Isolation of infectious Theileria parva sporozoites secreted by infected Rhipicephalus appendiculatus ticks into an in vitro tick feeding system

Authors: VIMONISH, RUBIKAH - Washington State University; DINKEL, KELCEY - Washington State University; Fry, Lindsay; Johnson, Wendell; CAPELLI-PEIXOTO, JANAINA - Washington State University; BASTOS, REGINALDO - Washington State University; Scoles, Glen; KNOWLES, DONLAD - Washington State University; MADDER, MAXIME - Clinglobal; CHAKA, GEORGE - Lilongwe University Of Agriculture And Natural Resources; Ueti, Massaro

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2021
Publication Date: 12/24/2021
Citation: Vimonish, R., Dinkel, K.D., Fry, L.M., Johnson, W.C., Capelli-Peixoto, J., Bastos, R.G., Scoles, G.A., Knowles, D.P., Madder, M., Chaka, G., Ueti, M.W. 2021. Isolation of infectious Theileria parva sporozoites secreted by infected Rhipicephalus appendiculatus ticks into an in vitro tick feeding system. Parasites & Vectors. 14. Article 616. https://doi.org/10.1186/s13071-021-05120-7.
DOI: https://doi.org/10.1186/s13071-021-05120-7

Interpretive Summary: Tick-borne diseases, including theileriosis, babesiosis, and anaplasmosis, are an important threat to livestock and food security globally. Improved control of these diseases, through the development of better diagnostic tests, vaccines, and drugs, is important to the long-term sustainability of livestock production world-wide. A major limitation to scientific advancement of control measures for tick-borne diseases has been the inability to isolate and purify tick stages of these pathogens for close study and manipulation. In this work, we used an in vitro tick feeding chamber to isolate tick stages of the tick-borne cattle parasite, Theileria parva. In this, ticks were fed for short periods on sterile medium in the chamber and allowed to excrete infectious T. parva parasites into the medium. We were then able to concentrate these parasites and use them to infect bovine cells, demonstrating that the isolated parasites retained infectivity. This is the first description of T. parva tick-stage parasite isolation using an in vitro tick feeding system. This system can be applied to many different tick-borne disease systems of livestock, and the purified parasites used to discover new targets for improved vaccines, diagnostic assays, and drug therapy for tick-borne diseases of livestock.

Technical Abstract: Vector-borne diseases pose an increasing threat to global food security. Vaccines, diagnostic tests, and therapeutics are urgently needed for tick-borne diseases that affect livestock. However, the inability to obtain significant quantities of pathogen stages derived from ticks has hindered research. In vitro methods to isolate pathogens from infected tick vectors are paramount to advance transcriptomic, proteomic, and biochemical characterizations of tick-borne pathogens. In this study, we isolated Theileria parva sporozoites from tick salivary glands, secreted into an in vitro tick feeding system. Infected R. appendiculatus adult ticks attached to and successfully fed on silicone membranes in the in vitro tick feeding system. Bovine blood in the receptacle was replaced with cell-free medium and ticks allowed to feed for three hours to collect secreted T. parva sporozoites. Secreted sporozoites infected in vitro bovine lymphocytes, demonstrating that isolated sporozoites remained viable and infectious. This novel system to isolate tick-stage parasites will facilitate investigation of the vector-pathogen-mammalian host interface, thereby accelerating the development of improved diagnostics, next-generation vaccines, and treatment interventions for tick-borne pathogens.