Studies on Pasteurella Pestis in Fleas. V. The Experimental Plague-Vector Efficiency of Wild Rodent Fleas Compared with Xenopsylla Cheopis, Together with Observations on the Influence of Temperature

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Abstract
Summary and Conclusions Experimental studies are reported on the plague vector capacity of 13 different flea species compared with Xenopsylla cheopis. Of 12 wild rodent fleas tested, vector efficiency values of the following 8 species are presented for the first time: Epitedia wenmanni wenmanni × testor, Megabothris clantoni johnsoni, Monopsyllus exilis kansensis, Thrassis fotus, Thrassis bacchi johnsoni, Histrichopsylla sp., Meringis shannoni, and Catallagia decipiens. None of the species tested approached the high vector efficiency of X. cheopis. Of the wild rodent fleas used, Thrassis bacchi johnsoni and Hystrichopsylla sp. had the highest vector efficiencies. The overall vector capacity of these two species, as shown by their vector indices, was much better than any of the other species and approached the value shown for X. cheopis. Confirmation was obtained of the vector capacity of some flea species used in these tests and in tests by other workers. Experiments with the ground squirrel flea, Diamanus montanus, showed this species to be a very poor vector under laboratory conditions. These results confirmed former work, and tended to support the hypothesis of Burroughs (1947) that biological strain differences in this species may account for the finding of both low and high plague vector capacity in fleas from different locations. A mean temperature of about 8°C. was apparently responsible for the prevention of proventricular blocking in D. montanus, although the infection potential under these conditions was quite comparable to that of fleas held at higher temperatures. The plague vector capacity of Xenopsylla cheopis, held at an average temperature of about 21°C., was close to that shown by other studies under similar thermal conditions. At mean temperatures of about 8°C. and 20°C., surprisingly high vector efficiencies were obtained. The lowest values were obtained at a mean temperature of 30°C. When the blocking-survival potentials and the vector indices were calculated, the overall plague vector capacity of X. cheopis kept at from 20°C. to 22°C. was generally better than that shown by the fleas maintained at 8°C. The poor survival, after blocking, of X. cheopis held at 30°C., probably accounts for their very poor transmission potential. A major effect of temperature was apparently its influence upon the extrinsic incubation period of Pasteurella pestis in the flea. With X. cheopis, the average incubation period at 8°C. was 34.4 days; at from 20°C–22°C., it was 18.6 days; and at 30°C. it was 11.9 days.