Dengue Fever

Dengue Fever

Medical Clinics of North America May, 1943. New York Nwnber DENGUE FEVER JAMES STEVENS SIMMONS, M.D., Ph.D., Se.D., Dr.P.H., F.A.C.P.· Definition.-D...

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Medical Clinics of North America May, 1943. New York Nwnber

DENGUE FEVER JAMES STEVENS SIMMONS, M.D., Ph.D., Se.D., Dr.P.H., F.A.C.P.·

Definition.-Dengue fever is an acute, nonfatal, widely dis. tributed, febrile disease of tropical and subtropical regions. It is caused by a filtrable virus. It is transmitted by mosquitoes. The typical infection is characterized by paroxysms of fever with aches and pains in. the joints and muscles, an extreme leukopenia and variable initial and terminal rashes. As a rule these symptoms subside within a week or ten days, but they may be followed by a period of convalescence lasting several weeks and characterized by malaise and mental depression. Synonyms.-The term "dengue" is said to have originated as a corruption of "danguero," the Spanish equivalent of dandy, which was applied to the disease by inhabitants of St. Thomas, because of the stiff gait of those affected. According to Hirsh (1883): "Men's wits have been taxed to find names for this disease. Thus the Spanish called it dengue (corresponding in meaning to the French minanderie and the English dandy) or colorado; The English and Americans have called it break-bone and broken-wing; the French, giraffe and bouquet (whence the English corruption, buoket) and the Brazilians polka fever. By the medical profession the .disease has been named, according to the view taken of its nature, rheumatismus febrilis exantbematicus, scarlatina mitis extmtbemis artbrosia and insolation fever; while some physicians have placed it beside febris remittens biliosa, or have professed to discover it in a mild form of yellow fever." Subsequent ob. servers have added various other synonyms including tbreeday fever, six-day fever and seven-day fever. GEOGRAPHIC DISTRIBUTION

Dengue fever has long been recognized in many of the tropical and subtropical regions of the world. It has also been • Brigadier General, Army of the United States; Director, Preventive Medicine Division, Office of the Surgeon General, United States Army, \Vashington, D. C. 808

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PREPARED BY THE MEDICAL INTELLIGENCE DIVISION PREVENTIVE MEDICINE SERVICE OFFICE OF THE SURGEON GENERAL U. S. ARMY 1942

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AREAS WHERE DENGUE OCCURS MOST FREQUENTLY. AREAS WHERE DENGUE HAS BEEN SPORADIC. [i§J DISTRIBUTION OF MOSQUITOES CAPABLE OF TRANSMITTING DENGUE FEVER. (EDES JlEGYPTI AND AEDES ALBOPICTUS)

Fig. 83 . •

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common in certain temperate locations during warm seasons of the year. The first clear descriptions of the disease now available were contributed .during the latter part of the eighteenth century by Bylon who in 1799 reported an outbreak in Batavia, Java; and by Benjamin Rush who described an epidemic which occurred in Philadelphia, Pennsylvania, during 1780. Numerous publications since that time indicate that the disease is endemic in many parts of the world and that it frequently occurs in epidemic form. Our present knowledge of the geographic distribution of dengue is indicated on the map (Fig. 83) which was prepared by the Medical Intelligence Branch, Preventive Medicine Division, Office _ of The Surgeon General, United States Army. The geographic distribution of the disease appears to be influenced by several factors, including (1) the presence of insect vectors, (2) the existence of susceptible individuals in the population, and (3) possibly by the existence of other forms of life susceptible to the infection and thus capable of affording a reservoir for the virus. As a rule the disease is endemic in the warmer regions where climatic conditions favor the breeding of the mosquito vectors throughout the year, and in such regions epidemics may occur at any time, depending on the exposure of numbers of susceptible human individuals. Likewise, epidemics may occur among the. susceptible populations of certain north temperate' climates if the disease is introduced during the summer months when the mosquito vectors are abundant. However, in certain tropical islands such .as Oahu and Bermuda where both mosquito vectors and· susceptible populations are constantly present, it has been reported that the disease appears only as explosive epidemics at intervals of several years, suggesting that it may not be endemic, possibly because of the absence of a lower animal reservoir (Simmons, 1931) and that each epidemic depends on the introduction of virus from abroad. ETIOLOGY

