A new inactivated Tritrichomonas foetus vaccine that improves genital clearance of the infection and calving intervals in cattle

Systematic Review of Vaccine Strategies Against Tritrichomonas foetus Infection in Cattle: Insights, Challenges, and Prospects

Tritrichomonas foetus is a protozoan parasite that causes bovine trichomonosis (also referred to as trichomoniasis) resulting in substantial economic loss in extensive grazing systems. The parasite colonises the reproductive tracts of both male and female cattle, being asymptomatic in males but causing early reproductive failure in infected females. This systematic review aimed to examine research manuscripts describing the development of T. foetus vaccines, the strategies employed, and the immune response associated with T. foetus infection. A systematic review was conducted using indexed sources on Scopus, PubMed, Web of Science, and Embase to search for published vaccine development studies in English utilising either experimental or commercial T. foetus vaccines for bovine trichomonosis. Search terms (cattle, bull, heifer, vaccine, immune response, and Tritrichomonas foetus) were entered into the indexed sources and with no limit was set for the year of publication. Among 374 studies imported for screening, 96 were duplicates, and 255 were excluded for irrelevancy as these studies did not meet the inclusion criteria (report original data, vaccine tests in cattle, and used either commercial or experimental vaccines that incorporated antigens from T. foetus). A further five studies were excluded after full-text review as either the publication described a different target pathogen or the full text was not in English. Eighteen studies met the inclusion criteria and were subjected to data extraction using the Covidence platform. Studies included in the systematic review reported three vaccine strategies, including subunit, cell fraction, and whole-cell killed vaccines. This review considers the design, rationale, and results of each of the 18 studies to provide a comprehensive overview of the current knowledge and to inform future research agendas. While whole-cell killed vaccines are most prevalent, they have shown superior efficacy compared to subunit vaccines studied to date. One study using a purified fractions of T. foetus cell membranes as vaccine demonstrated higher efficacy and higher calving rates compared to the whole-cell killed vaccine. All of these methods require cell culture growth of T. foetus which can be challenging compared to the production of recombinant proteins. At this stage, no T. foetus recombinant antigens have been reported. Advances in understanding the parasite's genome, pathogenesis, host-parasite interactions, and host immune responses to T. foetus will provide opportunities for the development of novel vaccine strategies for bovine trichomonosis.

Bovine neutrophils kill the sexually-transmitted parasite Tritrichomonas foetus using trogocytosis

The protozoan parasite Tritrichomonas foetus (T. foetus) is the causative organism of bovine trichomonosis (also referred to as trichomoniasis), a sexually-transmitted infection that reduces fertility in cattle. Efforts to control trichomonosis on cattle farms are hindered by the discouragement of antibiotic use in agriculture, and the incomplete, short-lived protection conferred by the current vaccines. A more complete mechanistic understanding of what effective immunity to T. foetus entails could enable the development of more robust infection control strategies. While neutrophils, the primary responders to infection, are present in infected tissues and have been shown to kill the parasite in vitro, the mechanism they use for parasite killing has not been established. Here, we show that primary bovine neutrophils isolated from peripheral blood rapidly kill T. foetus in vitro in a dose-dependent manner, and that optimal parasite killing is reduced by inhibitors of trogocytosis. We also use imaging to show that bovine neutrophils surround T. foetus and trogocytose its membrane. These findings are consistent with killing via trogocytosis, a recently described novel neutrophil antimicrobial mechanism.

Activation of murine macrophages by membrane proteins from Tritrichomonas foetus grown on iron- and calcium-rich conditions

Tritrichomonas foetus is a protozoan parasite that causes a venereal disease in cattle limiting reproduction by abortions and sterility. The immune response against this parasite is poorly understood. Since the iron and calcium ions are important regulators of the microenvironment of the urogenital tract in cattle, we decided to evaluate the role of these divalent cations on the antigenicity of membrane proteins of T. foetus on macrophage activation as one of the first inflammatory responses towards this pathogen. Colorimetric methods and ELISA were used to detect the nitric oxide and oxygen peroxide production and expression of cytokines in culture supernatant from macrophage incubated with membrane proteins from T. foetus cultured in iron- and calcium-rich conditions. qRT-PCR assays were used to evaluate the transcript expression of genes involved in the inflammatory response on the macrophages. The membrane proteins used for in vitro stimulation caused the up-regulation of the iNOS and NOX-2 genes as well as the generation of NO and H2 O2 in murine macrophages on a dependent way of the metal concentrations. Additionally, after stimulation, macrophages showed a considerable rise in pro-inflammatory cytokines and a downregulation of anti-inflammatory cytokines, as well as up-regulation in the transcription of the TLR4 and MyD88 genes. These data suggest that membrane proteins of T. foetus induced by iron and calcium can activate an inflammatory specific macrophage response via TLR4/MyD88 signalling pathway.