Host responses during experimental infection with
Fasciola gigantica or Fasciola hepatica in Merino sheep
I. Comparative immunological and plasma biochemical
changes during early infection
H.W. Raadsmaa,*, N.M. Kingsforda, Suharyantad, T.W. Spithillb, D. Piedrafitac
aReprogen, Centre for Advanced Technologies in Animal Genetics and Reproduction, Faculty of Veterinary Science,
University of Sydney, Camden, NSW 2570, Australia
bInstitute of Parasitology, Centre for Host–Parasite Interactions, McGill University, Ste-Anne-de-Bellevue, Quebec, Canada H9X 3V9
cPhysiology Department, School of Biomedical Sciences, Monash University, Wellington Road Clayton, Vic. 3800, Australia
dResearch Institute for Veterinary Science, Bogor, West Java, Indonesia
Received 13 June 2006; received in revised form 29 August 2006; accepted 5 September 2006
This study reports the early biochemical changes in plasma, comparative host-immune responses and parasite recovery data in
four groups of sheep received incremental challenge doses of F. gigantica metacercariae (50, 125, 225 and 400, respectively) and the
sixth group was challenged with 250 F. hepatica metacercariae. At 10 weeks post infection (wpi), sheep challenged with F. hepatica
showed the greatest fluke recovery (mean 119, range 84–166); a significantly higher biomass of parasites recovered (2.5-fold greater
gigantica. WithinthegroupsdosedwithF. giganticaa strong dose-dependentresponsewas observedinbothflukerecovery andfluke
25%,respectively, suggesting a uniformviability ofparasiteestablishmentindependentofinfection dose.At 6 wpi, elevatedlevelsof
plasmaGLDHwereobservedintheF.giganticainfectedgroupscomparedtotheuninfectedsheep(p < 0.005)whereastheF.hepatica
challenged group had four-fold higher levels of GLDH compared to the F. gigantica infected group (p < 0.001). Elevated levels of
frombelow100 IU/ltoapproximately250 IU/l(p < 0.0001)whereasnodetectableincreaseinGGTwasobservedinanyofthegroups
challenged with F. gigantica. The white blood cell response to F. hepatica infection was biphasic with the initial peak at 4 wpi and a
F. gigantica or F. hepatica burdens suppress IgG2responses. The findings of this study suggest that, in early infection in a permissive
host, F. hepatica appears to be more pathogenic than F. gigantica because ofits rapid increase in size and the speed ofits progression
through the migratory phases of its life cycle.
# 2006 Published by Elsevier B.V.
Keywords: Fasciola gigantica; Fasciola hepatica; Liver fluke; Sheep; Helminth; Eosinophil; Lymphocyte; Antibody level; GLDH
Veterinary Parasitology 143 (2007) 275–286
* Corresponding author. Tel.: +61 2 93511603; fax: +61 2 93511618.
E-mail address: firstname.lastname@example.org (H.W. Raadsma).
0304-4017/$ – see front matter # 2006 Published by Elsevier B.V.
Fasciolosis (infection with Fasciola gigantica or
Fasciola hepatica) is a major parasitic disease of
livestock with over 700 million production animals at
risk of infection and worldwide economic losses
estimated at >US$3.2 billion pa (Spithill et al.,
1999). In temperate regions F. hepatica commonly
infects sheep and cattle while, in tropical regions, F.
gigantica infects sheep, cattle and buffalo.
Many sheep breeds are susceptible to Fasciola
infection including most sheep selected for enhanced
production traits such as wool production in Merino
sheep. However, in contrast to F. hepatica, it has been
demonstrated that some sheep breeds are resistant to
infection by F. gigantica (A’Gadir etal., 1987; reviewed
in Spithill et al., 1999). High resistance to F. gigantica
infection has been observed in Indonesian Thin Tail
(ITT) sheep (Wiedosari and Copeman, 1990; Roberts
et al., 1997a,b,c). ITT sheep express resistance to
F. gigantica within the prepatent period of a primary
infection and acquire a higher level of resistance
after exposure (Roberts et al., 1997a,c). In addition,
numerous studies have shown that sheep do not acquire
resistance to a secondary F. hepatica infection (Boyce
et al., 1987; Chauvin et al., 1995; Roberts et al., 1997a;
Piedrafita et al., 2004).
