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Tropical

diseases, tropics, fever, parasites, disease and various

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TROPICAL DISEASES.—The various diseases of mankind are not evenly iistributed throughout the various quarters of the globe, and those diseases which are more prevalent or are peculiar to the warm climates claim special attention. In the realm of infectious diseases it is a striking fact that the tropical countries are particularly rich in many forms. This is an observation which, by analogy, would probably be true a priori, for in the tropics there is to be found a great richness of all forms of both animal and plant life. As one travels toward the poles it is well known that, whereas the numbers of individual species increase, the varieties of forms diminish, and this general biological fact has its correlation in the field of disease, particularly where parasitic animal and vegetable forms arc the exciting causes.

It is further well known that the tropical regions afford better developing places for certain forms of parasites which are known to be able to live and cause disease also in temperate climes, and this is true of the majority of pathogenic organisms. For this reason the ordinary diseases of the temperate climes are very widely distributed in the tropics as well ; in fact, most of them are universal. Tuberculosis, measles, scarlet fever, diphtheria, pneumonia, typhoid fever, smallpox, whooping-cough, syphilis, gonorrhcea—these are found everywhere. They depend for their distribution on the migrations of man, and wherever he can live these parasites live with and upon him. There are, however, two important ideas to be borne in mind. In the first place, there are some more or less universal disease-producers which attain an undue prominence in tropical countries i.e., are very widely and fatally prominent ; and, secondly, there are some forms of disease which are practically limited to the tropics. These constitute a minor part of the general aggregate, but are entitled to special consideration.

Just as in the temperate zones it is found that scarlet fever, typhus, and acute articular rheumatism are very common, while they are rarely observed in the tropics, so there are diseases more limited to the tropics, such as yellow fever, pernicious malaria, cholera, etc., and some others which are exclusive

to these regions, trypanosomiasis, and a few intestinal parasitic diseases.

Since the tissues of the human body are the special food-supply of these various infectious disease-parasites, it may be asked why it is that certain diseases can be limited to the tropics, for the human body of negro or of Esquimau varies little in its composition. The general law of biological distribution helps to meet the question, since there are certain climatic conditions which affect the parasites very materially, much as the climatic conditions affect the growth of tropical exotic plants or animals- of higher organisation than the plants and animals causing disease. It thus comes about that there are a few non-transportable tropical diseases, as well as a host of transportable ones.

The diseases of the tropics, or those more particularly characteristic of these regions, may be divided into five different series : (t) Those due to known minute parasites, or general infectious diseases : Malaria, yellow fever, plague, dengue, Mediterranean fever, Indian Nasha fever, beriberi, climatic buboes, leprosy, yaws, verrugas of Peru and the Ponos.

(2) Diseases due to poisons : Pellagra, atriplicism, lathyrism, kubisagari ; also poisoning by lacquer, and by poisonous snakes or other venomous creatures.

(3) Diseases due to animal parasites : Dystomas of various kinds, Bilharzia, Medina-worm, filaria, anchylostoma, and rarer paraSites, including forms of tapeworm and of fleas (chiggers, etc.).

(4) Orginic diseases : Tropical tropical dysentery, kala azar, tropical liver affections, lata disease, sleeping-sickness.

(5) Cutaneous diseases : Prickly heat, kro kro, tinea umbricata, pinta, Oriental sores, tropical sloughing diseases, ainhum, Medina foot, etc.

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