Human history has been riddled by diseases spread by flea vectors including the bubonic plague. Recently, Madagascar has documented more than 100 cases. Fleas were part of God’s “very good” (Genesis 1:31) creation that transformed to an ectoparasitic condition after the Curse. Creation biologists continue to synthesize a working model of this conversion from environmental recyclers to parasites as a secondary state. Morphological design of the flea combined with its unique feeding ability has resulted in it being an exceptional vector for Yersinia pestis, the causative bacterium of the plague.
Gillen, Alan L., "The Origin of Fleas and the Genesis of Plague" (2015). Faculty Publications and Presentations. 134.