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

Fasciolosis: pathogenesis, host-parasite interactions, and implication in vaccine development

Fasciola hepatica is distributed worldwide, causing substantial economic losses in the animal husbandry industry. Human fasciolosis is an emerging zoonosis in Andean America, Asia, and Africa. The control of the disease, both in humans and animals, is based on using anthelmintic drugs, which has resulted in increased resistance to the most effective anthelmintics, such as triclabendazole, in many countries. This, together with the concerns about drug residues in food and the environment, has increased the interest in preventive measures such as a vaccine to help control the disease in endemic areas. Despite important efforts over the past two decades and the work carried out with numerous vaccine candidates, none of them has demonstrated consistent and reproducible protection in target species. This is at least in part due to the high immunomodulation capacity of the parasite, making ineffective the host response in susceptible species such as ruminants. It is widely accepted that a deeper knowledge of the host-parasite interactions is needed for a more rational design of vaccine candidates. In recent years, the use of emerging technologies has notably increased the amount of data about these interactions. In the present study, current knowledge of host-parasite interactions and their implication in Fasciola hepatica vaccine development is reviewed.

Histopathology and antibody responses describe the seasonal pattern of dicrocoeliosis in small ruminants in the Himalayan ranges of Pakistan

In some parts of the world, Dicrocoelium spp. lancet flukes cause significant production loss in pastoral livestock, and accurate diagnosis of infection is important. The aims of the present study were to describe the histopathology and to investigate the transmission patterns of Dicrocoelium amongst ten sheep and goat farms in Khyber Pakhtunkhwa and Gilgit Baltistan, Pakistan. The liver histology and indirect enzyme-linked immunosorbent assay (ELISA) analyses followed standard procedures. The liver histopathology showed intensive tissue destruction and biliary hyperplasia associated with presence of adult flukes, severe inflammatory cell infiltration, congestion of blood vessels, damaged hepatocytes, and sinusoids in the infected areas. The time of onset of infection was investigated by ELISA detection of antibodies in sheep (n = 164) and goats (n = 152). Colostral transfer of Dicrocoelium antibodies from seropositive mothers was detected in sheep and goats up to 16 weeks of age. In both sheep and goats, the estimated time of infection differed between farms and years. Infection was seen in both sheep flocks and goat herds, with high variation between flocks and herds, and the highest infection rate in lambs. Dicrocoelium infection was most prevalent in sheep and goats in September (n = 84) and August (n = 63) respectively. This study concluded Dicrocoelium causes severe inflammation and necrosis of liver tissues in sheep and goats. Colostral transfer of antibodies can be detected up to about ten weeks of age. Higher infection rates are observed during August and September in sheep than in goats, putatively due to effects of different grazing and browsing behaviors on the ingestion of ants. The results will aid in the development of effective disease control strategies to ensure optimal growth and productivity of sheep and goats.

The Incidence of Liver Damage Found during Postmortem Examination at the Slaughterhouse

We monitored liver damage in cattle (cows, heifers, fattening bulls, and calves culled from the herd), pigs (sows, finishing pigs, and piglets culled from the farm), sheep (ewes and lambs), goats (does and kids), rabbits, and poultry (end-of-lay hens, broiler chickens, turkeys, domestic ducks, and domestic geese) in the period from 2010 to 2021. All animals (n = 1,425,710,143) reared on Czech farms and slaughtered at slaughterhouses in the Czech Republic were included in the analysis. We determined the total number of damaged livers for individual categories of animals and also analyzed separately the incidence of damage of acute, chronic, parasitic, and other origin. The overall incidence of liver damage was higher in adult animals compared to fattening animals in all species. In cattle and pigs, the incidence was also higher in young animals culled from the herd compared to fattening animals. When comparing adult animals by species, the incidence of liver damage was highest in cows (46.38%), followed by sows (17.51%), ewes (12.97%), and does (4.26%). When comparing fattening animals by species, the incidence was highest in heifers (14.17%) and fattening bulls (7.97 %), followed by finishing pigs (11.26%), lambs (4.73%), and kids (0.59%). When comparing young culled from the herd by species, it was higher in piglets (32.39%) than in calves (17.6 %), and when poultry and rabbits were compared, the incidence was highest in turkeys (3.38%), followed by ducks (2.20%), geese (1.09%), broiler chickens (0.08%), and rabbits (0.04%). The results indicate that fattening animals have a better liver condition than mature animals and that culled young have a worse liver condition than older fattening animals. Chronic lesions represented the dominant proportion of pathological findings. Parasitic lesions occurred, first and foremost, in animals grazed on meadows with likely parasitic invasion, i.e., in ewes (7.51%), lambs (3.51%), and heifers (1.31%), and in animals in which antiparasitic protection is limited in view of the protection of meat from antiparasitic residues, i.e., finishing pigs (3.68%). Parasitic damage to the liver was rarely detected in rabbits and poultry. The results obtained represent a body of knowledge for measures to improve the health and condition of the liver in food animals.