1. The Virus.-Dengue is caused by a specific, filtrable virus which was discovered by Ashburn and Craig (I 907 , a, b, and c). The virus is demonstrable in the peripheral blood

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of patients from the day preceding the initial fever until the third or fourth day of the disease. When such blood is inoculated intravenously or subcutaneously into susceptible individuals the infection is reproduced. All attempts to demonstrate the virus microscopically or to grow it on nonliving culture media have failed; however, the cultivation of a dengue virus in India on the chorio-allantoic membrane of the chick embryo has been reported (Shorn, Rao and Swaminath, 1935-1936). The question naturally remains as to whether this observation is applicable to the virus or viruses responsible for dengue fever in other regions. 2. Mosquito Transmission.-Dengue is a noncontagious, insect-borne disease and its transmission by several species of mosquitoes has been demonstrated. . In 1903 Graham, in Syria, incriminated Culex quinquefasciatus (C. fatigans) as a vector and during 1907 Ashburn and Craig (1908, a, h, and c) working in the Philippine Islands, proved that this mosquito can transmit the disease mechanically. This observation, which was later questioned by certain workers, was confirmed in 1931 by Simmons, St. John and Reynolds, who proved that either C. quinquefasciatus or Aedes aegypti may act as mechanical· vectors, provided large numbers of mosquitoes take interrupted feedings first on patients and then on susceptible individuals. Biologic transmission by mosquitoes, however, is more important in the natural spread of the disease. In 1906 Bancroft in Australia transmitted dengue through Aedes aegypti, and his work was later confirmed and extended by Cleland, Bradley and McDonald (1916) in Australia, and by Siler, Hall and Hitchens (1926, a and h) in the Philippines. It was shown by these workers that the blood of a dengue patient can infect this mosquito during the six to eight hours before the onset of fever and during the first two and one-half or three days of the illness. After feeding on such blood the mosquito becomes infective after eight to eleven days depending on temperature (Schule, 1938) and remains so for life. In 1917 positive results were reported for Aedes alhopictus (Stegomyia scutellaris) another common Oriental household mosquito; and with Dewoidea ohturans (Koizumi, Yamaguchi and Tonomura). It appears, however, that there was a pos-

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sibility of confusion due to natural infections among the experimental mosquitoes. However, A. albopictus was again incriminated in Formosa in 1925 (Morishita), and later was found to be an effective vector both in the Philippines (Simmons, et a!., 1930) and in Sumatra (Snyders, Dinger and Schieffner, 1931). The mechanism of transmission is similar to that with A. aegypti. Simmons and his co-workers (1931) in Manila showed that dengue virus as it exists in A. aegypti is filterable; and that normal mosquitoes can be infected by the ingestion of suspensions prepared by macerating infected mosquitoes in normal blood (St. John et aI., 1930). It was later shown that in infected A. aegypti the virus is distributed throughout all the tissues of the mosquito (Holt and Kentner, 1930). 3. Meteorologic Influences.-In the tropics where dengue is endemic, outbreaks may occur at any season of the year, but usually the disease is most prevalent after the rainy season. In temperate climates the seasonal incidence has been similar to that of yellow fever, and the epidemics usually occur during the summer, reach a peak within about eight weeks, and stop abruptly after frost. Dengue epidemics have occurred most frequently at low altitudes near the seacoast or in other well watered localities. They may, however, penetrate inland for long distances, and outbreaks have been reported at elevations of several thousand feet. The importance of these factors is due to their influence on the prevalence and susceptibility of the insect vectors. 4. Lower Animal Reservoirs.-Certain early observers (Hirsch, 1883) reported that epidemics of dengue have been accompanied by epizootics among birds or lower animals, but most of the investigators who have attempted to infect lower animals have reported negative or inconclusive results. In 1928 Craig concluded that, while some of the lower animals might be susceptible to experimental infection, it could not be stated that success had attended the numerous efforts of many investigators to produce such infections. The need for a susceptible animal that might be substituted for human volunteers in dengue experiments led members of the Army board in Manila to renew the search during 1928 (Simmons et aI., 1931, a and b). They failed to produce

