time of the counting. Ten grams of feces was suspended in 150 ml of
water. All fecal counts were carried out twice and then compared for
repeatability (precision) by plotting them on a graph which tests how well the
replicate egg counts fit the Poisson distribution. If the technique is carried out
correctly, the repeated counts should follow a Poisson distribution (13).
Square roots of egg counts were then used in all subsequent calculations
since square root transformation of a Poisson variable converts the variance
to a near constant for all but very low values of the variable, and since root
egg counts are symmetrically distributed about a mean for all but very low
values while egg counts per gram is skewed (13). Also, use of square roots
converts integer results into continuous data allowing for a normal distribution
and parametric analysis.
Anthelmintics
Fenbendazole (Panacur®) suspension was used as the well established
anthelmintic in the positive control group. The dosage was 7.5 mg/kg and it
was administered orally.
Garlic was prepared by boiling 300 ml. of water for every head of garlic until
soft . The product was then mashed and administered orally with a syringe at
the dosage of one head of garlic per donkey.
Experimental design
Samples were taken one week prior to treatment, on the day of treatment
and two weeks thereafter.
Statistical analysis
The average of the square roots of the two pretreatment fecal counts (T -1
and T0) were tested for normality by the Wilk-Shapiro/rankit plot. The groups
were then tested for similar means in age, weight and initial fecal ova counts
by one-way ANOVA.
The average of the square roots of the pretreatment fecal counts were then
compared with the post-treatment sample by using a two-tailed paired
Students t-test to determine whether the post-treatment samples were
significantly different from the pre-treatment sample within each group.
The two factor ANOVA was used to determine whether there was a
difference in the fecal egg counts between the groups due to the treatment or
due to age (adult vs. juvenile). The Tukey (HSD) test was then applied to
determine which of the groups had a mean that was different from the other
groups.
All statistical calculations were performed by Statistix® software.
Results
Table 1 shows the age and weight of each donkey in each of the three
treatment groups.
The pretreatment fecal egg counts were > 300 eggs per gram indicating that
the minimal parasite load required for anthelmintic evaluation was present
(17). All the fecal egg counts had reasonable repeatability showing that the
technical performance of the fecal egg count calculation was reliable (data not
provided). The average number of the two counts is recorded in Table 2.
Table 1: The estimated age (years) and weight (wt) (kg) of each indivual donkey
in each treatment groups. weight estimates are +/- 20 kg if > 2 years of age and +/10 kg if < 2 years of age.
Control Group
ID No.
Age
Fenbendazole Group
Wt
ID No.
Age
Wt
Garlic Group
ID No.
Age
Wt
6
6.5
142
4
4.5
165
1
7
165
7
5
160
5
3.5
110
2
5
187
8
7
127
9
2
131
3
3
165
13
7
142
10
3.5
130
11
7
120
17
7
117
14
7
185
12
25
135
22
7
136
15
4
152
16
4.5
132
24
3.5
148
19
12
120
18
5
122
25
4
140
20
7
154
21
7.5
150
27
5
146
26
7
117
23
3.5
160
29
7/12
59
28
7
195
32
1
134
33
1.5
119.5
30
1
94
34
8/12
59
36
1.5
47.5
31
1.5
120
35
4
157
mean
4.5
124
mean
5
139
mean
6
140.5
Table 2: Number of eggs per gram of feces for each individual donkey (ID#) in
each treatment group, one week prior to treatment (T1), On the day of
treatment (T0), and two weeks post treatment (T2).
Control Group
Fenbendazole Group
Garlic Group
ID No.
T1
T0
T2
ID No.
T1
T0
T2
ID No. T1 T0 T2
6
100
125
150
4
75
350
0
1
100
7
175
200
325
5
25
75
0
2
1025 275 225
8
225
325
100
9
125
225
0
3
350 350 500
13
125
175
75
10
200
675
0
11
50
17
500
325
600
14
575
0
0
12
425 1050
22
225
600
900
15
350
250
0
16
600 625 1750
24
325
750
325
19
1125
150
0
18
75
25
125
800
850
20
600
875
25
21
150 550 625
27
75
150
475
26
0
0
0
23
475 400 1300
29
800
100
50
28
75
175
0
32
700 375 125
33
75
175
950
30
425
275
0
34
50
75
0
36
NA
150
50
31
75
250
0
35
100 100
75
25
0
100
150
0
0
75
Statistical Analysis
The Wilk-Shapiro/rankit plot supported the assumption of normality of the
pretreatment pooled data by a p value of 0.9808. The one way ANOVA
showed that there was no statistically significant difference in the means of
any of the treatment groups for the factors of age, weight and initial fecal ova
counts. The p value for age was 0.6692, for weights was 0.3848, and for
initial fecal ova counts was 0.8486.