Intrahepatic eosinophilic proliferative phlebitis in Japanese black cattle indicate allergies involving mast cell tryptase-dependent activation

Cow-specific feature hepatic lesion, termed as eosinophilic proliferative phlebitis (EPP), has been mainly detected in Japanese black cattle and identified histologically eosinophilic infiltration and endothelial hyperplasia in portal areas. We previously proposed EPP as a food allergy from the pathological characteristics and a significant increase of serum immunoglobulin E specific to curly dock (Rumex crispus) in allergens testing, however, first report had regarded EPP an atypical type of bovine fascioliasis. In EPP lesions, eosinophilic infiltration was observed to the hypertrophic endothelium and not to the intrahepatic bile duct, and that was related to eotaxin-1 expression. In EPP, the mast cells increased as well as in fascioliasis, and the mast cells producing tryptase without chymase increased with interleukin-4 production. In this context, hyperplasia of periendothelium expressing proteinase-activated receptor-2 (PAR-2) and not angiotensin II was observed. Contrastably, in fascioliasis, unique mast cells producing neither tryptase nor chymase infiltrated, and the periendothelium expressed neither PAR-2 nor angiotensin II. Interestingly, EPP had not occurred liver injury with raised hepatic enzymes like fascioliasis, and suggested to a correlation with severe serum hypo-vitamin A. Overall, this study suggests that EPP is an allergic disease by main difference between adaptive immunity to allergens and innate immunity to parasites.

Fasciolosis in sheep and goats slaughtered at abattoirs in Central Ethiopia and associated financial losses

Fasciolosis is a serious animal health problem in Ethiopia where livestock is crucial for the domestic economy. A study was conducted in two Ethiopian abattoirs to estimate the prevalence of Fasciola infection in goats and sheep, and the monetary losses resulting from liver condemnation. Post-mortem examination of 925 animals (424 sheep and 501 goats) were examined by incision of the liver parenchyma for presence of the liver fluke, Fasciola. The direct financial losses were calculated based on the estimated prevalence, the market price of the liver, and the average number of sheep and goats slaughtered annually. The overall prevalence of fasciolosis was 10.4% (20.7% sheep and 1.6% goats). Among the studied variables, species of the study animal and age in sheep showed a statistically significant association with infection (p < 0.05). Based on the annual average of 89,054 sheep and 76,374 goats slaughtered, the annual average economic loss due to the condemned liver was estimated at 3700 US$ (185,232 ETH Birr) for sheep and 245 US$ (12,220 ETH Birr) for goats.

This study revealed that the prevalence of fasciolosis was higher in sheep than in goats, and substantial economic losses occur for the sheep and goat industry. Hence, considering the irrigations schemes in the country, strategic control programs targeting Fasciola infection and intermediate hosts are warranted.

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20.7% of 424 sheep and 1.6% of 501 goats were infected with fasciolosis.

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Young sheep were more commonly affected than adults.

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Sheep and goat livers condemned annually were valued at $3700 US and $245 US, respectively.

