Studies in Tick-borne Fever of Sheep. I. Transmission by the Tick, Ixodes ricinus, with a Description of the Disease Produced

Abstract

1. The causal agent of tick-borne fever is transmitted by the adult female and the nymphal stage of the tick Ixodes ricinus. Two female ticks are sufficient to produce infection in a sheep. The larval stage does not appear to be infective. In a limited number of experiments the disease has not been produced in sheep by the inoculation of emulsions of presumably infective ticks.2. The disease as produced by tick infestation is characterised by a period of incubation which varies from 3 to 13 days, after which there is a sharp rise in temperature; a “plateau” type of febrile reaction follows which lasts from 6 to 22 days, the temperature gradually subsiding to normal. Affected animals usually recover. Mortality as a direct result of infection is rare, but there is evidence to suggest that tick-borne fever may predispose affected animals to death from secondary causes.3. The blood of a sheep which has reacted to the disease remains infective for some time after the subsidence of the thermal reaction.4. The goat is susceptible to tick-borne fever.5. The economic importance of tick-borne fever is discussed.