# Tropical Diseases/Chapter 15

CHAPTER XV
DENGUE *
Definition.— A mosquito - conveyed specific fever occurring usually as a rapidly spreading epidemic and, in typical cases, characterized by a suddenly developed primary fever of about three days' duration, succeeded by a period of apyrexia— actual or relative —and this again by a milder secondary fever accompanied by a rubeoloid eruption. Throughout the febrile stages, and often subsequently, severe rheumatic-like pains are 9 prominent symptom. The disease in its active form lasts about a week and is attended with little, if any, mortality.
Geographical distribution and mode of spread.— Most parts of the tropical world have been visited at one time or another by dengue. From a study of the dates of the various epidemics, it would seem that there is a tendency for it to assume pandemic characters about once in every twenty years. Perhaps of all places in the world it is most frequently met with in the West Indies.
Recently dengue has appeared in Syria, Asia Minor, on the Ægean shores of Greece and Turkey, and in North Queensland, Australia. Early in the last century it was seen in America, as far north as Charleston and Philadelphia in the United States, and as far south as São Paulo in the Brazils.
Like other specific communicable diseases, dengue tends to advance along trade routes and lines of communication. Thus, starting from Zanzibar, the epidemic of 1870-73 first reached Aden. Thence it travelled to Suez on the one side and to India on the other. Passing to Singapore, it followed the trade routes to ​Cochin China and China, spreading at the same time to the islands of the Eastern Archipelago. From India it was carried by the coolie ships to Mauritius and Réunion in 1873.
An epidemic which I witnessed in Amoy (1872) illustrated very well a characteristic feature of dengue epidemics— namely, the peculiar suddenness of their rise and extension, and the general prevalence of the disease in an affected community. I am under the mark when I say that in this particular epidemic quite 75 per cent, of natives and foreigners were attacked within a very few weeks. All ages and occupations, both sexes, and people in every condition of life, were alike subject to it. About the first week in August I heard that a peculiar disease had appeared in the town; by the end of the second week the cases were numerous, whole families being prostrated at a time. A week later the cases were still more numerous, and by the end of the month so general was the disease that the business of the town was seriously interfered with. By the end of the following month —that is to say, in about eight weeks from the first appearance of the epidemic all the susceptible apparently had passed through it, and, so far as Amoy residents were concerned, the disease was at an end, cases occurring for a few weeks longer only in visitors from unaffected districts. This course seems to be fairly typical of all dengue epidemics.*
Etiology.— Germ.— Various bacteria have been described. Graham describes an intracorpuscular amœba, resembling Babesia bigemina, which he states he found in great profusion in the blood of dengue patients in Beyrout, Syria. He maintains ​that his experiments tend to show that, like yellow fever, dengue is communicated by a mosquito, Culex fatigans. Acting on this hypothesis he was able to protect families from dengue by means of mosquito nets. Ross is said to have extinguished the yearly epidemics in Port Said by anti-mosquito measures. Bancroft, who considers that the germ is ultra- microscopic, has advanced the same view in Australia in favour of Stegomyia fasciata. Experiments by Ashburn and Craig, made under favourable conditions, seemed to show that the germ of dengue resides in the liquor sanguinis, that it is ultramicroscopic and therefore unfilterable, that injected into non-immunes it gives rise to typical dengue, that under natural conditions it is transmitted by Culex fatigans through the salivary glands, that the incubation period of the experimental disease is from three to fourteen days, and that it is not contagious in the ordinary sense of that word. In these and in some other respects dengue has a striking parallelism to yellow fever.
By a series of well-conceived and carefully- carried-out experiments Drs. Cleland, Bradley, and McDonald in Australia have now definitely proved that the virus of dengue is conveyed by Stegomyia calopus, and have rendered it highly improbable that Culex fatigans is a vector. They have shown, further, that the incubation period of the disease, dating from the infective bite, is from six to nine days. Important points still undetermined are the duration of the infective stage in the blood, and the ripening process of the germ in the mosquito.
Influences of meteorological conditions.— When dengue spreads beyond its ordinary tropical limits, as, for example, in the epidemics of Philadelphia and Asia Minor, the extension occurs only during the hottest part of the year— in the late summer and early autumn. Hitherto such epidemics have been arrested on the approach of winter. Even when occurring within the tropics, dengue prevails principally, though not exclusively, during the hottest part of the year. High atmospheric temperature, therefore, seems to be one of the conditions it demands. ​Epidemics occur indifferently during the dry or the rainy seasons, the hygrometric condition of the atmosphere being without manifest influence.
Usually a coast disease.— It would appear that dengue, like yellow fever, prefers the coast line and the deltas and valleys of great rivers to the interior of continents. There are many exceptions to this rule; in 1870-73 it spread all over India. The distribution and concentration of population on the seaboard and along rivers, the freedom of communication between communities that are so located, and the mosquito conditions probably determine this preference.
