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Open Access Publications from the University of California

Survey of Ectoparasites Collected from Norway Rats (Rattus norvegicus) in Homeless Camps in the City of Oakland, California


The City of Oakland is the largest city within Alameda County, the 8th largest city in California, and the 45th largest in the United States. Due to various socioeconomic factors, the number of homeless encampments within Oakland has been increasing over the past few years. A recently completed survey showed that there has been a 47.45% increase in the number of homeless living within the city limits. Approximately 4,071 people are now living in various encampments around the city, primarily concentrated underneath freeway/infrastructure overpasses and on adjoining lands. Surveillance by our staff found that several of these encampments also had active Norway rat populations as indicated by active burrows within and adjacent to the camps, as well as resident reports. Beginning in the fall of 2017, District biologists began live-trapping at a few of the larger encampments to try and ascertain the composition and load of ectoparasites on corresponding Norway rat populations. We specifically looked at flea abundance and species composition, as they are vectors of diseases, such as Murine typhus (Rickettsia typhi), flea-borne typhus (Rickettsia felis), and plague (Yersinia pestis). We trapped at four different camps in Oakland over a nine-month period and found that the flea, mite, and louse abundance, along with species composition, varied between the camps. To date, we have yet to determine the causes of these differences, but fleas tested at two of the four camps have come back as positive for R. felis. We are continuing to trap at these camps and are expanding our trapping program to include additional camps in an effort to determine what variables affect the ectoparasite composition on Norway rat populations within the City of Oakland.

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