Induction of protective antibody response in rabbits against fascioliasis with Toxocara/Fasciola cross- reactive defined antigen

A method of affinity chromatography purification of Toxocara vitulorum antigen cross- reacts with Fasciola gigantica antiserum is described. Characterization of the isolated cross- reactive fraction by SDS-polyacrylamide gel electrophoresis, isoelectric focusing and amino acid analysis resulted in a fraction consists of five polypeptides of 137.7KDa, 81KDa, 75KDa, 48KDa and 21.6KDa with isoelectric points of 8, 7.5, 7.2, 6.7 and 6.6. Seventeen amino acids were identified in the fraction with high proportions of only two of them (tyrosine and glutamic). Rabbits immunization with this identified T. vitulorum cross- reactive antigen in Freund's adjuvant followed by challenge with F. gigantica metacercariae resulted in 60% reduction in worm burden over control infected rabbits. Higher IgG level was detected in vaccinated rabbits four weeks post first immunization than control infected ones and remained high up to the end of the trial.

Vaccination of mice and sheep with Fh12 FABP from Fasciola hepatica using the new adjuvant/immunomodulator system ADAD

We evaluate the ability of a Fasciola hepatica FABP native antigen (Fh12) with a new vaccination system called ADAD to protect mice and sheep against an experimental F. hepatica infection. The vaccination protocol consists of a set of two injections. The first injection contains a micelle in which two components are included, saponin from Quillaja saponaria (Qs) and/or Anapsos (A) a Polypodium leucotomos hydroalcoholic extract, both emulsified in a non-mineral oil (Montanide) in a water/oil emulsion (30/70). This is subcutaneously injected to achieve the "adaptation" of the immune system to subsequent stimuli. The second injection contains in addition the Fh12 antigen. Two different experiments were carried out using two mouse strains (BALB/c and CD-1). Mice vaccinated with Qs+A+Fh12 presented a survival rate of 40%, when compared with control groups. Furthermore, we evaluated the efficiency of the vaccination in sheep against an experimental F. hepatica challenge. The vaccinated sheep presented lower fluke recovery (24.5%), number of eggs in bile fluid (58.1%) and faeces (40.3%) than control groups. The recovered flukes were shorter (32.7%), immature (34.0%) and with lower body mass (31.6%) than non-complete vaccinated sheep. Thus, the new ADAD system could be a good alternative for future vaccination experiments against fasciolosis.

A novel Fasciola hepatica saposinlike recombinant protein with immunoprophylactic potential

A member of the Fasciola hepatica saposinlike/NK-lysin protein family with lytic activity on human peripheral blood mononuclear cells and erythrocytes was recently described. The current study was designed to test the immunoprophylactic potential of this protein termed FhSAP-2 against infection with F. hepatica in rabbits. Two doses of 50 microg of recombinant FhSAP-2 (rFhSAP-2) emulsified in TiterMax were injected subcutaneously on the dorsal surface of 4 rabbits at 2-wk intervals. Four weeks after the second immunization, the rabbits were infected orally with 25 F. hepatica metacercariae. Four non-immunized-infected rabbits were used as controls. An enzyme-linked immunosorbent assay revealed high levels of antibodies to both rFhSAP-2 and F. hepatica excretory-secretory antigens by 2 wk after the first immunization, which were always significantly higher in immunized-infected rabbits than in control-infected rabbits. On the completion of the trial, vaccinated rabbits had 81.2% less flukes than controls. Moreover, F. hepatica egg counts in feces, as well as in bile collected from the gall bladders from vaccinated animals, were lower, 83.8 and 73%, respectively, compared with controls. The vaccinated rabbits also had significantly lower amounts of parasite antigen in stool and bile samples than controls. Last, evaluation of macroscopic liver lesions revealed that the rabbits vaccinated with rFhSAP-2 had milder lesions than the infected-control rabbits. These findings support the hypothesis that this novel rFhSAP-2 protein has immunoprophylactic potential against fascioliasis in rabbits including antifecundity and antipathology effects. This is the first report on experimental vaccination of rabbits against F. hepatica with a purified, defined, recombinant protein related to a member of the saposinlike protein family.

