Skip directly to site content Skip directly to page options Skip directly to A-Z link Skip directly to A-Z link Skip directly to A-Z link
Volume 9, Number 5—May 2003

Emerging Rickettsioses of the Thai-Myanmar Border1

Article Metrics
citations of this article
EID Journal Metrics on Scopus
Philippe Parola*†‡, R. Scott Miller*, Philip McDaniel§, Sam R. Telford‡, Jean-Marc Rolain†, Chansuda Wongsrichanalai*, and Didier Raoult†Comments to Author 
Author affiliations: *Armed Forces Research Institute of Medical Sciences (AFRIMS), Bangkok, Thailand; †Unité de Médecine, Marseille, France; ‡Harvard School of Public Health, Boston, Massachusetts, USA; §Kwai River Christian Hospital, Sangkhlaburi, Kanchanaburi, Thailand

Cite This Article


To investigate the presence of rickettsioses in rural residents of the central Thai-Myanmar border, we tested the blood of 46 patients with fever. Four patients had murine typhus, three patients had scrub typhus, and eight patients had spotted fever group rickettsioses, including the first case of Rickettsia felis infection reported in Asia.

Human rickettsioses known to occur in Thailand include mainly murine typhus and scrub typhus. Murine typhus is caused by Rickettsia typhi and is primarily maintained by fleas such as Xenopsylla cheopis, with various rodents reservoirs (1). Scrub typhus is caused by Orientia tsutsugamushi (formerly named R. tsutsugamushi), which is transmitted by the bites of the larvae of several species of trombiculid mites (commonly called “chiggers”) (2).

Spotted fever group (SFG) rickettsioses are associated with arthropods, mainly ticks but mites and fleas as well (3,4). In Thailand, few reports of serologically documented cases of SFG rickettsioses have been published (5). Although the specific etiologic agents of these diseases have not been identified, several SFG rickettsiae have been identified from ticks in Thailand. Thai tick typhus Rickettsia TT-118 was isolated from a pool of ticks in the 1970s (6). Despite its name, its pathogenic role in Thailand is not known. However, Stenos et al. have suggested that TT-118 is a strain of R. honei, an emerging pathogen prevalent on Flinders Island, Australia (7). Further, a rickettsia identified as R. honei type strain has also been recently detected by molecular methods in Thai Ixodes granulatus (8). In addition, several previously unrecognized rickettsiae of unknown pathogenicity have been detected from Ixodes and Dermacentor ticks, including species known to bite humans (8,9).

Thailand’s Sangkhlaburi District (Kanchanaburi Province) is a major gateway on the central part of the Thai-Myanmar border where newly arrived migrants from Myanmar become established as farm or factory laborers. There, the local Thai people, as well as Karen, Mon, and Burmese migrants, are commonly bitten by arthropods when working in the fields or at home. Scrub typhus has been previously reported in the province (10). Murine typhus was also described as a cause of fever in refugee camps along the Thai-Myanmar border (11). However, a serosurvey undertaken in 1997 suggested that residents of Sangkhlaburi were commonly exposed not only to the agents of scrub typhus and murine typhus but also to SFG rickettsiae and agents of human ehrlichioses (12). Here, we provide for the first time a more precise indication of rickettsioses in febrile patients from Sangkhlaburi.

