Molecular survey of Ehrlichia infection in ticks from animals in Yamaguchi Prefecture, Japan

Abstract

A total of 82 ticks collected from wild animals and dogs in Yamaguchi Prefecture, Japan were examined for Ehrlichia infection by using polymerase chain reaction (PCR) primers that amplify DNA of most members of the genus Ehrlichia. A DNA sample from an Ixodes ovatus nymph from a bear in Yamaguchi Prefecture, Japan, was positive in the screening PCR. Subsequent PCR using two sets of primers yielded a 1431 bp segment of the 16S rRNA gene and the sequence was very similar to those of E. chaffeensis and E. muris, and a strain variant of a recently described Ehrlichia species isolated from I. ovatus in other prefectures of Japan.

Introduction

Ehrlichia species are strict intracellular bacteria that parasitize blood cells such as monocytes, granulocytes and platelets (Rikihisa, 1991). They are responsible for various vector-borne diseases of human beings and other animals and their vectors include hard ticks, helminths and insects. Currently, five Ehrlichia species have been reported to occur in Japan. E. sennetsu and the Stellantchasmus falcatus agent, which belong to the E. sennetsu genogroup, occur only in southwestern Japan (Kyushu) and the vectors of these organisms are thought to be trematodes (Fukuda et al., 1972, Misao and Kobayashi, 1955). While E. sennetsu causes monocytic ehrlichiosis in people, it is unknown whether the S. falcatus agent is pathogenic in man. E. muris parasitizes monocytes and is closely related to E. chaffeensis and found in Japan (Wen et al., 1995). It is transmitted by Haemaphysalis flava and widely distributed (Kawahara et al., 1999). A fourth Ehrlichia species was recently isolated from I. ovatus ticks in Japan and is also closely related to E. chaffeensis (Shibata et al., 2000). Two strains of the Ehrlichia, HF565 and Anan, were recorded from Fukushima (northeast Japan) and Tokushima (southwest Japan) Prefectures, respectively. More recently, DNA of E. platys was detected from Rhipicephalus sanguineus ticks on Okinawa Island, southern island in Japan (Inokuma et al., 2000). We recently designed a set of primers based on the 16S rRNA sequences of Ehrlichia species that amplify DNA from most members of the genus Ehrlichia (Parola et al., 2000). Using these primers we screened ticks collected from wild animals and dogs in Yamaguchi Prefectures, Japan.