Part 35

It must be said, to avoid misunderstanding, that ‘the Tropics’ in the medical sense is a region considerably wider and far less well-defined than the geographical Tropics. Moreover, despite the existence of diseases peculiar to the Tropics, ‘tropical diseases’ form no natural group based on any common organic causation. The organisms that give rise to the various ‘tropical diseases’ differ from one another just as much as the organisms that give rise to the diseases of temperate countries.

Since we cannot speak of tropical diseases on the basis of their common causation, we are forced to deal with them as separate entities and especially from the point of view of their prevention. We will therefore select two diseases, the history of which illustrates the process by which the Tropics have been rendered safer both for European and for native races. These will serve as types, and we will choose one from the truly tropical group which does not invade temperate climes, and the other from the group which is being gradually excluded from temperate climes. No better instances of these two groups can be adduced than Yellow Fever and Malaria.

FIG. 120. A common Malaria-carrying mosquito × 3.

FIG. 121. The Yellow Fever-carrying mosquito × 3.]

(a) Yellow Fever.

In discussing the history of Yellow Fever, as of many other conditions, it is perhaps best to begin at the end, for modern knowledge of the organic cause of a disease often illumines and gives a meaning to historical records.

In 1918 the Japanese investigator Noguchi observed a very delicate and minute spiral organism in the blood of a case of Yellow Fever at Guayaquil, the principal port of Ecuador, on the West Coast of South America, one of the most important endemic centers of the disease. Noguchi showed that guinea-pigs inoculated with the blood of this infected case developed symptoms similar to those of Yellow Fever, and he was able to demonstrate the same organism in the sick guinea-pigs. He passed the disease by means of inoculation from one guinea-pig to another. He succeeded in obtaining pure cultures of the organism on artificial media. He passed such cultures through a series of guinea-pigs and finally recovered it in pure culture again. He showed that different strains vary greatly in virulence, a fact in accord with the great variability in the gravity of attacks of Yellow Fever.

One of the reasons why the discovery of this organism has been so long delayed is doubtless the very small numbers in the blood of patients suffering from Yellow Fever. Thus, the toxins must be extremely powerful. Indeed, it has been shown that 1/10,000 of a cubic centimeter of a virulent culture rapidly induces fatal symptoms in a guinea-pig.

There are other important points about the Yellow Fever organism. It passes through a stage in which it is so small as to be beyond the reach even of microscopic vision. This fact is known because the blood of a Yellow Fever patient is infective when passed through any but the finest filters. The organism in fact exists in what is called a ‘Filter-Passing’ stage. Of late years a number of infective diseases have been shown to be due to filter-passing organisms of this type. Among them is the organism of the disease known as Infantile Paralysis (p. 270). The study of ‘filter-passers’ bids fair to be in itself a special science.

Finally, Noguchi threw light on the nature of Yellow Fever epidemics. He was able to pass the parasite from one guinea-pig to another, not only by inoculation in the ordinary way, but also by means of the bite of a species of mosquito which has long been known to be the carrier of the disease for man. He showed that a period of some twelve days’ duration within the body of the insect is necessary for the parasite again to develop its dangerous phase. The period of incubation in man, that is, the time that passes between the infective insect bite and the appearance of the disease, is 3-5 days, but 12-14 days is the period that usually elapses after the introduction of a case of the disease before other cases occur. The discrepancy is now explained. The disease is not infectious except through the mosquito, so the developmental period of the parasite within the mosquito corresponds to the incubation period of the epidemic.

Outbreaks of Yellow Fever have struck the public imagination, have given rise to folk tales and have inspired poets. The story of the Flying Dutchman is that of a ship stricken with Yellow Fever. The specter ship is supposed by sailors to haunt the seas around the Cape of Good Hope, and to bode ill for those who see it. A murder was committed on the ship, and following it ‘Yellow Jack’ broke out. All ports were closed to the wretched crew, who finally all died of the disease. The Flying Dutchman was the subject of an opera by Wagner and a novel by Marryat. A picture of a ship smitten by Yellow Jack is to be found in Coleridge’s Ancient Mariner.

