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

Rubikah Vimonish,Maxime Madder,Wendell C Johnson,Janaina Capelli-Peixoto,Lindsay M Fry,Kelcey D Dinkel,Massaro W Ueti,George Chaka,Reginaldo G Bastos,Donald P Knowles,Glen A Scoles

doi:10.1186/s13071-021-05120-7

Abstract

BackgroundVector-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.MethodsNymphs of Rhipicephalus appendiculatus were infected with Theileria parva by feeding on a calf during an acute infection. Isolation of sporozoites was accomplished by feeding infected adult ticks on an in vitro tick feeding system. Sporozoite viability was tested using in vitro bovine lymphocytes.ResultsWe isolated infectious T. parva sporozoites secreted into an in vitro tick feeding system. Infected adult R. appendiculatus 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 the ticks were allowed to feed for 3 h to collect secreted T. parva sporozoites. Secreted sporozoites infected in vitro bovine lymphocytes, demonstrating that isolated sporozoites remained viable and infectious.ConclusionsThis work is the first to report the isolation of mature infectious T. parva sporozoites using an in vitro tick feeding system, which represents a significant step towards the development of a more efficient control strategy for T. parva. Isolation of infectious tick-stage parasites will facilitate the examination of the vector-pathogen interface, thereby accelerating the development of next-generation vaccines and treatment interventions for tick-borne pathogens.Graphical

Highlights

Vector-borne diseases pose an increasing threat to global food security
We demonstrated that isolated T. parva sporozoites from the in vitro tick feeding system were viable and infectious to bovine peripheral blood mononuclear cells (PBMC)
Infection of R. appendiculatus ticks with T. parva Rhipicephalus appendiculatus nymphal ticks were acquisition-fed on a calf exhibiting clinical signs of East Coast fever (ECF) including fever, enlarged lymph nodes, and anorexia

Summary

Introduction

Vector-borne diseases pose an increasing threat to global food security. Vector-borne diseases pose an increasing threat to animal health due to the movement of live animals and increasing geographic distribution of competent ticks [1,2,3,4]. After ingestion of the blood meal, pathogens enter midgut epithelial cells and undergo development, with subsequent migration to, and invasion of, the salivary glands where the pathogen replicates [8]. Following molting and transfer to a subsequent host, tick feeding stimulates pathogens to undergo a developmental cycle in tick salivary gland acini cells. Replication and development of pathogens in the midgut and salivary glands illustrates that ticks are efficient biological vectors [8,9,10]

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