Studies on Pasteurella Pestis in Fleas VII. The Plague-Vector Efficiency of Hystrichopsylla Linsdalei Compared with Xenopsylla Cheopis under Experimental Conditions

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Abstract
Summary An experimental study is reported on the plague-vector capacity of the wild-rodent flea, Hystrichopsylla linsdalei, compared with the rat flea, Xenopsylla cheopis. The average temperature under which the infected fleas were held (19°C) was lower than that in previous tests with H. linsdalei. Although the H. linsdalei blocked sooner than the X. cheopis, the rate of blocking in the latter species was more rapid and resulted in a greater number of blocked individuals. The plague-vector indices of male and female fleas combined were 0.002 for H. linsdalei and 0.03 for X. cheopis. The lower efficiency of H. linsdalei, under the conditions of the experiment, are partially ascribed to a lower blocking rate and a shorter survival period for the blocked individuals. Thus, the wild rodent flea had fewer opportunities to transmit P. pestis than the rat flea. There was no evidence that infectious feedings by the fleas on different mice with comparable plague septicemia influenced subsequent infection or blocking rates. Rather, differences between the two species suggested the presence of unknown physiological factors which may enter into the receptivity of a flea species to the growth of plague within its intestinal tract. The average death time of mice succumbing to plague transmitted by H. linsdalei was about 5 days, whereas the death time for mice infected by X. cheopis averaged about 4 days. This may have some bearing on the number of bacilli injected by blocked fleas. In confirmation of past work, it was found that culture of feces from, and microscopic observation of, fleas infected with P. pestis are useful procedures, but they do not provide an unequivocal basis for the determination of individual flea infection. The culture of individual fleas is the method of choice.