INSECT BORNE DISEASES IN PAN-AMERICA BY Dr. JUAN GUITERAS Director of Health of Cuba, Professor of general Pathology and Tropical diseases The above subject has been asigned to me by the Chairman of the Medical Section of the Congress, and, within the limitation of the time allowed for preparation, I shall endeavor to discharge this duty to the best of my ability, and with an eye more especially to such elements in the problem as may affect or interest the international relations of the countries here represented. The doctrine of insect borne diseases is a singular revival, under the egis of science, of the crude and direct notions of the people. They believed in the action of disease through the external surface of the body, as is implied in the idea expressed in the word contagion. Thus we find in the Homeric legend, Apollo aiming afar his shafts to spread contagion in the Grecian host, and later on, in the middle ages, we meet with the popular credence in ointments as the cause of the spread of plague. The discoveries made in recent years of various infections conveyed by insects, have confirmed these views, establishing an extensive and remarkable group of diseases introduced through the skin: filaria, yellow fever, malaria, plague, trypanosomyasis, the spirilloses, uncinariasis, Leishmaniasis, all among the most important diseases that infect man. To the common people, the skin, the more exposed part of the body, appeared the more vulnerable, and they naturally accepted this route of infection as the most direct and simple. But, so singularly was Science bound to the conception of more recondite and complicated methods of conveyanse, that, even when the first light broke upon these new fields of investigation, the great pioneer, Dr. Patrick Manson, could not accept the direct inoculation of the filaria by the mosquito, but invented the round about way of the death of the insect in water, and the subsequent swallowing of the worm by man. Even later on, when Finlay had been already for several years contending for the transmission of yellow fever from man to man, by the mosquito, directly through the skin, Manson was suggesting the same circuitous route, through the mosquito and water to the stomach of man for the conveyance of malaria. It is to be regretted that circunmstances, among which I count the selection of myself as an exponent, will prevent the developing of this theme in a manner more worthy of the occasion. And no subject more worthy of this distinguished assembly could have been proposed. The theme is preeminently an American theme, and one that has shed a greater lustre on American Science than perhaps all else that might be broughr before a Pan-American assembly. The first definite statement of the transmission of a general disease from man to man by an insect was made in America, by an American in the year 1881. That such infectious diseases might be inoculated or in some way produced by the bites of insects introducing some poison from the environment, from products of decomposition in swamps, in the ground or the air, had been long surmised by the common people in various countries, and by some scientists, such as Beauperthuy (3), Nott (38), and, subsequently to Dr. Finlay's positive declaration, also by King (31), and others. Abstracts from these contributions, with observations, will be found in the Bibliography at the end of this paper. But the precise statement that the microbe of yellow fever is transmitted from man to man by the bite of an insect, and that such an insect could be no oher than the mosquito we now call Aedes calopus; this came in 1881, from Dr. Carlos J. Finlay, founded on a masterful process of reasoning, and a series of most original and painstaking observations and experiments on the bionomics of the insect. Dr. Finlay became thereby the founder of the doctrine of insect borne diseases. Not only Iwas he the first to maintain that a disease was transmitted from man to man by an insect; but he also foresaw that the parasite of the disease must undergo some change in the intermediary host, since the bite of the latter became more virulent the longer the lapse of time since the drawing of the infected blood from the patient into the mosquito's gut. He was the first to apply, experimentally, a blood sucking insect to a patient, and subsequently to a healthy man with a view to transmitting a general infection. He thus gave us the method of experimentation with all the details of technique, upon which is founded the great advance in Tropical Medicine. He invented also, and published with all necessary details, the methods which must be applied for the erradication of yellow fever. (13). Dr. Finlay died on the 20th. of August of this year. I beg leave to move that we all rise in reverence to the memory of this great man. If such accomplishment were not enough to bring to America the title of leadership in this branch of studies, we have the masterful series of experiments which led to the demonstration by Smith and Kilborne of the transmission of the Texas cattle fever by the cattle tick, the Margaropus annulatus. (50). The investigations of Smith and Kilborne and the results obtained constitute the first complete demonstration of the theory of insect borne diseases promulgated by Finlay, and the first successful aplication of his method, namely, the training of insects, with a thorough knowledge of their bionomics, to live in captivity, and to obtain successive feedings on diseased and healthy animals, under conditions simulating as nearly as possible the natural conditions. (*) Finally, if all this were not sufficient to establish our American (*) The true precursors in this field of work are to be found in the investigators of Anthrax. Davaine, C. Etudes sur la contagion du charbon chez les animaux domestiques. Bullet. de l'Acad. de Med. de Paris 1870. Vol. XXXV. pp. 215 and 471. |