An historic case may be quoted. In 1837 a barque named Huskisson was at Sierra Leone. She was lading when Yellow Fever appeared among the crew. All but two or three died. Yellow Fever broke out in the colony, but gradually died down. The Huskisson, in the meantime, remained in harbor without hands for three months. At last, hands were obtained, tempted by very high pay. Again the Yellow Fever broke out among them and again nearly all died. They were bitten by infected mosquitoes which remained in the ship during the three months. Many cases, no less dramatic, are on record. The disease is among those which are peculiarly common and fatal among medical men. Thus, Senegal has twice been denuded of medical men by Yellow Fever. In 1830 six died out of twelve, and in 1878 twenty-two out of twenty-seven.

An attack of Yellow Fever confers Immunity. In children it assumes a mild form, and therefore, in countries where the disease is endemic, the population consists largely of the survivors of attacks. On this account terrible outbreaks of the Flying Dutchman or Ancient Mariner type are always either on immigrant ships or in places which have remained long unvisited by the disease, in other words such outbreaks occur under conditions in which immune persons are few or absent.

The distribution of the Yellow Fever mosquito is wider than the distribution of Yellow Fever at the present day, but Yellow Fever is never found, save in sporadic outbreaks, where the mosquito cannot live permanently. The distribution of the mosquito corresponds, however, to the areas where the disease has in the past, from time to time, established itself, but is smaller than the area wherein sporadic outbreaks have been reported.

During the seventeenth and eighteenth and even the nineteenth century there were repeated outbreaks of Yellow Fever far beyond the region to which it is now confined. Along the eastern shores of North America it has at times extended as far north as New York, and there have been destructive outbreaks in Baltimore, Philadelphia, and even Boston. The disease has been found along most of the littoral of South America. In the Old World it has visited chiefly West Africa, where it was imported very early by the slave trade. It has visited at times Spain, Portugal, and Italy with devastating epidemics, and has even occasionally made a call in France and once in England. The last considerable outbreak in Europe was at Madrid in 1878.

England has always had important interests in the West Indies. During the eighteenth and first half of the nineteenth century she had, moreover, large military establishments there, which were regarded as very bad stations. In Thackeray’s Vanity Fair, which refers to the period just after the Napoleonic wars, the disreputable and unfortunate Rawdon Crawley is sent as governor to ‘Coventry Island’ in the West Indies, and is not expected to last long! There are many historic occasions on which the British forces in the West Indies lost almost incredible numbers from Yellow Jack, garrisons being practically wiped out. In Jamaica the mean annual mortality in the garrison was for many years 185 per 1,000! In the Bermudas the mortality was about 80 per 1,000. One should remember that soldiers are picked men in the prime of life, and that these mortality rates were in places now regarded as health resorts! A hundred years ago, Jamaica had the highest death-rate in the Empire, with the exception of West Africa, where the mean annual mortality of whites at Sierra Leone was 362 per 1,000!

Conditions in the West Indies began to improve definitely from about 1850 onwards. At that time there was no effective knowledge of the organic cause of Yellow Fever, nor, for that matter, of any other tropical disease. Only lately has the basic reason for this early improvement become obvious. From about 1850 onwards the water-supply in the more settled parts of the West Indies, and notably in the larger towns, came to be arranged by pipes. Now these towns were the special resorts of the Yellow Fever mosquito. The removal of open standing water, the enclosure of water-supplies, and the introduction of ordinary modern sanitation in the clearing away of rubbish, did good work without any knowledge of the organic cause of the disease.

We now know the life-course of the Yellow Fever mosquito. We know her breeding habits and how the water-living larvae congregate specially in the small collections of water in the neighborhood of houses. Precautions have been taken against them and under favorable circumstances the disease has completely disappeared in well-managed districts under British and American control. The romantic story of the destruction of Yellow Fever in the Panama zone, in Cuba, Puerto Rico, Jamaica, Barbadoes, Trinidad, New Orleans, has been too often recited to be detailed again. Every one has heard of the tragic event in connection with the American Mosquito Commission of 1900 and of the death of Lazear. He and his colleagues, led by Walter Reed (1851-1902), finally proved that the disease is never conveyed by bedding, or by clothes, or by other objects, but always and only, in nature, by the bite of an infected mosquito.

During the experiments of the American Commission, cases of Yellow Fever were produced in volunteers by bites of infected mosquitoes, by injection of blood of infected patients, and by injection of filtered blood serum of infected patients (p. 74). With this knowledge in his hands, the American chief sanitary officer of Havana, William C. Gorgas (1854-1920), began to destroy mosquitoes systematically and to treat all Yellow Fever patients under mosquito nets. Within three months Havana was free from Yellow Fever for the first time for one hundred and fifty years. These wonderful results are brought out by a table:

Deaths in Havana from Yellow Fever.

