Till 1962 classical cholera had been prevailing in India and Bangladesh. El Tor cholera which began to spread from Indonesia in a pandemic form from 1961 entered India in 1964 and eliminated the classical biotype in 19661-2 ,However, in Bangladesh a few El Tor strains were first detected in Chittagong in 1963 and in Dhaka in 1964, and then disappeared in 1966 but were seen again in 19683-4 Ultimately El Tor biotype completely replaced the classical biotype in 19735. In urban areas this change may be due to migration of people from El Tor endemic areas.. To see whether this change had also occurred in rural areas we analysed the bio and serotypes of cholera patients admitted from 1966 to 1985 at the Matlab Hospital, the rural treatment centre of the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B). This Centre treats 10,000 — 12,000 diarrhoeal patients a year of which 12-14% have cultured confirmed cholera6.
The figure which displays the percentage of each bio-serotype isolated among all V. cholerae 01 isolated that year shows that the classical biotype, predominantly Inaba serotype caused all cholera until,1972. In 1973 El Tor replaced the classical biotype. Again in 1982 the classical biotype displaced the El Tor as the main epidemic strain in Bangladesh7. The shift from classical to El Tor and again return of classical still remain a mystery. Presently a majority of our cholera patients are infected with El Tor Ogawa. In the same villages within our surveillance area, one or both of the bio and serotypes of v. cholerae 01 may be present at different times. Why and how these changes occur require further research, particularly on body immunity, environmental and ecological factors which might influence these changes.
International Centre for Diarrhoeal K. Zaman
Diseases Research, Bangladesh, Md. Yunus
G.P.O. Box 128, Dhaka-2, K.M.B. Hossain
1. Mukherjee, S., Basu, S. and Bhattacharya, P. A new trend in cholera epidemiology. Br. Med. 1965 2: 837.
2. Sanyal, S.C., Dutta, N.K. and Mukherjee, S. Present status of classical cholera in India. Indian J.Med.Res.,
3. McCormack, W.M., Mosley, W.H., Fahimuddin, M. and Benenson, A.B. Endemic cholera in rural East Pakistan. Am. J. Epidemol., 1969; 89:393.
4. Khan, M., Bart, K.J. and Huq, Z. The changing pattern of cholera in East Pakistan: The appearance of El Tor Vibrio cholerae. JPMA., 1970; 20 : 43.
5. Samadi, A.R., Chowdhuiy, M.K., Huq, M.1. and Khan, M.U. Seasonality of classical and El Tor cholera in Dhaka, Bangladesh: 17 year trends. Trans. R. Soc. Trop. Med. Hyg., 1983; 77: 853.
6. Black, R.E. , Merson, M.H., Rahman, A.S.M.M., Yunus, M., AIim, A.R.MA., Huq, I., Yolken, RH. and Curlin, G.T. A two-year study of bacterial, viral, and parasitic agents associated with diarrhoea in rural Bangladesh. J. Infect. Dis., 1980; 142: 660.
7. Samadi, A.R.,Huq, M.I.,Shahid, N., Khan, M.U., Eusof, A., Rahman, A.S.M.M., Yunus, M. and Faruque, A.S.G. Classical Vibrio, cholerae biotype displaces El Tor in Bangladesh. Lancet, 1983;1 :805.