The Etiology of Yellow Fever

Abstract

YELLOW fever is an acute infectious disease, endemic in the West Indies, the shores of the Mexican Gulf, and in some parts on the West Coast of Africa, whence the disease has been repeatedly transported into other localities, causing here epidemic outbreaks. Like other infectious diseases, yellow fever is supposed to be caused by a specific living entity which, invading a predisposed person, multiplies there and causes the peculiar pathological changes in the gastrointestinal tract and the liver, characterising yellow fever. Within recent years the supposed specific microbe has been discovered several times. Dr. Domingos Freire, of Brazil, and Dr. Carmona y Valle, of Mexico, have announced such discovery, but Dr. Sternberg, of Washington, who has himself studied the disease on behalf of the United States Government, has shown that none of these discoveries are a reality, and after a prolonged investigation, including the examination of a great many cases affected with, or dead from the disease, has arrived at the following conclusions, embodied in a lengthy report to his Government: that none of the different species of bacilli and cocci, present in the intestinal canal, in the blood, the liver and other tissues of persons affected with yellow fever, can have a claim to be considered as the specific microbe; that in a number of cases the examination, microscopic and cultural, of the blood and tissues yielded no bacteria recognisable either by the known methods of staining or culture; and he finally implied that the specific microbe of yellow fever is most probably not of the nature of a bacterium at all. After these very definite conclusions by Dr. Sternberg, it came rather as a surprise when, some months ago, the announcement was made that Dr. Sanarelli, Professor of Experimental Hygiene in Montevideo, formerly in the Pasteur Institute in Paris, had discovered the true cause of yellow fever in the form of a bacillus, Bacillus icteroides. This surprise is still further heightened by the statement in Dr. Sanarelli's lecture, that the Bacillus icteroides is demonstrable by the ordinary methods of staining and by culture in the ordinary well-known media. The morphological and cultural characters of the bacillus show it to belong to the group of coli-like bacilli; it is rarely demonstrable in a pure state in the blood or tissues, being generally associated with a more or less copious admixture of other microbes—Bacillus coli communis, streptococci and staphylococci; as a rule it is present only in small numbers in the capillary bloodvessels of the liver, spleen and kidney. It reflects great credit on the perseverance and sagacity of Dr. Sanarelli to have been able, notwithstanding all these difficulties, to select out the Bacillus icteroides, and to have by animal experiment been able to demonstrate, at least, as highly probable that the Bacillus icteroides is the true microbe of yellow fever. As mentioned just now, the distribution of the microbe in the affected person, its morphological and cultural characters do not in themselves offer strong prima facie evidence, and Dr. Sanarelli himself fully recognises this; but when we come to the experimental evidence which he furnishes, the evidence as to the Bacillus icteroides being the specific cause of yellow fever assumes considerable power.