Myocastor coypus as a reservoir host of Fasciola hepatica in France

To clarify the role of the nutria Myocastor coypus in the epidemiology of domestic fasciolosis in Loire-Atlantique (department of western France), 438 nutrias were trapped in 9 humid areas of the department and 304 nutrias were trapped in 3 farms where Fasciola hepatica was present; all animals were necropsied. Liver flukes were found in 160 nutrias: 38 nutrias randomly taken in the department (8.7%) and 122 trapped in fasciolosis areas (40.1%). The average parasitic burden was 5.7 flukes per nutria. Sixty-five percent of the liver flukes measured more than 18 mm (size of sexual maturity). The coproscopic examinations carried out on 144 infected nutrias showed that 90% of the infected nutrias shed fluke eggs. The hatching rate was 39.6%. Two groups of 100 Lymnaea truncatula snails, originating from 2 different populations, were exposed to F. hepatica miracidiae hatched from eggs collected from infected nutrias. The prevalence of the infection was 74% and 58.6% in the 2 groups of snails. The average redial burden was 6.2 rediae per snail. The total number of metacercariae was 72.4 metacercariae per snail producing cercariae. Two groups of 5 sheep were orally infected by 150 metacercariae of nutria or sheep origin, respectively. The installation rates of F. hepatica in sheep were respectively 31.6% and 29.6% for the two groups. Specific antibody kinetics of sheep were similar whether the metacercariae were of nutria or sheep origin. M. coypus allows the complete development of F. hepatica and releases parasitic elements that are infective for domestic ruminants. Because of its eco-ethologic characteristics, the nutria could be a potential wild reservoir of F. hepatica in France.     

Responses of Fasciola hepatica infected sheep to various infection levels

The response to Fasciola hepatica was studied in sheep infected with 5, 30, 150 metacercariae. The animals were necropsied 12 weeks post-infection (p-i) for counting and measuring flukes. Cellular and humoral responses were detected by peripheral eosinophil count, peripheral blood lymphocyte proliferation with excretory-secretory products (FhESP) and ELISA. All sheep were infected at necropsy except one sheep which was infected with 5 metacercariae. Mean parasitic intensities were 40%, 44% and 27% of the infection dose in sheep infected with 5, 30, 150 metacercariae respectively. FhESP-specific lymphocyte responses of the 3 infected groups were significantly enhanced in weeks 3 and 4 p-i (p < 0.05). The kinetics of the specific humoral response were similar for the 3 infected groups but the antibody level was significantly lower in animals infected with 5 metacercariae than in the 2 other infected groups from week 5 p-i to week 12 p-i (p < 0.05). Peripheral eosinophil count was significantly enhanced (p < 0.05) in infected groups. The numbers of peripheral eosinophils were significantly different between the 3 infected groups in week 3, 4 and 6 p-i and were related to infection level. These results confirm that sheep are highly susceptible to F. hepatica infection, even when infection pressure is very low. Peripheral eosinophilia was dependent of the infection level. The immune response was similar in sheep infected with various numbers of flukes.     

The anthelmintic efficacy of netobimin against experimental infections of Fasciola hepatica in sheep

Netobimin (coded SCH 32481, Schering Corporation), a new broad-spectrum anthelmintic having both fasciolicidal and nematocidal properties was evaluated for efficacy against mature Fasciola hepatica infections in sheep. The trial was conducted with 30 cross-bred spring lambs, each experimentally infected with 250 F. hepatica metacercariae. A single treatment of netobimin was administered at 17 weeks post-infection (PI) by oral drench at 7.5 or 20 mg kg-1 body weight while 10 animals remained as untreated controls. At necropsy (either 1 or 2 weeks post-treatment), the mean number of adult flukes recovered from the control, 7.5 and 20 mg kg-1 groups were 94.7, 35.9 and 8.8, respectively. The resulting efficacies were 62% (P less than or equal to 0.05) and 90.7% (P less than or equal to 0.01), respectively. No clinical signs of fascioliasis were noted in any sheep during the trial. No signs of toxicosis nor any adverse reactions to the drug were observed.     

The effect of Taenia hydatigena infection on existing and concurrent infections of Fasciola hepatica in sheep

Sheep given a primary infection of Fasciola hepatica were challenged 18 weeks later with Taenia hydatigena or F hepatica, or both parasites together, or were not challenged. At the same time, control sheep were infected with T hydatigena and/or F hepatica separately or concurrently. All sheep were killed seven weeks after challenge and the number of cysts and flukes counted. Challenge infection with T hydatigena did not affect the numbers of flukes recovered from either primary or challenge F hepatica infections. On the other hand, the numbers of cysticerci were reduced in sheep previously infected with F hepatica but not in those given T hydatigena and F hepatica concurrently.     