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recognizable infections in chickens, lizards, mice, guinea pigs, rabbits, goats, or monkeys (Macacus philippinensis) obtained in and near the dengue-infested city of Manila. In other experiments, however, monkeys (M. philippinensis) caught at elevations above 4000 feet in the dengue-free mountains of Luzon and monkeys (M. fuscatus) from Japan were transported to Manila in screened cages, and were shown to be susceptible to dengue. The disease was transmitted by Aedes mosquitoes from infected human volunteers to the monkeys, and from these animals it was transmitted through mosquitoes to other monkeys and back to man. As the symptoms produced in the monkeys were not sufficiently characteristic for diagnosis, the infection was identified by testing the animals for virus daily from the second to the eighth day after they had been bitten by the infected mosquitoes. While these experiments were in progress, Blanc and his associates (1929) reported the production of symptomless infections in Asiatic and African monkeys by blood inoculations. From the Manila experiments it was concluded that the immunity of certain adult monkeys in endemic regions, like the resistance of the adult natives, was not a natural characteristic, but that it had probably been acquired by previous infection. The possibility was also suggested that the susceptible young of monkeys and other animals might be an important factor in maintaining a reservoir of dengue virus in certain endemic jungle regions, even though all human cases could be protected from insect vectors. Further study may incriminate other susceptible animals and vectors, and thus afford more information concerning the geographic distribution of this disease. This would be facilitated by the discovery of a convenient laboratory animal. CLINICAL CHARACTERISTICS

No simple laboratory test has been developed for the identification of dengue virus, and the specific diagnosis of an individual case may be difficult, even when one has available the facilities of a well equipped modern hospital. Consequently, in endemic localities, there is a tendency to report many other acute febrile conditions as dengue fever. This has led to some confusion in the symptomatology reported

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by different writers. Undoubtedly some observers have attributed to dengue the symptoms of other diseases, and others have failed to include some of the unusual symptoms which occur in atypical cases of dengue. It is therefore of interest to outline the clinical findings observed in more than eighty cases of dengue, all of which were produced in white American soldiers in Manila with a single strain of virus (Simmons et aI., 1931, a and b). Incubation Period.-The incubation period varied from three to thirteen days, with an average of 5.6 days. About half of the cases began abruptly either with a chill or with chilly sensations. Fever.-There was considerable variation both in the type and the duration of the fever. In 2 per cent of the cases the maximum temperature was from 100 0 to 101 0 F.; in 14 per cent from 101 0 to 102°F.; in 30 per cent from 102 0 to 103 0 F.; in 34 per cent from 103 0 to 104 0 F.; and in 17 per cent from 1040 to 104.6 0 F. The so-called "saddle-back" temperature curve was commonly observed, but was not a constant findmg. The average febrile period was 4.8 days, but in some patients the fever lasted for only one day and in others as long as nine days. In fact, it would have been impossible to differentiate these infections from other acute tropical fevers by the duration of the elevated temperatures alone, for fevers of one, two, three, four, five, six, seven and nine days were all produced by the same strain of virus. Pulse.-Generally the pulse rate was only slightly accelerated during the febrile period. Pain.-Among the most prominent symptoms noted were headache, postorbital pain, and severe backache. About 60 per cent of the patients complained of pain in the limbs, and 45 per cent had painful joints. While these symptoms were by no means mild, they were hardly severe enough to warrant the use of the old name, "breakbone fever." Changes in Blood Cells.- Various studies of the blood cells in naturally acquired dengue fever, reported from many parts of the world (Carpenter and Sutton, 1905; Stitt, 1906; Ashburn and Craig, 1907 a and b; Vedder, 1907; Siler, Hall and Hitchens, 192 6 a and b, etc.), indicate that the disease pro-