Characterization of the Pathology, Biochemistry, and Immune Response in Kunming (KM) Mice Following Fasciola gigantica Infection

As a putative model of Fasciola gigantica infection, detailed data in Kunming (KM) mice infected with F. gigantica are lacking. In this study, KM mice were orally infected with 15 metacercaria for 8 weeks. Macroscopic and microscopic changes, serum biochemistry, cytokine responses, and changes in parasite-specific immunoglobulin G (IgG) antibody levels were monitored at 1, 3, 5, 7, and 8 weeks post-infection (wpi), respectively. The serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) increased after infection, while that of albumin (ALB) decreased, which was positively correlated with the degree of liver damage. Between 5 and 7 wpi, the mice showed symptoms of anemia and weight loss, possibly caused by the decrease of alkaline phosphatase (ALP). Moreover, the changing tendencies of the levels of globulin (GLB) and parasite-specific IgG antibody were similar, suggesting a potential correlation between GLB production and adaptive immune response in the host. Coordinated variations in interferon gamma (IFN-γ) and interleukin 4 (IL-4) indicated a mixed T helper 1 (Th1)/Th2 cellular immune response. Furthermore, the serum IgG antibody increased after infection and peaked at 5 wpi, and it was positively correlated with the average parasite burdens. The worms collected from mice were approximately 1 cm in length at 8 wpi, their digestive and reproductive systems were well developed, and no eggs were found in the uterus. To the best of our knowledge, this is the first report describing detailed histological, biochemical, and immunological indices in KM mice infected with F. gigantica, which provides basic information on KM mice against infection with F. gigantica.

Autonomous Non Antioxidant Roles for Fasciola hepatica Secreted Thioredoxin-1 and Peroxiredoxin-1

Trematode parasites of the genus Fasciola are the cause of liver fluke disease (fasciolosis) in humans and their livestock. Infection of the host involves invasion through the intestinal wall followed by migration in the liver that results in extensive damage, before the parasite settles as a mature egg-laying adult in the bile ducts. Genomic and transcriptomic studies revealed that increased metabolic stress during the rapid growth and development of F. hepatica is balanced with the up-regulation of the thiol-independent antioxidant system. In this cascade system thioredoxin/glutathione reductase (TGR) reduces thioredoxin (Trx), which then reduces and activates peroxiredoxin (Prx), whose major function is to protect cells against the damaging hydrogen peroxide free radicals. F. hepatica expresses a single TGR, three Trx and three Prx genes; however, the transcriptional expression of Trx1 and Prx1 far out-weighs (>50-fold) other members of their family, and both are major components of the parasite secretome. While Prx1 possesses a leader signal peptide that directs its secretion through the classical pathway and explains why this enzyme is found freely soluble in the secretome, Trx1 lacks a leader peptide and is secreted via an alternative pathway that packages the majority of this enzyme into extracellular vesicles (EVs). Here we propose that F. hepatica Prx1 and Trx1 do not function as part of the parasite’s stress-inducible thiol-dependant cascade, but play autonomous roles in defence against the general anti-pathogen oxidative burst by innate immune cells, in the modulation of host immune responses and regulation of inflammation.

Molecular characterization and immunodiagnostics of Dicrocoelium dendriticum species isolated from sheep of north-west Himalayan region