Fasciola hepatica: comparative effects of host resistance and parasite intra-specific interactions on size and reproductive histology in flukes from rats infected with isolates differing in triclabendazole sensitivity

The efficacies of putative fasciolicides and vaccines against Fasciola hepatica are frequently monitored in clinical and field trials by determination of fluke egg output in host faeces and by worm counts in the host liver at autopsy. Less often used are parameters based on fluke size and histology, yet these can provide important indications of specific effects on the development of particular germ-line or somatic tissues, especially in relation to the timing and profligacy of egg production. In this study, F. hepatica metacercariae of two distinct isolates, the triclabendazole (TCBZ)-sensitive Cullompton isolate and the TCBZ-resistant Oberon isolate, were administered to rats as single-isolate or mixed-isolate infections. At autopsy 16 weeks later individual adult flukes were counted, measured and the reproductive organs were examined histologically. The degree of development of the testis tubules in each fluke was represented by a numerical score, based on the proportion of the histological section profiles occupied by testis tissue. The level of anti-F. hepatica antibody in the serum of each rat was determined by ELISA. It was found that Cullompton flukes were significantly larger than Oberon flukes, and that significantly more Cullompton metacercariae developed to adults than Oberon metacercariae. The Cullompton flukes showed histological evidence of aspermy and spermatogenic arrest, which was reflected in quantitatively reduced testicular development, as compared with the Oberon isolate. In Cullompton flukes, parthenogenetic egg development is implied. The size of Cullompton and Oberon flukes was significantly related to the number of adult flukes recovered, to the number of metacercariae administered, and to the percentage success of infection. The testis development score in both isolates was significantly related to the number of adult flukes recovered but not to the number of metacercariae administered, or to the percentage success of infection. Fluke size was positively related to testis score for both isolates, and a significant negative relationship was found between percentage success of infection and metacercarial dose. The results are interpreted in terms of differing interactions between various numbers of young flukes and host immunity during invasion of and migration in the hepatic parenchyma, and of fluke intra-specific (possibly pheromonal) stimulatory effects in the final stages of development, within the host bile ducts. No significant relationships were found between host antibody levels and fluke size or testis score. False positive serological reactions were found in some rats that had been infected, but found to harbour no flukes at autopsy. Clearly the act of eliminating the flukes involved generation of an immune response.     

Worm recovery, haemagglutinating antibodies and IgE-levels after immunisation against Fasciola hepatica in rats

Female inbred Hooded Lister (HL) rats were each infected with 20 metacercariae (Mc) of Fasciola hepatica. Remarkable variations between the number of flukes established in the bile ducts suggest the presence of individual, perhaps genetically controlled, differences in immune responsiveness of HL rats to F. hepatica. Serum (4 ml) from HL rats infected with 20 Mc 6 weeks prior to transfer partially protected rats against a F. hepatica challenge infection. However, 1 X 10(6) lymphoid cells originating from rats of the same age and stage of infection did not show the same protective qualities. Furthermore, attempts to immunise HL rats i.p. with either juvenile or adult excretory/secretory (ES) products, or somatic tissue antigens and AlOH3-gel as adjuvant failed. When compared to other investigations, the present results further suggest that both the adjuvant and the route of administration are crucial for the stimulation of a protective immunity to F. hepatica. Low titers and low anamnestic responses of haemagglutinating antibodies after prior immunisation with juvenile ES antigens or both juvenile ES and somatic tissue antigen suggest the occurrence of an immunosuppressive effect caused by juvenile ES products. The total serum IgE-levels in immunised groups were generally lower when compared to the challenge control group, whereas the F. hepatica ES-specific IgE-levels rose after challenge, but immediately decreased again when compared to challenge controls. These findings support the hypothesis of an immunomodulatory effect caused by the vaccination scheme.     

