Northern rat fleas are external parasites, living by hematophagy off the blood of rodents.

[5] N. fasciatus is endemic to Europe but has a worldwide distribution because of their dependence on rodents and other mammals for survival.

[2] The genus, Nosopsyllus, is native to the Palearctic Realm but has spread through human transportation to other regions of the world.

Other areas populated by N. fasciatus are the United States, including some islands that have been spread from the mainland.

It is a vector for plague and is known to be a host of the rat tapeworm Hymenolepis diminuta in South America, Europe, and Australia.

[9] However, fleas simultaneously infected by the plague and Salmonella died within 2-3 days due to bloody diarrhea.

[11] Studies in gerbil hosts have found that flea infestation reduced Gerbillus dasyurus body mass and immune defences.

[11] In common vole hosts, it has also been found that flea infestation reduces body mass and immune defences and also induces an iron deficiency.

[3] Rise in rodent outbreaks of zoonotic diseases can spread to humans, like the plague, rickettsioses, and bartonelloses.

[3] The highest infestation rate occurs during the summer because of increased activity in the mammal hosts that help spread the fleas and their disease vectors.