A number of patients in recent Shichito lever endemic in Miyake Island was relatively small and only one isolation of avirulent strain (Miyake strain) from a field rodent was succeed in nude mice. These facts might indicate that presence of virulent strain which could isolate in conventional mice was limited in nature. Four time seroepidemiological surveys of field rodentsstudies by indirect immunofluorescence in Miyake Island showed that antibody positive rate was increased rapidly from 0%(0/25) in January 1977 to 83.3%(15/18) in November 1978 (isolation ofRt was negative). Field rats, Rattus norvegicus (Rn) and Apodemus speciosus (Apo) which were primarily living outdoors, showed rapid increase and reached high seropositive (from 0% to 85.7% in Rn and from 66.7% to 100% in Apo). On the contrary, Rattus rattus (Rr) which was mainly livingindoors, showed slow raise seropositive rate (from 0% to 50%). In nature, life span and maintenance of antibody of field rodents were about 1 year. These facts might indicate that in Miyake Island, high percentage of field rodents got infection in the last 2 years and the infected Rt was an avirulent strain like Miyake strain which could grow only in nude mice.
During the endemic of Shichito fever, an avirulent R. tsutsugamushi (Rt) (Miyake strain) was isolated from a field rat. This isolate could grow only in nude mice. On the other hand, rate of seropositive field rodents was increased rapidly from 0% to 83.3% in the last 2 years. These results suggested that recent endemic of Shichito fever was caused by the avirulent strain of Rt. To confirm possibility, seropositive rate in inhabitants of Miyake and Toshima Islands was surveyed by indirect immunofluorescence. When assayed upon the sera obtained during May to October 1978, seropositive rate of people in Miyake Island was 26.1%(42/162), while that in Toshima Island was 23.5%(23/98). There was no sexual difference and antibody titers of inhabitants were lower than those of Shichito fever patients. All control groups including 40 normal healthy men, 43 infectious mononucleosis like disease patients and 58 malignancy patients were seronegative. Seropositive men in Miyake Island were inquired individually. They did not have any clinical signs and prehistory of Shichito fever in the last 2 years. These fact might indicate that about 1/4 of the population in Miyake and Toshima Islands was inapparently infected with avirulent strain of Rt and recent endemic of Shichito fever might be caused by the avirulent Rt.
A new type scrub typhus which was transmitted by chiggers other than L. akamushi was known at foothill of Mt. Fuji since 1948. After small endemic in 1959, a few cases were reported from this area every year. Recently, a number of scrub typhus patient began to increase and we surveyed a number of patients, clinical signs and presence of inapparent infections. 1. In 1978, 20 cases were clinically diagnosed as scrub typhus and 14 cases were confirmed etiologically by our indirect immunofluorescence. In 1978, patients among inhabitants outnumbered those among the self-defence force soldiers first time, probably due to the spreading of noxious areas in this district. 2. Clinical symptoms of patients among inhabitants varied considerably from very mild to severe (one died). 3. Only 2.2%(2/92) of self-defence force soldiers manoeuvering around these areas had anti-Rtantibody. However these 2 cases belonged to one squad (33 soldiers) which moved along with patients. Antibody positive percentage was 6.1 %(2/33) in this squad. This rate was much lower than the results obtained in Izu Shichito Islands and might indicate fewer inapparent infections around Mt. Fuji district.
One hundred and two strains of virulent S. typhimurium were examined for SPA (Soluble Protective Antigen) producing ability. Experimental methods were identical to those described in the previous paper. A wide variety of results ranging from strains capable of producing SPA to protect mice against the challeng of 100, 000 times LD50 of bacteria to non-SPA producing strains incapable of protecting animals, was obtained, Many high SPA-producing strains of S. typhimurium, namely, 4 strains with a potency >100, 000 LD50 (3.9%) and 46 strains >10, 000 LD50 (45.1%), were found along with several weak and non-SPA producing strains. Protective ability of formol vaccines (FV) of the above 102 strains was examined. 86 strains (84.4%) capable of rendering a strong protection to mice against 10, 000 LD50 of bacteria were found among a wide variety of strains rainigng from capable to incapable of imparting a protecteve immunity to animals. These results were similar to those obtained with the SPA immunity test above. The FV of those high SPA-producing strains also showed a marked protecting effect on animals against infections by imparting an immunity as a killed vaccine. Whereas, those FVs of non-SPA producing strains were unable to protect mice against infection. Thus, there was a definite relation in producing protective immunity between SPA and killed vaccine with a correlation coefficient of 0.747. As shown above, most of the strains of S. typhimurium capable of rendering a protective immunity to animals against infections were found, and killed vaccine tended to give a positive immunity.
Studies were made of a method of suspension culture for MDCK cells which enables us to prepare a sufficient quantity of cells in a regularly available condition in preparation for an unexpected occurrence of influenza epidemics, and examination of HA yield in suspension cultured cells and virus isolation from patient's specimen were performed. A silicon coated spinner flask as culture bottle and a Joklik modification of MEM added with foetal bovine serum, tryptose phosphate broth and methyl cellulose solutions as growth medium. Examination of HA yield with the inoculation 1.5×103PFU/ml of viruses (average quantity of viruses in throat washings) upon the suspension cultured cells in 8 steps from 1.1×106 cells/ml to 9.2×103 cells/ml of cells revealed that HA yield became better in higher concentration of cells to 2.3×105 cells/ml, but conversely fell down in much higher concentration. In contrast with HA yield with the monolayer cells, HA yield with the suspension cultured cells was poor with low m.o.i. Using 2×105 cells/ml of suspension cultured cells, 20 strains of influenza virus were isolated from 60 specimens. The rate of isolation was a little lower than that with the fertile hen's egg (27 strains were isolated), but the number of days necessary for the pathogenic determination could be lessend.
The anti-deoxyribonuclease B (ADNase B) test is valuable in the serological detection of group A streptococcal infections. The present paper reports on the evaluation of ADNase-B titer compared with anti-streptolysin O (ASO) titer from a population sample. The samples were collected from healthy people living in Saitama, Japan. This sample was divided into six age groups: less than 2 years, 3-5 years, 6-10 years, 11-15 years, 16-25 years and 26 years or more. ADNase B titers were determined by measuring the enzyme inhibition method and also ASO titers were determined by the modified method of Rantz-Randall. In this study, aniibody responce was poor with children 5 years old or younger. The geometric mean titer was the highest in the 11-15 years old group, and moderate in the adult group. The epidemiological study must be accomplished for the further evaluation of antibody distribition.