The Study

This study was based at the Armed Forces Research Institute of Medical Sciences (AFRIMS)–Kwai River Christian Hospital Clinical Center, Sangkhlaburi District, Kanchanaburi Province, Thailand. (The protocol was approved by the Human Subjects Research Review Board of the U.S. Army, Ethical Review Committee for Research in Human Subjects of the Thai Ministry of Public Health, and Scientific Review Committee of AFRIMS.) Patients were selected from those enrolled and sampled from June 1999 to February 2002 in an on-going “fever study,” which focuses on the etiology of undifferentiated febrile illnesses (oral temperature >38°C or history of fever within the past 48 h) in local residents >20 years of age. Criteria leading to the suspicion of rickettsioses included 1) a rash or eschar, 2) arthropod bites or recent exposure to the jungle, 3) a negative Giemsa-stained malaria smear, and 4) serum specimens that tested positive by enzyme-linked immunosorbent assay (ELISA) for SFG–specific immunoglobulin (Ig) M (PanBio, Brisbane, Australia) or dot-ELISA for total Ig of R. rickettsii or R. typhi (PanBio-INDX, Baltimore, MD). Serum specimens were sent to the Unité des Rickettsies in Marseille for specific diagnosis of rickettsioses. Serologic testing was performed by indirect immunofluorescence (IF) on acute-phase (day 0) and convalescent-phase (approximately day 21) samples. Serum specimens were tested by using a panel of 13 rickettsial antigens, including SFG rickettsiae (R. conorii Indian, R. japonica, R. honei, R. helvetica, R. slovaca, AT1 Rickettsia [13], R. felis, “R. heilongjiangii”) typhus group rickettsiae (R. typhi), Orientia tsutsugamushi (strain Gilliam, Kato, Karp, and Kawazaki), Anaplasma phagocytophilum, Ehrlichia chaffeensis, and Coxiella burnetii. The rationale for the antigen screening panel included the presence of the strains in Asia and results of previous serosurveys for A. phagocytophilum and E. chaffeensis. The standard procedure was followed for the use of Western blot and cross-adsorption studies to complete the IF assay at the Unité des Rickettsies (14,15). An immunofluorescence assay was considered positive for 1) IgG with titers >128 and/or IgM titers >64 for R. conorii; and 2) for IgG titers >64 and/or IgM titers >32 for other rickettsial antigens. When cross-reactions were noted between several rickettsial antigens, the standard procedure comprised three steps: 1) A rickettsial antigen was considered to represent the agent of infection when titers of IgG and/or IgM antibody against this antigen were at least two serial dilution higher than titers of IgG and/or IgM antibody against other rickettsial antigens. 2) When the difference in titers between several antigens was lower than two dilutions, Western blot assays were performed. A rickettsial antigen was considered to represent the agent of the infection when acute-phase or convalescent-phase sera reacted only with the specific proteins of this antigen. 3) When Western blot assays were not diagnostic, cross-absorption studies were performed: IgG/IgM titers had to be >128/32. Specific diagnosis criteria after cross-absorption studies included a) IF serologic test results positive for a single antigen or b) a Western blot assay showing an exclusive reactivity with specific proteins of a sole agent.

From June 1999 to February 2002, 46 patients were selected to be specifically tested for rickettsioses. These 46 patients were empirically treated by a 7-day doxycycline regimen (200 mg/d). Rickettsioses were serologically confirmed in 15 (33%) patients by evidence of seroconversion, IgM at significant titers, or both. Three patients (nos. 1–3) had scrub typhus caused by O. tsutsugamushi. Serum specimens from patients 1 and 3 provided the highest titers against Gilliam and Karp strains, and serum from patient 2 had titers against Gilliam strain only. No further study was conducted to identify the strain responsible for the disease. Two of these patients had returned from a trip into the jungle, and the third became sick several days after cutting grass in the fields. One patient was initially thought to have bacterial meningitis and had been treated unsuccessfully by a broad-spectrum third-generation cephalosporin for 3 days before doxycycline was started. Four patients (nos. 4–7) had murine typhus caused by R. typhi. All had fever and unspecific signs. The patients recalled no arthropod bite, and none had a rash. Eight cases were SFG rickettsioses (nos. 8–15). Of the patients with SFG rickettsioses, only one (no. 9) had fever, eschar, and rash. One patient (no.13) had an eschar at a tick bite site, and another had a rash (no.15). Others presented with unspecific signs. Cross-reactions were noted mostly within the SFG rickettsia antigens. One patient (no. 8) with SFG rickettsioses seroconverted to R. felis, indicated by high level of antibody titers. Further, although IgG titers were more than two serial dilutions higher than those for R. typhi, Western blot assay was performed to confirm IF findings. Two patients (nos. 9 and 10) were shown to have the highest titers to R. conorii strain Indian. Five patients (nos. 11–15) had the highest titers to R. helvetica. For patients 4, 9, 10, 13, and 15, IF results showed differences lower than two dilutions in IgG titers, IgM titers, or both, between several antigens. Thus, IF assays were completed by Western blot and with cross-absorption studies for patient 4 (Table). No cases of infection due to C. burnetii or ehrlichioses were diagnosed in the 46 tested patients.