These findings suggest that F. hepatica and F.
gigantica differ in some fundamental biological trait(s)
which renders F. gigantica more susceptible to immune
effector mechanisms (Spithill et al., 1997; Piedrafita
et al., 2004). However, the relative rates of development
of the F. gigantica and F. hepatica parasites, when
compared to the development of host response factors,
is poorly understood. A comparison of the humoral
response during infection of Belle Islois sheep to F.
hepatica and F. gigantica (Zhang et al., 2004) as well as
the modulation of lymphocyte and eosinophil responses
(Zhang et al., 2005a,b) suggested that sheep are less
susceptibile to F. gigantica compared with F. hepatica.
Although studies have suggested that the host immune
response to the parasite plays an important role in the
susceptibility of sheep to Fasciola spp. (Wiedosari and
Copeman, 1990; Roberts et al., 1997a,b,c; Piedrafita
et al., 2004) it has been shown that parasite modulation
of the immune response may also play a role in immune
et al., 1983; Chauvin et al., 1995; Prowse et al., 2002;
Zhang et al., 2005a,b).
There are numerous studies of sheep breeds infected
with F. hepatica, but few on the biological and
immunological responses of sheep to F. gigantica
infection. In addition, there are almost no comparative
studies on the immuno-biology of host responses to
infection with a concurrently performed challenge with
F. gigantica or F. hepatica in sheep of a similar genetic
background and identical rearing practices (Zhang
et al., 2004, 2005a,b). Here, we report physiological
changes and comparative host immune responses in
Merinosheep during early infection with F.gigantica or
F. hepatica. This is the first direct comparative report of
the early biochemical and immunological changes in
sheep challenged with these parasites. A better under-
standing of the immune response to both F. gigantica
and F. hepatica would be helpful in the development of
rational control strategies of these parasites.
2. Materials and methods
2.1. Experimental animals
Fifty-nine young (6 months old) Merino wethers
were purchased from areas in NSW classified as low
risk for F. hepatica and located on site (University of
Sydney, Camden campus) 3–4 weeks before com-
mencement of the experiment. The Merino is a highly
valued commercial sheep breed and was chosen for the
comparative infections since this breed is susceptible to
infection by both F. hepatica and F. gigantica. The
naivety of the animals was confirmed by a negative
reaction in an ELISA and a Western blot using Fasciola
whole worm extract as antigen (Estuningsih et al.,
1997). The sheep were treated for nematode parasites
by drenching with Ivomec at the recommended dose
rate. Sheep were introduced to a commercial pelleted
sheep ration consisting of 13% protein, 11.5 MJ ME/kg
energy. Following stabilisation of feed intake, sheep
were given ad libitum access to feed and water. Sheep
were weighed weekly, 2 weeks prior to and during the
experimental period. All sheep were allocated to 1 of 6
experimental treatment groups based on stratified
sampling following ranking on body weight at time
of challenge, and held in group pens of 10 sheep/group
in groups 1–5 and 9 sheep/group in group 6 for the
duration of the experiment (Table 1). Animal ethics
guidelines were strictly adhered to in the care of the
2.2. Parasites, parasite extracts and reagents
Metacercariae for infections were obtained from
infected Lymnaea rubiginosa snails collected at Surade,
tomentosa snails collected from laboratory snail
H.W. Raadsma et al./Veterinary Parasitology 143 (2007) 275–286 276
cultures at Elizabeth Macarthur Agricultural Institute,
Menangle, NSWAustralia (for F. hepatica). Sheep were
NJ, USA) and delivered orally using a dosing gun.
Adult F. gigantica and F. hepatica parasites were
obtained from the livers of infected cattle collected from
local abbatoirs in Jakarta, Indonesia; and Tongala,
Australia, respectively and used to obtain whole worm
extracts. Briefly, adult flukes were removed from bile
put into 100 ml PBS at 37 8C for 15 min. Initial
regurgitant, containing blood, bile and debris, was
removed by washing parasites in PBS containing an
antibiotic and then live flukes were removed and
homogenised in 0.1% Triton X in 90 mM HEPES,
5 mM EDTA (0.05 g parasite/500 ml of buffer) using an
4 8Cfor1 handthenthewholewormextractsupernatant
was collectedafter centrifugingat13,000 rpm(355 ? g)
for 20 s. The antigen supernatant was stored in small
aliquots at ?80 8C until required.
