Emerging Plasmodium falciparum in an endemic area in Calcutta.

Calcutta is now intensely malarious. Malarial infections are detected in every month. In an endemic area in central Calcutta a year-long study from August 1996 to July 1997 reveals that 31.47% of all cases are due to Plasmodium falciparum infection. A competition is going on between P vivax and P falciparum to gain upperhand. An equilibrium is there in the month of January (1997), when P vivax and P falciparum cases constitute 51.13% and 49.43% respectively. The highest and lowest percentage of P falciparum infection is in December 1996 (67.98%) and in May 1997 (0.89%) which is just reverse in the case of P vivax in December 1996 (33.60%) and in May 1997 (99.10%). Three imported cases of P malariae have been detected but the patients cannot be traced. Six cases of mixed infections have been found.