As a rule, elevated places enjoy a relative immunity; if the disease is introduced into such localities, it does not spread. To this, again, there are exceptions, for the Syrian epidemic referred to prevailed in certain spots 4,000 to 5,000 ft. above the sea. In the Mediterranean basin dengue is a disease of autumn months and generally follows the summer outbreak of phlebotomus fever.
The incubation period seems to be somewhat variable. It is certainly not a long one. I have seen a case in which it could not have exceeded twenty-four hours. Some observers place it at five and even seven days; this, I feel sure, is an over-estimate. One to three days seems to be near the truth.*
Symptoms. Initial fever and eruption.— An attack of dengue may be preceded for a few hours by a feeling of malaise, or, perhaps, by painful rheumatic-like twinges in a limb, toe, finger, or joint. Usually it sets in quite suddenly. A patient, describing his experience, said that in the morning he got up feeling quite well, but before he could complete his dressing he was so prostrated by pain and fever that further exertion was impossible, and he had to crawl back to bed again. Similar stories, illustrative of the sudden incidence of the symptoms, circulate during every epidemic of dengue. Sometimes the fever is ushered in by a feeling of chilliness or even by a smart ​rigor; sometimes a deep flushing of the face is the first sign of the disease.
However introduced, fever rapidly increases. The head and eyeballs ache excessively, and some limb or joint, or even the whole body, is racked with peculiar stiff, rheumatic-like pains, which, as the patient soon discovers, are very much aggravated by movement. The loins are the seat of great discomfort, amounting in some cases to actual pain; the face particularly the lower part of the forehead, round the eyes, and over the malar bones may become suffused a deep purple; and often the skin over part or the whole of the body, and all visible mucous surfaces, are more or less flushed, that of the mouth and throat being sore from congestion and perhaps from small superficial erosions. The eyes are usually much injected; very often the whole face is bloated and swollen. This congested erythematous state of the skin constitutes the so-called initial eruption.
These symptoms becoming in severe cases rapidly intensified, the patient, in a few hours, is completely prostrated. His pulse has risen to 120 or over; his temperature to 103° F., in some cases to 105°, or even to 106°. He is unable to move owing to the intense headache, the severe pain in limbs and loins, and the profound sense of febrile prostration. From time to time the skin may be moistened by an abortive perspiration, but for the most part it is hot and dry. Gastric oppression is apt to be urgent, and vomiting may occur. Gradually the tongue acquires a moist, creamy fur which, as the fever progresses, tends to become dry and yellow.
Defervescence.— In this condition the patient may continue from one to three or four days, the fever declining somewhat after the first day. In the vast majority of cases this, the first and most acute stage, is abruptly terminated about the end of the second day by crisis of diaphoresis, diarrhœa, diuresis, or epistaxis. When epistaxis occurs the relief to the headache is great and immediate. On the occurrence of crisis the erythematous condition of the skin, if it has not already disappeared, rapidly subsides. In ​a proportion of cases, and particularly in certain epidemics, crisis does not occur, the fever slowly declining during a period of three or four days. Thus the urgent symptoms abate, and the patient rapidly, or more slowly, passes from what, in many cases, may be described as the agony of the first stage to the comparative calm and comfort of the second.
'The interval.— When the second stage is established and the thermometer has sunk to normal, the patient is sufficiently well to leave his bed and even to attend to business. An occasional twinge in leg, arm, or finger, or a tenderness of the soles of the feet, and perhaps giddiness in walking, may remind him of what he has gone through and warn him that he is not quite well yet. But the tongue cleans, and the appetite and sense of well-being return to some extent.
Terminal fever and eruption.— This state of comparatively good health continues to the fourth, fifth, sixth, or even to the seventh day, counting from the commencement of the illness. Then there is generally a return of fever, slight in most cases, more severe in others. It is usually of very short duration— a few hours. Sometimes this secondary fever does not occur; probably it is often overlooked. With the recurrence of the fever an eruption of a rubeolar character appears. The pains likewise return, perhaps in more than their original severity. Though the fever subsides in a few hours, the eruption, at times very evanescent, may keep out for two or three days longer, to be followed very generally by an imperfect furfuraceous desquamation. It seldom happens that the fever or pains at this stage keep the patient in bed, although that is the best place for him if a comfortable and speedy convalescence is desired. Rarely, in this secondary fever, does the thermometer rise to 103 F. The temperature falls rapidly to below normal on the setting-in of diaphoresis, or diarrhœa, or of some form of crisis.
