Jpn. J. Med. Sci. Biol., 43, 123-131, 1990. AMEBIASIS IN INSTITUTIONS FOR THE MENTALLY RETARDED IN KANAGAWA PREFECTURE, JAPAN Kouichi NAGAKURA, Hiroshi TACHIBANA, Yoshimasa KANEDA, Hidekatsu SUZUKI1, Katsushi SASAOKA2, Seiki KOBAYASHI3 and Tsutomu TAKEUCHI3 Department o f Parasitology, Tokai University School o f Medicine, Bohseidai, Isehara-shi, Kanagawa 259-11, 1Odawara Public Health Center, Minami-cho, Odawara, Kanagawa 250, 2Fujisawa Public Health Center, Kugenumakami, Fujisawa, Kanagawa 251 and 3Department of Parasitology, School of Medicine, Keio University, Shinanomachi, Shinjuhu-ku, Tokyo 160 (Received May 15, 1990. Accepted July 30, 1990) SUMMARY: A parasitologic survey of 620 mentally retarded patients, institutionalized in five different facilities in Kanagawa Prefecture, revealed a high incidence (12.6%) of infection with Entamoeba histolytica. A concomitant serologic survey, by the indirect fluorescent antibody test, gave a much higher incidence (26.5%). Moreover, most zymodeme patterns of the amebae isolated from infected individuals were of a pathogenic type (Zymodeme II). Our findings demonstrate that the mentally retarded in Japan, as in the United States, still are plagued by a high rate of amebic infection. INTRODUCTION Entamoeba histolytica infection has a world-wide distribution. In large cities of developed countries, amebiasis is commonly found within two closed 永倉貢一 ・橘 裕司 ・金田良雅(東 海大学医学部寄生虫学教室 神奈川県伊勢原市 望星台) 鈴木秀勝(神 奈川県小 田原保健所 神奈川県小田原市南町2-4-45) 笹岡克至(神 奈川県藤沢保健所 神奈川県藤沢市鵠沼上2-7-1) 小林正規 ・竹内 勤(慶 応 大学医学部寄生虫学教室 東京都新宿区信濃町35) 123 communities; in homosexual men (1-3) and in mental hospitals (4). The disease seems to be more common in institutions for the mentally retarded, because they exhibit frequently abnormal hand-to-mouth and object-to-mouth behavior. In surveys performed in the United States, the incidence of amebic infection in 11 facilities ranged from 0 to 71.0% and some deaths from invasive amebiasis were reported (4). High rates of amebic infection have also been reported from Japan (5). To further assess the incidence and status of amebiasis in mental hospitals, the stools and sera of 620 residents in five institutions were examined for E. histolytica during the years 1986-1989. The results of this epidemiological survey are reported herein. SUBJECTS AND METHODS The numbers of residents in the wards of five institutions are listed in Table II. The procedures of stool examination and serodiagnosis for amebiasis were as reported previously (5,6). For isolation of amebae, cultivation of stool was carried out in Robinson's medium (7). The zymodemes of isolated organisms were determined by electrophoretic isoenzyme patterns of hexokinase [Enzyme Commission number (EC); 2.7.1.1], phosphoglucomutase (EC 2.7.5.1), malic enzyme (1.1.1.40) and glucosephosphate isomerase (EC 5.3.1.9). All of these procedures were conducted according to Sargeaunt and his group (8,9). RESULTS The results of the stool examinations and indirect fluorescent antibody (IFA) tests on the 620 mentally retarded patients are summarized in Table I. About 13% of the residents (78 of 620) had cysts or trophozoites of E. histolytica in their stools. Five out of the stool-positive group were symptomatic (amebic colitis); the remaining 73 subjects were classified as asymptomatic cyst-carriers. As a control, 192 sera from normal adult Japanese with a similar geographical distribution were tested; none was positive by IFA. However, 164 (26.5%) of the 620 residents in five institutions were seropositive. This shows 124 Table I. Survey of 620 individuals residing in institutions for the mentally retarded for amebic infection *Titers of 1: 64 or higher were judged as IFA-test positive . Table II. E. histolytica infections among patients in the wards of five institutions for the mentally retarded *Amebic colitis defined as bloody diarrhea with E, histolytica tropho- zoites isolated from stools and respondinq to antiamebic therapy. Died from invasive amebiasis, Novembr, 1989.E. Histolytica tropho- zones were identified postmortem. Table III. Serologic tests and zymodeme determinations in a survey for E . histolytica infection among mentally retarded individuals in Japan *SerologicallY positive on three examinations during the years 1988 -1989. that the mentally retarded individuals examined in this study had a higher rate of positive anti-amebic antibody than did the control Japanese. As shown in Table I, 102 of the seropositive cases (16.5%) were negative by stool examination or cultivation. Of these, three individuals were symptomatic; two of them have been cured of an amebic liver abscess and the other died from hepatic amebiasis in November, 1989. The remaining subjects were apparently asymptomatic. To find out more about the mode of transmission of the ameba, the relationship between positive cases for E. histolytica in their ward and those in five mental hospitals was investigated (Table II). The incidences of amebic infection by serodiagnosis ranged from 0 to 62.3% in the ward (mean; 26.3%) and from 11.4% to 41.8% in the mental hospitals. The highest rates in the ward and in mental