The diagnosis of dengue at the time of an epidemic is very easy. Mild cases, and especially undeveloped cases, can be differentiated from influenza, especially when the latter is complicated by an eruption and respiratory complications are absent, only by the demonstration of the specific influenza bacilli. The diagnosis of dengue need be considered only in the tropical zone and in countries bordering thereon, and of these, chiefly in coast districts. A sudden development of the disease in the interior of a country has never yet been observed with certainty. Endemic dengue is endemic only upon the coast.
The disease may sometimes be mistaken for polyarthritis rheu matica, and especially for the tropical "sun fever," erythema solare, and may be occasionally confused with erythema exudativum multiforme, which arises epidemically.
We have already called attention to the exceedingly slight mortality of dengue. Dengue is, in an overwhelming proportion of the cases, a harmless affection.
Among 7435 patients of the English army in India in 1872, only one died. As the highest noted mortality figure, Zulzer gives 0.5 per cent. Von During considers the estimated mortality of 1 pro mille in the epidemic of 1889 in Constantinople as too high. In Athens, according to Orenstein, not a single fatal case occurred; in Smyrna, among 100,000 dengue patients, only a few (10) already suffering from chronic disease died (Chrysochoos). Kartulis says the same about Cairo. In the descriptions of the earlier extensive epidemics it is frequently noted that there were no fatal cases. Unquestionably the mortality is exceedingly low compared with the enormous morbidity. Nevertheless, I am convinced that, if in a country in which dengue exists, the mortality statistics were well kept, the occurrence of a dengue epidemic would at once appear from them. Everywhere we find it emphasized that dengue shows a deleterious effect (von During and others) upon patients suffering from cardiac affection or tuberculosis, and it is in old, feeble persons and sickly children that complications like hemorrhages from the stomach, enteritis, severe cerebral disturbances carry off one or more persons. No doubt both the direct and the indirect mortality from dengue is much less than from influenza, in which the fatal complication of pneumonia exacts so many victims.
We shall not consider the therapy of dengue in any detail. Salicylic acid, antipyrin, and phenacetin have often shown themselves as efficacious sedatives. Quinin, which "in the Orient is the favorite drug in all sorts of fevers, and was formerly considered a specific, has, in the judgment of all later observers (de Brun, Apery, Floras, von During, Orenstein, and others), proved to be of no effect, and frequently useless, and by many is regarded even as harmful. (Compare section on Therapy of Influenza, p. 694.)
Von During says the usual mode of treatment of dengue in the Orient with violent purgatives cannot be too severely condemned.
In a disease which is transmitted almost exclusively by shipping, prophylactic measures, such as quarantine, the prohibiting of the landing from unclean ships, if effectually carried out, may produce the desired result. At the actual locality of the epidemic, measures of prevention, such as isolation and disinfection, have only slight chance of success. Intercourse, commerce, and travel will not allow themselves to be hindered by such a harmless affection.