Diagnosis of ovine fascioliasis by a dot enzyme-linked immunosorbent assay: a rapid microdiagnostic technique

A microenzyme-linked immunosorbent assay (dot-ELISA) was modified for making an immunodiagnosis of Fasciola hepatica infections in sheep. Sheep were alloted as follows: group I-3 controls and 4 principals, each inoculated with 500 metacercariae; group II-3 controls and 7 principals, each inoculated with 250 metacercariae; and group III-3 controls and 7 principals, each inoculated with 500 metacercariae. Blood and fecal samples were collected from each animal every 2 weeks for 16 weeks. Presence (or absence) of flukes was confirmed by fecal examinations and examination of dissected livers at necropsy of the sheep. The dot-ELISA incubations were done at ambient room temperature. Nitrocellulose disks dotted with 1 microliter (50 ng of protein) of F hepatica excretory/secretory products were placed in 96-well tissue culture plates. After nonspecific binding sites on the disks were bound with bovine serum albumin-triethanolamine-buffered saline solution, dilutions (1:2) of positive- and negative-control serum samples or experimental serum samples were placed in appropriate wells for a 30-minute incubation. Wells were washed (3 times), and 50 microliters of horseradish peroxidase conjugated rabbit anti-sheep immunoglobulin G was added to each well for a 30-minute incubation and then aspirated. Substrate solution (4-chloro-1-naphthol, methanol, triethanolamine-buffered saline solution, and H2O2; 50 microliters) was added for a 30-minute incubation and then aspirated. Disks were air dried for visualization: solid purple dot = positive sample, or no dot = negative sample.(ABSTRACT TRUNCATED AT 250 WORDS)     

The establishment and duration of Fasciola hepatica infections in two strains of rats and the development of acquired resistance.

Male and female rats of the inbred Piebald Virol Glaxo ( PVG) and Sprague Dawley (SD) strains were infected with 20 metacercariae of Fasciola hepatica. Three months after infection there was a highly significant difference (P LESS THAN 0-001) in the fluke burden of the two strains. The PVG rats (average 9-4 flukes) were more susceptible than the SD strain (average 2-8 flukes). The PVG males (11-6 flukes) were also found to be significantly more susceptible than the PVG females (average 7-2 flukes) whereas the sex of the SD rats did not affect the fluke burdens significantly.Seven to eight months after infection the PVG rats had eliminated their flukes. These 'self cured' PVG rats were significantly resistant to oral challenge with 20 metacercariae. In marked contrast the SD rats had not eliminated their flukes at the termination of the experiment 12 months after infection.     

The ability of diamphenethide to control immature Fasciola hepatica in sheep at a lower than standard dose level

Groups of eight Welsh Mountain sheep were dosed with diamphenethide at the rate of 70 mg/kg bodyweight at either one, four, six or eight weeks after artificial infection with approximately 300 Fasciola hepatica metacercariae. Comparisons were made with similarly infected but undosed sheep and with sheep which were neither infected nor dosed. The good clearance of flukes up to six weeks of age (above 97 per cent on pooled data) was reflected in the plasma concentrations of the accepted liver damage marker enzymes glutamate dehydrogenase and gamma-glutamyl transpeptidase. Highly significant correlations were demonstrated between the numbers of flukes recovered, the plasma levels of these enzymes and haemoglobin and plasma albumin values. At 70 mg/kg, diamphenethide was shown to be able to control F hepatica populations of up to six weeks of age. The systematic use of diamphenethide at this dose level at intervals of up to six weeks during the period of metacercarial challenge should prevent ovine fascioliasis.     

Experimental Haemonchus contortus infection in three breeds of sheep

Nine- to 10-month-old Florida Native, St. Croix and Dorset/Rambouillet sheep were infected with Haemonchus contortus. The primary infection was terminated by anthelmintic treatment 9 weeks later and animals were then reinfected with H. contortus. Dorset/Rambouillet sheep showed higher fecal egg counts and decreased packed cell volumes and plasma protein levels compared with the other two breeds during the primary infection. However, no breed differences were found in total worm burdens in either primary or secondary infection. Differences between breeds were also not detected in lymphocyte responsiveness to parasite antigen, H. contortus specific mucosal antibody levels, numbers of abomasal mast cells and globule leukocytes or abomasal histamine levels.     

