Evaluation of Immunogenicity and Efficacy of Fasciola hepatica Tetraspanin 2 (TSP2) Fused to E. coli Heat-Labile Enterotoxin B Subunit LTB Adjuvant Following Intranasal Vaccination of Cattle

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.

Eukaryotic Infections in Dairy Calves: Impacts, Diagnosis, and Strategies for Prevention and Control

Eukaryotic infections are common among dairy calves and can have significant impacts on their health and growth rates. Fungal infections caused by Aspergillus fumigatus, Trichophyton verrucosum, and Candida albicans can cause respiratory diseases, dermatophytosis, and diarrhea, respectively. Protozoan parasites, including Cryptosporidium parvum, Giardia duodenalis, and Eimeria spp., are also common in dairy calves. C. parvum is highly contagious and can cause severe diarrhea and dehydration, while Giardia duodenalis can lead to poor growth and is transmissible to humans through contaminated food or water. Eimeria spp. can cause coccidiosis and lead to reduced growth rates, poor feed conversion, and death. The common helminthic infections in dairy calves include Ostertagia ostertagi, Cooperia spp., Fasciola hepatica, and Strongyloides papillosus. These parasitic infections significantly impact calf health, growth, and dairy industry productivity. Diagnosis of these infections can be made through fecal samples using microscopy or molecular methods. However, diagnosis of the infections can be challenging and requires a combination of clinical signs and laboratory tests such as culture and PCR. Preventing and controlling eukaryotic infections in dairy calves requires several measures. Good hygiene and sanitation practices, proper management strategies, and timely treatment of affected animals are important. It is also necessary to avoid overcrowding and consider vaccination against ringworm. Further research is needed to better understand the epidemiology and characterization of eukaryotic infections in dairy calves, which will help in the development of more effective prevention and control strategies. In general, good hygiene practices, appropriate management strategies, and timely treatment of affected animals are crucial in preventing and controlling the infections, ensuring the health and well-being of dairy calves.

Combination Vaccines of Fasciola gigantica Saposin-like Protein-2 and Leucine Aminopeptidase

Saposin-like protein-2 (SAP-2) and leucine aminopeptidase (LAP) are major proteins involved in the digestive process of Fasciola gigantica (Fg). Both SAP-2 and LAP are highly expressed in F. gigantica; therefore, they could be vaccine candidates for fasciolosis. The aims of this study are (1) to observe the tissue expression of F. gigantica SAP-2 (FgSAP-2) and F. gigantica LAP (FgLAP) in F. gigantica by indirect immunofluorescence technique under confocal microscopy and (2) to test the vaccine potentials of individual and combined recombinant (r) FgSAP-2 and rFgLAP against F. gigantica in Imprinting Control Region (ICR) mice (n = 10 per group). By indirect immunofluorescence-confocal microscopy, FgSAP-2 and FgLAP were localized in the caecal epithelium but at different sites: FgSAP-2 appeared in small granules that are distributed in the middle and lower parts of the cytoplasm of epithelial cells, while FgLAP appeared as a line or zone in the apical cytoplasm of caecal epithelial cells. For vaccine testing, the percent protection of combined rFgSAP-2 and rFgLAP vaccines against F. gigantica was at 80.7 to 81.4% when compared with aluminum hydroxide (alum) adjuvant and unimmunized controls, respectively. The levels of IgG1 and IgG2a in the sera were significantly increased in single and combine vaccinated groups compared with the control groups. Vaccinated mice showed reduced liver damage when compared with control groups. This study indicates that the combined rFgSAP-2 and rFgLAP vaccine had a higher vaccine potential than a single vaccine. These results support the further testing and application of this combined vaccine against F. gigantica infection in farmed livestock animals.

Proteomic analysis of exosome-like vesicles from Fasciola gigantica adult worm provides support for new vaccine targets against fascioliasis

BACKGROUND

Extracellular vesicles (EVs) released by helminths play an important role in parasite-host communication. However, little is known about the characteristics and contents of the EVs of Fasciola gigantica, a parasitic flatworm that causes tropical fascioliasis. A better understanding of EVs released by F. gigantica will help elucidate the mechanism of F. gigantica-host interaction and facilitate the search for new vaccine candidates for the control and treatment of fascioliasis.

