Volume 20, Issue 2
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



Flea-borne bubonic plague cannot exist in epidemic proportions when the mean monthly ambient temperature exceeds 27.5°C. At temperatures in excess of 27.5°C, many fleas do not become blocked with , thus decreasing the transmission potential. The blocking process is associated with fibrin formation from ingested blood by a coagulase and a trypsin-like enzyme associated with the stomach of . Fibrin provides the matrix for the lodgement of in the flea proventriculus that is required for the blocking process. When temperatures are elevated above 27.5°C, fibrin is rapidly destroyed by a fibrinolytic factor of and the trypsinlike enzyme. Deprived of fibrin matrices, are rapidly eliminated from the flea proventriculus. There is an inverse straight-line relationship between the activities of the fibrinolytic factors and the blocking of fleas with . These observations provide a physiological explanation for the spontaneous decline of plague epidemics observed with the advent of hot weather.


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