Tropical disease

“ When we consider that a knowledge of malaria, blackwater fever, amoebic dysentery, bacillary dysentery, liver abscess, pellagra and hookworm disease is just as important for the medical man in the Southern States of the United States as for the physician in tropical colonial possessions, it will be realized that there is more of a practical side to tropical medicine than is usually admitted. ”

“ In such people a definite finding of a cause sufficient to account for an illness is usually the key to the diagnosis. With those from the tropics, however, it is different. A single individual may be found upon examination to have amoebiasis, malaria, filariasis and syphilis, yet none of these infections prevent him from following his usual occupation. When such a patient comes to a ward it requires a correlating mind to eliminate four or five definite diagnoses, and fix upon some disease which is common to both tropics and temperate climates, as for example, typhoid fever. ”

“ A predisposition to certain diseases, and a tendency to degenerative changes, may be brought about in this way; but acute disease, with active tissue change, is not so caused. In the tropics, as in temperate climates, in the European and in the native alike, nearly all disease is of specific origin. It is in their specific causes that the difference between the diseases of temperate climates and those of tropical climates principally lies.
Modern science has clearly shown that nearly all diseases, directly or indirectly, are caused by germs. ”

“ Germs and worms love to visit around. The northern-born influenza has swept away thousands in the South Pacific; neglected, its germ may bide its time for a plunge back into the North. Amoebic dysentery is a “tropical disease”—yes, and a few years ago it appeared in Chicago. The distinctly tropical filariasis (often manifested in elephantiasis) has been identified in several cases in an incomplete survey of the Carolinas. Dr. Boyd, investigating in Florida, asserted that our temperate-climate mosquito can carry a tropical strain of malaria. ”

“ Everyone taking up the study of tropical disease should first study the geographical distribution of such diseases and those practising in temperate climates should remember that the first question to be asked a man suspected of having a tropical disease is “Where have you been during the past months and years?” ”

“ Heat and moisture, he contended, are not, in themselves, the direct cause of any important tropical disease. The direct causes of ninety-nine per cent, of these diseases are germs, and to kill the germs is simply a matter of knowledge and the application of that knowledge—that is to say, sanitary science and sanitation. ”

“ He noted, however, that this epidemic had no bad consequences, patients getting rid of it in three days under moderate diet and copious beverages.
Ashburn and Craig, in 1907, proved that the disease could be transmitted by injections of blood, unfiltered as well as filtered.
Geographical Distribution.—The disease may occur in epidemic form in almost any part of the tropical or subtropical world. It is very common in the countries about the China Sea and in the West Indies. ”

“ In the majority of instances disease germs are true parasites, and therefore, to keep in existence as species, require to pass from host to host. If, during this passage from host to host, the temperature of the transmitting medium—be it air, water, or food—be too high or too low for the special requirements of the germ in question, that germ dies and ceases to be infective. In this way may be explained the absence from the tropics of a class of directly infectious diseases represented by scarlet fever, and the possible absence from temperate climates of a similar class of diseases. ”

“ Doubtless, although it has escaped notice by most medical writers, it is common enough elsewhere in the tropics, or wherever heat and moisture combine to bring about a state of skin favouring its development on the infective material being applied. It is especially common in schools and similar institutions where large numbers of children are thrown much together; they readily pass the disease one to the other. ”

“ The rate of mortality among the natives from tropical diseases is also high, one of the most fatal being that known as sleeping sickness. (The ravages of this disease, which also attacks Europeans, reached alarming proportions between 1893 and 1907, and in the last-named year an international conference was held in London to consider measures to combat it.) When removed to colder regions natives of the equatorial districts suffer greatly from chest complaints. ”

“ In tropical work we combine the large mononuclears and transitionals in a differential count. They are the phagocytes of animal cells or parasites. The disease in which their increase is best recognized is malaria and an increase to 15% where the blood shows moderate leucopenia is very significant. The melaniferous leucocytes of malaria are cells of this type.
Other protozoal infections, as kala-azar, trypanosomiasis and amoebiasis cause it. Filterable-virus diseases may show a mononuclear increase, thus yellow fever and dengue both give an increase about the fifth or sixth day. ”

“ There is one factor which undoubtedly has contributed powerfully to delay the diffusion of certain tropical diseases—the circumstance that most of them depend on protozoal or some other kind of animal germ requiring for its transmission an animal intermediary. Diseases which depend on bacterial germs, if their special bacterium be introduced, social and sanitary conditions being favourable, will spread in any country or climate, and thus it is that all bacterial diseases, with hardly an exception, are found, or are capable of existing, everywhere ”

“ Villages are seldom affected; nor does the disease readily spread if introduced into rural localities. In spreading inland it follows the lines of communication railways, canals, navigable rivers. A ship disease.— Ship epidemics were common occurrences formerly. The ideal haunt of yellow fever is the low-lying, hot, squalid, insanitary district in the neighbourhood of the wharfs and docks of large seaport towns.
A place disease.— It is, in a sense, a place disease like malaria. ”

“ There is strong reason for believing that the recent influx of Europeans into tropical Africa and the consequent increased movement of the natives is spreading the disease, and that this extension has by no means reached its limit. ”

“ 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. ”

