SEROLOGIC EVIDENCE OF INFECTION WITH EHRLICHIAE AND SPOTTED FEVER GROUP RICKETTSIAE AMONG RESIDENTS OF GAG ISLAND, INDONESIA ALLEN L. RICHARDS, SUTANTI RATIWAYANTO, EKO RAHARDJO, DARYL J. KELLY, GREGORY A. DASCH, DAVID J. FRYAUFF, AND MICHAEL J. BANGS U.S. Naval Medical Research Unit No. 2, Jakarta, Indonesia; Communicable Diseases Research Center, National Institute of Health Research and Development, Jakarta, Indonesia; U.S. Naval Medical Research Center, Silver Spring, Maryland; Walter Reed Army Institute of Research, Washington,DistrictofColumbia Abstract. The causative agents of scrub and murine typhus are considered endemic to Indonesia. However, the presence of spotted fever group rickettsiae and ehrlichiae have not been previously described in this country. During an investigation of arthropod-borne diseases on Gag Island, located northwest of the island of New Guinea in eastern Indonesia, the prevalence of antibody to the etiologic agents of monocytic ehrlichiosis, spotted fever rickettsiosis, and scrub and murine typhus were determined. Analysis of 55 blood samples from residents of Gag Island showed serore- activity to antigen preparations of Ehrlichia chaffeensis (7 of 48, 14.6%), two spotted fever group rickettsiae: Rickettsia rickettsii (5 of 48, 10.4%) and R.conorii (10 of 49, 20.4%), Orientiatsutsugamushi (5 of 53, 9.4%), and R.typhi (1 of 48, 2.1% [by an indirect immunofluorescence assay] and 1 of 50, 2.0% [by an enzyme-linked immunosorbent assay]). These results show serologic evidence of infection with ehrlichiae and spotted fever group rickettsiae for the first time in Indonesia in a location where the prevalence of antibody to O. tsutsugamushi and R. typhi was lower. INTRODUCTION Rickettsial diseases are endemic to Indonesia. 1 Murine ty- phus (Rickettsia typhi) has been reported on many of the larger islands of the archipelago, including Java, 2–7 Sumatra, 8,9 Bali, 4,10 Muna, 4 and Irian Jaya. 11 The closely re- lated etiologic agent of epidemic typhus, R. prowazekii, does not occur in Indonesia 2,4,12,13 due to the absence of the ar- thropod vector, the human body louse Pediculus humanus humanus. 2 Scrub typhus (Orientia tsutsugamushi) has been recognized throughout Indonesia, especially during World War II when the occurrence of the disease on the island of New Guinea and neighboring islands was found to be a major impediment for military forces. 14–16 In addition to New Guinea, scrub typhus has been reported on the islands of Java, 5–7,17–19 Sumatra, 8,9 Borneo, 20 and Sulawesi. 21 Other rickettsiae and Rickettsia-like organisms, such as spotted fe- ver group rickettsiae and ehrlichiae, have not been previously reported occurring in Indonesia, 1,13,22 although they have been reported in the surrounding Asia-Pacific region, includ- ing Australia, 12,23–25 Malaysia, 22,26–29 Thailand, 30–34 Ja- pan, 32,35–38 India, 12,31 Pakistan, 30,31 Nepal, 31 China, 39,40 Mon- golia, 31 and Taiwan. 32 This report was the outcome of an investigation to deter- mine the presence and level of arthropod-borne diseases on Gag Island, a small, isolated island located northwest of the Province of Irian Jaya, Indonesia. An investigation on malaria prevalence and parasite drug resistance has been reported elsewhere. 41 Herein we describe, for the first time, serologic evidence of life-long inhabitants of Indonesia infected with spotted fever group rickettsiae and ehrlichiae. Additionally, we report a lower prevalence of antibody to O.tsutsugamushi and a near absence of seroreactivity to R. typhi among resi- dents of Gag Island, Indonesia. MATERIALS AND METHODS Study population. Gag is a small island located in the Hal- mahera Sea, northwest of Irian Jaya and along the eastern edge of the Maluku Island Chain in the Republic of Indonesia (Figure 1). Approximately, 500 indigenous people lived on this island at the time of the survey, most of them in the village of Gambir. In addition, approximately 200 non- indigenous mining personnel were temporarily residing on the island. The local inhabitants were primarily subsistence farmers and fishermen. Gambir is located on the coast along the northeast side of the island, surrounded by sago swamp, coconut groves, and native forest. Most people lived in well- constructed, cement homes; however, the houses still allowed easy excess to rodents and arthropod vectors. Four hundred fifty-six residents of Gambir and 112 mining employees were screened for malaria and lymphatic filariasis. Of these, 80 villagers and three mining employees were enrolled in a study of in vivo resistance of malaria parasites to chloroquine and Fansidar® (F. Hoffmann-La Roche, Basel, Switzerland). 41 From these 83 individuals, 55 sera (53 from villagers and two from mining employees) were available for testing of expo- sure to rickettsiae and rickettsia-like organisms. Human blood was collected by venipuncture, separated, and the serum was stored at -70°C. For the indirect immuno- fluorescence assay (IFA), the serum was assayed for reactiv- ity to R. typhi, R. rickettsii, and E. chaffeensis as describe by the manufacturer (MRL Diagnostics, Cypress, CA). Sera were also assessed for reactivity to R. typhi, R.conorii, and O. tsutsugamushi with an enzyme-linked immunosorbent assay (ELISA) format previously described. 6 This study was reviewed and approved by the Committee for the Protection of Human Subjects of the U.S. Naval Medi- cal Research Unit No. 2 and the Communicable Disease Re- search Center, National Institutes of Health, Research and Development (Jakarta, Indonesia). Informed consent was ob- tained from all human adult participants and from parents or legal guardians of minors. RESULTS Fifty-five human serum specimens from Gag Island were examined for serologic reactivity to E. chaffeensis, R. rick- ettsii,R.conorii,O.tsutsugamushi, and R.typhi antigen prepa- rations. The seroreactivity prevalence is shown in Table 1. Agreement was found between the results obtained with dif- ferent assays (IFA and ELISA) for detecting antibodies to Am. J. Trop. Med. Hyg., 68(4), 2003, pp. 480–484 Copyright © 2003 by The American Society of Tropical Medicine and Hygiene 480