The protein concentration of worm homogenates
was estimated using a standard assay and reagents from
Biorad according to the manufacturer’s specification,
using Bovine Serum Albumin as standard. All ELISA
plates and 24-well tissue culture plates were purchased
from Flow Laboratories Inc., USA and Greiner
Labortechnik, Austria, respectively.
2.3. Experimental treatments
A summary of the design of the experiment is shown
in Table 1. Group 1 acted as a control uninfected group,
and groups 2–5 received incremental challenge doses of
F. gigantica metacercariae (50, 125, 225 and 400
metacercariae, respectively). The doses were chosen to
represent a linear incremental F. gigantica challenge
of 250 F. hepatica metacercariae. The experiment was
conducted over 10 weeks in order to comply with
Australian quarantine regulations to dispose of all
animals during the pre-patent period of F. gigantica.
2.4. Haematological and serological measurements
Blood samples were collected in 10 ml EDTA tubes
from all sheep before challenge, at time of challenge
and 3 days after challenge, and on weekly intervals
following challenge. The blood was processed for
assessment of total and differential leucocyte counts,
haemoglobin level, and packed cell volume (PCV)
using a Technicon H1 full haematological analyser.
of anti-Fasciola antibodies in serum determined by
ELISA. Briefly, ELISA plates (NUNC) were coated
overnight at 4 8C with 10 mg/ml of whole worm extract
antigen of F. gigantica or F. hepatica (for the detection
of anti-F. gigantica or anti-F. hepatica antibodies,
respectively) in 100 ml of carbonate buffer, pH 9.6.
ELISA analysis was performed as previously described
by Hansen et al. (1999). For the detection of sheep IgG
antibodies a 1/1000 dilution of HRP conjugated donkey
anti-sheep/goat total IgG (H + L; Silenus) was used.
Antibody isotypes were detected with specific non-
conjugated mouse anti-sheep IgG1, IgG2(Beh, 1987,
1988) added at 1:500 and 1:1000 dilution, respectively,
IgA (VRMD) added at 1:1000. Following incubation,
plates were incubated with sheep anti-mouse Ig-HRP
(1:1000; Amrad Biotech). Sheep endpoint ELISA titres
defined as the highest dilution of sera yielding an OD450
of 0.2, were calculated as described by Windon et al.
2.5. Production traits
Individual non-fasted body weight and group feed-
intake were recorded weekly for the duration of the
experiment. Feed intake was determined by weighing
H.W. Raadsma et al./Veterinary Parasitology 143 (2007) 275–286 277
Challenge protocol and parasite recovery in sheep given varying challenge doses
(mean ? S.E.)
13 ? 6
29 ? 14
57 ? 20
86 ? 47
119 ? 28
% take of metacercariae
(mean ? S.E.)a
26 ? 13
23 ? 11
26 ? 9
25 ? 14
39 ? 10
aPercentage take is the average percentage of infecting metacercariae recovered as a proportion of counted parasites.
daily feed residues after offer of known amounts offood
on a daily basis.
2.6. Plasma enzyme assays
Liver damage was assessed spectrophotometrically
by measurement of plasma levels of the two hepatic
enzymes, glutamate dehydrogenase (GLDH) and
gamma glutamyl transferase (GGT) on a Cobas Mira
chemical analyser using commercial kits (Roche).
Levels are expressed as international units per litre
All sheep were euthanised through intravenous
injection with 20 ml of Valabarb at 10 weeks post
challenge. The sheep were euthanised over a 3-day
days, respectively). All livers, bile ducts and gall
bladders were collected and examined for the presence
of either F. gigantica or F. hepatica parasites as
described (Roberts et al., 1997b). Total parasite number
determined from each processed liver. Livers were
weighed and subjective scores of macroscopic liver
damage (ranging from 0 to 5) were obtained at the time
of dissection: where 0 represented no overt signs of
tissue necrosis or liver nodules, 1 represented slight
liver necrosis or nodules generally confined to less than
5% of the liver, 2 represented light liver damage with
liver damage up to 15% of liver surface, 3 moderate
liver damage with nodules confined to approximately
30% of the liver surface, 4 represented heavy liver
damage with nodules up to 50% of liver surface, and 5
represented extensive liver necrosis with >50% of liver
surface showing signs of liver nodules.