Fasciola gigantica: immunization of rabbits with proteins isolated from coproantigen

Two fractions were isolated from coproantigen by ion-exchange chromatography in which DEAE cellulose was utilized. Both fractions and crude antigen were characterized by SDS-polyacrylamide gel electrophoresis which revealed 13 bands of molecular weight ranged from 205-31 in crude coproantigen. While fraction I resolved into six bands of molecular weight 198, 178, 148, 111, 101 & 45. Fraction II showed seven bands of 191 KDa, 178KDa, 166KDa, 118KDa, 98.5KDa, 72KDa & 32KDa. Fraction 1I was higher immunoreactivity than fraction by ELISA. Three immunoreactive bands of 191KDa, 118KDa & 98.5KDa were identified in fraction II using immunoblot assay. Five bands of 178KDa, 148KDa, 111KDa, 101KDa & 45KDa were detected in fraction I. Immunization of rabbits twice with fraction II in Freund's adjuvant with two weeks interval followed by challenge with F. gigantica metacercariae resulted in 66.6% protection from infection. The protection was assessed by detect-ion of hepatic damage, worm recoveries and antibody response. High level of IgG response in vaccinated rabbits than control infected ones occurred and being responsible for the recorded protection.

Behavioural responses of the snail Lymnaea acuminata to carbohydrates in snail-attractant pellets

Snail control is one of the most important tools in the campaign to reduce the incidence of fascioliasis. In order to attain this objective, the method of bait formulation in order to contain an attractant and a molluscicide is an expedient approach to lure the target snail population to the molluscicide. This study identifies certain carbohydrates, namely sucrose, maltose, glucose, fructose and starch, for preparing such baits. These were tested on Lymnaea acuminata, an intermediate host of the digenean trematodes Fasciola hepatica and Fasciola gigantica. The behavioural responses of snails to these carbohydrates were examined. Significant variations in behavioural responses were observed in the snail even when the five carbohydrates were used in low concentrations in snail-attractant pellets. Starch emerged as the strongest attractant for Lymnaea acuminata, followed by maltose.

An experimental bivalent peptide vaccine against schistosomiasis and fascioliasis

With a view to producing peptides capable of inducing a protective immune response against Schistosoma mansoni and Fasciola hepatica, the sequence and structure of the protective antigens Sm14 and Fh15 were analyzed. Their C-termini showed a high level of sequence conservation which, together with models for their three-dimensional structures, aided in peptide selection. Vaccination trials in Swiss mice challenged with S. mansoni cercaria or F. hepatica metacercaria showed that peptides which included the sequences VTVGDVTA or EKNSESKLTQ were capable of inducing levels of protection equivalent to the recombinant form of Sm14. These peptides may represent an alternative to r-Sm14 for the development of a bivalent anti-helminth vaccine.

Immunization of rats against Fasciola hepatica using crude antigens conjugated with Freund's adjuvant or oligodeoxynucleotides

Chronic Fasciola hepatica infection is correlated with the development of a T helper (Th2)-predominant immune response. To determine whether immunostimulatory CpG-containing oligodeoxynucleotides (CpG-ODN) or Freund's complete adjuvant (FCA), known to promote a Th1 (T helper 1) immune responses, could provide protection from F. hepatica infection, total homogenate (TH) of F. hepatica mixed with CpG-ODN or FCA were injected subcutaneously (s.c.) into Wistar rats. A F. hepatica-specific Th1-predominant immune response was induced with CpG-ODN or FCA in lymph nodes of immunized animals. Lymph node cells from TH-CpG-ODN or TH-FCA immunized rats showed increased antigen-specific proliferation with high levels of INFgamma, compared to lymphocytes from rats injected with TH alone. In contrast, these two groups of immunized animals did not modify IL-4 release by draining lymph node cells, when they were subsequently stimulated with TH in vitro. However, a significant reduction in the burden of flukes (76.7%) was only observed in rats immunized with TH-FCA. Conversely, immunization of rats with TH-CpG-ODN did not promote protection against the parasite. Therefore, even though CpG-ODNs and FCA induced Th1 type responses, only FCA provided a significant protection to rats infected with F. hepatica.

