Studies in Tick-borne Fever of Sheep

Abstract

(1) Female Ixodes ricinus ticks which feed on a sheep infected with tick-borne fever are not capable of transmitting the infective agent to their progeny. Only the nymphs and females, therefore, can be infective to sheep. In the case of an infective female, the infection may have been acquired, (a) in the immediately preceding stage, or (b) in the larval stage, the infective agent remaining in the tissues of the tick during the nymphal engorgement and subsequent moult. This appears to occur irrespective of whether the host on which the nymph feeds is a susceptible or an insusceptible. animal.(2) Ticks which have acquired infection are infective as soon after moulting to the next stage as they are able to attach to hosts. Unfed ticks were not found to be infective after a period of about 14 months.(3) Infection is transmitted to the sheep in the course of the 2nd day after attachment of infective nymphs.(4) The disease may be transmitted to sheep by inoculation of emulsions of infective ticks, if these have been allowed to commence engorgement. The use of saline for such emulsions appears to be inadvisable.