Abstract
Sheep scab, caused by infestation with the mite Psoroptes ovis, is highly contagious, causing intense pruritus and represents a major welfare and economic concern. Disease control strategies rely upon chemotherapy, however, sustainability is questionable due to issues of chemical residues, eco-toxicity and acaricide resistance. Control by vaccination is supported by demonstration of protective immunity in sheep previously infested with P. ovis. We identified vaccine candidates for P. ovis based on: (1) antigens selected by their interaction with host signalling pathways and the host immune-response; and (2) those shown to be either immunogenic or involved in mite feeding. This resulted in the development and validation, in repeated immunisation and challenge trials, of a seven recombinant protein sub-unit cocktail vaccine. Sheep were inoculated on three occasions, 2 weeks apart, along with QuilA adjuvant. Vaccination resulted in highly significant reductions in both lesion size (up to 63%) and mite numbers (up to 56%) following challenge. Mean lesion size in vaccinates was significantly smaller than controls from 1 week post infestation (wpi) until the end of the experiment at 6 wpi. All antigens elicited serum IgG responses following immunisation and prior to infestation, whereas controls did not produce antigen-specific IgG during the pre-infestation period. Vaccinated animals showed an amnestic response, with levels of antigen-specific IgG against muGST, Pso o 1 and Pso o 2 increasing following infestation. This vaccine represents the greatest reduction in lesion size to date with a sheep scab vaccine, providing encouragement for future production of a commercially-viable means of immunoprophylaxis.
Highlights
Psoroptic mange caused by infestation with Psoroptes ovis, is highly contagious, causes intense pruritus and is a major welfare and economic concern [1, 2]
The vaccine resulted in highly significant reductions in both lesion size (57%) and mite numbers (56%) following challenge in repeated protection trials
Disease is transmitted via direct contact or fomites, so even modest decreases in lesion size and the concomitant reductions in mite numbers may limit disease spread [26–29]
Summary
Psoroptic mange (sheep scab) caused by infestation with Psoroptes ovis, is highly contagious, causes intense pruritus and is a major welfare and economic concern [1, 2]. The concept of control by vaccination is supported by the demonstration of partial immunity in sheep following previous infestation with P. ovis [4–6]: During primary infestation an initial “lag phase”, with small numbers of mites and tight, focal lesions, is followed by a more rapid “growth phase”, with increasing mite numbers and expanding lesions. Attempts to vaccinate sheep against P. ovis using mite extracts have shown promise, with a 13-fold reduction in mite numbers and >65% reduction in lesion size in vaccinated sheep compared to controls [8]. P. ovis extracts induce protection against mite challenge in cattle [9]. The practicality of a vaccine based on native P. ovis antigens is limited due to an inability to culture P. ovis in vitro, meaning that native antigen extracts would be prohibitively expensive to produce
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