Year. Deaths. Year. Deaths. 1885 165 1895 553 1886 161 1896 1,282 1887 532 1897 858 1888 468 1898 136 1889 303 1899 103 1890 308 1900 310 1891 356 1901 18 1892 357 1902 0 1893 496 1903 0 1894 382 1904 0

Except for the semi-civilized states of Central and South America, Yellow Fever is now generally under control. It is perhaps not always realized, however, that, while the local extinction of this disease may be among the future triumphs of modern science, its substantial control over large areas is part of the history of world hygiene (p. 278), and that it is part of the very same movement that has made our own cities healthier and more habitable than they were in the Middle Ages.

(b) Malaria.

The history of Malaria, which is also carried by a mosquito, is very different from that of Yellow Fever. Malaria was, till recent times, a disease of temperate as well as of tropical countries. The old name for the disease is Ague. The word Malaria is of no great antiquity in the English language. It came into use only in the eighteenth century. Like the word Influenza, it is of Italian origin, and, like Influenza, it carries with it a forgotten pathological theory. Malaria is simply mal aria, that is, ‘bad air’. So Influenza is the influence, that is to say, the influence of unpropitious planets or comets that were held to rain down poison into the air. It was believed that these diseases were the result of local atmospheric conditions. In Rome and the Campagna the natives still believe that just as the sun goes down the air becomes specially poisonous.

While the term Malaria is comparatively modern, nevertheless, recognizable accounts of the condition are perhaps more ancient than those of any other disease. Of all diseases produced by micro-organisms, Malaria has perhaps changed its type least during the course of historic time. The disease is distinctly described in several places in the Hippocratic Collection.

The conception of diseases as separate entities is, of course, modern. In the case of most infectious diseases, therefore, we cannot hope to follow the history very far back. But the symptoms associated with a malarial attack are so definite that there is no difficulty in tracing the disease with certainty as far back as 1000 B.C. The real division into ancient and modern times comes, for this disease, with the use of Cinchona, which is the plant from which Quinine (p. 326) is now derived. Very soon after the introduction of Cinchona in the seventeenth century, fevers came to be habitually divided into those which respond to Cinchona and those which do not. Cinchona--and therefore its derivative, Quinine--is one of the drugs that we owe to the discovery of the New World (p. 95). The rind of the Cinchona tree was taken as a remedy by the aborigines. In Europe, where it was introduced by Jesuit missionaries, it became known as ‘Jesuits’ bark’. It was popularized by Sydenham (p. 100) and has ever since been widely used in medicine.

Sydenham gave a good description of Malaria. During the seventeenth and eighteenth centuries epidemic after epidemic of ‘Ague’ swept over England as over other European countries. These epidemics spread from their endemic centers, the low-lying ill-drained, swampy districts, where the Malaria mosquito could breed freely in the slowly flowing water. Of such places the principal in England were the Fens of Cambridgeshire, Lincolnshire, and the surrounding counties, the marshes on either side of the estuary of the Thames in Kent and Essex, the marshes of Romney and Pevensey on the South coast, and those around Bridgewater near the Bristol Channel (Fig. 122). There Malaria was never absent, though it differed greatly in prevalence and severity in different years. Ague remained prevalent in London as late as 1859. The proportion of ague cases to the total number of in-patients and out-patients at St. Thomas’s Hospital in London from 1850-60 varied from between 12 per 1,000 at lowest to over 60 per 1,000 at highest. Thus, over one-twentieth of the patients in a large London hospital suffered from what we now regard as a tropical disease, within the lifetime of men who are still with us!

In London the rise in the value of land led to the erection of the Thames Embankment, which effectually reclaimed the land around the river. Extensive works of drainage were at the same time being undertaken in other infested districts. These soon had their now well-known effect. In 1864 Malaria was found to be rapidly diminishing everywhere, and to have left many of its old haunts. The disease retreated rapidly. At the beginning of the twentieth century a systematic search was made for a native case in England. After much labor one single case was at last found. It may safely be prophesied that native Malaria will never again be anything but a rare disease in any temperate country with an efficient sanitary service.