Yellow Fever is also known as Yellow Jack, Bronze John, El Vomitito (Span.), Fièvre Janne (Fr.), Gelbes Fieber (Ger.), Vomitito Prieto or Vomitito Amarilli (Central America). It is a pestilential, contagious fever of a continuous and special type, presenting at least two well-defined stages, the first occupying 36 to 150 hours, marked by a rapid circulation and high temperature, the second being characterised by general depression and black vomit; as a rule it occurs but once in the same individual. Negroes and Mongolians are little susceptible to yellow fever, and it is noteworthy that strangers are the more liable to be attacked the farther north or south from its area they have been born. New arrivals in an endemic area are most liable to contract the disease; should they escape it at first, they are less liable to suffer from it the longer they reside in one place; should they, however, travel about, they lose what protection they may have gained. The area of distribution of yellow fever is limited. Its endemic areas are on the seacoasts and along the banks of the great rivers in the West Indies, on the Mexican part of the Gulf coast, and on the Guinea coast of Sierra Leone. Epidemics, however, may extend from these foci, but their distribution is limited in Africa to the west coast, from 19° N. to a point on the mainland opposite Fernando Po; in the western hemisphere, from 38° N. to 32° S. lat.—though on the western shores of South America epidemics have occurred from 5° S. to 42° S. They also occur throughout the whole of the West Indies. For the production of yellow fever a dense population is necessary, as also a temperature of above 70° F., a moderate amount of moisture in the atmosphere, and a low altitude. An epidemic of yellow fever will be cut short if the temperature falls to freezing-point, and abundant rains frequently bring an epidemic to an end. As a rule yellow fever does not ascend higher than 3000 feet above sea-level. Domingo Freire of Rio Janeiro believes that a micro-organism (which he calls the cryptococcus xanthogenicus, or micrococcus amarilli) is the cause of yellow fever, but further observations are necessary to substantiate this. The yellow-fever poison can be transported farther by sea than on land, and may be carried by clothing, bedding, &c., which may retain the poison for a considerable time. The symptoms of the disease may be briefly described as follows: The patient usually suffers for two or three days from loss of appetite, lassitude, and discomfort. Then suddenly he will be attacked by severe rigors, alternating with flushes of heat. There is violent headache, the pulse is regular but throbbing, thirst is usually severe; the tongue, coated in the centre, presents a red edge, and deep-seated pain at the back of the eyeball is almost invariably complained of. Constipation, which obtains throughout the disease, should be noticed, and the patient vomits at short intervals. The skin assumes a yellowish or livid colour, and is covered by cold perspiration. The urine is acid and contains a large amount of albumen. The respirations are frequent, and the temperature is about 105° or 106° in the axilla. On the third or fourth day the vomiting becomes more distressing, the urine is scanty or may be suppressed, the temperature rises still higher, and the skin grows harsh and dry. The skin becomes exceedingly yellow, and may be even the colour of mahogany. The face is flushed, the conjunctivæ injected, and the eyes are protruded. The vomited matter at this time is limpid, slightly opalescent, and aërid; it is called the white vomit. The patient is very distressed and often delirious.
At this point the condition of the patient will improve somewhat, and in rare cases convalescence may set in, but as a rule the improvement only lasts from eight to twenty hours, during which period all untoward symptoms subside, with the exception of a certain amount of gastric irritation. If these favourable symptoms do not continue, the patient sinks into a state of extreme prostration; pains in the head, the orbits of the eyes, the loins, and joints return, the pain in the stomach being so severe that the patient can hardly endure the weight of the bedclothes. The tongue becomes parched and grey, the gums and teeth black with sordes, the lips dry, brown, and bleeding, and then the terrible 'black vomit' (vomitito negro) sets in. At first it may be of a bright red colour, but it soon becomes a deep, brownish black. The patient may vomit thirty or more times in the twenty-four hours. This characteristic vomit is produced by severe irritation. The disease may terminate in various ways, the mortality varying from 10 to 70 per cent. Death may result from the direct action of the poison upon the blood and nervous system, or from suppression of the functions of the liver or kidneys, from syncope due to fatty degeneration of the heart, or from hæmorrhage. In rarer cases pyæmia may ensue and the patient succumb to blood-poisoning.
The treatment of yellow fever may be considered under two heads: (1) prophylactic; (2) curative. Hitherto no prophylactic treatment has been proved certainly effective. Freire claimed that inoculation with an attenuated virus will in most cases render patients insusceptible to yellow fever; but hostile critics doubted his successes, and held that the risks were too great. Meyrignac claimed to have inoculated Panama Canal labourers with success by a quite different preparation of virus. Finlay of Havana used the mosquito for inoculating healthy individuals with yellow fever, and such apparently escaped the scourge. Sanarelli discovered the Bacillus icteroides, and in 1898 used successfully a serum method. The curative treatment presents innumerable difficulties, and it must be remembered that drugs which are successful in one epidemic are apparently useless in another; therefore the general lines of treatment alone can be indicated. The patient should be kept in bed in the recumbent position; each patient requires 2000 cubic feet of space; draughts should be avoided, and the temperature should be carefully regulated; the patient should be warmly but lightly clad, heavy bedclothes being avoided. We know of no drug which will arrest yellow fever, and quinine is useless unless malaria should complicate the fever. It follows, therefore, that symptoms must be combated as they arise. Calomel and jalap and sweet nitre are useful, as are stimulating frictions over the spine and lower extremities. Hot-air baths are also useful, especially if there is any tendency to suppression of urine. The patient's thirst may be relieved by iced water or ice, and the irritability of his stomach may often be allayed by the administration of dilute hydrocyanic acid. The black vomit will be best controlled by the administration of turpentine and sulphuric ether. Opium may be used to alleviate pain if the kidneys are acting freely. Hyperpyrexia must be combated by the administration of aconite, or by sponging the body with cold water. The diet must be light and nutritious, and should be given in small quantities at regular intervals throughout the disease. It should consist of chicken-broth, beef-tea, corn-flour, barley-water, or iced milk and lime-water, all solid food, even bread, being best avoided. For the suppression of the urine perhaps the best treatment is the administration of an enema of iced cold water. During convalescence the bowels must be kept open, light and nourishing diet with small doses of brandy should be given, or if preferred, the patient may take port wine. If during the course of yellow fever the prostration is very great, alcohol will be necessary, but in moderation; champagne is the best form in which to administer it.