2.8. Statistical analyses
Datafrom each biochemicalindicatorwere
analysed separately using Genstat. For analysis of
the host responses to infection the data was analysed
initially by repeated measures analysis of variance to
determine if the data needed to be transformed. A split
plot general analysis of variance with contrasts was
used to account for changes in all parameters between
and within groups. Where significant effects were
found comparisons were made using least squares
differences of the means (LSD, Genstat). This allowed
for adjustment of unbalanced data with only nine
animals in group 6.
A strong dose response was evident in the number
of parasites recovered, as well as the parasite biomass,
in the groups dosed with incremental numbers of F.
gigantica metacercariae (Fig. 1a and b; Table 1).
Across the four experimental groups challenged with
F. gigantica, parasite recovery ranged from 4
(observed in group 2) to a maximum of 153 flukes
(observed in group 5). Mean wet weight per fluke was
relatively constant among the three experimental
groups challenged with 125, 225 and 400 F. gigantica
metacercariae at 0.013–0.014 g/fluke (Fig. 1c) with
the individual fluke wet weights ranging from 0.003 to
0.023 g/fluke. Despite the increasing challenge dose of
F. gigantica, % parasite recovery or ‘‘take’’, defined as
the mean percentage of infecting metacercariae
recovered as adult flukes, was uniform within the
range of 23–26% across the four experimental groups
(Fig. 1d, Table 1).
The group challenged with F. hepatica showed the
greatest number of flukes recovered/sheep (mean 119,
range 84–166) (Fig. 1a); a significantly higher biomass
of parasites recovered (on average 2.5-fold greater than
the highestdoseofF.gigantica) (mean 2.6 g, range 0.9–
4.7 g, Fig. 1b), a higher average fluke wet weight
(Fig. 1c; and on average a greater % take at 39.3%
(range 27–55%) than any of the four groups challenged
with F. gigantica (Fig. 1d).
Livers from all control sheep were macroscopically
normal (all score 0). Livers from sheep given the
highest dose of F. gigantica and F. hepatica (groups 5
and 6, respectively) showed on average the greatest
liver damage with mean lesion scores of 3.0 and 3.3,
respectively, and group 6 had significantly higher
scores than those of groups 1–4 (Fig. 1e) (p < 0.05).
No significant increase in liver weight was observed
for the sheep challenged with F. gigantica compared
with the non-infected control sheep. Sheep challenged
with F. hepatica showed a significant increase in
liver weight over control sheep or sheep challenged
with F. gigantica (p < 0.01, Fig. 1f). A positive
correlation across the groups challenged with F.
gigantica was evident between liver score, challenge
dose and total number of parasites recovered. There
appeared to be a positive correlation, at the individual
sheep level, between fluke wet weight and fluke
burden for F. gigantica (r2= 0.36, p < 0.01 poly-
nomial regression, Fig. 2a) and F. hepatica (r2= 0.47,
p < 0.04, Fig. 2b).
H.W. Raadsma et al./Veterinary Parasitology 143 (2007) 275–286278
3.2. Plasma levels of glutamate dehydrogenase
(GLDH) and gamma glutamyl transferase (GGT)
The plasma GLDH and GGT levels were measured
at day 0 and then at 4, 6, 8 and 10 weeks post infection
(Fig. 3a and b). The group challenged with the lowest
dose of F. gigantica (group 2) showed no detectable
increase in GLDH over uninfected controls. By 6 wpi F.
giganticainfected groups 3–5 had significantly elevated
levels of GLDH compared to the uninfected sheep
(p < 0.005). The F. hepatica challenged group had an
even higher level (four-fold) of GLDH compared to the
F. gigantica infected groups at 6 wpi (p < 0.001). By
10 wpi the GLDH levels in the group challenged with F.
hepatica had declined to those seen in the groups
challenged with the highest three doses of F. gigantica:
at this time point all four F. gigantica groups still
showed a significantly higher level of GLDH over
uninfected control animals. Elevated levels of GGT, as
an indicator of epithelial damage in the bile duct, was
only seen in the group challenged with F. hepatica at
10 wpiwhenitrosefromameanof<100 IU/ltoamean
of 250 IU/l (p < 0.0001, Fig. 3b) whereas no detectable
increase in GGT was observed in any of the groups
challenged with F. gigantica (Fig. 3b).
White blood cell (WBC) counts were measured 1
week prior to challenge, at time of challenge and every
H.W. Raadsma et al./Veterinary Parasitology 143 (2007) 275–286 279
(e) macroscopic liver lesion scores, and (f) liver weight (g). Individual points represent individual sheep receiving different doses of Fasciola
metacercariae. Groups 1–5 were given 0, 50, 125, 225 and 400 F. gigantica metacercariae, respectively, and group 6 received 250 F. hepatica
metacercariae. Columns represent mean and S.D.
