The Topic of This Month Vol.19 No.5(No.219)
Cholera was originally an endemic disease localized within the delta region of the River Ganges. As the Indian trade with Western European countries increased from 1817, cholera spread to all over the world, bringing forth as many as six pandemics before 1923. No other pandemic of such classical cholera has ever broken out since then.
Indonesia-indigenous cholera (El Tor cholera), being distinct from classical one, however, has spread to neighboring Southeast Asia, Indian Subcontinent, Near East, and Africa, and more recently to South America from about 1961. This is the seventh cholera pandemic, which is still the threatening of people's health.
1. Incidence of cholera in Japan
The cholera incidence in Japan during the period from 1975 through 1997 is shown in Fig. 1. Although cholera cases in Japan used to be restricted to returnees from cholera-endemic areas, those among people who never experienced overseas traveling have increased noticeably in recent years.
As cholera endemic in this country, there was an outbreak in Arida City, Wakayama Prefecture, in 1977, of which the source of infection was ascribed to a returnee from the Philippines. Another outbreak occurred in the next year presumably due to consumption of lobsters of Indonesian origin served at a wedding parlor at Ikenohata, Tokyo. In 1989, there was an outbreak starting from Nagoya, involving patients living in seven different prefectures, and in 1991, another outbreak occurred in Tokyo Metropolis (see IASR, Vol. 15, No. 6, 1994).
As an imported incident worth special mentioning, many cholera patients appeared among travelers to Bali Island in 1995. Cases of cholera infection exploded in as many as 37 different prefectures involving 296 cases (see IASR, Vol. 17, No. 4, 1996).
Cholera cases in 1996 numbered 62, comprising 49 (79%) imported ones and 13 (21%) domestic ones without history of overseas traveling; the total cases were markedly less than those in the preceding year (377) (see IASR, Vol. 18, No. 8, 1997). The difference may be attributed to the markedly decreased cases (three) among Bali returnees.
Cholera cases numbered 101 in 1997 (see p. 101 of this issue). Of these cases, those with no history of overseas traveling were 36 living in 17 different prefectures (Fig. 2), accounting for 36% of the total cases in this year. The largest number of cases was found in August, and next in July, showing an incidence pattern similar to that of Vibrio parahaemolyticus food poisoning (Fig. 3). On the other hand, the imported cases numbered the largest, being 16, in April. This was due to the outbreaks involving 11 patients in two groups of sightseeing tours to Thailand.
The ages of the patients without history of overseas traveling ranged from 13 to 86 years (average 60 years), of which those aged over 60 years accounted for more than half, being about 51%. The ages of the patients who had history of overseas traveling ranged from 6 to 72 years (average 46 years) and those over 60 years accounted for only about 17%. The cases without history of overseas traveling were mostly old people, but no case was found among their family members.
Thirty-four strains of Vibrio cholerae O1 isolated from cases with no history of overseas traveling in 1997 were analyzed for the phage type, drug sensitivity and genotype by pulsed-field gel electrophoresis (PFGE) after digestion with NotI restriction enzyme. Identical or very similar patterns were obtained with all strains. The patterns were identical to those of the strains prevailing recently in Southeast Asia, and different from those of the strains responsible for the past domestic outbreaks (see p. 99 of this issue). It was difficult to identify the route of infection from these analytical results.
2. Incidence of Vibrio cholerae O139 in Japan
V. cholerae O139 was first isolated from a traveler to India in Saitama Prefecture in April 1993 and from a Nepalese visitor to Nagano Prefecture in July of the same year (Table 1). These cases both developed severe cholera symptoms, but the case in Tochigi Prefecture in October returning from India showed only mild diarrhea. Other four cases reported during February to April 1994 were infected in Thailand. V. cholerae O139 was isolated from two cases returning from the Indian subcontinent in August and also from other two cases returning from India and China in October.
There was no report of cases of V. cholerae O139 infection for some period after the above-mentioned, but in September 1997, infection was found in a returnee (24 years old male) from Nepal.