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1.
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.  相似文献   

2.
The antibody and lymphocyte responses to Fasciola hepatica were studied in rats. Infested rats were shown to produce antibodies against excretory-secretory (ES) products of adult flukes as early as the first week after infestation. Immunoblotting revealed fractions of ES products of adult flukes to which antibodies were progressively produced during the course of the infestation. Proliferation of peripheral blood lymphocytes, splenocytes and thymocytes when incubated with different mitogens (Concanavalin A (ConA) or Pokeweed mitogen (PWM) or different liver fluke antigens (metacercariae antigen (EM) or ES products of adult flukes) have been studied. In response to these mitogens or antigens, splenocytes were stimulated on the second and fourth weeks after infestation. Thymocytes were significantly activated by PWM on the second week but peripheral blood lymphocytes did not show any statistically significant response. Results obtained in antibody production, immunoblotting and lymphocyte proliferation suggested sequential releases of F. hepatica substances and the existence of common proteins between adult and juvenile parasite stages. Cellular and humoral responses observed in this work did not seem to confer a complete resistance to liver fluke primary infestation on the rat.  相似文献   

3.
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.  相似文献   

4.
Fasciola hepatica metacercariae were present on pasture throughout the year at the trial site. The highest infection rate in trial sheep occurred in the first year after the beginning of the wet season, in December/January, when contamination of the pasture was maintained by other sheep. Variation in rates of infection in consecutive years was linked to differences in grazing pressure and to a change from sheep to cattle as accompanying grazing stock. A minimum precipitation of 125 mm over 4 consecutive weeks appears to be necessary for infected snails to move from their normal habitats and to contaminate wet pasture with cercariae. Infection of sheep can occur during a dry season if pasture has permanent seepage sites or swampy areas where infected snails can remain active and continue to liberate cercariae.  相似文献   

5.
A peripheral blood mononuclear cell (PBMC) proliferation assay was used to study the cell-mediated immune response in eight calves experimentally infected with Fasciola hepatica. Hypersensitivity-related eosinophil and mast-cell responses were also assessed. The primary infection of 500 metacercariae was administered either as a single-dose or as a trickle infection over a 4-week period. Calves were challenge-infected 4 months later with 100 metacercariae and slaughtered 24 weeks postprimary infection. Skin eosinophil counts (SEC) were determined prior to infection on the basis of the intradermal reaction (IDR) to phytohaemagglutinin (PHA). These counts correlated negatively with the mean fluke length but not with the fluke burden found at necropsy. At the end of the experiment, non-specific (PHA) and specific (excretory-secretory parasite, products, FhESAg, and whole-worm extract, FhSomAg) immediate type hypersensitivity IDR were elicited in contrast to delayed type hypersensitivity (DTH) responses. The SEC correlated with blood eosinophilia but not with parasite parameters. These findings suggest that the eosinophil response does not correlate clearly with the development of resistance to F. hepatica infection in cattle. A specific mononuclear cell response to FhSomAg was detectable as early as 7 days after infection in both infected groups, being significantly higher during the very early migratory phase of the juveniles in the single-dose infected calves than in the trickle infected calves. This response remained significantly higher in infected groups than in the control group throughout the experiment. Challenge elicited a significant proliferative response, less pronounced than after primary infection. No production of gamma-interferon (INF-gamma) was recorded 3 weeks after challenge. At necropsy, the mean number of flukes recovered was similar in both infected groups, suggesting that the rate at which the infection is administrated has no effect on protective immunity. Hepatic lesions, similar in both infected groups, were characterised by marked eosinophil and mast-cell infiltration. Liver biopsies were performed and their diagnostic value is discussed. All results suggest that F. hepatica infection predominantly induces a Type-2 response in cattle, and that this response has little protective effect.  相似文献   

