Three-year study of mosquito-borne haemorrhagic fever in Calcutta

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Abstract
A new type of fever characterized by hemorrhagic manifestations or shock or both occurred in Calcutta as a double-peak epidemic in 1963. The epidemic was almost as severe in 1964 as in 1963, but in 1965 the morbidity was much less. Of the 302 cases diagnosed clinically as hemorrhagic fever which were virologically and serologically investigated during this period 55% had arthralgia, 18% had skin rash, 14% had lymphadenitis and 28% had frank hemorrhage. Chikungunya virus, was isolated from 64 patients and dengue virus (3 type 2, 2 type 4, and 1 probably type 1) from 6. A number of cases were diagnosed serologically as either chikungunya or Group B arbovirus infection. In many of the cases with severe hemorrhagic manifestations or shock, dengue virus etiology could be established, and in some, chikungunya etiology without any evidence of simultaneous dengue infection could be shown. Ten of the 302 patients died. Positive reactions against chikungunya antigen by the HI [hemagglutination inhibition] test were found in 18.8% of 439 human sera collected in 1964 and 32.3% of 537 sera in 1965, and 14% of sera collected in 1960. This indicated that chikungunya or a similar virus was present in the country before the outbreak of hemorrhagic fever in 1963. Chikungunya virus was isolated from 2 of 15 pools of Aedes aegypti. Laboratory-bred A. aegypti fed on acute chikungunya fever cases were capable of transmitting the infection to infant mice.