Cattle co-infection of Echinococcus granulosus and Fasciola hepatica results in a different systemic cytokine profile than single parasite infection

Abstract

E. granulosus is a cestode that causes Cystic Echinococcosis (CE), a zoonotic disease with worldwide presence. The immune response generated by the host against the metacestode induces a permissive Th2 response, as opposed to pro-inflammatory Th1 response. In this view, mixed Th2 and regulatory responses allow parasite survival. Overall, larval Echinococcus infections induce strong regulatory responses. Fasciola hepatica, another common helminth parasite, represents a major infection in cattle. Co-infection with different parasite species in the same host, polyparasitism, is a common occurrence involving E. granulosus and F. hepatica in cattle. 'While it is known that infection with F. hepatica also triggers a polarized Th2/Treg immune response, little is reported regarding effects on the systemic immune response of this example of polyparasitism. F. hepatica also triggers immune responses polarized to the Th2/ Treg spectrum. Serum samples from 107 animals were analyzed, and were divided according to their infection status and Echinococcal cysts fertility. Cytokines were measured utilizing a Milliplex Magnetic Bead Panel to detect IFN-γ, IL-1, IL-2, IL-4, IL-6, IL-10, IL-12 and IL-18. Cattle infected only with F. hepatica had the highest concentration of every cytokine analyzed, with both 4.24 and 3.34-fold increases in IL-10 and IL-4, respectively, compared to control animals, followed by E. granulosus and F. hepatica co-infected animals with two-fold increase in IL-10 and IL-4, compared to control animals, suggesting that E. granulosus co-infection dampens the cattle Th2/Treg immune response against F. hepatica. When considering Echinococcal cyst fertility and systemic cytokine concentrations, fertile cysts had higher IFN-γ, IL-6 and IL-18 concentrations, while infertile cysts had higher IL-10 concentrations. These results show that E. granulosus co-infection lowers Th1 and Th2 cytokine serological concentration when compared to F. hepatica infection alone. E. granulosus infections show no difference in IFN-γ, IL-1, IL-2, IL-6 and IL-18 levels compared with control animals, highlighting the immune evasion mechanisms of this cestode.

Fig 1. Serological cytokine concentration in cattle.

Animals are divided in Control (Ctrl), Cystic Echinococcosis (CE), Fascioliasis (FH) and, co-infected animals (CE+FH). Cytokine concentrations for IL-4 (A), IL-10 (B), IL-12 (C), IL-2 (D), IL-6 (E), IL-18 (F), IL-1 (G) and IFN-γ (H) are shown. Dots represent individual cytokine values in cattle and the horizontal bar represents the mean for each group. Statistical significance was tested between groups using the Kruskal-Wallis test, with * = p < 0.05, ** = p< 0.01 and *** = p< 0.001.

Fig 2. Comparison of serological concentration between fertile and infertile Echinococcal cysts.

Animals are grouped in Cystic Echinococcosis with fertile cysts (CE Fer) and Cystic Echinococcosis with infertile cysts (CE Inf) for IFN-γ (a), IL-1 (b), IL-2 (c), IL-4 (d), IL-6 (e), IL-10 (f), IL-12 (g) and IL-18 (h). Dots represent individual cytokine values in cattle and the horizontal bar represents the mean for each group. Statistical significance was tested between groups using the Mann-Whitney U-test, with * = p < 0.05, ** = p< 0.01 and *** = p< 0.001.