At 3 wpi all groups challenged with F. gigantica and F.
hepatica had a mean WBC count significantly greater
than the uninfected group (p < 0.05). The changes in
WBC profile in the group infected with F. hepatica
appearedtobebiphasic with the initialpeakat4 wpi and
a further substantial increase in the WBC count at 9 wpi
(p < 0.001). This biphasic response was not evident in
the groups challenged with F. gigantica. In the final 2
weeks of the experimental period the group challenged
with the lowest dose of F. gigantica had a WBC
concentration which was no different from uninfected
the other hand reached a peak WBC response at week 9
immediately prior to slaughter (Fig. 4a).
The levels of haemoglobin (HGB) (g/L) generally
increased steadily for all groups over the first 8 weeks
post infection (Fig. 4b). The uninfected group of sheep
showed no significant difference to any of the groups
infected with F. gigantica. By 9 wpi there is a
significant fall in HGB level in the group infected with
F. hepatica compared to all other groups (p < 0.001).
The packed cell volume (PCV%) in all groups mirrors
the trend seen in the HGB profiles. PCV gradually
increased in all groups and at 9 wpi there was a sharp
decrease in the F. hepatica infected group relative to the
rest of the groups (p < 0.001, Fig. 4c).
occurred at 2 wpi in all infected groups. At 3 wpi the
mean eosinophil numbers increased from basal levels of
less than 3 ? 109up to 15 ? 109l?1in the groups
infected with F. gigantica (p < 0.001) and to almost
25 ? 109l?1(p < 0.0001) in the F. hepatica challenged
group (Fig. 5a). Relative to the control group, the mean
eosinophil counts in groups 2–5 remained elevated
throughout the entire experimental period post infection
until time of slaughter. A strong biphasic response in
eosinophil count was observed in the group challenged
with F. hepatica, peaking for the first time at 4 wpi
(27 ? 109l?1) followed by a decline to 14 ? 109l?1at
H.W. Raadsma et al./Veterinary Parasitology 143 (2007) 275–286 280
Fig. 2. Relationship between fluke biomass and liver fluke recovery
of average flukewet weight (g/fluke) and total fluke numbers/sheep in
sheep challenged with F. gigantica (groups 2–5) r2= 0.36, p < 0.01.
(b) Correlation of average fluke wet weight (g/fluke) and fluke
numbers/sheep in sheep challenged with F. hepatica (group 6)
r2= 0.47, p < 0.04.
Fig. 3. Plasma glutamate dehydrogenase (GLDH) and gamma glu-
tamyl transferase (GGT) levels (mean ? S.E.M., IU/l).
6 wpi and followed by a steady increase to a mean
30 ? 109l?1at 9 wpi. This biphasic response was not
When the eosinophil count of the combined groups of F.
gigantica infected animals are compared to the single F.
hepatica challenged group of animals at 9 wpi there is a
clear indication that F. hepatica appears to induce a
greater eosinophilia (p < 0.01).
There was no significant difference in lymphocyte
counts between groups until 8 wpi when the group
challenged with F. hepatica fell significantly below
control levels (p < 0.05) and continued to fall by 9 wpi
(p < 0.001, Fig. 5b). Compared to the control group,
there was a steady decrease in neutrophil numbers in all
infected groups until 3 wpi when all groups showed a
plateau (data not shown). There was no significant
difference in basophil or monocyte numbers between
any of the groups across the experimental period (data
3.4. Specific serum immunoglobulin responses to
whole worm extract during infection with F.
gigantica and F. hepatica
At 1 wpi all groups infected with either F. gigantica
or F. hepatica showed an elevation in anti-Fasciola IgA
titres which remained high until week 5 when they
began to decline to control levels (Fig. 6a). There was
in all groups throughout the period of measurement
H.W. Raadsma et al./Veterinary Parasitology 143 (2007) 275–286 281
Fig. 4. Longitudinal profiles of infection parameters throughout the
study period. (a) White blood cell counts (WBC) (?109cells/l); (b)
haemaglobin (HGB) (g/l); (c) packed cell volume (%). Error bars
indicate the standard error of the mean where n = 10 for groups 1–5
and n = 9 for group 6.
