Unravelling the Immunity of Poultry Against the Extracellular Protozoan Parasite Histomonas meleagridis Is a Cornerstone for Vaccine Development: A Review

Abstract

The protozoan parasite Histomonas meleagridis is the causative agent of histomonosis in gallinaceous birds, predominantly in turkeys and chickens. Depending on the host species the outcome of the disease can be very severe with high mortality as observed in turkeys, whereas in chickens the mortality rates are generally lower. The disease is known for more than 100 years when in vitro and in vivo investigations started to understand histomonosis and the causative pathogen. For decades histomonosis could be well-controlled by effective drugs for prevention and therapy until the withdrawal of such chemicals for reasons of consumer protection in Europe, the USA and additional countries worldwide. Consequently, research efforts also focused to find new strategies against the disease, resulting in the development of an efficacious live-attenuated vaccine. In addition to efficacy and safety several studies were performed to obtain a deeper understanding of the immune response of the host against H. meleagridis. It could be demonstrated that antibodies accumulate in different parts of the intestine of chickens following infection with H. meleagridis which was much pronounced in the ceca. Furthermore, expression profiles of various cytokines revealed that chickens mounted an effective cecal innate immune response during histomonosis compared to turkeys. Studying the cellular immune response following infection and/or vaccination of host birds showed a limitation of pronounced changes of B cells and T-cell subsets in vaccinated birds in comparison to non-protected birds. Additionally, numbers of lymphocytes including cytotoxic T cells increased in the ceca of diseased turkeys compared to infected chickens suggesting an immunopathological impact on disease pathogenesis. The identification of type 1 and type 2 T-helper (Th) cells in infected and lymphoid organs by in situ hybridization did not show a clear separation of Th cells during infection but revealed a coherence of an increase of interferon (IFN)-γ mRNA positive cells in ceca and protection. The present review not only summarizes the research performed on the immune response of host birds in the course of histomonosis but also highlights the specific features of H. meleagridis as a model organism to study immunological principles of an extracellular organism in birds.

Supplementation of probiotics in water beneficial growth performance, carcass traits, immune function, and antioxidant capacity in broiler chickens

“…These confirmed our results that the treatment of probiotics increased the levels of IgG and IgA in the serum of broilers at all growth stages. IL-2 and IL-10 were the cytokines that reflected the immune level secreted by Th1 and Th2 cells [ 36 ]. Wang et al (2015) reported that L. plantarum strain P-8 activated the protective immune response in broilers, and the upregulated IL-2 and the downregulated IL-10 transcriptions were detected in an age-dependent manner [ 20 ].…”

Vaccination against the Protozoan Parasite Histomonas meleagridis Primes the Activation of Toll-like Receptors in Turkeys and Chickens Determined by a Set of Newly Developed Multiplex RT-qPCRs

“…Experimental vaccination with in-vitro attenuated parasites was shown to be effective in turkeys and chickens against a challenge and might be used in the future to protect birds [ 4 ]. However, knowledge of the immune response of poultry against the parasite is limited and mainly focused on the adaptive immunity [ 5 ]. So far, no studies have been performed investigating the innate immune response against H. meleagridis , especially toll-like receptors (TLRs), together with pro-inflammatory cytokines expression.…”

Early infection with Histomonas meleagridis has limited effects on broiler breeder hens' growth and egg production and quality

“…Infection with H. meleagridis has varying consequences dependent on the gallinaceous bird host ( Lund and Chute, 1972 ). Chickens have milder clinical signs than the turkey, where there is pathologic lesions and inflammation in the ceca with minimal, if any, damage to the liver ( Lund, 1967 ; Powell et al., 2009 ; Mitra et al., 2018 ). Cecal lesions and an inflammatory response have been found as early as 3 D after inoculation and can be seen up to 3 wk after ( Hauck and Hafez, 2013 ).…”