Quantitative analysis of Anaplasma marginale acquisition and transmission by Dermacentor andersoni fed in vitro

Authors: VIMONISH, RUBIKAH - Washington State University; Johnson, Wendell; Mousel, Michelle; BRAYTON, KELLY - Washington State University; Scoles, Glen; Noh, Susan; Ueti, Massaro

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2019
Publication Date: 1/16/2020
Citation: Vimonish, R., Johnson, W.C., Mousel, M.R., Brayton, K.A., Scoles, G.A., Noh, S.M., Ueti, M.W. 2020. Quantitative analysis of Anaplasma marginale acquisition and transmission by Dermacentor andersoni fed in vitro. Scientific Reports. 10:740. https://doi.org/10.1038/s41598-019-57390-y.
DOI: https://doi.org/10.1038/s41598-019-57390-y

Interpretive Summary: In this study, we describe a new in vitro tick feeding system that can facilitate the study of ticks and tick-borne pathogens. As a tick-pathogen interaction model to optimize the system, we used Dermacentor andersoni and Anaplasma marginale. Ticks were fed on 10-fold diluted bacteremia to determine the effect of dose on tick infection rate. After feeding on infected blood, ticks were transferred to uninfected blood to stimulate bacteria replication within the tick vector. During stimulation feeding, blood samples were collected daily to determine if infected ticks secreted viable A. marginale. The results demonstrated similar attachment rates between the first and second tick feeding on silicone membranes. Tick midgut and salivary glands were infected with A. marginale. However, salivary gland infection rates decreased as bacteremia decreased during tick acquisition feeding. Bacteria recovered from the in vitro system infected naïve bovine. Using the highly transmissible A. marginale St. Maries strain, we demonstrated the artificial tick feeding system is a suitable tool to study tick-pathogen interactions and A. marginale tick salivary gland infection is dose dependent. This work demonstrates the utility of an artificial tick feeding system to directly study the association between the acquired pathogen level and transmissibility by ticks.

Technical Abstract: Tick-borne diseases pose an increasingly wider threat to global public and animal health. The development of a versatile in vitro tick feeding system to study tick and tick-borne pathogens of humans and animals is paramount to advance control strategies. In this study, we describe the development of an innovative in vitro tick feeding system that facilitates the study of ticks and tick-borne pathogens. As a tick-pathogen interaction model to develop the in vitro system, we used Dermacentor andersoni and Anaplasma marginale, a cattle pathogen. To test if adult ticks acquired and transmitted A. marginale through the in vitro system, we fed ticks with A. marginale-infected cattle blood. Adult ticks were fed on 10-fold diluted bacteremia to determine if A. marginale levels during acquisition feeding affected tick infection. After feeding on infected blood, ticks were transferred to uninfected blood to stimulate Anaplasma replication in the midgut and salivary glands. During tick feeding stimulation, blood samples were collected daily to determine if infected ticks secreted viable A. marginale into the in vitro system. The results demonstrated similar attachment rates between the first and second tick feeding on silicone membranes. Anaplasma marginale colonized tick midgut and salivary glands at a sufficient level for successful transmission. However, salivary gland infection rates decreased as the number of bacteria was reduced during tick acquisition feeding. Bacteria recovered from the in vitro system infected naïve cattle. Using the highly transmissible A. marginale St. Maries strain, we established that the in vitro tick feeding system is a suitable tool to study tick-pathogen interactions and demonstrated that A. marginale tick infection is dose dependent. This work demonstrates the usefulness of an artificial tick feeding system to directly study the association between the acquired pathogen level and transmissibility by ticks.