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duces little or no change in the erythrocytes or hemoglobin, but that one of the most constant features is an extreme leukopenia. The reports do not agree as to the duration and degree of the leukopenia, or as to the type of cells involved. These factors were therefore considered during our clinical studies made in Manila (1931 a and b) on American soldiers experimentally infected with a single strain of virus. In each case, total leukocyte counts were made daily, from the beginning of the period of isolation and preliminary observations, throughout the periods of incubation, illness and convalescence. From an analysis of these counts, the following conclusions were drawn: 1. There was no significant change in the erythrocytes or hemoglobin. 2. All of the patients developed leukopenia. 3. By averaging the leukocyte counts obtained on successive days after the onset of fever, it was observed that, regardless of the duration of fever, the total leukopenia usually began by the second day, and progressed to a low point of about 2000 cells on the fourth or fifth day after onset. The counts returned to normal levels several days later than did the temperature. 4. The leukopenia was produced by a decrease in both the mononuclear and the mature neutrophilic polymorphonuclear cells. The latter showed marked degenerative changes during the fever and decreased numerically from a normal of about 3000 cells to levels as low as 300 cells. 5. Coincident with this decrease in the mature cells there was a marked increase in the immature granulocytes, which often began on the day preceding the initial fever and lasted throughout the infection. This early "shift to the left" was a constant reaction which often made it possible to anticipate the onset of the disease in the experimental infections. It is of interest to add that although the strain of virus used to infect these individuals was maintained by passage in various ways for more than a year and a half, there was no evidence of any consistent loss or gain in virulence. Also it appeared that the severity of the infections was not influenced detectably by the numbers of mosquitoes used. In some instances, the feeding of fifty or more mosquitoes was followed

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by a mild case of dengue, and in others one or two mosquitoes produced severe infections. Rashes.-It has been claimed that the rashes are a constant and characteristic sign of dengue but this must be modified. Siler, Hall and Hitchens (1926 a and b) commented: "Evidently the eruption is a very variable symptom, requiring careful and frequent observation if all its details are to be noted; in some cases it may fail altogether to develop." During our work (1931 a and b) the primary rash was seen in only 38 per cent, and the terminal rash in 86 per cent of the cases. The primary rash is characterized by a congested erythema, or flushing, of the skin and mucous membranes; the terminal rash is of a rubeolar character, consisting of dusky spots which may be evanescent or may last several days, to be followed by an imperfect desquamation and in some instances by itching, especially of the palms of the hands and soles of the feet. Glandular Enlargement.-A large proportion of the patients showed enlargement of the cervical or inguinal lymph glands, and in about 30 per cent there was tenderness in the region of the parotid glands. The parotid was enlarged in only two patients (lgarotes), and in one of these the swelling suggested mumps. Five per cent of the patients complained of tenderness or swelling of the testicles. Gastro-intestinal Symptoms.-Most of the patients complained of loss of appetite, and 65 per cent observed disturbances of the senses of taste or smell. Nausea was common early in the disease; 20 per cent of the patients vomited; and 30 per cent were constipated. H emorrhage.-The only evidence of hemorrhage occurred in three volunteers who suffered with nosebleed. Convalescence.-The period of convalescence was often prolonged and accompanied by neuralgic pains, weakness and mental depression. None of the patients died. PATHOLOGY

Because of the low mortality there have been only a few reports of postmortem examinations of dengue patients. According to Manson-Bahr (1921) in the autopsies recorded, the special features were localized pulmonary and intracranial

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inflammation. "Serous effusions in the neighborhood of joints and inflammation of the crucial ligament of the knee have also been noted." Meekins (1936) observed that in the few uncomplicated cases that had been examined up to that time, general cloudy swelling of the viscera, particularly of the liver which was also fatty, and a few petechial hemorrhages chiefly in the gastro-intestinal tract were seen. DIAGNOSIS

Dengue fever has been confused with a number of acute febrile conditions, including yellow fever, malaria, rheumatic fever, the eruptive diseases of childhood and influenza, from which it can be differentiated by a knowledge of the diagnostic features of these diseases. There are other diseases, however, includingpappataci fever and Rift Valley fever (Findlay, 1932-1933), said to be caused by immunologically different viruses, in which the symptoms and leukopenia resemble those observed in dengue. Still other dengue-like diseases have been reported from various parts of the world, as, for example, the seven-day fever of Rogers in India, and the six-day fever of Deeks in Panama. It is suspected that these may be dengue, although it is possible that they may be caused by different types of viruses which fail to immunize against one another, just as the immunities of the eastern and western types of encephalomyelitis are not mutually protective. If a susceptible animal convenient for diagnostic laboratory use can be found, it will be possible to obtain definite information as to whether dengue is produced by a single virus or by several different types of virus. At present, the clinical diagnosis must be presumptive and based on the' typical symptoms, including the leukopenia, and these must be considered in connection with certain epidemiologic features of the disease. TREATMENT