Characters of the eruption.— The terminal eruption of dengue possesses very definite characters. It is absent in a very few cases only; in many of those ​cases in which it is supposed to be absent, being slight, it is overlooked. As stated, the eruption is rubeolar in character. It usually commences on the palms and backs of the hands, extending for a short distance up the forearms Its development is often associated with sensations of pricking and tingling. On the palms of the hands the spots are at first about the size of a small pea, circular, dusky red, and sometimes slightly elevated. The eruption quickly extends, and is best seen on the back, chest, upper arms, and thighs. In these situations it appears at first as isolated, slightly elevated, circular, reddish-brown, rubeoloid spots, from one-eighth to one-half of an inch in diameter, thickly scattered over the surface, each spot being isolated and surrounded by sound skin. After a time the spots, enlarging, may coalesce in places; thus irregular red patches from 1 to 3 in. in diameter are formed. Or perhaps there is a general coalescence of spots, isolating here and there patches of sound skin; in this case the islands of sound skin give rise, at first sight, to the impression that they constitute the eruption— a pale eruption, as it were, on a scarlet ground. In a few instances the whole integument may be covered with one unbroken sheet of red. The rash is usually most profuse on the hands, wrists, elbows, and knees; in these situations it is generally coalescent, and there, too, it may be detected though absent elsewhere. The spots disappear on pressure, and never or rarely become petechial. They fade in the order in which they appear— first on the wrist and hands; then on the neck, face, thighs, and body ; last on the legs and feet. Slowing of the pulse as the fever advances, and leucopenia as in yellow fever, have been remarked.
Desquamation.— Desquamation may go on for two or three weeks. In many it is trifling in amount; for the most part it is furfuraceous. Rarely does the epidermis peel off in flakes of any magnitude; never in the broad sheets seen after scarlatina. Often for a day or two desquamation is accompanied by intense pruritus.
Convalescence.— In some instances, and in some ​epidemics, the disease terminates with the fading of the eruption; appetite and strength gradually return, and the patient, after a few days of debility, feels well again. Bradycardia may persist for a time.
The rheumatoid pains.— With most, their troubles do not end so soon. For days or weeks some muscle, tendon, or joint is the seat of the peculiar pains, which may become so severe as to send their victim back to bed again. Sometimes, three or four weeks after all apparent trace of the disease has vanished, a joint or a muscle will be suddenly disabled by an attack of this description. This may occur in patients who, during the acute stage, suffered little or no pain. A finger or toe, or a joint of a finger or of a toe, may alone suffer. Of all the joints, perhaps the knee is most frequently affected; but wrists or shoulders are often attacked, and their associated muscles may even undergo considerable atrophy from enforced disuse. The soles of the feet, too, and the tarsal articulations are favourite sites.
The pains of dengue— those occurring during the initial fever as well as those that may be regarded as sequelæ— are difficult to locate with precision; the joints or muscles affected may be percussed, pressed, or moved with impunity. Du Brun locates those associated with the knee in the thigh muscles, which, he says, are painful on deep pressure.
The pains are worst usually on getting out of bed in the morning, and on moving the affected part after it has been at rest for some time; they are relieved somewhat by rest and warmth. Passive movements are, as stated, not painful, but any resistance to the movement of the limb may cause acute suffering. When a muscle is affected the pain is accompanied by a sense of powerlessness.
Other complications and sequelœ—. Convalescence may be very much delayed by the persistence of these pains; also by anorexia, by general debility, mental depression, sleeplessness, evanescent feverish attacks, by boils, urticarial, lichenoid, and papular eruptions, and by troublesome pruritus. Among sequelæ and complications may be mentioned enlarge​ment of the lymphatic glands (particularly the superficial cervical), orchitis, possibly endocarditis and pericarditis, hyperpyrexia, purpura, and hæmorrhages from the mouth, nose, bowel, and uterus. Miscarriage is rare. The urine sometimes contains a trace of albumin, but true nephritis does not occur.
Variability of epidemic type.— Judging from the published descriptions, there is considerable variety in the symptoms of this disease in different places and in different epidemics. Some authors mention swelling and redness of one or more joints as a common and prominent symptom; others refer to metastasis of the pains, enlargement of submaxillary glands, orchitis, mental depression, hæmorrhages, and so forth, as being frequently present. However this may be, the essential symptoms in well-marked cases are the same practically everywhere, and in all epidemics; these are, suddenness of the rise of temperature, an initial stage of skin congestion, limb and joint pains, and a terminal rubeoloid eruption.
Relapses are not uncommon in dengue, and second and even third attacks during the same epidemic have been recorded. As a rule, however, susceptibility to the disease is exhausted by one attack. According to Hare, in a recent Australian epidemic the immunity acquired by an attack did not persist beyond one year.