The mean fecal counts of both the control group and the garlic group two
weeks after treatment were 404. The mean fecal count of the fenbendazole
group two weeks after treatment was 2. The mean fecal counts of the control
group and the garlic group increased two weeks after treatment compared to
the average of the pretreatment counts by 116 and 69 respectively. The
mean fecal count for the fenbendazole group dropped by 289 two weeks after
treatment.
A two-tailed paired Students t-test demonstrated that only in the
fenbendazole group were the post-treatment fecal ova counts significantly
different from the pre-treatment counts. The p value was p=0.3207 for the
control group, p=0.0000 for the fenbendazole group and p=0.8577 for the
garlic group.
The two factor ANOVA showed a difference in the means of the groups (at
p=0.0000) for treatment, but not for age (p=0.0815).
The Tukey (HSD) test showed that only the fenbendazole group was
significantly different from the other two groups at a rejection level of 0.001.
Discussion
In Israel, garlic is considered by some horse and donkey owners to be an
efficacious method to control internal parasites. Owners report that the
treated individuals appear to improve in weight, coat quality and general wellbeing. The main purpose of this study was to investigate a commonly used
method which was found to be totally ineffective in reducing the herd egg
count of strongyle spp. This is a significant finding because the use of garlic
as an anthelmintic, by this method, could endanger the health of the animals
in two ways; by replacing an effective means of controlling parasitism with an
ineffective method, thereby exposing the individuals to a potentially fatal
disease, and by administration of a potentially toxic substance (8). Garlic is a
member of the onion family (Allium) and as such can cause
methemoglobinemia, although this has not been reported in horses (18).
Another possible toxic effect is the theoretical contribution of garlic
compounds containing active thiol groups in the development of pemphigus
(19).
The failure of garlic as an anthelmintic (13,17) may have been due to the
method used to prepare the garlic, the dose administered, the method of
evaluating the outcome, or that garlic has no anthelmintic effect at all.
Many reports describe ways of preparing garlic extract, and many studies
have attempted to find the major extract which produces the desired effect
(1,8,15,20). Recently, the consensus is that organosulfur compounds are
responsible for the medicinal effects of garlic (1,8,10). The most significant of
these compounds is allicin (2), which is not actually found in the garlic until it
is crushed. Upon crushing, the precursor of allicin, known as alliin, is
enzymatically converted by alliinase to allicin (2,21,22).
Allicin is extracted in the organic layer of raw garlic homogenate. It can be
found in dry garlic powder (20) and can also be synthesized in the laboratory
(22). Allicin was found to be the
active compound in many of the cases where a medicinal effect was
recorded. The molluscicidal (20), antiplatelet (3), lipid-lowering agent (1), and
the antibacterial effects (2) have been attributed to allicin. Allicin can disable
two groups of enzymes (dehydrogenases and cysteine proteinases) which
provide infectious agents with the means to damage and invade tissues. The
more significant reported mechanism is due to the chemical modification of
the free SH group of L-cysteine in an S-thiolation reaction which inhibits the
cysteine proteinase enzyme activity in a reversible reaction (22).
Allicin is also responsible for the characteristic odor of garlic (8). It is,
however, unstable (8), and is destroyed by boiling (2). In this study the garlic
was boiled, so as to follow the method used by horse owners, despite the fact
that the allicin was likely destroyed in the process. Therefore, the ability of
crushed garlic containing allicin to have anthelmintic properties cannot be
ruled out by this study. minced garlic, which contains large amounts of allicin,
was reportedly effective in reducing parasite egg counts in carp infected with
Capillaria spp (15).
An additional explanation for the lack of demonstrable effect by the garlic in
this study, may be because the method used to evaluate the outcome may
not have been appropriate. Despite its many limitations, the method used in
this study is the classical method for the evaluation of the efficacy of new
anthelmintics in eliminating ova-laying parasites (13,17,23,24). However, if
the mode of action of garlic is not by pharmacological elimination of adult
parasites, but rather by enhancing the immunological reaction of the host to
the parasites, then the method used in this study would not have been
appropriate to demonstrate success.
Recent research on the anticarcinogenic effect suggests that garlic enhances natural immunity (25). If
there were an immunologically based anthelmintic action of garlic, further
studies including a series of treatments would be required. Also, more post
treatment measurements may need to be taken over a longer period of time
than carried out in this study.
Additional research would be desirable since there remains the possibility
that allicin may be a successful anthelmintic. Since there is increasing
resistance by both large and small strongyles to modern control methods
(14,26), new control methods are being sought. The potential toxicity of
garlic, however, must not be ignored.
In summary, horse and donkey owners should be warned regarding the
results of this study in order to prevent the use of an ineffective anthelmintic
program which could lead to unnecessary pain and suffering of animals.
Further studies, however, may reveal a method of garlic use which would be
an effective herd anthelmintic.
Acknowledgments:
Dr. Hilliary Voet for statistical advice. Avner Maduel and Shemi Bar-Natan
of the Shefa Bateva Donkey Farm - The Farm for Donkey Rides, for providing
the experimental animals.
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