[Diversity of flea vectors as a function of plague foci].

The Indian model of plague transmission by Xenopsylla cheopis, discovered by P.L. Simond, has been largely adopted even though it is flawed. X. cheopis cannot be the primitive vector, for neither its nor the rats' cradle is the same as for plague. Furthermore, the insect's vital cycle is impaired by proventriculus blocking. The combination of three factors--the synathropic rat, X. cheopis and Yersinia pestis--coupled with man's seafaring was what led to the multiplication of plague foci. This in turn "created" the third pandemic only because the disease was thus spread to very diverse biogeographical zones. The perennial establishment of the cycle happened through the bacillus' adaptation to many endemic fleas and parasites of numerous endemic animals. Indeed, in many countries, X cheopis is not involved in the persistence of selvatic plague.