Host responses during experimental infection with Fasciola gigantica or Fasciola hepatica in Merino sheep I. Comparative immunological and plasma biochemical changes during early infection

This study reports the early biochemical changes in plasma, comparative host-immune responses and parasite recovery data in Merino sheep during the first 10 weeks of infection with Fasciola gigantica and Fasciola hepatica. One group of sheep were uninfected, 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 than the highest dose of F. gigantica); and a greater mean % parasite recovery (39.3%, range 27-55%) than any group challenged with F. gigantica. Within the groups dosed with F. gigantica a strong dose-dependent response was observed in both fluke recovery and fluke biomass with increasing dose of metacercariae. The mean % parasite recovery of F. gigantica infected groups 1-5 were 26, 23, 26 and 25%, respectively, suggesting a uniform viability of parasite establishment independent of infection dose. At 6 wpi, elevated levels of plasma GLDH were observed in the F. gigantica infected groups compared to the uninfected sheep (p<0.005) whereas the F. hepatica challenged group had four-fold higher levels of GLDH compared to the F. gigantica infected group (p<0.001). 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 wpi when it rose from below 100 IU/l to approximately 250 IU/l (p<0.0001) whereas no detectable increase in GGT was observed in any of the groups challenged with F. gigantica. The white blood cell response to F. hepatica infection was biphasic with the initial peak at 4 wpi and a second peak at 9 wpi, corresponding to the period of migration of juvenile fluke in the liver and the time when adult flukes are migrating into the bile duct, respectively. This biphasic response was also evident in the changes in the eosinophil counts and serum haemoglobin levels. There was a trend toward higher parasite-specific IgG2 titres in sheep infected with lower worm burdens, suggesting that higher F. gigantica or F. hepatica burdens suppress IgG2 responses. 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 of its rapid increase in size and the speed of its progression through the migratory phases of its life cycle.     

THE EFFECT OF PRIOR INFECTION WITH FASCIOLA HEPATICA ON THE RESISTANCE OF SHEEP TO THE SAME PARASITE

The development of flukes that resulted from a challenge dose of 175 F. hepatica metacercariae was compared in 4 groups of sheep that were maintained under grazing conditions on fluke-free pasture. One group had been previously uninfected and all subgroups of each of the other 3 groups had been exposed to one of a range of previous doses of metacercariae. The preliminary infections of 2 of the 3 groups had been terminated respectively after 7 and 14 weeks. The third previously infected group had received its preliminary infection as 2 doses of metacercariae, 7 weeks apart. The latter infection had been terminated after 14 weeks. No appreciable differences in the mean numbers, length, prepatent period or fecundity of flukes, established as a result of the challenge dose of metacercariae, were detected between the control group and the 3 previously infected groups. It was concluded that under the conditions of the present experiment no evidence was detected that would suggest that previous infection with F. hepatica conferred any significant resistance to a future challenge.     

Antipyrine, erythromycin and oxytetracycline disposition in experimental fasciolosis.

The effects of fasciolosis on drug disposition were studied by administration of antipyrine, erythromycin and oxytetracycline to sheep and cattle. Fasciolosis was produced by administration of 200 or 400 metacercariae (MC) of Fasciola hepatica to sheep and 500 MC to cattle. The disease was subsequently confirmed by determination of plasma glutamate dehydrogenase and gamma-glutamyl transferase and identification and quantitation of mature flukes in the liver at necropsy. Acute or subacute fasciolosis in sheep was accompanied by a significant decrease in the elimination rate constant (beta) and increase in the elimination half-time (t 1/2) for antipyrine and erythromycin when compared with controls or infected sheep which had been treated with the anthelmintic luxabendazole. An increase in apparent volume of distribution (Vd) was seen only for erythromycin in sheep given 400 MC. There were no changes in the disposition of oxytetracycline in sheep with either acute or subacute infection and no effects on disposition of the three test drugs in chronically infected sheep. With early chronic disease in calves, only the disposition of oxytetracycline was affected; not that of antipyrine or erythromycin.     

Fasciola hepatica: Histology of the testis in egg-producing adults of several laboratory-maintained isolates of flukes grown to maturity in cattle and sheep and in flukes from naturally infected hosts

