Rickettsia felis infection in a common household insect pest, Liposcelis bostrychophila (Psocoptera: Liposcelidae)

Abstract

Many species of Rickettsia are well-known mammalian pathogens transmitted by blood-feeding arthropods. However, molecular surveys are continually uncovering novel Rickettsia species, often in unexpected hosts, including many arthropods that do not feed on blood. This study reports a systematic molecular characterization of a Rickettsia infecting the psocid Liposcelis bostrychophila (Psocoptera: Liposcelidae), a common and cosmopolitan household pest. Surprisingly, the psocid Rickettsia is shown to be Rickettsia felis, a human pathogen transmitted by fleas that causes serious morbidity and occasional mortality. The plasmid from the psocid R. felis was sequenced and was found to be virtually identical to the one in R. felis from fleas. As Liposcelis insects are often intimately associated with humans and other vertebrates, it is speculated that they acquired R. felis from fleas. Whether the R. felis in psocids causes disease in vertebrates is not known and warrants further study.

FIG. 1.

Unrooted maximum-likelihood phylogenetic tree of Rickettsia species based on a concatenated alignment of ompA, ompB, and cell surface antigen sca4 (gene D), using a general time-reversible and gamma-distributed rate heterogeneity (GTR+G) model of nucleotide substitution (a), and a concatenated alignment of 16S rRNA and gltA genes, using a transversion and invariable sites (TVM+I) model of nucleotide substitution (b). Values above and below branches indicate likelihood and parsimony bootstrap support, respectively. Only bootstrap values greater than 70% are shown. Whenever possible, we used Rickettsia spp. for which a genome sequence was available: R. bellii strain RML369-C (NC_007940), R. bellii strain OSU85 389 (NZ_AARC00000000), R. canadensis strain McKiel (NZ_AAFF01000001), R. prowazekii strain Madrid E (NC_000963), R. typhi strain Wilmington (NC_006142), R. akari strain Hartford (NZ_AAFE01000001), R. felis strain URRWXCal2 (NC_007109), R. conorii strain Malish 7 (NC_003103), R. rickettsii strain Sheila Smith (NC_009882), R. rickettsii strain Iowa (NC_010263), R. massiliae strain MTU5 (NC_009900), and R. sibirica strain 246 (NZ_AABW01000001). For Rickettsia spp. for which full genome sequence is not available, we used the following accessions from previous studies (21-25): R. australis strain Phillips (L36101, U59718, AF149108, AF123709, and AF187982), R. helvetica strain C9P9 (L36212, U59723, AF123725, and AF163009), R. montanensis strain M56 (L36215, U74756, U43801, AF123716, and AF163002), R. aeschlimannii strain MC16T (U74757, U59722, U43800, AF123705, and AF163005), R. rhipicephali strain 376 (L36216, U59721, U43803, AF123719, and AF155053), R. japonica strain YM (L36213, U59724, U43795, AF123713, and AF155055), R. slovaca strain 13B (L36224, U59725, U43808, AF123723, and AF155054), R. parkeri strain Maculatum 20 (L36673, U59732, U43802, AF123717, and AF155059), R. africae strain ESF-5 (L36098, U59733, U43790, AF123706, and AF151724), R. honei strain TT118 (L36220, U59726, U43809, AF123724, and AF163004), and R. rickettsii strain R (L36217, U59729, U43804, X16353, and AF163000).

FIG. 2.

Circular representation of the L. bostrychophila-associated R. felis pRF plasmid generated by using the CGView server (http://stothard.afns.ualberta.ca/cgview_server/index.html). The inner circle represents GC content bias [(G − C)/(G + C)], with positive values in green and negative values in purple; the second circle represents G+C content; the third circle represents a nucleotide BLAST comparison with R. felis URRWXCal2 pRF plasmid, with matches in light blue, differences in dark blue, and gaps in white. The outer 12 circles represent predicted ORFs on the reverse and forward strands. Sp, split ORF; A, absent ORF; M, merged ORF; L, longer ORF; Sh, shorter ORF. The inner scale is marked in kilobases.