Typhus and typhuslike rickettsiae associated with opossums and their fleas in Los Angeles County, California

Abstract

The recent discovery of cat fleas (Ctenocephalidesfelis) infected with a typhuslike rickettsia (designated the ELB agent) raises the question of whether similar rickettsial infections exist in wild cat flea populations. We verified the presence of the ELB agent and Rickettsia typhi in urban and suburban areas of Los Angeles, Calif. Opossums trapped in close proximity to the residences of human murine typhus cases in Los Angeles county and other areas within the city of Los Angeles were tested for the presence of typhus group rickettsiae by the polymerase chain reaction (PCR). The presence of rickettsiae in the spleen tissues of three opossums (n = 9) and in 66 opossum fleas (n = 205) was determined by PCR and was verified by dot blot and Southern transfer hybridization. Further analysis of the amplified PCR products generated by a series of primer pairs derived from either the 17-kDa antigen gene or the citrate synthase gene revealed that both R. typhi and the ELB agent were present in the tested samples. Dual infection was not noted in the samples; however, the fleas were infected with either R. typhi or the ELB agent. The presence of the ELB agent in the cat flea population may have implications for public health. Whether this agent is responsible for the mild cases of human murine typhus in urban and suburban areas of Los Angeles or in other endemic foci remains to be determined.

Cofeeding intra‐ and interspecific transmission of an emerging insect‐borne rickettsial pathogen

“…Serological-based studies have implicated several peri-domestic animals (e.g. cats, dogs, opossums, rats) based on seropositive individuals independent from laboratory experiments (Williams et al 1992;Schriefer et al 1994b;Boostrom et al 2002;Richter et al 2002;Case et al 2006;Labruna et al 2007;Bayliss et al 2009); yet, these retrospective diagnoses only provide signs of the presence of R. felis in the environment as opposed to identification of a reservoir vertebrate host. The mouse strain C3H/HeJ has been utilized in previous studies to examine transmission of Rickettsia that produce mild infections, such as R. conorii and R. parkeri (Jordan et al 2008;Grasperge et al 2012).…”

“…Vectorial capacity for R. felis has not been assessed in these additional arthropod species, and a vertebrate reservoir has not been identified for R. felis, in spite of numerous field studies and laboratory attempts to delineate a host based on animals naturally infested with R. felis-infected cat fleas (e.g. cats, dogs, opossums and rats) (Williams et al 1992;Schriefer et al 1994b;Boostrom et al 2002;Richter et al 2002;Case et al 2006;Hawley et al 2007;Labruna et al 2007;Bayliss et al 2009). Although most peri-domestic animals implicated in the transmission of R. felis are seropositive to rickettsial antigen, certain individuals may show no correlation between seroprevalence and R. felis-infected cat fleas (Williams et al 1992;Bayliss et al 2009).…”

“…cats, dogs, opossums and rats) (Williams et al 1992;Schriefer et al 1994b;Boostrom et al 2002;Richter et al 2002;Case et al 2006;Hawley et al 2007;Labruna et al 2007;Bayliss et al 2009). Although most peri-domestic animals implicated in the transmission of R. felis are seropositive to rickettsial antigen, certain individuals may show no correlation between seroprevalence and R. felis-infected cat fleas (Williams et al 1992;Bayliss et al 2009). Moreover, R. felis has been identified by molecular detection from the blood, skin and internal organs of suspected reservoir hosts (Schriefer et al 1994b;Abramowicz et al 2011;Panti-May et al 2014;Tay et al 2014Tay et al , 2015Kuo et al 2015), but viable bacteria have never been isolated from these tissues.…”

Detection of Rickettsia felis and Rickettsia typhi in an area of California endemic for murine typhus

“…It has usually been associated with a transmission cycle involving rats, Rattus norvegicus and Rattus rattus, and the oriental rat flea, Xenopsylla cheopis [1]. A second transmission cycle has been described involving peridomestic opossums, Didelphis virginiana, and their associated flea, Ctenocephalides felis [2]. Another rickettsial agent, Rickettsia felis, has also been associated with C. felis [3], and has been implicated in a murine typhus-like disease of humans, cat flea rickettsiosis [4].…”

The Science and Fiction of Emerging Rickettsioses

“…In this context, cases of murine typhus were frequently misidentified as louse-borne typhus until the recognition of Rickettsia typhi, 18 just as some cases of R. felis infection are now misidentified as infections caused by R. typhi. 3,19 In a similar manner, infections caused by Rickettsia africae, R. massiliae, R. aeschlimannii, and R. monacensis were for many decades classified incorrectly as Mediterranean spotted fever (MSF) by clinicians, rickettsiologists, and epidemiologists. 20 It is conceivable that the most severe SFG rickettsioses are rarely encountered when compared with the occurrence of milder rickettsial infections.…”