A total of 8 calves approximately 6 months old and 22 lambs of similar age were infected with metacercariae of Fasciola hepatica of various laboratory-maintained isolates including: Cullompton (sensitive to triclabendazole) and Sligo, Oberon and Leon (reported as resistant to triclabendazole). Ten to 16 weeks after infection, flukes were harvested from these experimental animals and the histology of the testis tissue was examined in a representative sample of flukes from each population. Adult wild-type flukes were also collected from 5 chronically infected cattle and 7 chronically infected sheep identified at post-mortem inspection. The testis tissue of these flukes was compared with that of the various laboratory-maintained isolates. Whilst the testes of the wild-type, Oberon and Leon flukes displayed all the usual cell types associated with spermatogenesis in Fasciola hepatica (spermatogonia, spermatocytes, spermatids and mature sperm), the Cullompton flukes from both cattle and sheep showed arrested spermatogenesis, with no stages later than primary spermatocytes represented in the testis profiles. The presence of numerous eosinophilic apoptotic bodies and nuclear fragments suggested that meiotic division was anomalous and incomplete. In contrast to the wild-type flukes, no mature spermatozoa were present in the testes or amongst the shelled eggs in the uterus. A high proportion of the eggs collected from these flukes hatched to release normal-appearing miracidia after an appropriate incubation period, as indeed was the case with all isolates examined and the wild-type flukes. It is concluded that the eggs of Cullompton flukes are capable of development without fertilization, i.e. are parthenogenetic. The implications of this for rapid evolution of resistant clones following an anthelmintic selection event are discussed. Amongst the Sligo flukes examined, two subtypes were recognised, namely, those flukes with all stages of spermatogenesis and mature spermatozoa present in the testes (type 1), and those flukes with all stages of spermatogenesis up to spermatids present, but no maturing spermatozoa in the testes (type 2). Each sheep infected with the Sligo isolate had both type 1 (approximately 60%) and type 2 (approximately 40%) flukes present in the population. Spermatozoa were found amongst the eggs in the uterus in 64% of flukes and this did not necessarily reflect the occurrence of spermatozoa in the testis profiles of particular flukes, suggesting that cross-fertilization had occurred. The apparent disruption of meiosis in the spermatocytes of the Cullompton flukes is consistent with reports that Cullompton flukes are triploid (3n=30), whereas the Sligo and wild-type flukes are diploid (2n=20). In the Sligo flukes the populations are apparently genetically heterogenous, with a proportion of the flukes unable to produce fully formed spermatozoa perhaps because of a failure in spermiogenesis involving elongation of the nucleus during morphogenesis.     

Serum antibody isotype responses of Fasciola-infected sheep and cattle to excretory and secretory products of Fasciola species

This study investigated the immunoglobulin isotype responses of sheep and cattle chronically infected with Fasciola hepatica and Fasciola gigantica to adult F. hepatica excretory/secretory products (Fh-ES) or F. gigantica excretory/secretory products (Fg-ES), respectively. An antibody enzyme-linked immunosorbent assay (Ab-ELISA) was used to determine serum antibody (total Ig, IgG(1), IgM, IgG(2) and IgA) responses. At necropsy, the mean number of flukes recovered was lower in cattle than in sheep. All F. hepatica and F. gigantica infected sheep and cattle showed an increased total Ig levels from 3 to 4 weeks post-infection (wpi). Among isotypes IgG(1) was most dominant while IgM was the earliest (2 wpi) to be detected in both sheep and cattle infected with both F. hepatica and F. gigantica animals. IgG(2) response was early (2 wpi) in sheep infected by F. hepatica but there was no response in sheep infected with F. gigantica. There was a late and strong IgG(2) response in cattle infected with both flukes. The IgA isotype showed an early and a clear biphasic response in sheep with F. hepatica but was less pronounced in F. gigantica infected sheep. While IgA response to Fh-ES was noticed 5 wpi in F. hepatica infected cattle, it appeared much later (21 wpi) in those infected with F. gigantica. The dominance of IgG(1) isotype in infected sheep and cattle suggest an associated Th2 response. This early response to adult Fasciola spp. ES antigen suggests an early exposure to the antigen presumably through the cross-reacting ES products of juvenile flukes. There is clearly difference in IgG(2) isotype response in cattle (resistant) compared to sheep (susceptible). The late IgG(2) response in cattle may suggest late Th1 involvement in bovine cellular responses to adult Fh-ES/Fg-ES.     

The susceptibility of the goat to Fasciola hepatica infections

Mixed breed goats were infected with metacercariae of Fasciola hepatica and the resulting worm burdens were quantitated after primary and secondary exposure of the goats to the parasite. Mean length and width of the parasite recovered after all primary exposures were 1.91 +/- 0.2 cm and 0.91 +/- 0.2 cm, respectively. A mean of 71.8 +/- 5.9% of the flukes were recovered from all of the primary infections. In the secondary infections, the mean length and width of the flukes from the physically smaller population was 0.88 +/- 0.27 cm and 0.53 +/- 0.19 cm, respectively. A mean of 67 +/- 6.7% of the flukes were recovered from this secondary infection. It appears that the goat is susceptible to challenge infections with F. hepatica and that its response to this infection is much like that of sheep.     

Experimentally induced Faciola hepatica infection in white-tailed deer. I. Clinicopathological and parasitological features.

