By Tara Roth, Ph.D.
Fleas are blood-feeding parasites that are common on most mammals and well known for their ability to spread pathogens such as plague, tularemia, typhus, and a variety of parasites. They can bite multiple times in a feeding session and travel far and fast to find new hosts. This is what makes them so fearsome as vectors—their ability to explosively spread diseases through a community.
While it may seem like fleas will bite anything that moves, some species are so specific about which host they want that some individuals may choose to starve to death rather than accept an alternative. This may be because of specific nutritional requirements, an inability to control the immune system of other types of hosts, or behavioral differences between the host and the flea that make finding and staying with anything besides their preferred host difficult or impossible.
While approximately 94 percent of flea species prefer to feed on mammals, the remaining 6 percent specialize on birds. Research published in 2008 by a team at Brigham Young University determined through genetic analysis that it’s likely many bird-preferring species had ancestors that parasitized chipmunks and squirrels and that switching to birds is a recent evolution. One rather common group of bird fleas are those in the genus Dasypsyllus, which prefer small songbirds that build nests low to the ground. The subspecies Dasypsyllus gallinulae perpinnatus is the only known variant found in the western coastal area of the United States and, although common, it is rarely documented by scientists and public health professionals. For this reason, many entomologists can go their entire career without seeing a single bird flea.
As a vector ecologist, my job is to conduct surveillance for vector-borne diseases, monitor vector populations, and provide insect identification services for the people of San Mateo County, located just south of San Francisco, California. While home inspections are not a common part of my working day, I am occasionally called out to handle special cases. So, you can imagine my surprise when my colleagues and I responded to a bird flea infestation in a home, the details of which were reported in April 2024 in the Journal of Medical Entomology, part of a forthcoming special collection on One Health.
Our story begins in March 2023 when we received a request for service from a resident living in a condominium infested with fleas. Four people were living in the home; however, only one reported receiving bites. Seven fleas were submitted, which I identified as D.g. perpinnatus. At the time, I had only identified this species once as an incidental collection while sampling for ticks. None of us knew anything about this species, and brief consultations with other entomologists typically ended with, “The identity is correct, but how did you get these?”
Upon visiting the home, we found an abandoned bird’s nest behind a fire alarm bell in the front entryway of the residence. This nest was bagged up and removed, and we flagged for fleas in the entryway under the nest using a flannel cloth attached to a wooden dowel.
A total of 31 fleas were recovered by flagging from the front entryway of the residence, 20 were collected by the resident from indoors, and 387 were removed from the abandoned bird nest. All life stages (egg, larvae, pupa, and adult) were present in the nest, and all the adults were identified as D.g. perpinnatus.
As far as we are aware, this is the first record of a structural infestation by D.g. perpinnatus, but that statement warrants investigation: Is this indeed the first case? Or have we just not been looking? And, a more worrisome question, could bird fleas spread avian pathogens to humans?
Integrated pest management (IPM) practices encourage identifying any collected fleas to species before beginning a treatment plan. However, slide-mounting fleas for ID is time-intensive and reliant on an experienced entomologist with a good taxonomic key. It is valuable for pest control professionals (whether private pest control operators, extension staff, or other public health staff) to collaborate with experienced academic institutions and vector control agencies, but this isn’t always possible.
In our growing understanding that human health is inextricable from our environment and the animals with which we share it, we need widely available tools and training to help encourage people to learn about insect behavior and species ID. As this case study illustrates, having more entomologists available will help pest control professionals and those working on the front lines of public health perform their duties to modern IPM standards.
Tara Roth, Ph.D., is a vector ecologist at the San Mateo County Mosquito and Vector Control District in northern California. Email: troth@smcmvcd.org.
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