Fleas transmit plague to humans and animals when biting and feeding on blood.
Close-up of an unmagnified flea on a human arm. This flea is the primary vector of plague in most large plague epidemics in Asia, Africa, and South America. Both male and female fleas can transmit the infection. Infection with plague bacteria can result in swollen lymph glands called bubos. Yersinia pestis can usually be cultured from biopsy material from infected lymph nodes.