Cloning and expression of the major secreted cathepsin B-like protein from juvenile Fasciola hepatica and analysis of immunogenicity following liver fluke infection

The functions of the cathepsin B-like proteases in liver flukes are unknown and analysis has been hindered by a lack of protein for study, since the protein is produced in small amounts by juvenile flukes. To circumvent this, we isolated and characterized a cDNA encoding the major secreted cathepsin B from Fasciola hepatica. The predicted preproprotein is 339 amino acids in length, with the mature protease predicted to be 254 amino acids long, and shows significant similarity to parasite and mammalian cathepsin B. Only one of the two conserved histidine residues required for cathepsin B exopeptidase activity is predicted to be present. Recombinant preproprotein was produced in yeast, and it was shown that the recombinant proprotein can undergo a degree of self-processing in vitro to the mature form, which is active against gelatin and synthetic peptide substrates. The recombinant protein is antigenic in vaccinated rats, and antibodies to the protein are detected early after infection of rats and sheep with F. hepatica. The kinetics of the response to cathepsin B and cathepsin L after infection of sheep and rats confirm the temporal expression of these proteins during the life cycle of the parasite.

[Flow cytometry analysis of leukocytes response in rats immunized and infected with Fasciola hepatica]

Flow cytometry analysis of leukocytes response in rats immunized and infected with Fasciola hepatica. In the present experiment the differences in blood leucocytes between rats immunised intranasally with cDNA encoding F. hepatica GST, challenged with the parasite (group 1) and non-immunised infected rats (group 2) were compared. The number of leukocytes were estimated by flow cytometry on the 1, 5, 9 week after infection. Changes in the level of blood lymphocytes and monocytes were similar, with an increasing tendency in both groups. The level of eosinophils decreased to the 9th week after infection in both groups, however the number of these cells was seven times higher in control rats than in immunised rats.

Fasciola hepatica cathepsin L-like proteases: biology, function, and potential in the development of first generation liver fluke vaccines

Fasciola hepatica secretes cathepsin L proteases that facilitate the penetration of the parasite through the tissues of its host, and also participate in functions such as feeding and immune evasion. The major proteases, cathepsin L1 (FheCL1) and cathepsin L2 (FheCL2) are members of a lineage that gave rise to the human cathepsin Ls, Ks and Ss, but while they exhibit similarities in their substrate specificities to these enzymes they differ in having a wider pH range for activity and an enhanced stability at neutral pH. There are presently 13 Fasciola cathepsin L cDNAs deposited in the public databases representing a gene family of at least seven distinct members, although the temporal and spatial expression of each of these members in the developmental stage of F. hepatica remains unclear. Immunolocalisation and in situ hybridisation studies, using antibody and DNA probes, respectively, show that the vast majority of cathepsin L gene expression is carried out in the epithelial cells lining the parasite gut. Within these cells the enzyme is packaged into secretory vesicles that release their contents into the gut lumen for the purpose of degrading ingested host tissue and blood. Liver flukes also express a novel multi-domain cystatin that may be involved in the regulation of cathepsin L activity. Vaccine trials in both sheep and cattle with purified native FheCL1 and FheCL2 have shown that these enzymes can induce protection, ranging from 33 to 79%, to experimental challenge with metacercariae of F. hepatica, and very potent anti-embryonation/hatch rate effects that would block parasite transmission. In this article we review the vaccine trials carried out over the past 8 years, the role of antibody and T cell responses in mediating protection and discuss the prospects of the cathepsin Ls in the development of first generation recombinant liver fluke vaccines.

Failure of a recombinant Schistosoma bovis-derived glutathione S-transferase to protect cattle against experimental Fasciola hepatica infection

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.

