Plague Vectors

The Human Flea, Pulex irritans
Image: CDC

The most studied of the bubonic plague vectors is the Oriental rat flea, Xenopsylla cheopis. This flea is considered the primary vector of bubonic plague in urban areas. The island of Madagascar, the site of a worrisome number of plague cases, is considered to have endemic plague. The plague was first detected on the island in 1898 after visits from rat infested ships that had sailed from plague infested areas.

Madagascar has also received another imported pest, the human flea, Pulex irritans. Pulex irritans is likely a native of South America where it infests guinea pigs. In Madagascar, it bites a variety of animals including cats, dogs, chickens and humans. A group of scientists* collected fleas from areas reporting plague including the house of a plague victim. They found plague bacteria, Yersinia pestis in 9 P. irritans individuals. No plague was detected in the other 4 other flea species including the rat flea and dog flea.

The human flea is not found on rats in Madagascar and is probably not responsible for plague transmission from the rodent population to humans. However, once humans are infected, the human flea could transmit plague from person to person. Control of human fleas may be important in stopping the spread of plague in some areas.

*Jocelyn Ratovonjato, Minoarisoa Rajerison, Soanandrasana Rahelinirina, and Sébastien Boyer. Yersinia pestis in Pulex irritans Fleas during Plague Outbreak, Madagascar. Emerg Infect Dis. Aug 2014; 20(8): 1414–1415.
doi:  10.3201/eid2008.130629