Isolation of “CandidatusRickettsia andeanae” (Rickettsiales: Rickettsiaceae) in Embryonic Cells of Naturally InfectedAmblyomma maculatum(Ixodida: Ixodidae)

Abstract

The Gulf Coast tick, Amblyomma maculatum Koch, has become increasingly important in public health for its role as a vector of the recently recognized human pathogen, Rickettsia parkeri. More recently, these ticks were also found to harbor a novel spotted fever group rickettsia, "Candidatus Rickettsia andeanae." First identified in Peru, and subsequently reported in ticks collected in the United States, Chile, and Argentina, "Ca. R. andeanae" remains largely uncharacterized, in part because of the lack of a stable isolate. Although the isolation of "Ca. R. andeanae" was recently described in DH82, Vero, and Drosophila S2 cells, its stability in these cell lines was not shown. To evaluate "Ca. R. andeanae" transmission and pathogenicity in vertebrates, as well as further describe biological characteristics of this candidate species to fulfill criteria for its establishment as a new species, availability of a stable isolate is essential. Here we describe the propagation of "Ca. R. andeanae" by using a primary culture derived from naturally infected A. maculatum embryos. Subsequent passage of the "Ca. R. andeanae" isolate to ISE6 (Ixodes scapularis embryonic) and Vero (African green monkey kidney epithelial) cell lines demonstrated limited propagation of the rickettsiae. Treatment of the infected primary cells with tetracycline resulted in cultures negative for "Ca. R. andeanae" by polymerase chain reaction and microscopy. Establishment of an isolate of "Ca. R. andeanae" will promote further investigation into the significance of this tick-associated rickettsia, including its role in spotted fever and interactions with the sympatric species, R. parkeri in A.

Rickettsial agents in avian ixodid ticks in northeast Brazil

“…The role of "Ca. R. andenae" as a human pathogen is unknown (Ferrari et al, 2013); however A. parvum is an important human-biting tick in South America and the infested ticks reported here were found on the clothes of our field team.…”

High prevalence of “Candidatus Rickettsia andeanae” and apparent exclusion of Rickettsia parkeri in adult Amblyomma maculatum (Acari: Ixodidae) from Kansas and Oklahoma

“…R. andeanae” from naturally infected embryonic cells of A. maculatum implies that “ Ca . R. andeanae” is vertically transmitted in Gulf Coast ticks (Ferrari et al, 2013). Multiple studies suggest that hard ticks cannot maintain simultaneously separate Rickettsia species by vertical transmission, as demonstrated by the exclusion of transovarial transmission of Rickettsia rickettsii by Rickettsia peacockii in Dermacentor andersoni (Burgdorfer et al, 1981), Rickettsia rhipicephali by R. montanensis in Dermacentor variabilis (Macaluso et al, 2002), and R. rickettsii by Rickettsia bellii in Amblyomma dubitatum (Sakai et al, 2014).…”

“…“ Ca R. andeanae” has been isolated recently in culture, although some difficulties remain in establishing continuously infected cell lines (Luce-Fedrow et al, 2012 and Ferrari et al, 2013). To our knowledge, no cases of R. parkeri rickettsiosis have been described from Kansas or Oklahoma, despite well-established populations of A. maculatum in those states which have existed for more than 40 years.…”

Feeding byAmblyomma maculatum(Acari: Ixodidae) EnhancesRickettsia parkeri(Rickettsiales: Rickettsiaceae) Infection in the Skin

“…Recent isolation of C. “Rickettsia andeanae” showed tick cells to be permissive while a mammalian cell line was unable to sustain infection, suggesting that replication of this organism is host cell dependent (Ferrari et al 2013). This inability to sustainably infect mammalian cells provides further support for the limited transmission of C. “Rickettsia andeanae” to the vertebrate host observed in the current study.…”