Despite its extensive presence among grazing ruminants, dicrocoeliosis, also known as 'small liver fluke' disease, is poorly known and often underestimated by researchers and practitioners in many countries. The accurate identification and prepatent diagnosis of Dicrocoelium dendriticum infection is an essential prerequisite for its prevention and control. In the present study, the morphologically identified specimens isolated from the bile ducts of sheep (Ovis aries) were validated through molecular data. The sequence analysis of the second internal transcribed spacer (ITS-2) of our isolates showed a high degree of similarity with D. dendriticum using the BLAST function of the National Center for Biotechnology Information (NCBI). The phylogenetic analysis of our isolates showed a close relationship with previously described D. dendriticum isolates from different countries. The antigenic profiles of somatic and excretory/secretory (E/S) antigens of D. dendriticum were revealed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting using sera from sheep naturally infected with D. dendriticum. By SDS-PAGE, 16 distinct bands were revealed from crude somatic fraction. Immunoblotting analysis of these proteins with positive sera exhibited six seroreactive bands ranging from 27 to 130 kDa. Among these, the 84 and 130 kDa bands were quite specific, with high diagnostic specificity and sensitivity. The E/S fraction comprised nine distinct bands, as revealed by SDS-PAGE analysis. Immunoblotting analysis of these proteins with positive sera exhibited five antigenic bands ranging from 27 to 130 kDa. Among these, the 130 kDa band was found to be quite specific, with high diagnostic specificity and sensitivity. The present study concludes that the protein bands of 84 and 130 kDa in somatic fraction and 130 kDa in E/S fraction can be used for the immunodiagnostic purpose for this economically important parasite, which may also encourage further studies regarding their vaccine potential.

Molecular Characterization and Immunodiagnostic Potential of Various Antigenic Proteins of Fasciola Gigantica Species Isolated from Sheep of North West Himalayan Region

The control of the digenetic trematode Fasciola gigantica has been the major challenge in both cattle and small ruminants as there is a paucity of an effective and commercial vaccine. Thus, the accurate identification and prepatent diagnosis of F. gigantica is an essential prerequisite for its successful prevention and control. In the present study, the morphologically identified specimens isolated from the liver and bile ducts of sheep (Ovis aries) were validated through molecular data. The sequence analysis of ITS2 of our isolates showed high degree of similarity with F. gigantica and F. hepatica using BLAST function of NCBI. The phylogenetic analysis of our isolates showed a close relationship with previously described F. gigantica and F. hepatica isolates from different countries. The antigenic profile of somatic and E/S antigens of F. gigantica were revealed by SDS-PAGE and immunoblotting using sera from sheep naturally infected with F. gigantica. By SDS-PAGE, 20 distinct bands were revealed from crude somatic fraction. Immunoblotting analysis of these proteins with positive sera exhibited 8 sero-reactive bands ranging from 14 to 97 kDa. Among these 38 and 44 kDa bands were quite specific with high diagnostic specificity and sensitivity. The E/S fraction comprised 7 distinct bands, as revealed by SDS-PAGE analysis. Immunoblotting analysis of these proteins with positive sera exhibited 6 antigenic bands ranging from 23 - 54 kDa. Among these 27 and 33 kDa were found to be quite specific with high diagnostic specificity and sensitivity. The present study concludes that the protein bands of 38 and 44 kDa in somatic fraction and 27 and 33 kDa in E/S fraction can be used for the immunodiagnostic purpose for this economically important parasite, which may also entice further studies regarding their vaccine potential.

Th2-related cytokines are associated with Fasciola gigantica infection and evasion in the natural host, swamp buffalo

The infection of ruminants by Fasciola spp. always induces a non-protective Th2-type immune response. However, little is known about changes in the local and systemic immune environment during F. gigantica migration in buffalo. In this study, native swamp buffaloes were each infected with 500 viable F. gigantica metacercariae. Mesenteric lymph node (MLN), hepatic lymph node (HLN), spleen, and serum samples were collected from control and infected buffaloes at 3, 10, 28, 42, 70, and 98 days post-infection (DPI). The mRNA expression levels of the Th1- and Th2-related cytokines IL-2, IL-4, IL-5, IL-6, IL-10, IL-12p40, IFN-γ, TNF-α, and CD4 were measured during different infection stages in the MLNs, spleens, and HLNs using quantitative real-time PCR (qRT-PCR). Levels of the specific anti-ESP isotype antibodies IgG, IgG1, and IgG2 were used to reflect changes in humoral immunity. The results of this study indicated that swamp buffaloes were susceptible to F. gigantica infection, and that susceptibility to this infection was closely related to the cytokine environment associated with the Th2-type immune response. The MLNs showed a mixed Th1- and Th2-type immune response during the acute infection stages, after which the production of these cytokines returned to normal. Cytokine expression in the HLNs also expressed a mixed Th1- and Th2-type immune response during the early infection stages. When the infection became chronic, the typical Th2 immune response was induced in the HLNs. At the acute infection stages, the spleen exhibited a Th2 immune response. Nevertheless, cytokines associated with the Th1 and Th2 immune responses were upregulated at 98 DPI. In addition, the total IgG and IgG1 of the parasite-specific antibodies increased. This suggested that the Th2-related cytokines and IgG1 induced by F. gigantica infection might mediate successful F. gigantica infection in the natural host, swamp buffalo.

