Detection of "Rickettsia sp. strain Uilenbergi" and "Rickettsia sp. strain Davousti" in Amblyomma tholloni ticks from elephants in Africa

Abstract

Background: To date, 6 tick-borne rickettsiae pathogenic for humans are known to occur in Africa and 4 of them were first identified in ticks before being recognized as human pathogens.

Results: We examined 33 and 5 Amblyomma tholloni ticks from African elephants in the Central African Republic and Gabon, respectively, by PCR amplification and sequencing of a part of gltA and ompA genes of the genus Rickettsia. The partial sequences of gltA and ompA genes detected in tick in Gabon had 99.1% similarity with those of R. heilongjiangensis and 97.1% with those of Rickettsia sp. HL-93 strain, respectively. The partial gltA and ompA gene sequences detected in tick in the Central African Republic were 98.9% and 95.1% similar to those of Rickettsia sp. DnS14 strain and R. massiliae, respectively. Phylogenetic analysis showed Rickettsia sp. detected in Gabon clusters with R. japonica and R. heilongjiangensis in a phylogenetic tree based on the partial gltA and ompA genes. The genotype of the Rickettsia sp. detected in the Central African Republic is close to those of R. massiliae group in the phylogenetic tree based on partial gltA gene sequences, and distantly related to other rickettsiae in the tree based on partial ompA gene.

Conclusion: The degrees of similarity of partial gltA and ompA genes with recognized species indicate the rickettsiae detected in this study may be new species although we could only study the partial sequences of 2 genes regarding the amount of DNA that was available. We propose the Rickettsia sp. detected in Gabon be provisionally named "Rickettsia sp. stain Davousti" and Rickettsia sp. detected in the Central African Republic be named "Rickettsia sp. strain Uilenbergi".

Figure 1

Phylogenetic tree based on gltA gene partial sequences. The GenBank accession numbers used to construct the phylogenetic tree were as follows: R. parkeri, U59732; R. sibirica, U59734; R. sibirica mongolotimonae, U59731; R. africae, U59733; R. conorii, U59730; R. rickettsii, U59729; R. honei, U59726; R. slovaca, U59725; R. japonica, U59724; R. montanensis, U74756; R. massiliae, U59719; R. rhipicephali, U59721; R. aeschlimannii, U59722; R. helvetica, U59723; R. australis, U59718; R. akari, U59717; R. typhi, U59714; R. canadensis, U59713; R. prowazekii, U59715; R. amblyommii, AY375163; R. heilongjiangensis, AY280709.

Figure 2

Phylogenetic tree based on ompA gene partial sequences. The GenBank accession numbers used to construct the phylogenetic tree were as follows: R. australis, AF149108; R. heilongjiangensis, AF179362; R. honei, U43809; R. slovaca, U43808; R. sibirica, U43807; R. rickettsii, U43804; R. rhipicephali, U43803; R. parkeri, U43802; R. montanensis, U43801; R. aeschlimannii, U43800; R. massiliae, U43799; R. japonica, U43795; R. conorii, U43806; R. africae, U43790; R. amblyommii, AY062007; R. monacensis, AF201329; and R. conorii caspia, AY112668.