At present we have no specific cure for dengue, and it appears that regardless of the treatment used the disease will run its course. The patient should be kept in bed in a screened room, and the treatment should be symptomatic. Hydrotherapy may be used to reduce the fever. The salicylates or small

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doses of morphine may be employed to relieve pam, and tonics may be used during convalescence. MORTALITY

The general experience indicates that uncomplicated dengue is a nonfatal disease, although a few deaths have been reported among infants and aged persons, in whom the condition was complicated by other diseases. According to Sharp and Hollar (1935), one death per 1000 cases was reported in an epidemic at Brisbane in 1905 (Robertson), and one per 5000 at Cairo in 1929 (Schrumpf-Pierron). During the 1928 outbreak in Greece, the reported mortality was higher, being something less than 1 per cent (Pontano, 1928). Griffiths and Hanson (1936) state that according to the records of the City of Athens, Greece, for August, 1928, 32.6 per cent of the deaths were certified as due to dengue, and in Piraeus during the same period, 29.7 per cent of the deaths were reported as caused by dengue. In view of the insignificant mortality reported elsewhere, it is believed that these relatively high rates should not be accepted as representative of dengue fever. IMMUNITY

There is no proof that the individuals of any race are naturally immune to dengue, and it appears that the immunity observed among the adult inhabitants of certain endemic localities probably results from previous infection. During epidemics which follow the introduction of the disease into a new locality, from 50 to 100 per cent of the population may be attacked. When individuals from dengue-free places move to endemic areas, they usually contract dengue within such a short time that the disease is often referred to as an acclimatization fever. It has also been claimed that most individuals who have passed through an epidemic become immune for an unknown period of time. These observations appear to be borne out by the experience of United States troops stationed in the Philippines. On arrival most of the soldiers from the north,ern United States were susceptible to dengue, and a large proportion became infected during their two years of Philippine service. Infection has been rare, however, among soldiers who return for a second tour of duty.

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There has been some controversy as to the frequency of second and third infections. Many of the clinicians in dengueinfested regions believe that it is not uncommon for individuals to experience repeated attacks of the disease within· a few years. Moreover, certain investigators have been able to produce experimental infections in volunteers who believe they have been infected previously or whose previous medical records show a diagnosis of dengue. Obviously, such evidence has little value as an indication of specific immunity or susceptibility to dengue virus. In 1930, Green made a critical analysis of the clinical records of 1285 dengue patients admitted to the Sternberg General Hospital in Manila during a period of three years. He concluded that if any of these soldiers had suffered from a second attack, the percentage was so small as to be of no practical significance. Moreover, a number of workers have failed to reproduce the disease by injecting virus into individuals within one to ten months after they had recovered from an experimental infection (Cleland, Bradley and McDonald, 1917-1918, 1919-1920; Siler, Hall and Hitchens, 1926 a and b; Manoussakis, 1928; Blanc and Caminopetros, 1929). During our experimental work in Manila (Simmons, 1931, a and b) about 100 soldiers recovered from experimental infections and continued to reside where the disease was prevalent for different periods up to eighteen months; only one individual subsequently developed an infection which might have been dengue, and this was not proved. An effort was also made to reinfect thirty-five of these men by the inoculation of large amounts of virus after intervals of twelve to 400 days, but none of them developed dengue. It was therefore concluded that in individuals living in an endemic region, infection with the strain of virus used in these experiments produced a protective immunity lasting as long as thirteen months and possibly for life. The degree of protection which can be attained is indicated by experimental attempts to infect Philippine scout soldiers living in the lowlands near Manila. About 93 per cent of these soldiers were immune to either the bites of infected mosquitoes or to inoculations of blood. When an attempt was made to overcome this immunity by a series of daily inocula-