In this study, we report rickettsioses in Sangkhlaburi, including the first case of R. felis infection reported in Asia. R. felis is an emerging pathogen responsible for flea-borne spotted fever. R. felis was likely first detected (as R. ctenocephali) in European cat fleas (Ctenocephalides felis) in 1918 (16), then rediscovered in 1990 in the United States (17). R. felis was then cultivated and characterized as a unique SFG rickettsia (18). Its pathogenic role was recently demonstrated in patients with serologic evidence of infection in Brazil, France, and Germany. R. felis DNA has also been detected in sera in Texas, Mexico, Brazil, and Germany (19). This rickettsia has also been recently detected in fleas in Brazil, Africa, Spain, and France (20). Further, during an entomologic survey, R. felis–like rickettsiae were detected in fleas collected in Sanghklaburi (P. Parola, unpub. data). These data suggest that R. felis infection is endemic in Sanghklaburi and perhaps globally.

Murine typhus, a mild disease with nonspecific signs (21), was found in four of our patients. Although this disease has a worldwide distribution, it is often unrecognised, and documented cases are rarely reported. The classic triad of fever, headache, and skin rash is observed in <15% of cases (22). For example, our four patients did not have a rash. Arthralgia, myalgia, and respiratory and gastrointestinal symptoms (as demonstrated by one of our patients) are frequent (21,22). Regarding disease transmission, although rats and mice are very common within and around houses in the villages, our patients did not report contact with rat fleas or a flea bite.

In this study, seven patients with SFG rickettsioses may have been infected by R. helvetica (five patients) or R. conorii Indian strain (two patients), according to IF assays completed for some cases by Western blot and cross-adsorption studies. R. helvetica is an emerging pathogen known to be prevalent in Europe (23) and Japan (13). In both areas, R. helvetica is associated with Ixodes ticks, which are also found in Thailand, although they have not previously been reported in Sangkhlaburi (24). R. conorii Indian is known as an agent of tick-borne rickettsioses prevalent in India, where it is associated with the dog tick (Rhipicephalus sanguineus) (25), which is found worldwide. However, an unknown Rickettsia sp. that is cross-reactive with R. conorii Indian and R. helvetica could also be responsible for the cases reported here. In particular, we have recently detected, by polymerase chain reaction, Rickettsia spp. from ticks that have bitten people in the Sangkhlaburi area, including Dermacentor auratus and Dermacentor sp. larvae (9). The pathogenic role of these rickettsiae has yet to be demonstrated.

Scrub typhus is essentially an occupational disease among rural residents in the Asia-Pacific region (2). This disease is often underdiagnosed or misdiagnosed when the classic eschar at the chigger bite sites and the rash are absent, as reported for two of our three patients (2). The severity of the disease varies from asymptomatic to fatal (up to 30%). Delayed or inappropriate treatment such as with third-generation cephalosporins, as reported for one of our patients, is associated with a severe outcome. The four major serotypes studied here have been shown to have sufficient cross-reactivity with antigens from other strains to be used for serologic diagnostic testing. In our patients, although the highest titers were obtained by using O. tsutsugamushi strain Gilliam antigens, other strains that share common epitopes and cross-react with this strain could be involved.

Patients with rickettsioses may have isolated fever or fever with nonspecific clinical and laboratory findings. These diseases are easily misdiagnosed because rash or eschar (the hallmark for rickettsial diseases) is absent, the diseases are not recognized by local physicians, or the diseases have never been reported in the area. More studies are needed on tropical rickettsioses, in particular, molecular detection or rickettsial isolation from patient samples, complemented by detailed case reports. Studying possible vectors and animal reservoirs would provide estimates of the degree of zoonotic potential. Ultimately, such studies will provide the basis for determining prevalence of rickettsiosis in the tropics and their effects on public health.

Dr. Parola obtained his M.D. and Ph.D. degrees at the Faculté de Médecine, Marseille, France. This work is part of his postdoctoral research project at the Harvard School of Public Health, Boston, Massachusetts, USA. His research interests include tropical diseases and medical entomology.



