Due to a resurgence of flea-borne rickettsioses in Orange County, California, we investigated the etiologies of rickettsial infections of Ctenocephalides felis, the predominant fleas species obtained from opossums (Didelphis virginiana) and domestic cats (Felis catus), collected from case exposure sites and other areas in Orange County. In addition, we assessed the prevalence of IgG antibodies against spotted fever group (SFGR) and typhus group (TGR) rickettsiae in opossum sera. Of the 597 flea specimens collected from opossums and cats, 37.2% tested positive for Rickettsia. PCR and sequencing of rickettsial genes obtained from C. felis flea DNA preparations revealed the presence of R. typhi (1.3%), R. felis (28.0%) and R. felis-like organisms (7.5%). Sera from opossums contained TGR-specific (40.84%), but not SFGR-specific antibodies. The detection of R. felis and R. typhi in the C. felis fleas in Orange County highlights the potential risk for human infection with either of these pathogens, and underscores the need for further investigations incorporating specimens from humans, animal hosts, and invertebrate vectors in endemic areas. Such studies will be essential for establishing a link in the ongoing flea-borne rickettsioses outbreaks.

In response to the 1984 St. Louis encephalitis (SLE) epidemic in the Los Angeles Basin of southern California (USA), an investigative program was initiated to evaluate the interactive components of the SLE virus transmission cycle. From 1987 through 1996 (10 yr), 52,589 birds were bled and their sera tested for SLE and western equine encephalomyelitis (WEE) virus antibodies by the hemagglutination inhibition (HAI) test. Eighty-three percent of the birds tested were house finches (Carpodacus mexicanus) (48.7%) and house sparrows (Passer domesticus) (34.6%); 1.1% of these birds were positive for SLE antibodies. Prevalence of WEE antibodies was negligible. The analysis of 5,481 sera from rock doves (Columbia livia) yielded 3.6% SLE positives and 0.4% WEE positives. Collection sites were maintained as study sites when identified as positive bird, mosquito, and SLE virus activity localities; others were abandoned. Serial serum samples from 7,749 banded house sparrows and 9,428 banded house finches from these selected sites demonstrated year-round SLE virus transmission. One location exhibited significant numbers of house finches undergoing annual SLE seroconversion and a number of seroconversion-reversion-reconversion sequences suggesting either viral reinfection from mosquitoes or recrudescence by latent virus. A proportion of both bird species also lived for longer than 1 yr, thus, increasing the possibility of virus carry-over from autumn to spring. Assessment of concurrently collected mosquitoes indicated no correlative association between mosquito populations and SLE seroconversion and reconversion. European house sparrows introduced in the 1800's may have provided a supplemental link to the existing SLE virus enzootic cycle involving endemic house finches. Meteorological factors are reviewed as possible important correlates of SLE epidemics. The house finch/house sparrow serosurveillance system is also evaluated for use as an "Early Warning" indicator of SLE virus activity.

Flea-borne typhus has emerged as an important vector-borne disease in Los Angeles and Orange Counties, California, with over 400 human cases having been reported since the mid-1980s. In Orange County alone, 127 human cases have been investigated by the Orange County Vector Control District since 2006. Results from a collaborative study with the Centers for Disease Control and Prevention from 2006-2008 identified the suburban cycle of flea-borne typhus transmission (backyard wildlife/pets -fleas -humans) in Los Angeles and Orange counties. Free-ranging feral and companion cats and the Virginia opossum were identified as the primary host animals of the cat flea, the insect vector responsible for maintenance and transmission of the etiologic agents, Rickettsia typhi and R. felis, for disease in humans. Although the causes of the increase in human flea-borne typhus cases are not well-defined, this rise has been accompanied by changes in how public and privately-sponsored animal control groups manage nuisance animal populations in the affected southern California counties. Instead of elimination through euthanasia of unwanted feral cats and non-native opossums, rehabilitation, relocation, and "no-trap" policies have become the preferred practice of local animal control agencies. The public health obligation for which governmental animal control agencies were created must be re-emphasized as one way of preventing further outbreaks of flea-borne typhus infections in Orange County and the surrounding California counties. Proc. 26 th Vertebr. Pest Conf. (R. M. Timm and J. M. O'Brien, Eds.) Published at Univ. of Calif., Davis. 2014. Pp. 316-322.

Opossums and cat fleas have been epidemiologically linked to flea-borne rickettsial disease transmission in residential backyards of Orange County, California. In 2013, a study was initiated to better elucidate the life history of opossums and their role as vectors of disease and hosts for both internal and external parasites. The study population consisted of adult opossums collected year-round from flea-borne rickettsial disease exposure sites, and moribund opossums submitted by wildlife rehabilitators in Orange County. Carcasses were examined for ectoparasites and necropsied, which included the removal and collection of endoparasites, organ tissues, feces, and urine. Reproductive life history data suggested one brood of young per year, with an average litter size of 7 (n = 9, range 2-11). Average adult weight was 2.49 kg (range 1.30-4.41 kg). Cat fleas were present on each opossum with an average of 96 fleas per opossum (n = 82, range 2-725). Thirty of 33 cat flea pools tested PCR-positive for one of the following bacteria: Rickettsia felis (53%), R. typhi (3%), the R. felis-like organisms, Candidatus Rickettsia senegalensis (28%) and Ca. Rickettsia asemboensis (3%), or Bartonella vinsonii subsp. arupensis (1.5%). Sticktight fleas (Echidnophaga gallinacea), the only other flea detected, were present on less than 6% of opossums, and ticks were not detected on any carcasses (n = 83). Endoparasitic nematodes Cruzia americana and Physaloptera turgida were present in each stomach and cecum, and Didelphostrongylus hayesior or Heterstongylus heterostrongylus was noted in lung samples of opossums (n = 83). Salmonella spp. were detected in 52% of fecal samples (n = 50), with subsequent typing of strains indicating the presence of human pathogens in all but three of the samples (n = 26). Blood and spleen samples were negative for Bartonella spp., Brucella spp., and Yersinia pestis (n = 33). Sera were negative for Leptospira-specific antibodies and Leptospira DNA was not detected in urine (n = 83). Results from this multi-agency study show that the presence of opossums in the backyard environment put Orange County residents and their pets at risk of flea-borne bartonella and rickettsial diseases and salmonellosis.

In 2006