Evaluation of tick salivary and midgut extracellular vesicles as anti-tick vaccines in white-tailed deer (Odocoileus virginianus)

Authors: GONZALEZ, JULIA - Texas A&M University; HARVEY, CRISTINA - Texas A&M University; DE SOUZA RIBERIRO-SI, CARITA - Federal University Of Goias; LEAL-GALVAN, BRENDA - Texas A&M University; PERSINGER, KELLY - Texas Agrilife Research; Olafson, Pia; JOHNSON, TAMMI - Texas Agrilife Research; OLIVA CHAVEZ, ADELA - University Of Wisconsin

Submitted to: bioRxiv
Publication Type: Pre-print Publication
Publication Acceptance Date: 9/20/2024
Publication Date: 9/24/2024
Citation: Gonzalez, J., Harvey, C., De Souza Riberiro-Si, C., Leal-Galvan, B., Persinger, K.A., Olafson, P.U., Johnson, T.L., Oliva Chavez, A. 2024. Evaluation of tick salivary and midgut extracellular vesicles as anti-tick vaccines in white-tailed deer (Odocoileus virginianus). bioRxiv. https://doi.org/10.1101/2024.09.20.614210.
DOI: https://doi.org/10.1101/2024.09.20.614210

Interpretive Summary: Current tick control measures are focused on the use of pesticides and personal protective measures. Nevertheless, the emergence of pesticide resistance and the maintenance of tick populations by wildlife has impacted the efficient management of ticks. Host-targeted, non-chemical control measures are needed that can reliably reduce ticks on those wildlife that are reservoirs of disease-causing pathogens. This project aimed to evaluate extracellular vesicles (EVs) from lone star tick females as anti-tick vaccine candidates for white-tailed deer. EVs can harbor different biological molecules, like proteins, DNA, RNA, and lipids, and these molecules can be transported by EVs to various tissues within an organism or secreted by tick cells into the skin environment where ticks attach. EVs from tick salivary glands (SG) and midguts (MG) were isolated and formulated to vaccinate three deer. Two control (non-vaccinated) deer were injected with PBS only. Levels of anti-EV antibodies were measured over the course of a year to evaluate long-term immunity. Vaccination resulted in significant increases in anti-EV levels that remained higher than controls and pre-vaccination levels at year 1. In parallel, deer were infested with 100 lone star tick nymphs, 50 adult females, and 50 adult males at 58 days post vaccination. Nymphal and adult female ticks were allowed to feed until they were fully engorged and dropped from the host. The on-host and off-host mortality were evaluated as were the tick engorgement weight, nymph molting, time to oviposition, and egg hatchability. No negative effects were observed on nymph biological paraemters, but on-host mortality of female lone star ticks was significantly higher in vaccinated animals compared with non-vaccinated controls. No effects were observed on reproductive parameters. These results indicate that proteins within female tick vesicles are not good candidates for vaccine design against nymphs; however, the on-host adult mortality suggests that tick EVs harbor protective antigens against lone star tick females.

Technical Abstract: Current tick control measures are focused on the use of synthetic acaricides and personal protective measures. Nevertheless, the emergence of acaricide resistance and the maintenance of tick populations in wildlife has precluded the efficient management of ticks. Thus, host targeted non-chemical control measures that can reliably reduce ticks within sylvatic reservoirs are needed. This project aimed to evaluate extracellular vesicles (EVs) from Amblyomma americanum as vaccine candidates for white-tailed deer (Odocoileus virginianus; WTD). Salivary glands (SG) and midguts (MG) EVs were isolated by ultracentrifugation. Three deer were vaccinated with SG and MG EVs and received two boosters at days 28 and 50. Two control deer were injected with adjuvant and PBS only. Serum samples were recovered every seven days and at one year (Y1) and 1-year and 1-month (Y1M1) to assess long-term immunity levels. At 58 days post vaccination/boost, WTD were infested with 100 A. americanum nymphs, 50 females, and 50 males that were allowed to feed to repletion. On-host and off-host mortality, tick engorgement weight, nymph molting, time to oviposition, and egg hatchability were evaluated. Vaccination resulted in seroconversion and significant increases in IgG levels that remained significantly higher than controls and pre-vaccination levels at Y1 and Y1M1. No negative effects were observed in nymphs, but on-host mortality of female A. americanum was significantly higher in vaccinated animals. No effects were observed on reproductive parameters. These results indicate that proteins within female tick vesicles are not good candidates for vaccine design against nymphs; however, the on-host adult mortality suggests that tick EVs harbor protective antigens against A. americanum females.