ROM 1961 through 1966 the writer was involved in studies of endemic dengue at Vellore, South India. 1 In 1964 the recurrent, yearly cycle of dengue in the area was broken by a massive wave of chikungunya virus infection that swept through Madras State. 2 Although chikungunya illness has generally been described as' dengue-like,'the patients seen in 1964 presented certain features that were distinct from the usual symptoms of classical dengue fever3 as observed at Vellore.

Subsequently, in reviewing reports of previous fever epidemics in India, I found a paper dealing with the 1923 dengue outbreak in Calcutta. 4 It was immediately apparent that the authors were describing not an epidemic of the disease presently called dengue, but rather an epidemic similar in all respects to that associated with chikungunya virus in 1964 in South India. This discovery led to a more extensive search for early articles on the occurrence of dengue and acute fevers both in India and elsewhere. The evidence uncovered provides a good basis for believing (a) that the term'dengue'was originally applied, in the early nineteenth century, to a clinical syndrome closely resembling that now associated with chikungunya virus infection, and (b) that present-day'dengue fever'corresponds to the'break-bone fever'described by Rush5 in 1789, which disease is quite distinguishable from the one that first received the name'dengue.'