We are grateful to the Armed Forces Research Institute of Medical Sciences Fever Study Team and staff of Kwai River Christian Hospital for technical assistance.

This work was supported partly by the U.S. Department of Defense – Global Emerging Infections Surveillance and Response System and National Institute of Health Grant AI 39002. During this work, Dr. Parola was supported at different periods by Fondation Bayer Santé, Ministère Français des Affaires Etrangères (Programme Lavoisier), Fondation pour la Recherche Médicale, Assistance Publique–Hôpitaux de Marseille, Institut de Recherche International Servier, Association des Professeurs de Pathologie Infectieuses et Tropicales, and the European Society of Clinical Microbiology and Infectious Diseases.



  1. Azad  AF, Radulovic  S, Higgins  JA, Noden  BH, Troyer  JM. Flea-borne rickettsioses: ecologic considerations. Emerg Infect Dis. 1997;3:31927. DOIPubMedGoogle Scholar
  2. Silpapojakul  K. Scrub typhus in the Western Pacific region. Ann Acad Med Singapore. 1997;26:794800.PubMedGoogle Scholar
  3. Raoult  D, Roux  V. Rickettsioses as paradigms of new or emerging infectious diseases. Clin Microbiol Rev. 1997;10:694719.PubMedGoogle Scholar
  4. Parola  P, Raoult  D. Ticks and tickborne bacterial diseases in humans: an emerging infectious threat. Clin Infect Dis 2001;32:897–928. Erratum: Clin Infect Dis. 2001;33:749.
  5. Sirisanthana  T, Pinyopornpanit  V, Sirisanthana  V, Strickman  D, Kelly  DJ, Dasch  GA. First cases of spotted fever group rickettsiosis in Thailand. Am J Trop Med Hyg. 1994;50:6826.PubMedGoogle Scholar
  6. Robertson  RG, Wisseman  CL Jr. Tick-borne rickettsiae of the spotted fever group in west Pakistan. II. Serological classification of isolates from west Pakistan and Thailand: evidence for two new species. Am J Epidemiol. 1973;97:5564.PubMedGoogle Scholar
  7. Stenos  J, Roux  V, Walker  D, Raoult  D. Rickettsia honei sp. nov., the aetiological agent of Flinders Island spotted fever in Australia. Int J Syst Bacteriol. 1998;48:1399404. DOIPubMedGoogle Scholar
  8. Kollars  TM Jr, Tippayachai  B, Bodhidatta  D. Short report: Thai tick typhus, Rickettsia honei, and a unique rickettsia detected in Ixodes granulatus (Ixodidae: Acari) from Thailand. Am J Trop Med Hyg. 2001;65:5357.PubMedGoogle Scholar
  9. Parola  P, Cornet  JP, Sanogo  YO, Miller  RS, van Thien  H, Gonzalez  JP, Identification of Ehrlichia spp, Anaplasma spp and Rickettsia spp in ticks from the Thai-Myanmar border and Vietnam. J Clin Microbiol. 2003; 41.
  10. Chanyasanha  C, Kaeburong  K, Chenchittikul  M, Sujirarat  D. Seroprevalence of scrub typhus infection in patients with pyrexia at some malaria clinics in three western provinces of Thailand. Asian Pac J Allergy Immunol. 1998;16:11925.PubMedGoogle Scholar
  11. Duffy  PE, Le Guillouzic  H, Gass  RF, Innis  BL. Murine typhus identified as a major cause of febrile illness in a camp for displaced Khmers in Thailand. Am J Trop Med Hyg. 1990;43:5206.PubMedGoogle Scholar
  12. Heppner  DG, Wongsrichanalai  C, Walsh  DS, McDaniel  P, Eamsila  P, Thimasarn  K, Serosurvey of Rickettsiaceae and other disease threats at a sentinel site for emerging infectious diseases. Abstract 433. 1997. Orlando, Florida, 46th Annual Meeting of the American Society of Tropical Medicine and Hygiene.
  13. Fournier  PE, Fujita  H, Takada  N, Raoult  D. Genetic identification of rickettsiae isolated from ticks in Japan. J Clin Microbiol. 2002;40:217681. DOIPubMedGoogle Scholar
