[Histological study of Xenopsylla cheopis fleas infected with the ulegeic subspecies of the plague microbe, Yersinia pestis ulegeica].

The plague microbe of the Ulegei subspecies is able to cause the stable infection of fleas of X. cheopis, which is accompanied by the formation of "block" in most individuals. The preservation of the plague agent in these ectoparasites is characterized by its variation in the number that undergoes cyclic changes depending on the feeding rate and digestion. The bloodsucking is accompanied by the excretion of some microbes and by the reproduction of the remaining ones in the midgut and proventriculus which lasts the whole 1 st stage while dense clots of erythrocytes are preserved in the intestine. In the course of blood digestion the reproduction of microbes is replaced by their dying off and when the digestion is over the quantity of microbes increases again. In this period small cocci, which form dense clots in the midgut and proventriculus, are the dominant form of microbes.