From the Wikipedia entry on Dr. Shambu Nath De (1915-85):
De made significant contributions to our recent understanding of cholera and related diarrheal diseases and set a permanent milestone in the modern view of diseases caused by bacterial exotoxins. [...] The seminal works of De in Calcutta (now, Kolkata), during 1950-60 breached several qualms pertaining to the enteric toxin produced by bacteria including V. cholerae and Escherichia coli. [...]
Says Eugene Garfield, founder-editor of Current Contents and Science Citation Index and publisher of The Scientist, in his 1986 tribute to De: "In 1959 De was the first to demonstrate that cholera bacteria secrete enterotoxin. This discovery eventually promoted research to find a treatment aimed directly at neutralizing the cholera enterotoxin. De’s paper “Enterotoxicity of bacteria-free culture-filtrate of Vibrio cholerae,” while initially unrecognized, today is considered a milestone in the history of cholera research." [...]
... De was never elected a fellow of any Indian academy and never received any major award. Indeed as Professor Padmanabhan Balaram pointed out in an editorial in Current Science, “De died in 1985 unhonoured and unsung in India’s scientific circles. That De received no major award in India during his lifetime and our Academies did not see it fit to elect him to their Fellowships must rank as one of the most glaring omissions of our time.
In 1990, some five years after his death, Current Science devoted a special issue to Dr. S.N. De and his pioneering work on cholera [contents can be accessed through links in this page -- scroll down to July]. Even if you don't read all of it, do read Eugene Garfield's 1986 article on the impact of De's work. This issue also carries a short piece by Prof. Balaram -- the above quote is from this piece.
I learned about Dr. S.N. De, his scientific work and the lack of appreciation of his work by the Indian scientific community over several conversations with Prof. Subbiah Arunachalam, whose views are featured in Garfield's article.