Fig. 5. Longitudinal profiles of infection parameters throughout the
study period. (a) Eosinophil counts (?109cells/l) and (b) lymphocyte
counts (?109cells/l). Error bars indicate the standard error of the
mean where n = 10 for groups 1–5 and n = 9 for group 6.
(Fig. 6b). Anti-Fasciola IgG1antibodies were induced
within 1 wpi and remained elevated throughout the
experimental period in infected animals (Fig. 6c)
whereas there was no change in IgG1levels of the
uninfected animals (group 1) throughout the experi-
ment. By 3 wpi the titre of anti-Fasciola IgG1in all
groups infected with F. gigantica and F. hepatica had
peaked around 4.4 1og10and showed a slow decline
throughout the remaining infection period to around
3.8 log10antibody titre. The groups challenged with the
lower doses of F. gigantica (groups 2–4) produced
higher levels of IgG2after infection than either the
uninfected control group or groups challenged with the
highest dose of F. gigantica or with F. hepatica (groups
5 and 6, respectively) (Fig. 6d). Interestingly, IgG2
antibody titres in the latter two groups were not
H.W. Raadsma et al./Veterinary Parasitology 143 (2007) 275–286 282
Fig. 6. Specific antibody responses to whole worm extracts. (a) IgA (mean log10); (b) IgM; (c) IgG1; (d) IgG2; (e) the ratio of IgG1/IgG2. Antibody
titres are expressed as mean log10.
significantlydifferent fromthe uninfected controlgroup
at 5 and 7 wpi. The ratio of IgG1to IgG2showed no
clear responses consistent with the challenge dose or
species of Fasciola (Fig. 6e).
Measurement of IgE in all samples was attempted:
however, unlike the other isotypes which were
measured within 2 months of sampling there was a
delay in the analysis and IgE levels were low or
undetectable following long term storage and trans-
portation, possibly due to degradation of the samples.
3.5. Body weight and feed intake
The cumulative changes in body weight over the
duration of the experiment are shown in Fig. 7a. All
animals gained weight during the entire experimental
period as a consequence of being on ad libitum food
intake and at a young growing age. However, when
comparative relative growth rates in infected animals
were compared with non-challenged control animals,
significant differences were detected between parasite
infected groups (Fig. 7b). The body weights taken every
3dayspriortochallenge showed verylittlechange inall
groups. In the first wpi the body weights of all sheep
decreased by 1.5 kg on average. The animals in the
groups challenged at the two highest doses of F.
gigantica (groups 4 and 5) and the group challenged
with F. hepatica (group 6) showed a similar and
significant decrease in bodyweight relative to unin-
fected controls by 2 wpi and were not able to recover by
way of compensatory growth for the remainder of the
experimental period. Group 4 sheep (mean 57 flukes)
were infected with about 50% of the parasite burden
observed in group 6 (119 flukes), suggesting that, above
a parasite threshold of about 57 F. gigantica parasites,
the loss in body weight is similar even though the mean
biomass of F. gigantica flukes in group 4 is about three-
fold lower than that seen with F. hepatica in group 6
(Fig. 1b). The two groups challenged at the lower doses
of F. gigantica tended to retain growth rates above or
near those seen in the control group, indicating that at
these levels of infection (mean 13–29 flukes) the
animal’s body weight is uncompromised. Feed intake
measurements were not started until week 1 post
challenge. There was no significant difference between
groups in feed intake during the post challenge period
indicating no decrease in appetite (data not shown).
Relativeto groups 1–3, the reduced growth rate in sheep
challenged with F. hepatica, and two groups challenged
with the highest dose of F. gigantica, may therefore
indicate a real reduction in energy expenditure
attributable to disease and fasciolosis.
There have been few studies that directly compare
et al., 1987; Spithill et al., 1999; Piedrafita et al., 2004;
Zhang et al., 2004, 2005a,b). Earlier studies have
suggested that F. gigantica is more pathogenic than F.
