Vector Control Has a Role to Play in Mitigating the High Incidence of Flea-borne Typhus in Los Angeles County, California

Abstract

More than 500 human cases of flea-borne typhus have been reported from Los Angeles and Orange Counties over the past 20 years. Only West Nile virus exceeds flea-borne typhus as an important vector-borne disease in these counties. Despite this, flea-borne typhus garners insignificant public attention compared to West Nile virus. In Los Angeles County alone there were 121 human cases of flea-borne typhus from 2000 to 2009, and 292 human cases from 2010 to 2015. Results from previous studies in Los Angeles and Orange Counties identified a suburban cycle of flea-borne typhus transmission involving backyard wildlife, pets, and the cat flea Ctenocephalides felis. Prior studies and recent observations in Los Angeles County showed that the flea burden of opossums and feral cats is onerously high, and the cat flea is the main vector of the pathogens (Rickettsia typhi and R. felis) responsible for human typhus. The rise of cases in recent years has been accompanied by policy changes in public and private animal control groups that manage nuisance animals in Los Angeles and Orange Counties. Instead of trapping and removing strays and supporting a policy of not feeding wild or stray animals, some governmental agencies and private organizations prefer trap, neuter, and release (TNR) programs and support rehabilitating/relocating feral animals. We believe these policy changes have contributed to the increased incidence of human typhus.