Evaluation of tick salivary and midgut extracellular vesicles as anti-tick vaccines in White-tailed deer ( Odocoileus virginianus )
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Abstract
Current tick control measures are focused on the use of synthetic acaricides and personal protective measures. However, 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 are needed to reliably reduce ticks parasitizing sylvatic reservoirs. This project aimed to evaluate extracellular vesicles (EVs) from Amblyomma americanum as vaccine candidates for white-tailed deer ( Odocoileus virginianus ; WTD). Salivary gland (SG) and midgut (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. On day 58, 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. Serum samples were recovered every seven days until the last day of tick drop off, and then at one year (Y1) and 1-year and 1-month (Y1M1). Vaccination resulted in seroconversion and significant increases in total 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 SG and MG 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.
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Thank you so much for all your responses, Adela! Super useful and much appreciated.
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We decided to eliminate those ticks because we do not know for certain what was their fate. We think they "ate" them. We want to put cameras within the pens next time because we do think that it is causing discomfort to the animals. #929, which was the one with the strongest immune response, complete removed its patch with nymphs, even though the others did nothing to the nymphs. We want to make videos and actually evaluate the behavior next time.
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Hello,
We have the comparison as well. They have what I call "core cargo" that are proteins that are shared between vesicles secreted by different organs (i.e. heat shock poteins, GTPases, and others), but they also contain organ specific cargo. We have the proteomic comparison of the vesicles that were used for this vaccination. We just need to prepare the manuscript. It should be coming by the end of the year along with the proteins that are recognized by the immune response of the deer.
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Hello Seemay,
We did quantitative the proteomics of Amblyomma EVs at D3, D5, and D7 during feeding on rabbits. Both organs present temporal changes in their cargo. However, there were several proteins that showed not significant change. D5 falls within the "slow feeding", when the tick is modulating the immune responses and before they start the process of ingesting large amounts of blood (which results in contaminants from the host during EV isolation) and start the process of dislodging from the bite site. Given that we were targeting slow feeding, we decided to use D5.
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These ticks were considered “non-recovered”
Did you note a higher rate of "non-recovery" on the vaccinated animals? I'm wondering whether you'd hypothesize that vaccination against the EVs could be the cause of increased itching or irritation that alerts the animals to the ticks.
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allowed to feed for 5 days
Would you mind sharing your rationale for isolating EVs at this time point? Do you know how EV cargo or composition might vary depending on the feeding time point when you harvest?
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both organs predominantly secreted exosomes and microvesicles of small size
Curious if you know anything about the composition of these vesicles relative to each other? Are they carrying very distinct cargo?
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