  14. La Scola  B, Rydkina  L, Ndihokubwayo  JB, Vene  S, Raoult  D. Serological differentiation of murine typhus and epidemic typhus using cross-adsorption and Western blotting. Clin Diagn Lab Immunol. 2000;7:6126.PubMedGoogle Scholar
  15. La Scola  B, Raoult  D. Laboratory diagnosis of rickettsioses: current approaches to diagnosis of old and new rickettsial diseases. J Clin Microbiol. 1997;35:271527.PubMedGoogle Scholar
  16. Sikora  H. Beitrage zur Kenntnis der Rickettsien. Arch f Schiffs und Tropenhyg Liepzig. 1918;xxii:4426.
  17. Adams  JR, Schmidtmann  ET, Azad  AF. Infection of colonized cat fleas, Ctenocephalides felis (Bouche), with a rickettsia-like microorganism. Am J Trop Med Hyg. 1990;43:4009.PubMedGoogle Scholar
  18. La Scola  B, Beconi  S, Fenollar  F, Rolain  JM, Roux  V, Raoult  D. Amended description of Rickettsia felis (Bouyer et al. 2001), a temperature-dependent cultured bacterium. Int J Syst Evol Microbiol. 2002;52:203541. DOIPubMedGoogle Scholar
  19. Richter  J, Fournier  PE, Petridou  J, Haussinger  D, Raoult  D. Rickettsia felis infection acquired in Europe and documented by polymerase chain reaction. Emerg Infect Dis. 2002;8:2078. DOIPubMedGoogle Scholar
  20. Rolain  JM, Franc  M, Davoust  B, Raoult  D. Molecular detection of pathogenic Bartonella and Rickettsia in cat fleas from France. Emerg Infect Dis. 2003;9:33842.PubMedGoogle Scholar
  21. Silpapojakul  K, Chayakul  P, Krisanapan  S, Silpapojakul  K. Murine typhus in Thailand: clinical features, diagnosis and treatment. Q J Med. 1993;86:437.PubMedGoogle Scholar
  22. Dumler  JS, Taylor  JP, Walker  DH. Clinical and laboratory features of murine typhus in south Texas, 1980 through 1987. JAMA. 1991;266:136570. DOIPubMedGoogle Scholar
  23. Fournier  PE, Grunnenberger  F, Jaulhac  B, Gastinger  G, Raoult  D. Evidence of Rickettsia helvetica infection in humans, eastern France. Emerg Infect Dis. 2000;6:38992. DOIPubMedGoogle Scholar
  24. Tanskul  P, Stark  HE, Inlao  I. A checklist of ticks of Thailand (Acari: Metastigmata: Ixodoidea). J Med Entomol. 1983;20:33041.PubMedGoogle Scholar
  25. Parola  P, Fenollar  F, Badiaga  S, Brouqui  P, Raoult  D. First documentation of Rickettsia conorii infection (strain Indian tick typhus) in a traveler. Emerg Infect Dis. 2001;7:90910. DOIPubMedGoogle Scholar




Cite This Article

DOI: 10.3201/eid0905.020511

1These results were presented in part at the 3rd International Conference on Emerging Infectious Diseases, March 24–27, 2002, Atlanta, Georgia, USA.

Table of Contents – Volume 9, Number 5—May 2003

EID Search Options
presentation_01 Advanced Article Search – Search articles by author and/or keyword.
presentation_01 Articles by Country Search – Search articles by the topic country.
presentation_01 Article Type Search – Search articles by article type and issue.



Please use the form below to submit correspondence to the authors or contact them at the following address:

Didier Raoult, Unité des Rickettsies, CNRS UMR 6020 IFR 48, WHO Collaborative Center for Rickettsial Reference and Research, Faculté de Médecine, 27 Bd Jean Moulin, 13385 Marseille Cedex 5, France; fax: (33) 4 91 83 03 90

Send To

10000 character(s) remaining.


Page created: December 08, 2010
Page updated: December 08, 2010
Page reviewed: December 08, 2010
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.