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tions of massive doses of virus, the men failed to develop symptoms, and normal mosquitoes fed on them daily for a period of ten days remained uninfected. Thus the possibility even of a symptomless infection was ruled out. In contrast to this immunity of the lowland Filipino, natives of a tribe of Igarotes living in the dengue-free mountains a few hundred miles north of Manila were highly suseeptible. After being bitten by a few infected mosquitoes, each of four individuals of this tribe developed severe and typical cases of dengue fever. A similar difference was observed between the immunity and susceptibility of monkeys (Macacus philippinensis) caught in these two locations. Specific antibodies undoubtedly are produced in dengue fever, but because of the difficulties incident to the use of human volunteers in experimental work this aspect of the infection has not been adequately studied. Manoussakis (I928) observed that convalescent serum, collected during the first month after recovery and inoculated into volunteers. before and after the injection of virus, failed to protect against infection. Others have obtained negative results in the few attempts that have been made to treat dengue fever with such serum. PREVENTION

Because of the high incidence of dengue among American troops in the Philippines, attempts have been made by Army . workers to develop a prophylactic vaccine. No protection, however, has been afforded by those used, including blood rendered noninfective by freezing, drying and storage and saline suspensions of macerated infected Aedes aegypti mosquitoes, rendered bacteria-free by the addition of phenol or formalin (Simmons et aI., 1931 a and b). Blanc and Caminopetros (1929) failed to protect against dengue with vaccines sterilized by heat or chemicals, but reported favorable results using virus attenuated by the addition of bile. The development of an effective vaccine against dengue is of practical importance, especially to the Army, as this disease is a potential handicap to troops during field campaigns in the tropics. As an approach to obtaining such an agent, new technical methods should be developed which will elim-

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inate the necessity 'for using human volunteers for the identification of dengue, and more information should be made available as to whether dengue is caused by one or by several immunologic types of virus. BIBLIOGRAPHY

Ashburn, P. M. and Craig, C. F.: Experimental Investigations Regarding the Etiology of Dengue Fever, with a General Consideration of the Disease. Philippine J. SC. Sect. B., 2:93, 1907 a. Idem: ExperImental Investigations Regarding the Etiology of Dengue Fever. J. Infect. Dis., 4:440, 1907 h. Idem: Study of Tropical Diseases in the Philippine Islands. JA.M.A., 48: 691, 1908 c. Bancroft, T. L.: On the Etiology of Dengue Fever. Australasian Med. Gaz., 25:17, 1906. Blanc, G. and Caminopetros, J.: Contribution a l'etude de la vaccination contre la dengue. Bull. Acad. med., 1929, 3me Ser., 102, 37. Abstr. in Trop. Dis. Bull., 27:146, 1930. Blanc, G .. Caminopetros, J., Dumas, J., and Saenz, A.: Recherches experimentales sur la sensibilite des singes inferieurs au virus de la dengue. Compt. rend. Acad. sc., 188:468, 1929. Carpenter, D. N. and Sutton, R. L.: Dengue in the Isthmian Canal Zone. Including a Report on the Laboratory Findings. J.A.MA., 44:214, 1905. Cleland, J. B., Bradley, B. and McDonald, W.: On the Transmission of Australian Dengue by the Mosquito Stegomyia fasciata. Med. J. Australia, 32:179, 1916. Idem: Dengue Fever in Australia. Its History and Clinical Course, Its Expermental Transmission by Stegomyia fasciata, and the Results of Inoculation and Other Experiments. J. Hyg. (Cambridge, Eng.), 16: 317, 1917-1918. Idem: Further Experiments in the Etiology of Dengue Fever. J. Hyg. (Cambridge, Eng.), 18:217, 1919-1920. ' Craig, C. F.: Dengue. Oxford Medicine, Vol. V, Part 11, Infectious Diseases and Animal Parasites. Ed. by Henry A. Christian, New York, Oxford University Press, 1928, p. 485. Findlay, G. M.: The Relation between Dengue and Rift Valley Fever. Trans. Roy. Soc. Trop. Med. & Hyg., 26:157, 1932-1933. Graham, H.: The Dengue: A Study of Its Pathology and Mode of Propagation. J. Trop. Med. (London), 6:209, 1903. Green, M.: Report on Second Attacks of Dengue Fever Admitted to the Sternberg. General Hospital, Manila, from 1927 to 1930. Unpublished report to Artny Medical Research Board, Manila, 1930. Griffiths, T. H. D. and Hanson, H.: Significance of an Epidemic of Dengue. JAM A., 107:1107, 1936. Hirsch, A.: Dengue. Handbook of Geographical and Historical Pathology. Vol. I, Acute Infective Diseases. Trans. from the 2nd German edition by Charles Creighton. London, The New Sydenham Society, 1883, p. 55. . Holt, R. L. and Kintner, J. H.: Location of Dengue Virus in the Body of Mosquitoes. Am. J. Trop. Med., 11:103, 1931.