hepatica based on the finding that fewer parasites killed
sheep and the larger size of F. hepatica flukes in mature
infections (Roberts et al., 1997a). However, these
studies measured comparative pathogenicity after long
term infections with mature parasites. In addition, many
of the early studies on these two parasite species
assumed that infection with F. gigantica was essentially
similar to infection with F. hepatica, since the two
parasites infect the liver and have a similar life cycle:
this has led to the assumption that they are essentially
similar organisms epidemiologically and in terms of the
host-parasite relationship (Spithill et al., 1999). How-
ever, F. gigantica is slower to develop in ruminant hosts
and takes greater than 14 weeks following infection to
reach the bile ducts while F. hepatica parasites establish
within the bile ducts after just 8–10 weeks of infection
(Wiedosari and Copeman, 1990; Behm and Sangster,
H.W. Raadsma et al./Veterinary Parasitology 143 (2007) 275–286 283
Fig. 7. Longitudinal profiles of production parameters in different
groups of sheep challenged with F. gigantica or F. hepatica. (a)
Cumulative body weights and (b) changes in body weight as a %
of control sheep. Error bars indicate the standard error of the mean
where n = 10 for groups 1–5 and n = 9 for group 6.
1999). Just prior to the migration of F. hepatica into the
bile ducts, a rapid growth of the parasite occurs during
livermigration from 5to8 weeks post-infection (Dawes
and Hughes, 1964). We wondered whether this putative
earlier development and maturation of F. hepatica in
sheep would cause more host damage early in infection
when compared to F. gigantica infections. We, there-
fore, conducted a detailed comparative trial in the
susceptible Merino breed for the first 10 weeks post
infection as this is the pre-patent period of F. gigantica,
and would allow the evaluation of the early comparative
host immune responses to both F. gigantica and F.
Previous limited studies have shown that when an
equal number of F. hepatica or F. gigantica metacer-
cariae are administered to ruminants, more flukes are
recovered from the F. hepatica infected ruminants than
the F. gigantica infected ruminants (Zhang et al., 2004,
2005a,b). In order to compare the pathogenicity in early
infection between the fluke species we, therefore,
attempted to attain similar worm burdens between the
two groups by performing an incremental response
challenge with increasing F. gigantica metacercariae in
groups of Merino sheep. In this study fluke recovery
was similar to the recent reports from Zhang et al.
(2005a,b) in that more flukes were recovered from
sheep infected with F. hepatica (39%) than were
recovered from F. gigantica infected sheep (26%, group
4) receiving similar numbers of metacercariae. Within
the groups dosed with F. gigantica a strong dose-
and fluke biomass with increasing dose of metacercar-
iae. Interestingly the % take between all the F.gigantica
infected groups was very even, suggesting a uniform
viability of parasite establishment independent of
infection dose. The dose of challenge or fluke recovery
impact on average fluke size, suggesting that there is no
obvious sign of competition between flukes for host
liverdamage, plasma GLDH levels and GGTresponses,
this experiment suggests that F. hepatica is more
pathogenic than F. gigantica in the first 10 weeks of
5 and 6 where similar worm burden recoveries were
obtained. Within the first 10 weeks of infection, F.
hepatica develops more rapidly than F. gigantica
resulting in increased plasma levels of GLDH,
indicating greater damage to the liver parenchyma
(Boyd, 1962; Meeusen et al., 1995). The earlier
maturation of F. hepatica was also demonstrated by a
decrease in GLDH in this group of sheep at 8–10 wpi,
corresponding to the migration of F. hepatica into the
bile ducts, and a corresponding increase in the GGT
levels at 10 wpi, indicating epithelial damage in the bile
duct (Chauvin et al., 1995). In contrast, in the sheep
infected with F. gigantica, the plasma levels of GLDH
were beginning to rise at 6 wpi and continued to rise
steadily but did not reach the same peak as the F.
hepatica infected animals; GGT levels were unaffected
by 10 wpi in the F. gigantica groups. A slower
maturation of F. gigantica is also indicated by the
finding of smaller, immature flukes in the liver
parenchyma at slaughter at 10 wpi compared to F.
hepatica, where most flukes were observed within the
bile ducts. The greater damage to the F. hepatica-
infected Merino sheep was also evident by the
subjective scoring of greater lesions in the F.
hepatica-infected livers and the compensatory hyper-
trophy of the liverleading to a significant increase in the
relative liver weights. The greater pathogenicity of F.
hepaticawas also evident from the significant decreases
in haemoglobin levels and packed cell volume late in
infection (9 wpi) compared with all the F. gigantica
infected groups. It is known that F. gigantica remains in
the liver for 12–14 wpi and only then migrates to the
bile ducts (Spithill et al., 1999).