METHODS

Two different populations of EVs (15k EVs and 100k EVs) were purified from adult F. gigantica culture media by ultracentrifugation. The morphology and size of the purified EVs were determined by transmission electron microscopy (TEM) and by the Zetasizer Nano ZSP high performance particle characterization system. With the aim of identifying diagnostic markers or potential vaccine candidates, proteins within the isolated 100k EVs were analyzed using mass spectrometry-based proteomics (LC-MS/MS). Mice were then vaccinated with excretory/secretory products (ESPs; depleted of EVs), 15k EVs, 100k EVs and recombinant F. gigantica heat shock protein 70 (rFg-HSP70) combined with alum adjuvant followed by challenge infection with F. gigantica metacercariae. Fluke recovery and antibody levels were used as measures of vaccine protection.

RESULTS

TEM analysis and nanoparticle tracking analysis indicated the successful isolation of two subpopulations of EVs (15k EVs and 100k EVs) from adult F. gigantica culture supernatants using differential centrifugation. A total of 755 proteins were identified in the 100k EVs. Exosome biogenesis or vesicle trafficking proteins, ESCRT (endosomal sorting complex required for transport) pathway proteins and exosome markers, heat shock proteins and 14-3-3 proteins were identified in the 100k EVs. These results indicate that the isolated 100k EVs were exosome-like vesicles. The functions of the identified proteins may be associated with immune regulation, immune evasion and virulence. Mice immunized with F. gigantica ESPs, 15k EVs, 100k EVs and rFg-HSP70 exhibited a reduction in fluke burden of 67.90%, 60.38%, 37.73% and 56.6%, respectively, compared with the adjuvant control group. The vaccination of mice with F. gigantica 100k EVs, 15k EVs, ESP and rFg-HSP70 induced significant production of specific immunoglobulins in sera, namely IgG, IgG1 and IgG2a.

CONCLUSION

The results of this study suggest that proteins within the exosome-like vesicles of F. gigantica have immunomodulatory, immune evasion and virulence functions. This knowledge may lead to new strategies for immunotherapy, vaccination and the diagnosis of fascioliasis.

Bovine Natural Antibody Relationships to Specific Antibodies and Fasciola hepatica Burdens after Experimental Infection and Vaccination with Glutathione S-Transferase

Fasciola hepatica is the causative agent of fasciolosis, a significant parasitic disease occurring worldwide. Despite ongoing efforts, there is still no vaccine to control liver fluke infections in livestock. Recently, it has been suggested that natural antibodies (NAbs) can amplify specific antibodies (SpAb) and have a direct killing effect, but it is unknown if this phenomenon occurs during parasitic helminth infection or targeted vaccination. NAbs are antibodies produced by the innate immune system, capable of binding antigens without prior exposure. This study explores the role of bovine NAbs, using the exogenous glycoprotein keyhole limpet hemocyanin (KLH), in response to F. hepatica infection and SpAb production after infection and vaccination. The cattle’s NAbs were differently influenced by parasite infection and vaccination, with an increase in KLH-binding IgG and IgM levels after infection and reduced KLH-binding IgM levels following vaccination. Underlying NAbs reacting to KLH showed no correlations to the final fluke burdens after experimental infection or vaccination. However, NAbs reacting to whole-worm extract (WWE) prior to infection were positively correlated to increased fluke burdens within the infected bovine host. Furthermore, after infection, the specific IgG reacting to WWE was positively reflected by the underlying NAb IgG response. Following subcutaneous vaccination with F. hepatica native glutathione S-transferase (GST), there was a non-significant 33% reduction in fluke burden. Vaccinated animals with higher underlying NAbs had a higher induction of vaccine-induced SpAbs, with trends observed between KLH-binding IgM and anti-GST IgG and IgM. Our findings provide a platform to allow further investigation to determine if NAb levels could mirror fluke-SpAb production for exploitation in a combined selective breeding and vaccination program. Additionally, this work suggests that liver fluke could possibly evade the host’s immune system by utilising surface-bound IgM NAbs.