Abstract
Biologically there are 2 groups of relapsing fever spirochaetes, one being transmitted by lice and the other by ticks, chiefly of the Ornithodorus group. The Chinese strain of Spirochaeta recurrentis has been demonstrated by Robertson 1 and Chung 2 to be transmitted by the louse, Pediculus humanus corporis, and its development in this insect has been studied recently by Chung and Feng. 3 In order to see whether infection with the Chinese strain of relapsing fever spirochaetes can be established in Ornithodorus moubata, and whether infection can be transmitted to laboratory animals by these ticks, a series of experiments was carried out.
Four lots of young larval ticks and one lot of adult male and female ticks were fed on squirrels heavily infected with Chinese relapsing fever (30-40 spirochaetes to each oil immersion dark field of the fresh smear). After the infective feeding, the ticks were kept at a room temperature of 25-28°C. Examinations for infection of the ticks were made by dissection and searching for spirochaetes under darkneld illumination by the method used by Feng and Chung, 4 by feeding on clean squirrels and finally by injecting emulsified ticks into squirrels. The blood of the animals was examined daily with dark ground illumination for spirochaetes throughout the course of the experiment.
The dissections, as shown in Table I, demonstrate that the spirochaetes penetrated the stomach wall and reached the body cavity in some of the ticks during the first 4 days of infection. All the spirochaetes, including those which had already reached the body cavity and those still in the stomach gradually died, degenerated, and finally disappeared, beginning as early as the 4th day in some of the ticks.
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