Mortality.— In uncomplicated dengue the mortality may be said to be almost nil (O.l per cent., Hare), In the case of very young children, convulsions and delirium may occur and cause anxiety; and in the aged and infirm, and in those suffering from chronic exhausting disease, an attack of dengue may prove a serious complication. Charles describes a pernicious form which, though rare, was very much dreaded in Calcutta. In these cases the lungs became œdematous, and the patient, growing drowsy and cyanotic, rapidly passed into a comatose condition with a tendency to hyperpyrexia, and died. Some writers state that the gravity of any given case is in direct proportion to the abundance of the eruption; others deny this. ​In Europeans an attack of dengue very often leads to a condition of debility necessitating temporary change of climate, or even return to Europe. In both Europeans and natives the attendant lowering of the resisting powers predisposes to other and more dangerous diseases, such as malaria, dysentery, phthisis, and so forth; consequently dengue, otherwise a benign disease, may become a source of public danger. It is probable that it is in this indirect way that the general mortality is increased during a visitation of this disease, as has been observed in several epidemics.
Morbid anatomy.— On account of the low mortality, post-mortem records are few. Nogué, who observed two epidemics of dengue in Cochin China (1895-96), made four post-mortem examinations in this disease. In these, pulmonary and intracranial inflammation were the special features. The meningitis amounted to adhesions and sero-purulent infiltration of the pia mater.
Diagnosis.— Dengue must not be confounded with yellow fever, rötheln, scarlatina, measles, syphilitic roseola, influenza, cerebro- spinal meningitis, seven-days' fever, rheumatic and malarial fevers. A knowledge of the distinctive features of these diseases, and the fact that dengue is attended with a rash and with articular pains, and that it occurs in great and rapidly spreading epidemics, should prevent any serious error in diagnosis. According to Ashburn and Craig, there is a well-marked leucopenia in dengue averaging 3,800 per c.mm., with relative increase of the small leucocytes. This in some circumstances may prove an aid to diagnosis.
Treatment.— Were it possible to secure perfect isolation for the individual during an epidemic of dengue, doubtless he would escape the disease. Even comparative isolation is attended with diminished liability. In Amoy, in the epidemic of 1872, those foreigners who lived in a more or less isolated suburban situation were very much less affected than were those who lived in the native town, or than those whose occupations threw them much into ​contact with the natives. But, though this and similar facts point to the theoretical possibility of avoiding dengue during an epidemic, in the ordinary conditions of life in the tropics prophylactic measures for the mass are impracticable. Specially delicate individuals, particularly the subjects of tubercular or renal disease, should be isolated, or, better, should leave for a time the epidemic locality.
Like the allied fevers, dengue runs a definite course; therefore it is useless to attempt to cut it short. The patient should go to bed so soon as he feels ill, and he should keep his room till the terminal eruption has quite disappeared and he feels well again. Ten days is not too long to allow in severe attacks. As in influenza, light liquid diet, rest, and the avoidance of chill conduce powerfully to a speedy and sound convalescence. At the outset of the fever some saline diaphoretic mixture, with aconite, may be prescribed with advantage. If the pains be severe and the fever high, antipyrin, or phenacetin, or belladonna will give great relief. Cold applications to the head are comforting. If the temperature rises to 105° F. or over, cold sponging or the cold bath ought to be had recourse to. If the pains continue very distressing, a hypodermic injection of a minute dose (1/10 gr.) of morphia will afford welcome relief and do no harm. Purgatives and emetics should be avoided unless pronounced constipation, or a history of surfeit, urgently demands their exhibition. The pain caused by the muscular movements entailed by the efficient action of purgatives more than counter-balances any advantage the latter might otherwise bring. Wine in the early stage is not advisable. Freshly made lemonade, or iced water, will be found acceptable drinks during the fever.
For the pains experienced during convalescence, rubbing with opium or belladonna liniment, gentle massage, electricity, salicylates, small doses of iodide of potassium and quinine, have been advocated. Debility, or anorexia, indicates tonics such as quinine, strychnine, mineral acids, or vegetable bitters, and change of air.
* ↑ * According to Hirsch, the word "dengue" is derived from the Spanish equivalent of our word " dandy." The disease has received many names, such as " scarlatina rheumatica," " break-bone fever," etc.
* ↑ * It is on my experience in this epidemic that I have based my description of dengue. In the vast majority of the cases the characteristic primary and secondary fevers, the initial and terminal skin rashes, and the rheumatic-like pains were well marked. Of course, as with all specific fevers, there was a proportion of atypical cases in which some of the characteristic symptoms were absent or only slightly marked. Remembering my experience of this epidemic, I cannot understand the difficulty some recent Indian observers seem to have in differentiating dengue from seven-days' fever and the like. The skin rashes alone should suffice, especially if taken in conjunction with the double fever and the pains.
* ↑ * The observations on which these erroneous conclusions were based were made principally on the crews of ships, and before the role of the mosquito in dengue was suspected.