“ Every tropical practitioner should be provided with a travelling microscope, or, at least, carry about with him a few microscope slips for blood films. He must be on his guard, however, against concluding from the discovery of malaria parasites in his films that malaria is necessarily the only, or even the principal, disease his patient is suffering from. ”

“ Epidemiology.—The disease is rare in natives and is entirely endemic. Some authorities have suggested a greater frequency of the disease in those intimately exposed to a case, as in husband and wife or the members of a family.
Sprue is usually a disease of mature life and affects women more frequently than men. While climate cannot be considered as causing sprue yet the effects of hot climates in producing exhaustion states in Europeans must be borne in mind. The sprue patient should always leave a tropical climate. ”

“ Beriberi, sprue, pellagra, cholera, leprosy, amoebic dysentery, hookworm disease, filariasis, bilharziosis, endemic haemoptysis or paragonomiasis, liver fluke disease, malarial cachexia, yaws, verruga, oriental sore and ulcerating granuloma of the pudenda, as well as the various tropical skin diseases.
One should always keep in mind the fact that a latent malaria often gives way to frank malarial manifestations when some intercurrent disease still further reduces the body resistance. ”

“ The causes of the ardent continued fever of the tropics, which is usually recognized as a form of simple continued fever, do not differ materially, except in degree, from those of the simpler forms of the disease; but exposure to the direct rays of the sun would seem to be especially prone to give rise to the disease in those who are unaccustomed to the heat of a tropical climate. ”

“ Pneumonia and typhoid in the temperate climates cause greater ravages than tropical diseases in their field, nor is malaria in its manifold manifestations limited to a given area. Fever and ague in the United States, calentura in the West Indies, terciana in the forest regions of the Andes,—it all is essentially the breakbone fever. ”

“ 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. ”

“ Lemoine, as well as other writers on elephantiasis, has seen the disease become stationary by the removal of the patient to a colder climate. Europeans become susceptible to elephantiatic infection after a prolonged residence in tropical countries where the disease prevails. ”

“ DENGUE OR "BREAKBONE FEVER"
This is another disease of the tropics often occurring in widespread epidemics. It is probably most frequently met with in the West Indies, but may occur in any of the tropical countries or islands. Occasionally it spreads into subtropical or even temperate regions. Several extensive epidemics have occurred in the United States. Once introduced into a community it spreads very rapidly and nothing seems to confer immunity. ”

“ We may now profitably turn to the consideration of Malaria, a disease which is undoubtedly connected with the soil and which has its habitat in the soil of certain places. Malaria requires for its development decaying organic matter, a high or moderately high temperature, and usually an excess of moisture. Tropical marshes are the elected seats of malaria, but not the exclusive seats, for it is known that certain rocks and arid plains, as well as the sandy estuaries of rivers, are liable to be malarious. ”

“ While the disease responds to treatment in those who are not too far advanced yet it always should be considered a serious affection. The chances of a complete restoration to health are better for those who can leave the tropics and reside permanently elsewhere. ”

“ An Ifugao Dancer
I add the following extracts from a letter of Major P. M. Ashburn, Medical Corps, U.S.A., president of the army board for the study of tropical diseases:—
“A man can remain in the tropics indefinitely without being actually sick, if infectious diseases are avoided. This is fast leading to the fallacy that we can advantageously remain many years in these latitudes. The fact that while a man may never be sick, he yet may have his physical and mental vigour greatly impaired by prolonged exposure to heat is thus lost sight of. ”

“ Great engineering works employing tropical natives are frequently associated with very fatal epidemics of pneumonia, especially broncho-pneumonia. Again in the black races the infection tends to become generalized rather than localized in the lungs. It is more toxic and insidious in its course than is true of the infection in the white man; it has the fatal trend of pneumonia of the aged. Another tendency is to invasion of the meninges.
Influenza.—In temperate climates we associate this disease with bronchial and coryzal manifestations. ”

“ Lastly, I can conceive, and believe, that there is another and less directly-acting set of conditions influencing the distribution of disease conditions which as yet have been ignored by epidemiologists, but which, it seems to me, must have an important bearing on this subject. Disease germs, their transmitting agencies, or their intermediate hosts, being living organisms, are, during their extracorporeal phases, necessarily competing organisms, and therefore liable to be preyed upon or otherwise crushed out by other organisms in the struggle for existence. ”

“ Apart from plague and cholera, in all the big laboratories studies are uninterruptedly pursued, from one end of the year to the other, upon anthrax, glanders, influenza, Malta fever, various tropical diseases which do not exist at all or are rare in the countries where they are being studied. ”

“ While we advance through a geological epoch that increasingly reflects human intervention on a massive scale, we might expect to see the continued expansion of epidemic neglected tropical diseases, as we have recently seen for Zika and Ebola virus infections. ”

“ Such factors could be responsible for accelerating the geographic expansions of arbovirus infections [ [31] , [32] ] , leishmaniasis [ [33] ] , and Chagas disease [ [34] ] , but this concept requires further exploration. In addition, we are just beginning to understand the role of El Niño events in promoting these and other NTDs [ [35] , [36] ] . The fact that Zika virus expanded dramatically in an El Niño year is also of interest, but as yet, there are no proven links.
Many of the factors highlighted above were either manufactured or shaped by human activity. ”