6.
A characterization of the humoral immune response of alpacas to Fasciola hepatica Fas1 and Fas2 antigens, two abundant cysteine proteinases in the excretory/secretory (E/S) products, was performed over the course of 6 months of experimental infection. Six adult alpacas aged 1-2 years old received a single dose of 200 F. hepatica metacercariae; two non-infected alpacas were kept as control group. All infected animals shed eggs 8 weeks post-infection (PI) and the number of flukes recovered at necropsy averaged 41+/-4. The livers of infected animals showed regions with chronic inflammation, granuloma containing parasite eggs, necrosis and cirrhosis. Peripheral eosinophilia in infected animals was greatly enhanced 6 weeks post-infection and later. A single peak of serum glutamic piruvic transaminase (SGPT) was observed 4 weeks PI and serum glutamic oxalacetic transaminase (SGOT) elevated 3 weeks PI and later. Circulating IgG Abs against Fas1 and Fas2 were measured by enzyme-linked immunosorbent assay (ELISA). Fas2-ELISA detected the infection 10 days PI reaching to highest titer on 7-8 weeks PI and kept elevated, until the end of infection. Fas1-ELISA detected the infection 2 weeks PI and followed the same pattern as Fas2-ELISA. Anti Fas2 IgG Abs were in higher titers and showed stronger avidity than anti Fas1 IgG Abs. In addition, rabbit IgG antibodies raised against cysteine proteinase Fas2 showed infiltration of this parasite antigen associated to the degradation of bile ducts and liver parenchyma of infected alpacas. In the present study we have established a F. hepatica experimental infection of alpacas, Fas2 appears to have a role in the pathogenesis of the liver damage in alpacas caused by the liver fluke. Infected alpacas elicited a strong humoral immune response against fluke cysteine proteinases Fas1 and Fas2, which might be considered as candidates for immunodiagnosis and vaccine development against fasciolosis in alpacas.  相似文献   

7.
Despite intensive research efforts, progress in the development of effective anti-Fasciola hepatica vaccine has not been satisfactory. However, it has been found that cysteine proteinases of F. hepatica are very important candidates for a vaccine antigen because of their role in fluke biology and in the host-parasite relationship. In our previous experiments we found that recombinant cysteine proteinase which we have cloned from adult F. hepatica (CPFhW) can protect rats against the liver fluke infection when administered intramuscularly or when given intranasally in the form of cDNA. In the present experiments we aimed to evaluate the protectivity of the mucosal vaccination in calves and lambs with inclusion bodies containing recombinant CPFhW using different vaccination doses and various sites of antigen delivery. Female calves vaccinated intranasally with two doses of 300 microg of the recombinant CPFhW showed 54.2% protection against the subsequent challenge of 400 metacercariae (mc). Flukes which developed in vaccinated calves showed a reduction of reproductive potential. Male Corriedale lambs vaccinated at the age of 4 months demanded three doses of the antigen to gain 56.5% of protection to a challenge with 250 mc of F. hepatica. Vaccinated animals showed significantly lower blood eosinophil counts. No correlation was found between serum and mucosal IgG or IgA reacting with F. hepatica ES antigens and the protection level.  相似文献   

8.
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.  相似文献   

9.
In cattle experimentally infected with Fasciola hepatica, parasite specific IgG1 and IgG2 responses were studied. Additionally parasite specific IgE production was assessed by the Passive Cutaneous Anaphylaxis reaction. The primary infection was administered either as a single-dose or as a trickle infection over a 4-week period. Animals were challenged 4 months later. Titres of IgG1 and IgG2 against excretory-secretory parasite products (FhESAg), and against a whole-worm extract (FhSomAg) were measured by enzyme-linked immunosorbent assay (ELISA) in relation to weight gain, serum hepatic enzyme levels, and fluke infection rate. At necropsy, the mean number of flukes recovered was similar in both infected groups. The two ELISAs specific for bovine IgG1 showed analogous sensitivity and specificity (92% and 94%). Cross-reactivity was observed towards Echinococcus granulosus, Cysticercus tenuicollis, and C. ovis but not towards C. bovis, Cooperia spp., and Ostertagia spp. FhESAg gave rise to apparently more stable specific IgG1 titres as compared to FhSomAg. Mean IgG1 titres were significantly higher in the single-dose-infected group than in the trickle-infected group during the early migratory phase of the infection (week 2 to week 4 (FhSomAg) or week 6 (FhESAg)). IgG2 values were consistently lower than IgG1 levels. The kinetic response of both isotypes yielded a similar pattern. Specific IgE antibodies were detected in cattle of both infected groups from week 2 post-primary infection (PPI) onwards. The mean serum glutamate dehydrogenase (GLDH) and gamma-glutamyl transferase (gammaGT) activities were significantly higher in the single-dose-infected group for 3 weeks around peak levels (12-14 weeks PPI and 14-16 weeks PPI for GLDH and gammaGT respectively). Western blotting revealed a major antigenic fraction in FhESAg (26-30 kDa) recognized specifically by sera from F. hepatica infected calves as early as 6-8 weeks PPI. Experimental challenge caused no statistically significant modification of any parameter (IgG1 and IgG2 titres, enzymatic activities, immunoblotting) used to monitor the course of the infection. No correlation was found between fluke size and number, and antibody titres, suggesting that IgG1 production has little protective effect against F. hepatica infection.  相似文献   

