The Topic of This Month Vol.17 No.4 (No.194)

El Tor cholera originating from Sulawesi (former Celebes) Island spread to neighboring countries from around 1961 and in a very short time appeared in Thailand, Bangladesh, and India. This was the beginning of the seventh cholera pandemic.�@Later, the epidemic expanded to the whole areas of Asia including Southeast, the Middle and Near East, Africa, Europe and America, and further to Latin America.�@Although it has already been 35 years since this cholera pandemic started, no sign of extinction can be seen yet.

Cholera incidents in Japan before 1976 used to be restricted to returnees from such cholera-prevailing areas as Southeast Asia and India, whereas, since 1977, it has been occurring among those who have never traveled abroad (Fig. 1). Some of the noticeable incidents of cholera in this country were the one having occurred in 1977 in Arida City, Wakayama Prefecture, in which the source of infection was ascribed to a returnee from a cholera-prevailing area and another one having occurred in 1978, in which lobster served at a wedding parlor, Ikenohata, Taito-ku, Tokyo, was incriminated. In 1989, there was another outbreak in Nagoya City, Aichi Prefecture involving patients living in such wide areas as Aichi, Ehime, Tokyo, Shizuoka, Gunma, and Niigata Prefectures and Kyoto City. In 1991, occurred a Tokyo Metropolitan cholera outbreak, which mass media reported to have been caused by hen clams gathered in Tokyo Bay, bringing about a cholera panic.

The cholera incidents in 1994 numbered 114, of which 90 (79%) were imported ones and the other 24 (21%) domestic ones. The incidents outnumbered only slightly those in the preceding year (102), but the increase in domestic cases was striking (three in 1993 and 24 in 1994).

In 1995, the total incidents numbered 372, showing an unusual increase. Of these incidents, imported ones numbered 341 (92%) and domestic ones 31 (8%) (see p. 77 of this issue). The incidents were the largest in number since the first invasion of this country with El Tor cholera.

Cholera patients were found almost every year among the returnees from Indonesia, where El Tor cholera had first been recognized; 20 in 1985, 39 in 1991, eight in 1992, 16 in 1993, and 25 in 1994. After February 1995, cholera broke out among the returnees who joined sight-seeing tour groups to Bali Island, and by the end of December patients (278) and carriers (18), living in 37 different prefectures, totaled 296. Of these, 259 cases (88%) collectively arose during two months, February (154 cases) and March (105 cases) (Fig. 2). During April and May, however, the cholera cases originating from Bali Island decreased abruptly. Although a tendency of a slight increase was seen in June (nine cases), July (19 cases), and August (five cases), only one case was found after September. The cases among Bali returnees accounted for 80% of the total cholera cases (372) in 1995.Three patients acquiring cholera on Bali Island were reported also in Australia (see IASR, Vol. 16, No. 10, 1995). It is presumed that cholera was latently prevailing on Bali Island from the beginning of 1995.

On the other hand, sporadic domestic cases among those who had never been abroad were seemingly increasing from the preceding year and further increased in 1995 (31 cases). Surveillance of fish and shellfish specimens (17,001) carried out at quarantine stations in 1995 detected cholera-toxin-producing V. cholerae O1 from two prawn specimens imported from India. No one can rule out the possibility that imported fish and shellfish which were contaminated with V. cholerae O1 but evaded quarantine were associated with these sporadic cases. Since increased sporadic cases may possibly trigger cholera epidemics, the trend of such sporadic cases will have to be more strictly monitored.

Incidence of Vibrio cholerae O139 in Japan. A large-scale epidemic of new cholera due to V. cholerae O139 emerged in India in the latter half of 1992. The new cholera spread swiftly to neighboring countries and it was found in Southeast Asia already in 1993.

In 1993, V. cholerae O139 was isolated also in this country from two cases returning and another visiting from the Indian Subcontinent, all suffering from diarrhea. In the next year, 1994, additional eight cases were recognized among returnees, two from India, another from Bangladesh, other four from Thailand, and the other one from China. In 1995, however, no more case was found at all. Table 1 summarizes the four cases reported after May 1994 (the cases reported before April 1994 were summarized in IASR, Vol. 15, No. 6, 1994).

At present, cholera due to V. cholerae O139 is showing a tendency to decrease in the Indian Subcontinent, whereas to increase in Thailand and other Southeast Asian countries and China. Therefore, the trend of its incidents will require thorough monitoring.

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