Application of the Bengtson reaction for diagnosing the benign rickettsial diseases in São Paulo

Abstract

In a previous paper, the authors reported a human case of murine typhus that occurred in the city of S. Paulo, Brazil. The diagnosis of the case was made by the isolation and identification of a strain of Rickettsia mooseri. For a time, similar mild cases of infection observed in the State of S. Paulo had not been distinguished from cases of the so-called S. Paulo typhus. They were later diagnosed as cases of murine typhus although only on clinical grounds. In this paper, further work done to clear up the etiology of such cases is reported. Complement fixation tests with rickettsial antigens were carried out with a number of positive Weil-Felix sera, Many of the blood samples were taken during or after the course of a mild infection from people living in either urban or rural areas of the State of S. Paulo. At first a cocto-antigen was used, which was prepared from a strain of Rickettsia mooseri isolated in Santiago, Chile. Later, Bengtson antigens were employed, which were prepared either with Rocky Mountain spotted fever, murine or epidemic typhus rickettsiae. In 1944, sera from 7 cases reported in a rural area of S. Paulo State were tested with the cocto-antigen. At that time, the lack of a Rocky Mountain spotted fever antigen made it impossible to prove conclusively the occurrence of cases of an exanthematic disease of the typhus group in the State of S. Paulo. Two years later, complement fixation tests performed with Bengtson antigens provided definite evidence that part of the so-called "S. Paulo typhus" actually were cases of an infection of the typhus group. Of the clinical cases tested with Bengtson antigens for complement fixing antibodies, 58 were selected for discussion in this paper.  They were all mild cases with a positive Weil-Felix reaction. In two of them, a serologic diagnosis of R. M. s. f. was established. A positive test with either the murine or the epidemic antigen was obtained in 51 cases. In many of them there was not a significant difference between the murine and the epidemic antibody titers. Sometimes the titer was higher with the murine, at others with the epidemic antigen. From one of those 51 cases, a strain of Rickettsia mooseri was isolated and identified. Serum of 75 employees of the grain store where this patient worked were tested with Bengtson antigens. A positive test with the murine antigen was obtained in three of these people. None of them had shown any sign of infection for a period of at least a month previous to the bleeding for the test. The test was also used for the diagnosis of 4 cases of laboratory infection. All 4 were accidentally infected in the Rickettsial Diseases Laboratory of the Instituto Butantan, where the work reported in this paper was done. Complement fixing antibodies against the rickettsiae of the typhus group were found in the serum of all cases when tested with Bengtson antigens. Later, a strain of Rickettsia mooseri was isolated from each case and identified. In one of these accidental cases, not even using Plotz antigens could a specific serologic diagnosis be made. A blood sample taken 4 months after the infection from this case was tested for complement fixing antibodies at the Army Medical Center, Washington, D. C., U. S. A. The titer was slightly higher with the epidemic than with the endemic antigen. However, the agglutination titer with the murine was significantly higher than with the epidemic rickettsiae.