10.
Antibody and lymphocyte proliferative responses to fluke antigens were compared in rats and cattle following infection with Fasciola hepatica. Antibody responses differed between rats and cattle in that rats responded more quickly and with a greater rate of synthesis over the first three weeks of infection than did cattle. Lymphocyte proliferative responses developed and disappeared at similar times in both cattle and rats, being detectable early in infection, but returning to background levels by week 6 after infection. The presence of antibody but not of lymphocyte proliferative responses correlated with the timing of the development of resistance in cattle and rats as described by others. Sensitisation by intraperitoneal injection of fluke antigens in Freund's incomplete adjuvant (FIA) induced antibody production but not lymphocyte proliferative responses in both rats and cattle. Serum antibodies continued to rise after oral infection of sensitised animals although this was much more marked in the cattle than in the rats. On the other hand lymphocyte proliferative responses were absent when sensitised cattle were infected, while the findings with rats were much more variable. Cattle sensitised by intraperitoneal injection of fluke antigens in FIA were not protected against subsequent infection with F hepatica.  相似文献   

11.
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.  相似文献   

12.
The use of cysteine proteinases from Fasciola hepatica adult flukes for the serodiagnosis of caprine fasciolosis by means of an indirect ELISA test was studied. Two proteolytic fractions from adult fluke homogenates, with apparent molecular weights of 28 and 34 kDa (P28 and P34 respectively), were characterised as cysteine proteinases using azocasein assays and gelatin gel analysis. Both P28 and P34 fractions were electroluted and used as antigens in two different indirect ELISA tests. Serum IgG levels against P28 and P34 in goats given an experimental primary infection with 200 metacercariae or in goats given two experimental infections with 200 metacercariae were determined and compared with those observed in an uninfected control group. ELISA tests using both cysteine proteases showed a rapid and consistent detection of specific IgG in all experimentally infected goats. The IgG response to P28 was the first to be detected as early as 2-3 weeks post-infection and remained elevated throughout the experiment. The response to P34 was detected later (4-6 wpi) and disappeared in some animals at 18 wpi, while flukes were still present in the bile ducts. No significant differences were observed between the anti-P28 and anti-P34 IgG responses between animals receiving a primary or a challenge infection. The results of our study, although preliminary, are promising since the P28 ELISA described here may be a reliable method for the immunodiagnosis of F. hepatica infection in goats.  相似文献   

13.
The effect of Fasciola hepatica parasite burden on the detection of excretory/secretory (E/S) antigens in sera and feces of experimentally infected sheep was evaluated using a double antibody-based capture enzyme-linked immunosorbent assay (ELISA). Four groups of five sheep each were used. The first three groups were infected with 50, 100 and 200 metacercariae of F. hepatica, and the fourth group remained as non-infected control. On the day of infection and weekly thereafter, serum and fecal samples were taken. ELISA detected F. hepatica E/S antigen levels in serum from the first week post-infection (wpi) and in fecal supernatant from the fourth wpi, which were significantly (p<0.05) higher than controls. F. hepatica eggs were not detected until after the eighth wpi. The correlation between absorbance of E/S antigens in serum with the fluke burden was 0.77 (p<0.0001) and in feces 0.76 (p<0.0001) at 12th wpi. The sensitivity of the assay to detect E/S antigens in serum was 86.6% and in feces 93.3%. It is concluded that the ELISA technique used in this study offers a diagnostic alternative for detecting early infections of F. hepatica in sheep.  相似文献   