[Fascioliasis: diagnosis, epidemiology and treatment]

Fascioliasis is a trematode, disease of liver and bile ducts of sheep, cattle, and other ruminants throughout the world that is caused by the fluke, Fasciola hepatica. Human infection has been reported in Mexico, Cuba, Puerto Rico, Chile, Peru, Uruguay, Brazil, Argentina, the US, Europe, eastern Africa, Japan and Australia. The parasite's miracidium invades one of the various Lymnaea water snail hosts. Infection results from ingestion of encysted metacercariae attached to raw watercress (Nasturtium officinale). Symptoms recorded from human cases included irregular fever, epigastric pain and abdominal tenderness, obstructive jaundice and leucocytosis with eosinophilea up to 60%. Specific diagnosis is based on recovery of the eggs in the patient's stool or from biliary tract drainage. Treatment is with emetine hydrochloride given intramusculary. Bithionol is given orally at a dosage of 30-50 mg/kg but on alternate days from 10 to 15 doses. Praziquantel is probably effective. Preventive measures include education of the public on mode of transmission of life cycle of the parasite, and dipping fresh watercress into boiling water for a few sec, or drying suspected watercress.

Vaccination against Fasciola hepatica infection using a Schistosoma mansoni defined recombinant antigen, Sm14

Fasciola hepatica is the causative agent of fasciolosis in many areas in America, Europe, Africa, Asia and Australia. There is an urgent need for improved methods to control the parasite's transmission. We describe the use of an experimental vaccine based on a recombinant antigen cloned from another parasite, Schistosoma mansoni (Sm14), that induces high levels of cross protection in mice against both S. mansoni and F. hepatica. Sheep and mice vaccinated with Sm14 were significantly protected against challenge infection with metacercariae of Fasciola hepatica and were completely free of the histopathological hepatic damage related to liver fluke infection. The vaccine will provide a valuable new tool to aid in transmission control of this economically important disease.

Pathological and immunohistochemical study of the liver and hepatic lymph nodes of sheep chronically reinfected with Fasciola hepatica, with or without triclabendazole treatment

Hepatic lesions and changes in the hepatic lymph nodes were examined in groups of sheep infected, and sometimes reinfected, with metacercariae of Fasciola hepatica, with or without treatment with triclabendazole (TCBZ). Hepatic damage was more severe in sheep given small repeated ("trickle") infections than in those given two larger, spaced doses. Inflammatory infiltrates of eosinophils, CD3+ T cells, CD79 alpha+ B cells and IgG+ plasma cells, and the presence of granulomata, were particularly marked in trickle-infected groups, suggesting that the host response to certain fluke or egg antigens causes severe hepatic damage. TCBZ administration induced the elimination of flukes and healing of the majority of hepatic lesions but did not prevent severe hepatic damage produced by later infections.

Unusual snail species involved in the transmission of Fasciola hepatica in watercress beds in central France

Four freshwater pulmonate species (Lymnaea ovata, L. stagnalis, Physa acuta, Planorbis leucostoma) were living in several watercress beds known for their relationships with human cases of fasciolosis, whereas L. truncatula was never found. The aims of these studies were to determine the prevalence of natural infections with Fasciola hepatica in snails and to verify if these species might ensure the full larval development of this trematode (with cercarial shedding) when they were experimentally subjected to F. hepatica only, or to co-infections with an other trematode species. Investigations were so carried out in six snail populations living in watercress beds (including three for P. acuta) and in four others originating from three brooks or a pond (as controls). Snails naturally infected with F. hepatica were found in two watercress beds inhabited by L. ovata (prevalence of infection: 1.4%) and P. leucostoma (0.1%), respectively. The L. ovata from the watercress bed could be infected at a higher size than those from the control population and the prevalence of this infection was greater in the bed population. Similar findings were noted for L. stagnalis. Despite single or dual infections, the results obtained with the four populations of P. acuta were unsuccessful. In contrast, the co-infections of young P. leucostoma with Paramphistomum daubneyi and F. hepatica resulted in the shedding of some F. hepatica cercariae. According to the authors, the occurrence of fasciolosis in these watercress beds would be the consequence of frequent natural encounters between parasite and snails (L. ovata, L. stagnalis), or of co-infections with P. daubneyi and F. hepatica (P. leucostoma). In watercress beds only colonized by P. acuta, a lymnaeid species would have ensured the larval development of F. hepatica but it would have been eliminated by P. acuta, as this last species was known to be invasive and could colonize open drainage ditches on siliceous soil.

