Fasciola hepatica products can alter the response of bovine immune cells to Mycobacterium avium subsp. paratuberculosis

Fasciola hepatica infection modifies IgG1 specific immune response to foot-and-mouth disease virus induced by vaccination

Fasciola hepatica, a worldwide distributed helminth, has a robust immunoregulatory effect in the host, increasing the susceptibility to secondary infections. Foot and mouth disease (FMD) is a highly contagious acute vesicular viral disease effectively controlled by vaccination in endemic regions. Despite the evidence of immunoregulatory effects, the impact of fasciolosis on the immune response induced by FMD vaccination in cattle has never been assessed. Our objective was to evaluate whether the infection by F. hepatica in cattle influences the long-term immunity elicited by the currently used commercial FMD-inactivated vaccines. Aberdeen Angus steers negative for F. hepatica were vaccinated twice against FMD virus (FMDV) during the first 6 months of age using a commercial oil vaccine formulated with A24/Cruzeiro and O1/Campos strains. When maternal antibodies against F. hepatica were weaned (18--20 months of age) animals were divided into groups of 12 and infected or mock-infected with 500 metacercariae/animal. Individual serum samples were collected at 0-, 28-, 59-, 87- and 157-days post-infection (dpi). Indirect ELISAs were used to detect A24/Cruzeiro specific bovine IgG and IgG subtypes. The total IgG antibody levels and avidity against FMDV did not show significant differences between all the groups. The commercial vaccine induced higher IgG2 than IgG1 titers in vaccinated animals. Anti-FMDV IgG1 levels significantly decreased in the infected group at 28 dpi. In addition, the avidity of IgG1 FMDV-specific antibodies at day 28 in the infected group was reduced compared to the control. These results show that F. hepatica infection modified anamnestic responses against FMDV, reducing serum IgG1 titers and avidity. To our knowledge, this is the first report of immune-regulation of F. hepatica altering the immune response of FMD vaccines, one of the most globally used animal vaccines.

MAP, Johne's disease and the microbiome; current knowledge and future considerations

Mycobacterium avium subsp. paratuberculosis is the causative agent of Johne's disease in ruminants. As an infectious disease that causes reduced milk yields, effects fertility and, eventually, the loss of the animal, it is a huge financial burden for associated industries. Efforts to control MAP infection and Johne's disease are complicated due to difficulties of diagnosis in the early stages of infection and challenges relating to the specificity and sensitivity of current testing methods. The methods that are available contribute to widely used test and cull strategies, vaccination programmes also in place in some countries. Next generation sequencing technologies have opened up new avenues for the discovery of novel biomarkers for disease prediction within MAP genomes and within ruminant microbiomes. Controlling Johne's disease in herds can lead to improved animal health and welfare, in turn leading to increased productivity. With current climate change bills, such as the European Green Deal, targeting livestock production systems for more sustainable practices, managing animal health is now more important than ever before. This review provides an overview of the current knowledge on genomics and detection of MAP as it pertains to Johne's disease.

Alpha-2-Macroglobulin as a New Promising Biomarker Improving the Diagnostic Sensitivity of Bovine Paratuberculosis

Johne's disease (JD) is a chronic granulomatous enteritis of ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP), which induces persistent diarrhea and cachexia. JD causes huge economic losses to the dairy industry due to reduced milk production and premature culling. Infected animals excrete MAP via feces during the prolonged subclinical stage without exhibiting any clinical signs. Therefore, accurate detection of subclinical stage animals is crucial for successful eradication of JD in the herd. In the current study, we analyzed serum samples of MAP-infected and non-infected cattle to identify potential biomarker candidates. First, we identified 12 differentially expressed serum proteins in subclinical and clinical shedder groups compared to the healthy control group. Second, we conducted ELISA for three selected biomarkers (alpha-2-macroglobulin (A2M), alpha-1-beta glycoprotein, and transthyretin) and compared their diagnostic performance with that of two commercial ELISA diagnostic kits. Serum A2M levels were significantly higher in the MAP-exposed, subclinical shedder, subclinical non-shedder, and clinical shedder groups than in the healthy control group, suggesting its possible use as a diagnostic biomarker for MAP infection. Furthermore, A2M demonstrated a sensitivity of 90.4%, and a specificity of 100% while the two commercial ELISA kits demonstrated a sensitivity of 67.83 and 73.04% and a specificity of 100%, respectively. In conclusion, our results suggest that measuring A2M by ELISA can be used as a diagnostic tool to detect MAP infection, considerably improving the detection rate of subclinical shedders and MAP-exposed animals that are undetectable using current diagnostic tools.

Fasciola hepatica co-infection enhances Th1 immune response in the adventitial layer of non-fertile Echinococcus granulosus cysts

Cystic echinococcosis is a widespread zoonosis caused by the larval stage of the tapeworm Echinococcus granulosus. In intermediary hosts, two types of echinococcal cysts can be found: fertile, which produce protoscoleces, the infective form of the parasite to dogs; and infertile, that do not present protoscoleces and therefore are not able to continue with the parasite life cycle. The adventitial layer, the local immune response against the cyst, plays an important role in cyst fertility. Grazing cattle can often feature Fasciola hepatica co-infection, a parasite known to modulate the host systemic immune response. In this work the cellular Th1/Th2 immune profiles were evaluated in the adventitial layer of fertile and non-fertile cysts with and without co-infection with Fasciola hepatica. Measuring with immunohistochemistry and qPCR in adventitial layer, we report that non-fertile cysts present higher levels of Th1 cytokines (IFN-γ (P < 0.0001) and TNF-α (P < 0.05)), and fertile cysts have higher levels of Th2 cytokines (IL-4 (P < 0.001)). Co-infection with Fasciola hepatica is associated with a decrease in the expression of IL-4 (P < 0.05) and an increase in the expression of IFN-γ (P < 0.0001) in the adventitial layer of fertile cysts. Non-fertile cysts were associated with higher levels of Th1 cytokines in the adventitial layer, with IFN-γ expression enhanced by F. hepatica co-infection (P < 0.0001), confirming that polyparasitism should be considered in the treatment and control of naturally infected cattle.

Fasciola hepatica products can alter the response of bovine immune cells to Mycobacterium avium subsp. paratuberculosis

BACKGROUND

Fasciola hepatica causes economically important disease in livestock worldwide. The relevance of this parasitic infection extends beyond its direct consequences due to its immunoregulatory properties.

OBJECTIVES

Given the importance of the T helper 1 (Th1) immune response in controlling infections with Mycobacterium avium subspecies paratuberculosis (MAP) in cattle, we aimed to establish the immunological consequences that co-infection with F. hepatica might have on the course of Johne's disease (JD).

METHODS

This study compared the in vitro response of bovine immune cells to infection with MAP or exposure to MAP antigens following F. hepatica infection or stimulation with F. hepatica products.

RESULTS

We found a decreased proliferation of peripheral blood mononuclear cells (PBMCs) after infection with F. hepatica. This reduction was inversely correlated with fluke burden. Pre-stimulation with F. hepatica molecules produced a significant reduction of ileocaecal lymph node leucocyte proliferation in response to MAP antigens. Additionally,F. hepatica products reduced expression of the CD14 receptor by macrophages and increased levels of apoptosis and bacterial (MAP) uptake.

CONCLUSIONS

Overall, F. hepatica infection had little impact on the in vitro response of immune cells to MAP, whereas in vitro co-stimulation with F. hepatica molecules had a measurable effect. Whether this is likely to affect JD progression during in vivo chronic conditions remains unclear.