A Preliminary Study of a Lettuce-Based Edible Vaccine Expressing the Cysteine Proteinase of Fasciola hepatica for Fasciolosis Control in Livestock

Oral vaccination with edible vaccines is one of the most promising approaches in modern vaccinology. Edible vaccines are an alternative to conventional vaccines, which are typically delivered by injection. Here, freeze-dried transgenic lettuce expressing the cysteine proteinase of the trematode Fasciola hepatica (CPFhW) was used to orally vaccinate cattle and sheep against fasciolosis, which is the most important trematode disease due to the parasite's global distribution, wide spectrum of host species and significant economic losses of farmers. In the study, goals such as reducing the intensity of infection, liver damage and F. hepatica fecundity were achieved. Moreover, we demonstrated that the host sex influenced the outcome of infection following vaccination, with female calves and male lambs showing better protection than their counterparts. Since differences occurred following vaccination and infection, different immunization strategies should be considered for different sexes and host species when developing new control methods. The results of the present study highlight the potential of oral vaccination with plant-made and plant-delivered vaccines for F. hepatica infection control.

Anti-Fas2 IgM antibodies in Fasciola hepatica infected patients with positive IgG serology

Background

Fascioliasis is an infectious disease caused by parasites Fasciola hepatica and F. gigantica. Humans are infected by the consumption of vegetables and water contaminated with the infective form of the parasite.

Materials and Methods

In this study, an IgM-ELISA with the cysteine proteinase Fas2 antigen was evaluated with sera from 76 patients infected with F. hepatica, 24 patients with other parasite infections and 84 healthy volunteers.

Results

IgM-ELISA resulted in 43% positives in F. hepatica patients with positive serology to Fas2-ELISA, but no positives resulted from testing healthy volunteers and individuals infected with other parasites. The IgM-ELISA diagnostic parameters showed a sensitivity of 43.4% (95% CI 0.321-0.553), specificity of 100% (95% CI 0.957-1), and no cross-reactivity with other parasitic infection. Interference by rheumatoid factor in the IgM immunoassay was controlled by treating sera with rheumatoid factor absorbent before testing.

Conclusions

Fas2 antigen is detected by circulating IgM in patients infected with F. hepatica and IgM-ELISA using Fas2 appears as a specific immunoassay to detect the acute phase of the acute phase of F. hepatica infection in humans.

Prevalence of fascioliasis (liver flukes) infection in cattle and buffaloes slaughtered at the municipal abattoir of El-Kharga, Egypt

AIM

The main objectives of this study were to determine the prevalence of fascioliasis infections in cattle and buffaloes, slaughtered in El-Kharga city slaughterhouse at New Valley Governorate.

MATERIALS AND METHODS

The slaughtered animals were daily inspected for liver fascioliasis allover 2016. Macroscopic fascioliasis was detected from a total of 2251 basing on animals specie, sex, season, and Fasciola spp. in addition to microscopic examination of blood, fecal samples which collected from female cattle and buffalo (50 each).

RESULTS

The total prevalence rate of Fasciola sp. infection occurs in the study area were about 695/2251 (30.88%) from the total cattle and bovine slaughtered carcasses. The incidence of fascioliasis was 4/12 (33.33%) and 678/2200 (30.82%) for females and males cattle carcasses, respectively, while the infection rate in buffalo carcasses was 1/4 (25.00%) and 12/35 (34.29%) for females and males buffalo carcasses, respectively.