It has been well documented that infection of some
breeds of sheep with F. hepatica causes a large
infiltration of white blood cells into the liver (Meeusen
et al., 1995; Tliba et al., 2000). Here, the white blood
cell response and eosinophilia following F. hepatica
infection was biphasic with the initial peak at 4 wpi and
a second peak at9 wpi. Theeosinophiliareported inthis
study is similar to that documented by others in sheep
infected with F. hepatica (Chauvin et al., 1995; Zhang
et al., 2005b) or F. gigantica (Roberts et al., 1997a;
Hansen et al., 1999; Zhang et al., 2005b). This biphasic
response corresponds to the migratory phase of the
juvenile fluke in the liver (week 4) followed by a
reduction in peripheral cell counts as the parasite
matures in the bile duct (Rushton and Murray, 1977), a
finding confirmed by the elevated levels of GGT at
10 wpi in the F. hepatica infected group 6, indicating
evidence ofepithelialdamage inthe bile duct. When the
eosinophil numbers in the groups with incrementally
increasing doses of F. gigantica were analysed there
was no significant difference between the groups,
indicating that added worm burden had no additional
effect on the eosinophilia.
Pooled sera of each group were used to measure the
specific humoral immune response to whole worm
extracts to attain general trends in the antibody
H.W. Raadsma et al./Veterinary Parasitology 143 (2007) 275–286284
responses following Fasciola infection. Specific IgG1
was produced in all infected animals as early as 1–3 wpi
and maintained at high levels throughout the 10 weeks
of infection. This response was similar in all sheep
infected with varying doses of F. gigantica, and for the
F. hepatica infected group, as previously observed by
others (Santiago and Hillyer, 1988; Chauvin et al.,
1995; Moreau et al., 1998; Zhang et al., 2004). The
changes in IgA response were less defined with a small
peak around5 wpi, butotherwise no trend was observed
which couldbeclearly attributedtoinfectiondose.With
IgG2there was a trend toward higher titres in sheep
infected with the lower worm burdens (groups 2–4),
suggesting that higher F. gigantica and F. hepatica
burdens suppress IgG2 responses in Merino sheep.
Suppression of IgG2responses to F. gigantica infection
was observed in Indonesian Thin Tail sheep, relative to
Merino sheep (Hansen et al., 1999). Moreau et al.
(1998) have previously shown that the IgG2response to
a cathepsin L vaccine correlates with reduced worm
burdens in vaccinated cattle, implying a protective role
for this isotype against F. hepatica. These observations
raise the interesting prospect that Fasciola parasites
produce a factor (s) that can suppress IgG2responses.
In ruminants, the IgG2response is regulated by IFN-
gamma (Estes et al., 1994).
Very few studies have been able to successfully
compare the impact of F. gigantica and F. hepatica
parasitism on production, feed intake and host
responses. This study shows that the severity of
infection by both Fasciola species directly influences
weight gain within 2 wpi. In this experiment the levelof
nutrition was not restricted, as is normally seen under
production systems, and therefore the impact on
production may be expected to be of even greater
consequence under field conditions. High doses of both
F. gigantica and F. hepatica were able to induce similar
effects on production, despite the greater damage
caused by F. hepatica infection based on fluke biomass
and liver damage. This suggests that production losses
are not solely related to fluke biomass and liver
pathology; rather, there is a parasite threshold above
which production losses are comparable with F.
gigantica and F. hepatica.
In conclusion, the development and subsequent
effect on sheep of the two Fasciola species is quite
different. During the early stage of infection in a
permissive host, F. hepatica appears to be more
pathogenic than F. gigantica due to its faster rate of
growth and the speed of its progression through the
migratory phases to establishment in the bile duct.
Relativeto F.gigantica,F.hepatica appearsto expressa
greater capacity to induce eosinophilia, and an IL5-like
activity has been described in ES of F. hepatica
(Milbourne and Howell, 1993). Moreover, studies in
Indonesian Thin Tail sheep have shown that sheep can
acquire resistance to infection by F. gigantica but
not F. hepatica, suggesting that subtle biochemical
differences exist between these two parasite species
(Roberts et al., 1997a,b; Piedrafita et al., 2004). Further
comparative studies on these two Fasciola species are
needed to define the basis for these differences in their
parasite-host interactions which may identify parasite
mechanisms that could be targeted for control of
This work was supported by the University
of Sydney, Monash University, the University of
Melbourne and the Australian Centre for International
Agricultural Research (ACIAR), Canberra.
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