Project Number: 8042-32000-012-01-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2017
End Date: Dec 31, 2020
The current project has two objectives: (1) evaluate efficacy of two ARS novel anti-tick antigens, when used individually or in mixture, against adult blacklegged ticks (Ixodes scapularis) and lone star tick (Amblyomma americanum) infesting rabbit; and (2) determine how the anti-tick vaccine may block tick blood feeding and other physiological processes that lead to tick mortality.
This work will be conducted by a scientist and her research team at Department of Veterinary Pathobiology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University. Laboratory animals (New Zealand rabbits) will be purchased from commercial sources (Charles River) and maintained and used for this project following protocols approved by the university’s Institutional Animal Use and Care Committee (IAUCC), AUP#2017-0017. (1) Anti-tick antigen efficacy tests. New Zealand rabbits will be randomly assigned into one of four experimental groups (control, antigen-1, antigen-2, and mixture of antigens 1 and 2) with 5 animals in each group. Rabbits will be housed in individual spaces to facility handling, tick infestation, and sample collection. A small volume of the injectable anti-tick antigen formulation, or the adjuvant only formulation (control), will be administrated to individual rabbits through subcutaneous injection at days 0, 14 and 28. Each rabbit will be infested with 20 adults (10 males and 10 females) of the blacklegged tick and lone star tick (10 ticks per species) between days 42 to 56 post-priming by releasing ticks on the ears of the animal and isolating using stocking bandage around the ears and E-collars. Tick attachment will be examined at 6, 12 and 24 h post-infestation. Unattached ticks will be removed from experiments at 24 h post-infestation. Tick attachment rate will be recorded for each animal. Animals will be monitored daily for 10 days to collect and record ticks (live, dead, fed or unfed) dropped from each animal. A final examination of each animal will be performed on day 11 to remove any still attached ticks and record the status of each tick (live or dead). The attachment rate, percentage of blood fed, and percent mortality will be calculated for each experimental group. The experiment will be repeated two times so each treatment group will have a minimum of three replicates. The mean attachment rate, blood feeding rate, and mortality will be calculated for each treatment group. Control efficacy of antigen-1, antigen-2, and the mixture formulations will be calculated by comparing with the control group following an established formula. (2) Effects of host vaccination on tick blood feeding activity. An electric feeding monitor will be used to record blood feeding activities of an attached tick. Rabbits chosen from one of the experiment groups will be restrained in a holding tube. A fine silver electrode (150 µm in diameter) will be attached to the tick and a similar electrode will be attached to the rabbit next to the attachment site. Electrode wires will be connected to the feeding monitor for the system to record minute voltage changes associated with blood ingestion, salivation, and other activities during blood feeding. Recordings will be conducted to collect data from at least 5 ticks from each of the four experimental groups. Different wave forms will be compared among ticks feeding on animals in different experimental groups and effects of anti-tick vaccination on tick blood feeding activity will be determined.