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Koizumi, T., Yamaguchi, K. and Tonomura, K.: A Study of Dengue Fever. Taiwan Igakkai Zasshi (J. Med. Assn. Formosa), 1917, No. 177, p. 432. Abm. in China Med. J. 32:357, 1918; and in Abstr. Bact., 1918, 2:240. Manoussakis, E.: Recherches etiologiques sur la dengue. Bull. Soc. path. exot., 21:200, 1928. Abstr. in Trop. Dis.Hull., 26:41, 1929. Manson-Bahr, P. H.: Dengue. Manson's Tropical Diseases: A Manual of the Diseases of Warm Climates, 7th ed. Edited by P. H. Manson-Bahr. New York, William Wood &: Co., 1921, p. 221. Meekins, J. C.: Dengue Fever. The Practice of Medicine. St. Louis, The C. V. Mosby Co., 1936, p. 1219. . Morishita, K.: Changes and Progress in the Scientific View of the Relations between Mosquitoes and Dengue Fever. Taiwan Igakkai Zasshi (J. Med. Assn. Formosa), 1925, No. 247, English summary, p. 7. Abstr. in Trop. Dis. Bull., 23:361, 1926. Pontano, T.: Question del giorno. La pandemia di dengue in Atene Policlinico (Sez. med., Rome), 35:2143, 1928. Robertson: Report on the Dengue Epidemic in Brisbane in 1905. J. Trop. . Med., 8:355, 1905. Schrumph-Pierron, P.: Les complications fatales de la dengue. Presse med., 37:206, 1929. Schule, P. A.: Dengue Fever: Transmission by Aedes aegypti. Am. J. Med., 8:203, 1928. Sharp, W. B. and Hollar, E.: Immunity in Dengue FeveI'. Am. J. Trop. Med., 15:247, 1935. Shortt, H. E.,. Rao, R. S. and Swaminath, C. S.: Cultivation of the Viruses of Sandily Fever and Dengue Fever on the Chorio-allantoic Membrane of the Chick Embryo. Indian. J. Med. Research, 23:865, 1935-1936. Siler, J. F., Hall, M. W. and Hitchens, A. P.: Dengue. Philippine J. Se., 29: I, 1926 a. Idem: Dengue. Monograph No. 20, Bureau of Science, Manila, 1926 b. Simmons, J. S., St. John, J. H. and Reynolds, F. H. K.: Dengue Fever Transmitted by Aedes albopictus, Skuse. Am. J. Trop. Med., 10:17, 1930. Idem: Experimental Studies of Dengue. Philippine J. Se., 29: I, 1931 a. Idem: Experimental Studies of Dengue. Monograph No. 29, Bureau of Science, Manila, 1931 b. Snijders, E. P., I?inger, E. J. and Sehuffner, ~. A. P.: On the Transmission of Dengue ID Sumatra. Am. J. Trop. DIS., 11:171, 1931. St. John, J. H., Simmons, J. S. and Reynolds, F. H. K.: Transmission of Dengue Virus from Infected to Normal Aedes aegypti. Am. J. Trop. Med., 10:23, 1930. Stitt, E. R.: A Study of the Blood in Dengue Fever with Particular Reference to the Differential Count of the Leucocytes in the Diagnosis of the Di$ease. Philippine J. Se., I, 513, 1906. Vedder, E. B.: The Leucocytes in Dengue. New York Med. J., 86:203,1907.