Silencing expression of the Rhipicephalus microplus vitellogenin receptor gene blocks Babesia bovis transmission and interferes with oocyte maturation

Authors: HALA, HUSSEIN - Washington State University; Johnson, Wendell; Taus, Naomi; Suarez, Carlos; Scoles, Glen; Ueti, Massaro

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2018
Publication Date: 1/5/2019
Citation: Hala, H.E., Johnson, W.C., Taus, N.S., Suarez, C.E., Scoles, G.A., Ueti, M.W. 2019. Silencing expression of the Rhipicephalus microplus vitellogenin receptor gene blocks Babesia bovis transmission and interferes with oocyte maturation. Parasites & Vectors. 12(1):7. https://doi.org/10.1186/s13071-018-3270-1.
DOI: https://doi.org/10.1186/s13071-018-3270-1

Interpretive Summary: Babesiosis, caused by the parasite Babesia bovis, causes significant economic losses to the livestock industry. The parasite is acquired by uninfected Rhipicephalus microplus ticks feeding on B. bovis infected cattle. The parasite goes through developmental stages in the tick and migrates to various tissues including the ovaries, where they invade the tick eggs. Infected eggs develop into infected nymphs, which attach to cattle for feeding. During this feeding the tick transmits B. bovis to the cattle. One approach to breaking the transmission cycle is to interfere with parasite development and/or invasion of tick eggs. Vitellogenin (Vg) is the precursor of vitellin, a critical nutrient for tick embryo development. Vitellogenin receptors are important in transporting Vg from the tick hemolymph to the tick egg yolk granules. This study examined if silencing the Vg receptor in ticks had an effect on B. bovis transmission. In addition to negative effects on tick development, silencing the Vg receptor prevented transmission of B. bovis to the next generation of ticks. Therefore, the Vg receptor may be a potential target for the development of novel strategies to control both R. microplus by reducing tick reproduction and B. bovis transmission.

Technical Abstract: Rhipicephalus microplus is an efficient biological vector of Babesia bovis, a causative agent of bovine babesiosis. Babesia bovis is passed vertically to the next generation of ticks prior to transmission to naïve animals. Due to the importance of the R. microplus ovary for tick reproduction and transmission of B. bovis, we investigated if silencing vitellogenin receptor gene expression in the ovary during tick feeding on B. bovis infected cattle affected parasite transmission to the next generation of ticks. Silencing the vitellogenin receptor by RNA interference knocked down the receptor transcription in the ovary resulting in decreased tick fertility. We observed low egg mass production, low egg weight, low embryonic development rate, and a reduction in larval hatching. Down regulation of the R. microplus vitellogenin receptor interfered with B. bovis vertical transmission. This conclusion was supported by PCR results which demonstrated that 12% (7/58) and 17% (10/58) of larvae from the non-injected and buffer-injected control groups, respectively, were infected with B. bovis, while none of the larvae (0/58) from the RmVgR dsRNA group were PCR positive. These results indicate that the vitellogenin receptor is essential for tick reproduction and may play a vital role in B. bovis transmission.