14.
The turbidimetric analysis of IgG(T) in the serum of horses is described. Reference values are provided for 'worm-free' ponies (2.6 +/- 0.7 g/litre), stabled Thoroughbreds two years old and over (4.1 +/- 1.3 g/litre), grazing Thoroughbred broodmares (7.1 +/- 2.4 g/litre) and regularly wormed adult and young ponies grazing pasture contaminated with intestinal parasite eggs and larvae.  相似文献   

15.
Transmission of Mycobacterium avium subspecies paratuberculosis, the organism responsible for paratuberculosis (or Johne's disease) in ruminants, occurs through the faecal-oral route. As M. a. paratuberculosis has been isolated from rabbit faeces, cattle grazing rabbit faecal contaminated pasture may thus be at risk.A herd of 57 beef cattle was monitored on a farm in Perthshire, throughout the 1999 'grazing year', to investigate whether the cattle avoided rabbit faecal contaminated pasture and thus the potential for disease transmission. Grazing was measured every two days over eight rotations by sward heights on 40 marked treatment plots (0.5 m x 0.5 m) to which 0, 10, 50 and 250 rabbit faecal pellets were added. Cattle were also monitored by an active transponder system which enabled individual animals contacting two plots per field rotation (one control and one contaminated) to be recorded. During the monitored grazing year, grazing pressure was low with a net mean sward offtake of 18% of sward height per rotation. There were no significant differences between rabbit faecal treatments (0, 10, 50 and 250 pellets) with respect to the height or proportion of sward removed, or between the numbers of contacts made by cattle on contaminated and uncontaminated plots. Over 90% of all the cattle contacted contaminated plots, indicating that the potential for disease transmission was widespread among the herd.To our knowledge, this is the first reported instance of a lack of avoidance by grazing cattle towards swards contaminated with faeces, and implies that the potential for transmission of paratuberculosis from rabbit contaminated pasture is high.  相似文献   

16.
The potential of a recombinant Schistosoma bovis 28-kDa glutathione S-transferase (rSb28GST) to protect cattle against Fasciola hepatica was tested in a vaccination trial. Thirty two calves were randomly divided into four groups of eight animals. Calves of the three vaccine groups received two intramuscular injections at 3 weeks interval, of 0.250mg rSb28GST in either aluminium hydroxide (Al(OH)(3)), Quil A, or PBS emulsified in an equal volume of Freund's complete adjuvant (FCA).Animals of the control group received injections of Al(OH)(3)/PBS only. All animals were challenged orally with a total of 360 metacercariae of F. hepatica, spread over 6 weeks.All groups of vaccinated animals produced measurable IgG antibody titers to rSb28GST after vaccination. Animals immunised with FCA adjuvanted vaccine had the highest and more durable antibody titers and only sera from this group recognised an approximately 24kDa protein band from F. hepatica, that is thought to be a F. hepatica GST. Despite a good antibody response differences in cumulative faecal egg output between the groups were not statistically significant. In addition, no significant difference was found between groups in terms of total worm numbers or percentage of immature flukes recovered at necropsy. In conclusion, the recombinant S. bovis 28kDa GST was not found to adequately protect cattle against experimental F. hepatica challenge, using either aluminium hydroxide, Quil A or FCA as adjuvant.  相似文献   

