Molecular Evidence for Novel Tick-Associated Spotted Fever Group Rickettsiae from Thailand

Abstract

Ticks are of considerable medical and veterinary importance because they directly harm the host through their feeding action and indirectly through vectoring many bacterial pathogens. Despite many ticks being known from Thailand, very little is known about the bacteria they may harbor. We report here the results of a survey of tick-associated bacteria in Thailand. A total of 334 individuals representing 14 species of ticks in five genera were collected from 10 locations in Thailand and were examined for the human pathogens, Borrelia, Francisella, Rickettsia, and the common arthropod endosymbionts, Wolbachia, by polymerase chain reaction (PCR) assay using specific primers. Rickettsial DNA was detected in 30% (9/30) of Amblyomma testudinarium (Koch, 1844) collected from Khao Yai National Park, Nakhon Nayok Province and 16.84% (16/95) of Hemaphysalis ornithophila (Hoogstraal and Kohls, 1959) collected from Khao Yai National Park, Nakhon Nayok Province and Khao Ang Rue Nai Wildlife Sanctuary, Chachoengsao Province. Rickettsial DNA was not detected in any of the other tick species and no DNA of Borrelia, Francisella, or Wolbachia was detected in any of 14 tick species. Phylogenetic relationships among the rickettsiae detected in this study and those of other rickettsiae were inferred from comparison of sequences of the 17-kDa antigen gene, the citrate synthase gene (gltA), and the 190-kDa outer membrane protein gene (ompA). Results indicated that the three Thai rickettsiae detected in this study represent new rickettsial genotypes and form a separate cluster among the spotted fever group rickettsiae.

Rickettsial Infections in Southeast Asia: Implications for Local Populace and Febrile Returned Travelers

“…29 Another study in Thailand found 3 novel phylogentically distinct SFGR DNAs (ATT, HOT1 and HOT2) in 30% of Amblyomma testudinarium and 16.8% of Hemaphysalis ornithophila tick species collected from animals and vegetation in Khao Yai National Park. 39 However, it is unclear if these newly discovered SFGR could cause human disease and whether the ticks species carrying these rickettsiae could feed on humans as a host. 39 Despite extensive data, these epidemiologic studies may not have captured the true prevalence and regional variance of rickettsioses in Southeast Asia.…”

“…39 However, it is unclear if these newly discovered SFGR could cause human disease and whether the ticks species carrying these rickettsiae could feed on humans as a host. 39 Despite extensive data, these epidemiologic studies may not have captured the true prevalence and regional variance of rickettsioses in Southeast Asia. In addition, prevalence studies in popular tourist destinations are lacking.…”

Intracellular Symbionts and Other Bacteria Associated with Deer Ticks (Ixodes scapularis) from Nantucket and Wellfleet, Cape Cod, Massachusetts

“…Some previous reports of "wolbachiae" in ticks have been based on the detection of W. persica, a gammaproteobacterium that had been included in the wolbachiae based on ultrastructural characterization but is unrelated to the common insect symbionts (7,23). Studies looking specifically for Wolbachia (Anaplasmataceae) in ticks have generally yielded negative results (12,22,23), although a Wolbachia sp. sequence in GenBank (AF304445) originated from a semiengorged Rhipicephalus sanguineus tick in Okinawa (13).…”

Southeast Asian ticks (Acari: Ixodida): a historical perspective

“…These include Anaplasma, Babesia, Ehrlichia, and Rickettsia Suksawat et al 2001;Tay et al 2002;Hirunkanokpun et al 2003;Parola et al 2003). Over the last two decades, the number of new pathogens of potential veterinary (and human) importance discovered in ticks has increased markedly.…”

“…Over the last two decades, the number of new pathogens of potential veterinary (and human) importance discovered in ticks has increased markedly. In Asia, new species of Babesia (Luo et al 2002), Ehrlichia (Wen et al 2002), Rickettsia (Hirunkanokpun et al 2003), andTheileria (Sarataphan et al 1999;Chansiri and Sarataphan 2002) have been discovered. The medical and veterinary significance of these pathogens remains largely unknown.…”