The 1964 chikungunya epidemic at vellore, South India, including observations on concurrent dengue

Virological and serological studies on 477 fever patients seen at the Christian Medical College Hospital, Vellore, South India, from mid-August through December, 1964, indicated that 274 patients suffered infection with chikungunya virus alone (virus recovered from 224), 14 with both chikungunya and dengue viruses, either simultaneously (8) or sequentially (6), and 6 with dengue virus only. Arthralgia was the most prominent clinical feature in chikungunya infections; haemorrhagic manifestations were rare and uniformly mild. Myalgia was the chief complaint of dengue patients. Chikungunya virus was readily isolated only from human serum collected during the first 2 days of illness; viraemia levels were found to drop rapidly after the 2nd day, although viraemia remained detectable until after the 5th day. Serum virus titres were high, in some instances exceeding 6.0 log LD50 per 0.02 ml., and 2 high-titred sera exhibited viral haemagglutination when extracted with acetone. The virus was detected in human serum in the presence of low levels of haemagglutination-inhibiting (HI) and neutralizing antibody. HI chikungunya antibody appeared during the 4th to 6th days after onset of fever and reached a peak during the 2nd week; complement-fixing (CF) antibody appeared later and reached a peak in the 3rd month. By the 9th month, both HI and CF antibody had declined 4-fold in titre. Chikungunya virus was not recognized as being active in South India before the 1964 epidemic, but subsequent study of pre-epidemic survey sera suggests that the virus was present in the area during the 1930's. No case of chikungunya infection has been detected at Vellore since the end of 1964.