Fleas collected from Norway rats in downtown Los Angeles carry human pathogen

The research team limited their investigation to fleas of the species Xenopsylla cheopis, because they are known both to infest Rattus norvegicus, the Norway rat, which is a major pest in high density urban areas, as well as to bite humans, says first author Sarah Billeter of the Centers for Disease Control and Prevention, Fort Collins, CO.

Bartonella species are gram-negative bacteria that infect red blood cells and endothelial cells of the host. More than half are thought to cause some clinical disease in humans. B. rochalimae, found in 72 percent of the collected fleas, was first isolated from the blood of a patient who became ill after returning to the United States from a vacation in Peru, says Billeter. "She complained of fever, insomnia, nausea, headache, and mild cough. Upon examination at the hospital, she was found to have recurrent fever, splenomegaly, and anemia." B. rochalimae has also been identified as a cause of infectious endocarditis in a dog from San Francisco, says Billeter.

The remaining fleas harbored sequences most closely related to B. tribocorum, a bacterium that has been detected in rodents "from various parts of the world," including France, says Billeter, and was isolated from the blood of a febrile Thai patient. "At this point, it remains unclear whether B. tribocorum is a human pathogen," says Billeter. "From a public health standpoint, however, it is important to determine whether R. norvegicus are reservoirs for zoonotic Bartonella spp. due to their close contact with humans and their pets." The question of whether X. cheopis can actually spread such pathogens to humans also warrants further investigation, says Billeter.