Six white-tailed deer (Odocoileus virginianus) and six sheep were inoculated with metacercariae of Fasciola hepatica. Two animals of each species were given 100, 500 or 2500 metacercariae. Clinicopathological features of these infections were determined by analyses of blood samples collected each week from inoculated deer and sheep as well as from two noninoculated animals of each species. One animal in each inoculated group was killed and examined at six weeks postinoculation and the remainder at 15 weeks postinoculation. Compared with the values obtained from noninoculated controls, eosinophilia, hyperproteinemia and hyperglobulinemia occured in inoculated deer. There were no other significant changes in hematological values or in serum aspartate aminotransferase levels. Marked leukocytosis and eosinophilia, with hyperproteinemia, hyperglobulinemia, hypoalbuminemia, elevated serum aspartate aminotransferase levels and mild macrocytic normochromic anemia characterized the infection in lambs. Although approximately 29% of the inoculum was recovered from the hepatic parenchyma of the sheep, F. hepatica was found in only one of six inoculated deer. A patent infection was established in this deer and constitutes the second report of mature F. hepatica in this host.     

Concurrent daily infection of calves with Fasciola hepatica and Ostertagia ostertagi.

Three groups of calves were infected daily with either 1500 Ostertagia ostertagi larvae, 20 Fasciola hepatica metacercariae, or 1500 O ostertagi plus 20 F hepatica metacercariae. Weekly measurements were taken of calf weight, faecal egg output, plasma concentrations of albumin, plasma activities of sorbitol dehydrogenase, gamma glutamyl transpeptidase and pepsinogen and standard haematological indices. Calves were killed either 10 or 21 weeks after daily infections began. F hepatica infection had little influence on the size and structure of the O ostertagi worm population or vice versa. Mean worm burdens found at 20 weeks in those animals infected with both F hepatica and O ostertagi were 293 flukes and 20,641 nematodes. While this level of infection is similar to that seen in the disease complex in the field, there was no evidence of clinical disease or any difference in weight gain between the groups in this experiment. Factors other than additive worm burdens are obviously important for the expression of disease under field conditions.     

Light and scanning electron microscopic studies of the extrahepatic bile duct of sheep with experimentally induced Fasciola hepatica infection.

Changes in the common bile duct that contained adult Fasciola hepatica of sheep were evaluated by light (LM) and scanning electron microscopy (SEM). Nine ewes were inoculated with F hepatica metacercariae and necropsied 18 weeks after inoculation. The proximal portion of the common bile duct (CBD) that contained adult flukes was recovered and examined by LM and SEM. The CBD from 2 noninoculated ewes were used for control. On gross examination, CBD were markedly large because of the adult flukes, which were free in the lumen of the ducts. Extensive hemorrhage was not found either in intrahepatic or in extrahepatic bile ducts of any sheep. Histologic examination revealed changes, such as villous hyperplasia and hypertrophy of the epithelium; cell infiltration, predominantly with eosinophils or macrophages; and arterial intimal proliferation. By SEM, the epithelial surface of the CBD appeared intact. Villous hyperplasia and hypertrophy of the epithelium observed by LM was clearly seen by SEM. Epithelial damage, seen as small areas of denuded surface by LM and SEM, was confined to a few areas of the mucosa. Lack of extensive hemorrhage and confined epithelial damage were evaluated relative to the mode of feeding of adult flukes.     

High resistance to experimental infection with Fasciola gigantica in Javanese thin-tailed sheep

Innate resistance of Javanese thin-tailed sheep to Fasciola gigantica was investigated in animals infected with single doses of 150 or 500 metacercariae and killed 4, 8, 12 or 16 weeks after infection. Infected and non-infected sheep had similar values for packed cell volume, mean corpuscular volume, mean corpuscular haemoglobin concentration, serum glutamate dehydrogenase, serum gamma glutamyl transferase and serum aspartate transferase throughout the trial, except for one animal infected with 500 metacercariae from which the highest recovery of flukes (55) was made. This animal developed pathologically altered values from 12 weeks post infection, coincident with the period of greatest hepatic haemorrhage and destruction of hepatic tissue by migrating flukes and their entry into bile ducts. However, values were altered much less than those reported in other sheep given as few as 200 metacercaria of F. gigantica. Both susceptibility to infection with F. gigantica, as indicated by percentage take of metacercariae and the severity of pathological changes were low in this study in comparison with reports involving other breeds of sheep infected with this parasite. These findings support the conclusion that Javanese thin-tailed sheep have a high innate resistance to F. gigantica.