hospital were found in residents of ward J and institution III, respectively. The positive cases tended to concentrate in certain wards, and two mental hospitals (institutions III and V) had higher incidences of E. histolytica. To assess the status of amebiasis, zymodeme studies on isolated amebae were performed. Ten amebic isolates were obtained from cyst-carriers and determined for the zymodeme of amebic enzymes (Table III). Nine of the isolates had the same pathogenic zymodeme type [Zymodeme II, according to the classification of Sargeaunt (9)]. Only one ameba with nonpathogenic zymodeme (Zymodem I) was obtained from a cyst-carrier in ward R of institution V. The residents who were positive by stool examination and/or the IFA test were treated with metronidazole, 750-1,500 mg, tid, for one to two weeks, immediately after completion of the survey. The efficacy of treatment was evaluated monthly by stool examination and stool culture, and trimonthly by the IFA test. After treatment, however, 41.0% of the stool-positive residents still excreted cysts within two years. In some cases, treatment with metronidazole plus antibiotics (tetracycline and chloramphenicole) for 10 to 14 days was repeated in 32 recurrent carriers. As shown in Table III, in one patient, cyst excretion reoccurred six times. 128 DISCUSSION The majority of mentally retarded individuals with E. histolytica infections in England have been asymptomatic, and from them seven isolates with different nonpathogenic zymodeme patterns (Zymodeme I, III and IV) were obtained (8). In contrast, amebiasis in mental hospitals in the United States (4) and Japan (5), although showing a high rate of seropositivity, has not been characterized by zymodeme studies. To more fully understand the epidemiology of amebiasis in institutionalized populations, zymodeme studies are essential. A parasitologic study on 620 mentally retarded individuals, who were institutionalized in five different facilities in Kanagawa Prefecture, revealed a high incidence (12.6%) of infection with E. histolytica. In addition, a concomitant serologic survey by the IFA test yielded a much higher incidence (26.5%). These percentages were still higher than those of the control Japanese. The difference in the positive rate between the two groups obtained by IFA appears to be attributable to the higher sensitivity of mentally retarded individuals. A positive IFA reflects infection with pathogenic amebae, and the IFA test correlates well with pathogenicity of E. histolytica as follows. A higher rate of seropositivity in the stool-positive group (62/78, 79.5%) and the presence of amebae with a pathogenic zymodeme (Zymodeme II) were revealed in the present study. Though 102 of the seropositive individuals were judged as negative by stool examination or cultivation, it is likely that they had been infected with E. histolytica, because three individuals were symptomatic (amebic liver abscess). E. histolytica trophozoites were identified by the postmortem pathologic observation of one of the patients. These data seem to support our view that pathogenic strains of E. histolytica are spread among the mentally retarded, as well amebiasis in the homosexual population (10), in Japan. Sixteen seronegative but stool-positive individuals were detected in the present study. Ten of them resided in the same ward where a nonpathogenic ameba (Zymodeme I) was isolated. However, a high rate of seropositivity (30.0%) was observed in this ward, and a resident died from amebiasis. Moreover, the patient had had antibody to E. histolytica before nonpathogenic ameba was isolated. These data demonstrate that both pathogenic and nonpathogenic amebae were present in the ward's inhabitants and in the same person. We reported previously on the transmission of E. histolytica in an institution for the mentally retarded in Japan (5). There, the amebic infections 129 were likely due to such abnormal behaviors of the severely retarded patients as pica and fecal play. The present study revealed a high rate of seropositivity and the presence of pathogenic amebae in institutionalized individuals in Japan. Therefore, it seems certain that person-to-person spread is implicated in the transmission of the parasite in such institutions. The lack of more effective drugs for intestinal amebiasis and the special mode of transmission of ameba create special problems in eradication of E. histolytica from mental hospitals. We advise periodic health checks of the mentally retarded individuals to detect cases of invasive amebiasis. It is also obvious that urgent development of more effective drugs for intestinal amebiasis is needed. ACKNOWLEDGEMENTS We wish to thank Mr. Shoji Kumasaka, Mr. Makoto Hayashi, Dr. Shigeo Eto and Dr. Yoshitsugu Naito of the Kanagawa Prefectural Office for their critical advice, and Ms. Y. Kato of the Department of Parasitology and Ms. Y. Saishoji of the Odawara Public Health Center for their excellent technical assistance. REFERENCES 1. Felman, Y. M. (1981): Approach to sexually transmitted amebiasis. Bull. N. Y. Acad. Med., 57, 201-206. 2. Phillips, S. C., Midvan, D.