Immunization of sheep against Fasciola gigantica with glutathione S-transferase

Glutathione S-transferase in Fasciola gigantica (FgGST) was isolated by affinity chromatography, by which highly purified enzyme was obtained. FgGST on the SDS-PAGE showed three protein bands ranging 24.5-26.5kDa. Glutathione S-transferase (GST) activity was determined by HABIG method. FgGST was evaluated as vaccine alone or in combination with either aluminum hydroxide or saponin in sheep against F. gigantica infection. ELISA was used for detection of anti-FgGST IgG. After vaccination, all sheep were challenged with 120 metacercaria of F. gigantica. The results indicated that anti-GST IgG was not elevated after challenge. All sheep were slaughtered 24-26 weeks after challenge. The results indicated that, although after second vaccination, antibody titers rose markedly in GST-Al(OH)(3) and GST-saponin groups, but declined 4 weeks after challenge. No correlation between anti-GST IgG titers and protection was observed. The highest fluke burden reduction was observed in the group vaccinated with GST-saponin (32%), but this reduction was not statistically significant in comparison with the control group.

Passive protection against fasciolosis in mice by immunization with a monoclonal antibody (ES-78 MoAb)

Recently, we reported a partial characterization of the epitope recognized by the ES-78 monoclonal antibody (MoAb). This monoclonal antibody was obtained from spleen lymphocytes of a mouse immunized with excretory-secretory antigens of Fasciola hepatica adult worms. In the present study, we report the results obtained in experiments of passive protection using this MoAb in BALB/c mice infected with 15 Fasciola hepatica metacercariae. The monoclonal antibody was able to reduce the parasite burden when administered 24 h before challenge but not when delivered 7 days after challenge. The antibody recognition of digestive tract structures in 3-week-old parasites was demonstrated by immune histochemical techniques. The antigens purified by affinity chromatography using this antibody had molecular weights of 14-20, 25-29 and 36-45 kDa and demonstrated proteinase activity similar to cathepsin L. These results suggest that the antigens carrying the epitope recognized by the ES-78 MoAb may be used as target in the protection against fasciolosis.

[The immune response of various species to Fasciola hepatica infection]

The trematode F. hepatica is an internal parasite of many species of animals including men. In ruminants, fasciolosis is an economically important disease often resulting in a chronic and sub-clinical infection. The mechanisms of immune responses of final hosts to this infection are still poorly understood. Experimental and clinical studies reported so far suggest that both humoral and cellular effectors of the immune response are important to control the duration of F. hepatica infection. However, there are considerable variation both inter-species and between various strains of the same species in regulation of the response as well as abilities to develop resistance to subsequent infections.

Treatment vs non-treatment of helminth infections in cattle: defining the threshold

Helminth infections are an important cause of lost productivity in livestock world-wide, often necessitating anthelmintic treatment. However, a large part of the anthelmintics are used indiscriminately because the parasite levels are too low to justify treatment or because the treatments are not correctly programmed, resulting in undertreatment or overtreatment. The objective of this paper is to discuss possible thresholds for anthelmintic treatment of some of the more important helminth infections in livestock, i.e. gastrointestinal nematodes, lungworms and liver fluke, to promote a more appropriate use of anthelmintics. When possible, a distinction is made between therapeutic thresholds, production-based thresholds and preventive thresholds. A "therapeutic threshold" is intended to identify (an) animal(s) with parasite levels that necessitate immediate treatment. The therapeutic threshold is basically the diagnosis of clinical disease, and can be determined relatively easily for the parasites discussed in this paper. A "production-based threshold" is intended to measure the effects of sub-clinical parasitism on productivity parameters, such as weight gain and milk yield, before clinical disease occurs. Finally, a "preventive threshold" is meant to predict future infection levels, to enable the application of appropriate control measures.