CONCLUSION

The moderate fasciolosis infection in cattle and buffaloes slaughtered at the municipal abattoir of El-Kharga, Egypt. The highest fascioliasis infection was recorded during winter and autumn. It constitutes a major cause of economic losses at El-Kharga abattoir and threat public health.

Network Analysis of the Systemic Response to Fasciola hepatica Infection in Sheep Reveals Changes in Fibrosis, Apoptosis, Toll-Like Receptors 3/4, and B Cell Function

The Trematode Fasciola hepatica is an important cause of disease in livestock and in man. Modulation of immunity is a critical strategy used by this parasite to facilitate its long-term survival in the host. Understanding the underlying mechanisms at a system level is important for the development of novel control strategies, such as vaccination, as well as for increasing general understanding of helminth-mediated immunoregulation and its consequences. Our previous RNA sequencing work identified a large number of differentially expressed genes (DEG) from ovine peripheral blood mononuclear cells (PBMCs) at acute and chronic stages of F. hepatica infection, and yielded important information on host–parasite interaction, with particular reference to the immune response. To extend our understanding of the immunoregulatory effects of this parasite, we employed InnateDB to further analyze the DEG dataset and identified 2,458 and 224 molecular interactions in the context of innate immunity from the acute and chronic stages of infection, respectively. Notably, 458 interactions at the acute stage of infection were manually curated from studies involving PBMC-related cell-types, which guaranteed confident hypothesis generation. NetworkAnalyst was subsequently used to construct and visualize molecular networks. Two complementary strategies (function-first and connection-first) were conducted to interpret the networks. The function-first approach highlighted subnetworks implicated in regulation of Toll-like receptor 3/4 signaling in both acute and chronic infections. The connection-first approach highlighted regulation of intrinsic apoptosis and B-cell receptor-signaling during acute and chronic infections, respectively. To the best of our knowledge, this study is the first system level analysis of the regulation of host innate immunity during F. hepatica infection. It provides insights into the profound changes induced by F. hepatica infection that not only favors parasite survival into chronic infection but also impedes the host’s immune response to other pathogens, and render vaccination against fasciolosis a difficult challenge. The information provided will be useful in the design of specific vaccine protocols to overcome parasite-mediated immunoregulation and in furthering general understanding of the interplay between helminth infection and host immune systems.

Time-Course Study of the Transcriptome of Peripheral Blood Mononuclear Cells (PBMCs) from Sheep Infected with Fasciola hepatica

Fasciola hepatica is a parasitic trematode that infects a wide range of mammalian hosts, including livestock and humans, in temperate and tropical regions globally. This trematode causes the disease fascioliasis, which consists of an acute phase (≤ 12 weeks) during which juvenile parasites migrate through the host liver tissues, and a chronic phase (> 12 weeks) following the establishment of adult parasites in the liver bile ducts. Few studies have explored the progression of the host response over the course of Fasciola infection in the same animals. In this study, we characterized transcriptomic changes in peripheral blood mononuclear cells (PBMCs) collected from sheep at three time points over the first eight weeks of infection relative to uninfected controls. In total, 183 and 76 genes were found to be differentially transcribed at two and eight weeks post-infection respectively. Functional and pathway analysis of differentially transcribed genes revealed changes related to T-cell activation that may underpin a Th2-biased immune response against this parasite. This first insight into the dynamics of host responses during the early stages of infection improves the understanding of the pathogenesis of acute fascioliasis, informs vaccine development and presents a set of PBMC markers with diagnostic potential.

