Immunofluorescence Test with <i>Rickettsia montana</i> for Serologic Diagnosis of Rickettsial Infection of the Spotted Fever Group in Shikoku, Japan

Abstract

Rickettsial infections of the spotted fever group (SFG) have been experienced recently in areas along the coast from Anan city to the Muroto promontory, i.e., the southeast coast of Shikoku, one of Japan's four principal islands (15). This illness newly found in Japan was discovered by evaluation of a positive OX2 reaction in the Weil-Felix (WF) test (13, 14), which was obtained in a clinical examination of patients in Anan city, Tokushima Prefecture (7). Clinical features of the illness have been described A similar illness had been experienced in the Muroto area of Kochi Prefecture; three patients in 1983 and three in 1984, whose clinical course was characterized by response to tetracycline therapy. Patients' sera collected within 5 months after the onset of illness showed positive OX2 and OX19 agglutinations which were tested with WF antigens standardized against the appropriate convalescent-phase serum ( These sera reacted with antigens of Rickettsia rickettsii and R. akari in the complement fixation test like those from patients in Anan city, which was conducted by Tsuboi and Oya, National Institute of Health, Tokyo (15, Sera collected more than one year after onset were found to be reactive with R. akari. Serologic examination was carried out also by Suto, Akita University, Aki ta, Japan, who showed that the sera reacted with R. sibirica and Thai-tick typhus rickettsia in the immunoperoxidase test ( The rickettsial antigens of SFG employed in the above-mentioned tests were supplied from institutions overseas, except for the antigen of R. akari that had been stored in the National Institute of Health. It was urgently necessary to provide a constant supply of the antigen for serologic diagnosis of the illness. We chose R. montana VR-611 as the rickettsial strain of SFG, because R. montana is nonpathogenic for experimental animals (1) and there is no evidence that this species of SFG is associated with illness in humans (18). We found that sera from patients encountered in the Muroto area over the last 3 years including nine cases in 1985 reacted with R. montana in the immunofluorescence (IF) test and that the strain could be used as an antigen for specific serologic diagnosis of rickettsial infections endemic in areas along the southeast coast of Shikoku. 1061