Oriental Rat Flea

*Xenopsylla cheopis* is the classic plague vector flea, 1.5–4 mm, dark brown and laterally flattened, and readily separated from *Ctenocephalides* by the complete absence of genal and pronotal combs. Its normal hosts are commensal rats, chiefly *Rattus rattus* and *Rattus norvegicus*. Females lay eggs in nest material after each blood meal; larvae feed on nest debris and adult flea faeces, pupate in a cocoon, and emerge as adults in as little as two to three weeks in warm humid conditions. Adults can survive weeks off-host in a nest, which is why they are still infective after the host rodent dies.

Feeding is frequent and messy. In plague-infected fleas the *Yersinia pestis* biofilm blocks the proventriculus, the flea regurgitates bacteria into each new bite wound, and the starving flea bites repeatedly and indiscriminately — the mechanism that drives transmission. The same species transmits murine (endemic) typhus, *Rickettsia typhi*, through infected flea faeces scratched into the bite, and serves as intermediate host of the rodent tapeworms *Hymenolepis diminuta* and *H. nana*. When a rodent host dies or is removed, hungry fleas leave the carcass and readily bite people, which makes rodent control without concurrent flea treatment actively dangerous.