Transmission patterns of Fasciola hepatica to ruminants in Sweden

Transmission patterns of Fasciola hepatica were investigated on beef cattle (n=3) and sheep (n=3) farms in Sweden between 2011 and 2012. The dynamics of fluke infection, particularly estimated time of infection, were screened each grazing season by ELISA detection of antibodies in lambs (n=94) and first grazing season calves (n=61). Colostral transfer of F. hepatica antibodies from seropositive ewes was detected in sheep up to 11 weeks of age. In sheep, the estimated time of infection differed significantly between herds and years. Typical 'winter infection' was observed on two sheep farms in 2012, but the most prevalent transmission pattern was found to be 'summer infection', characterised by infection of animals in late summer by F. hepatica originating from overwintered and/or spring-excreted eggs. In contrast, beef calves were infected mainly in September-October ('summer infection'). Furthermore, lymnaeid and succineid snails were collected on the pastures used by these animals both in spring and in the autumn each year. In total, 1726, 588, 138, 130, 93 and 42 specimens of Galba truncatula, Lymnaea palustris, Lymnaea glabra, Lymnaea fuscus, Radix peregra and Succinea putris, respectively, were collected and identified. These were subsequently examined for the presence of F. hepatica DNA by species-specific PCR and the findings compared against mean monthly rainfall and temperature data for each farm. The main intermediate host of the liver fluke was G. truncatula, with a prevalence range of F. hepatica infection from 0% to 82%. Only 1 out of 42 terrestrial S. putris tested positive for F. hepatica, casting doubt on the role of this species in transmission of F. hepatica in Sweden. In conclusion, two main peak periods of infection were observed: May-June (from overwintered infected snails='winter infection') and August-September (from metacercariae developed and produced by snails during summer='summer infection'). The occurrence and frequency of 'winter infection' were dependent on local environmental factors such as snail habitat availability or grazing behaviour of animals, rather than on climatic factors.

Protective role of purified cysteine proteinases against Fasciola gigantica infection in experimental animals

Fascioliasis is one of the public health problems in the world. Cysteine proteinases (CP) released by Fasciola gigantica play a key role in parasite feeding, migration through host tissues, and in immune evasion. There has been some evidence from several parasite systems that proteinases might have potential as protective antigens against parasitic infections. Cysteine proteinases were purified and tested in vaccine trials of sheep infected with the liver fluke. Multiple doses (2 mg of CP in Freund's adjuvant followed by 3 booster doses 1 mg each at 4 week intervals) were injected intramuscularly into sheep 1 week prior to infect orally with 300 F. gigantica metacercariae. All the sheep were humanely slaughtered 12 weeks after the first immunization. Changes in the worm burden, ova count, and humoral and cellular responses were evaluated. Significant reduction was observed in the worm burden (56.9%), bile egg count (70.7%), and fecel egg count (75.2%). Immunization with CP was also found to be associated with increases of total IgG, IgG₁, and IgG₂ (P<0.05). Data showed that the serum cytokine levels of pro-inflammatory cytokines, IL-12, IFN-γ, and TNF-α, revealed significant decreases (P<0.05). However, the anti-inflammatory cytokine levels, IL-10, TGF-β, and IL-6, showed significant increases (P<0.05). In conclusion, it has been found that CP released by F. gigantica are highly important candidates for a vaccine antigen because of their role in the fluke biology and host-parasite relationships.

Humoral immune response in goats immunised with cathepsin L1, peroxiredoxin and Sm14 antigen and experimentally challenged with Fasciola hepatica

The humoral immune response was analysed in goats immunised with FhCL1, FhPrx, Sm14, and experimentally challenged with Fasciola hepatica. All immunised animals developed significant levels of anti-fluke specific antibodies and those immunised with FhCL1 showed the highest antibody titre. After experimental infection, an increase in the antibody level was detected only in goats immunised with FhCL1. In the adjuvant-control animals, the experimental challenge induced significant production of specific antibodies against FhCL1, FhPrx and Sm14. While liver fluke specific humoral responses were seen in all groups, no significant protection in any of the vaccinated groups was found.

Dicrocoelium dendriticum in cattle from Cypress Hills, Canada: humoral response and preliminary evaluation of an ELISA

Apparent changes in the distribution of Dicrocoelium dendriticum in western Canada and the absence of other liver flukes in the area prompted an examination of the humoral responses in naturally infected cattle sharing pasture with heavily infected wild cervids. Western blots using sera from the infected cattle indicated that the cattle had antibodies to various fluke antigens, however the pattern of response varied among isotypes. Isotype analysis indicated that Dicrocoelium-infected cattle produced IgG1, and IgM antibodies, but not IgG2 antibodies. Subsequent comparison of the efficiency of coprological and serological approaches for diagnosis showed that while 43.5% of a separate group of 26 yearlings had eggs in their faeces, the immunoblots indicated that all had detectable antibodies. A group of cattle necropsied for confirmation of fluke status was used to evaluate humoral immune responses and to provide baseline information in the preliminary development of an indirect ELISA for detection of anti-fluke antibodies.

