Recipient Organization
VST LLC
101 N MAIN AVE
SIOUX FALLS,SD 57104
Performing Department
(N/A)
Non Technical Summary
Tick-borne pathogens cause major economic losses to the livestock industry, leading to an estimated $19.7 billion in losses forthe U.S., including approximately $3 billion in losses for cattle producers. Among the 900 species of ticks, the Asian longhornedtick (ALT), an invasive, non-native tick species, poses a major threat to animal health and productivity in cattle and otherlivestock. Currently, tick management includes inspection and chemical control and can be a tedious and expensive process forlivestock producers. Unfortunately, there are no vaccines in the U.S. that target ALT. Medgene Labs will develop the first U.S.-based ALT anti-tick vaccine, which will be baculovirus derived and administered as a 2-dose regimen. This vaccine willsignificantly reduce the cost, time, and effort associated with herd management. This Phase II project will 1) demonstrate the efficacy of the vaccine in reducing tick loadand 2) determine the mechanism of action of the vaccine. Successfulcompletion of our Phase I project will generate data toestablish the utility of our vaccine against tick-borne disease in cattle and will provide a model for the development of effective vaccines against other tick species native to the U.S.
Animal Health Component
100%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Goals / Objectives
There are two goals for the study. One is to evaluate the Asian longhorn tick vaccine from Phase I in a field study in cattle. Vaccine will be given to 30-50 cattle at up to ten different sites in Virginia to assess the impact on ticks. Cattle will be evaluated for 6 months post vaccination. The other goal of the study is to evaluate the impact of the vaccine on the health of ticks. Blood from cattle that have been vaccinated with the Asian longhorn tick vaccine will be fed to ticks in a controlled artificial system. The ticks will be evaluated for engorgement, egg deposition, and larval development to better understand the mechanism of action on the ticks.
Project Methods
For the mechanism of action goal, six female calves aged 7-10 months (500-700 lb.) will be vaccinated using a two dose regimen and 6 additional calves will receive a control vaccination (adjuvant alone). Three 10-ml blood samples will be collected in serum separator tubes (SST) from each calf at 30, 60, 120, and 180 days post-vaccination. The first two samples (20 ml total) from each animal will be used to feed ticks and characterize the effect on feeding, reproduction, and development. The third sample will be sent to the project team at Medgene Labs for serological analysis to quantify the animal's individual immunological response to the vaccination.Serum samples will be prepared by allowing the whole blood samples to clot for 1 hour at room temperature and centrifuging the samples for 15 minutes at 1,300×g.Titers of specific antibodies to Hl86 will be determined by ELISA. The plates will include positive and negative controls to monitor assay performance. The results will be reported as the dilution at which Hl86-specific antibodies are no longer detected.The in vitro tick feeding system that will be used in this project was developed by Dr. Massaro Ueti and co-workers at the USDA Animal Disease Research Unit.The systemallows the feeding of ticks with blood via a silicone membrane under controlled conditions. Ticks will be allowed to feed for 5-14 days. This feeding system will be used in conjunction with standard methods for quantifying tick feeding (engorgement), egg laying (oviposition), egg hatching, and larval development to assay the effects of the vaccine (via anti-HL86 antibodies in the blood) on ticks at 30, 60, 120, and 180 days post-vaccination. Engorgement (a measure of tick feeding) will be quantified by counting and weighing the female ticks that have fed to repletion and detached from the feeding membrane. The mean tick weight per group (for vaccinated and control groups) will be used to calculate the effect of the vaccine on engorgement. Oviposition (a measure of tick reproduction) will be quantified after feeding by individually incubating 100 engorged female ticks per animal under appropriate conditions and recording the number of ticks laying eggs and the number of eggs laid. The number of eggs laid will be estimated by weighing a sample of the eggs from a cluster, counting them under a magnifying glass, weighing the cluster, and obtaining an estimate of the total egg number on this basis (i.e., [cluster weight/sample weight] × sample egg number).The mean egg number for each group (vaccinated and control) will be used to calculate the effect on oviposition. Hatchability (a second reproductive measure) will be quantified by gently mixing the eggs from the individual ticks in each group, weighing 3 equal samples corresponding to the mean cluster weight, and incubating them under appropriate conditions to hatch. The mean number of larvae for each group (vaccinated and control) will be determined along with the standard deviation and used to calculate the effect on hatchability. In addition, the effect of the vaccine on larval development will be determined through assessment of larval feeding (engorgement), percentage of larvae that molt into nymphs, and larva-to-adult developmental time for each group.Immunohistochemistry will be performed on ticks fed blood from vaccinated cattle to show where the antibodies are binding. Briefly, ticks will be fixed in 10% formalin and embedded in paraffin, and sectionswill be blocked with normal serum, and bovine antibodies in the midgut will be detected with conjugate anti-bovine detection antibodies. For the second goal,in collaboration with veterinarian Dr. Kiel Hausler, we will enroll up to 10 herds of ≥30 cattle (n = ≥180). The study will be aligned with normal herd health management activities, with vaccinations (2 doses, 28 days apart) starting in April 2025 to target the Spring 2025 tick season. The schedule of events for the field study is shown in Table 2. The cattle at each site will be randomized (by random selection of ID tags in non-chronological order) to receive either the Hl86 vaccine (Group 1) or a placebo (Group 2) administered by subcutaneous injection (2 ml). The day of this initial injection will be designated as Day 0. Each animal will receive a second ("booster") injection at Day 28. Blood will be collected for serology at Day 0 (pre-vaccination), Day 28, ~Day 60 (2-month visit), ~Day 120 (4-month visit) and ~Day 180 (6-month visit). The blood samples will be processed by Dr. Hausler to prepare serum samples that will be shipped to Medgene Labs to quantify the immune responses of the cattle by ELISA (for the ELISA method, see the description under "Serological analysis" in Objective 1 above). Dr. Hausler will conduct 3 follow up visits to assess the impact of the vaccine on tick load at 2 months, 4 months, and 6 months post-vaccination. Total tick loadwill be recorded for each animal at each timepoint. The health of the cattle will be monitored throughout the study, with an assessment of each animal performed by Dr. Hausler at each study visit. Tick load for the study groups will be summarized using descriptive statistics (mean, standard deviation), and the statistical significance of the differences in tick load between the treatment groups will be determined by performing t tests for independent samples (α = 0.05).