Immunoprophylaxis against Fasciola hepatica in rabbits using a recombinant Fh15 fatty acid-binding protein

Previous studies of ours have demonstrated that a recombinant protein (Fh15) related to fatty acid-binding proteins did not induce significant protection in rabbits challenged 2 or 4 wk postimmunization over nonimmunized controls. In the current study, rabbits were immunized with Fh15 and challenged with Fasciola hepatica metacercariae 12 and 20 wk later. In the current study in which longer lag periods for challenge infection after the second immunization were used, worm burden reductions compared to adjuvant controls were a significant 43% and 76%, respectively. Importantly, rabbits immunized with Fh15 had significant numbers of immature flukes, 66% in the 12-wk period and 84% in the 20-wk lag period as compared to controls. In addition, liver lesions were clearly diminished in the vaccinated rabbits. Enzyme-linked immunosorbent assay absorbance values showed that immunized rabbits developed high antibody levels to Fh15 from 8 wk after the first immunization and did not increase after challenge. These results suggest that a recombinant F. hepatica molecule related to fatty acid-binding proteins induces protective (worm burden reductions), anti-fecundity (immature flukes), and anti-pathology (less liver lesions) effects in rabbits and may serve as a model for the immunoprophylaxis of fascioliasis.

Vaccination of sheep against Fasciola hepatica with homologous fatty acid binding proteins

The current study was designed to test the immunoprophylactic properties of native (nFh12) and recombinant (rFh15) antigens from Fasciola hepatica in sheep subsequently infected with the fluke. Thirty lambs were divided into six groups according to various patterns of immunisation and times of infection and necropsy. The antigens were emulsified in Freund's adjuvant. Levels of specific anti-nFh12 and anti-rFh15 antibodies rose rapidly by 2 weeks after the first immunisation and were always significantly higher in immunised-infected sheep than in control-infected sheep. On completion of the trial there was no difference in fluke burden between groups vaccinated with either of the antigens and non-immunised controls. However, worm size and faecal egg counts were significantly diminished in the sheep vaccinated with either of the antigens, suggesting an anti-fecundity effect. This is the first report of experimental vaccination of sheep against F. hepatica with purified native and recombinant antigens related to fatty acid binding proteins.

Effects of parenteral administration of doramectin or a combination of ivermectin and clorsulon on control of gastrointestinal nematode and liver fluke infections and on growth performance in cattle

OBJECTIVE

To compare effects of an injectable doramectin preparation with those of an injectable ivermectin-clorsulon preparation on control of gastrointestinal nematodes and liver flukes and on growth performance in cattle.

DESIGN

Randomized complete block design.

ANIMALS

60 crossbred calves.

PROCEDURES

Calves (20/treatment group) were treated with doramectin or ivermectin-clorsulon or were not treated. Fecal samples were collected for nematode and Fasciola hepatica egg counts on day 0 and for up to 140 days after treatment. Cattle were weighed before treatment and at 28-day intervals until day 140.

RESULTS

From day 7 through day 49, nematode egg counts for calves treated with doramectin or with ivermectin-clorsulon were significantly lower than those for untreated control calves. As the study progressed beyond day 56, the percentages of cattle with fluke eggs in their feces increased, but differences in regard to these percentages were not detected among the 3 groups. Average daily gain for the doramectin-treated cattle (0.79 kg/d [1.74 lb/d]) was significantly greater than that for the cattle treated with ivermectin-clorsuIon (0.71 kg/d [1.56 lb/d]); values for both groups were significantly greater than that for the control cattle (0.62 kg/d [1.37 lb/d]).

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that doramectin had a greater impact on subclinical gastrointestinal tract parasitism in calves, as demonstrated by growth performance, than did ivermectin-clorsulon. In the Gulf Coast region of the United States, spring-born nursing beef calves may have minimal grazing exposure to F hepatica during the peak fluke transmission period; therefore, mature fluke burdens may be negligible at the beginning of the fall season.