Kinetics of anti-Fasciola IgG antibodies in serum and milk from dairy cows during lactation, and in serum from calves after feeding colostrum from infected dams

A study was carried out to compare anti-Fasciola hepatica IgG levels in blood serum and mammary secretions during the entire lactation period in dairy cows experimentally infected with different numbers of F. hepatica metacercariae. The kinetics of specific antibodies passively transferred to the offspring was also studied. The MM3-SERO ELISA, a specific and sensitive method of detecting antibodies against F. hepatica, was used to detect antibodies in milk and serum samples. The progress of infection was monitored by use of the MM3-COPRO ELISA, an immunoassay for detecting Fasciola antigens in faecal samples. The optical density of serum and milk from uninfected control cows remained low throughout the study. In the infected animals, a similar pattern of anti-F. hepatica IgG kinetics was observed in serum and milk throughout the entire observation period. This IgG response was characterized by the early appearance of high levels of specific antibodies in serum (detectable 1-4 weeks pi) and in milk (detectable at the beginning of lactation) and remained invariably high throughout the entire lactation period in cows infected with low-to-moderate infective doses (>or=50 metacercariae). However, in animals administered very low infective doses (<or=25 metacercariae) the levels of specific antibodies were variable, and would be difficult to interpret if only sporadic analyses were carried out. The MM3-SERO ELISA proved to be highly sensitive for use with milk samples, as it enabled detection of antibodies in cows infected with very low infective doses (<or=25 metacercariae) and therefore harbouring very few flukes (probably<10). Moreover, specific antibodies were able to be detected at any stage of lactation, in milk from cows infected with >or=50 metacercariae, even when samples were diluted al least 1:8. In newborn calves fed colostrum from infected dams, the levels of anti-Fasciola antibodies increased rapidly, then decreased sharply and were no longer detected in calves >12 weeks old. The results indicate that the detection of antibodies in milk samples may provide useful information about the status of F. hepatica infection in dairy herds if repeated analyses are carried out. Analysis of bulk samples may also be an inexpensive way of identifying herds infected with F. hepatica, provided highly sensitive tests are used.

Fasciola gigantica excretory-secretory products for immunodiagnosis and prevention of sheep fasciolosis

Excretory-secretory products (ESP) products of ex vivo Fasciola gigantica adult worms were used for immunodiagnosis of sheep experimental infection with F. gigantica and natural infection with Fasciola spp. by enzyme-linked immunosorbent assay (ELISA) and Western blotting. Specific IgG antibody binding to native or denatured ESP was detected as early as 2 weeks after experimental sheep infection with 100 or 200 metacercariae. No specific IgG antibody binding was displayed by sera obtained from 192 sheep considered to be Fasciola- and other parasite-free by microscopic examination of bile and feces. Additionally, sera from 200 apparently Fasciola-free sheep, yet infected with other parasites, were all negative. The data, thus, indicated that ESP-based ELISA reached nearly 100% sensitivity and specificity in immunodiagnosis of sheep fasciolosis. As expected, the ESP molecules were immunogenic in sheep eliciting interleukin-12p40 mRNA response and considerable amounts of antibodies, which were able to bind to the surface of newly excysted juvenile worms as judged by membrane indirect immunofluorescence, and mediate their attrition via antibody-dependent cell-mediated cytotoxicity. The ESP-induced cellular and humoral immune responses were associated with a modest reduction in worm count, yet with a highly significant (P<0.0001) decrease in size of recovered worms, thus suggesting that ESP immunization might be a safe and cost-effective strategy for reducing transmission of the infection.