17.
In a dosage-confirmation trial, anthelmintic activities of clorsulon and albendazole against Fasciola hepatica were evaluated and compared. Twenty-eight cattle (8 to 12 months old) with natural F hepatica infections were randomly allotted to 4 groups of 7 cattle each: group 1, no treatment (controls); group 2, clorsulon suspension given orally at 3.5 mg/kg of body weight; group 3, clorsulon suspension given orally at 7 mg/kg; and group 4, albendazole paste given orally at 10 mg/kg. At necropsies, performed 7 and 8 days after treatment, control cattle harbored a geometric mean of 133.2 F hepatica, 16.0 of which were immature. Clorsulon administered at 3.5 mg/kg or 7 mg/kg resulted in greater than 99% removal of F hepatica, including immatures. Albendazole treatment resulted in a 76% overall reduction in F hepatica, including a 91% reduction of immatures. Fascioloides magna also were found in the cattle, but neither clorsulon nor albendazole caused significant reductions of the parasite. Adverse reactions to the 2 drugs were not observed.  相似文献   

18.
Diagnostic antigens in bile and feces from Fasciola hepatica infected cattle were detected and characterized by enzyme-linked immunotransfer blot (EITB) techniques. As sources of antigen, samples of bile, intestinal contents and feces were collected from five uninfected calves and from 10 calves with known Fasciola hepatica burdens. A band detected by EITB using a densitometer in the area corresponding to 26 kDa reacted with rabbit anti-fresh fluke antigen and infected cattle sera but not with fluke-negative rabbit sera, rabbit anti-Fasciola hepatica egg sera, Fascioloides magna positive or negative cattle sera. This band was not detected by Coomassie blue in sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) gels or by Ponceau-S stained nitrocellulose strips. Band groups located at 104-66, 66-42, 42-26 and 25-16 kDa reacted inconsistently with the above sera. Sera from mice hyperimmunized with Fasciola hepatica excretory-secretory (ES) products detected only the 26 kDa band by EITB, without cross-reactivity with bands in the other molecular weight (MW) ranges. The results suggest that the 26 kDa antigen may consist of a stable component of ES products and/or tegument-related worm antigen. Diagnosis of Fasciola hepatica through detection of specific, stable antigens in feces of infected animals offers potential advantages over serum-based tests of better sample accessibility, discrimination between previous and current infections, and possible semi-quantitation of fluke burdens.  相似文献   

19.
Two groups of yearling cattle which had been treated with ivermectin either three and eight, or three, eight and 13 weeks after turn out to trichostrongyle contaminated pasture in their first grazing season were exposed in the following season to natural challenge with helminth parasites. To assess their immunity to this challenge each group shared a pasture with parasite naive first season calves. No anthelmintic treatments were administered at any time during the year. Throughout the grazing period the yearlings showed normal respiratory rates, negative faecal lungworm larval counts, and, relative to the calves, low faecal trichostrongyle egg counts. All the first season calves developed patent lungworm infections and on one occasion the mean respiratory rates of each group of calves were significantly greater than those of the yearling cattle. At the end of the grazing period, from early May until late September or October 1986, the cattle were removed from pasture and together with parasite naive controls challenged with either 10 or 22 third stage larvae of Dictyocaulus viviparus/kg bodyweight and necropsied between 18 and 23 days later. Although the experimental challenge resulted in relatively heavy lungworm infection of the naive controls, none of the yearlings and only three of the 11 calves which had been at pasture were found to be infected. However, large numbers of arrested fourth stage larvae of Ostertagia ostertagi were present in all the naturally infected yearlings and calves.  相似文献   

20.
Two experiments compared the protection against oral challenge with 20 metacercariae of Fasciola hepatica conferred on rats by intraperitoneal injection of serum from three breeds of sheep infected with F. hepatica (Barbados Blackbelly, St. Croix, Florida Native). Experiment 1 used serum from sheep 5-6 months of age following two infections of 250 metacercariae each, while Experiment 2 utilized serum collected from the same sheep at 10-11 months of age following either a primary (first exposure) or challenge (after two previous exposures of 250 metacercariae each) infection with 500 metacercariae. Similar numbers of flukes were recovered from rats given either immune or nonimmune (control) serum from each breed of sheep in Experiment 1. In Experiment 2, rats given serum from infected St. Croix sheep had significantly fewer flukes than rats given either control or immune serum from Barbados Blackbelly or Florida Native sheep. There was no significant correlation of fluke counts between individual serum donors (sheep) and serum recipients (rats).  相似文献   

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