Origin and Spread of Plague: (1) Endemic vs Non-Endemic. Miasmatic Disease. Contagion.
Although the above mentioned conditions are those in which plague originates, and may be considered in a general way essential to its continued existence, it is plain that they do not account for its origin. Poverty, overcrowding, fifth and marsh soil, which a temperature suited to plague, occurs in many parts of the world where disease has never been heard of or has ceased to exist. The geographical distribution of disease cannot, any more than the distribution of plants or animals, be explained by climate causes alone. With regard to plague it is quite clear that there are some parts of the world where it is at home, or, as the phrase is, "endemic." In other parts it is probable (or, as some think, certain) that its existence, and even its periodical recurrence, depend on importation from an endemic centre. Although it is not always easy to distinguish between these cases, they must be considered separately.
In the case of an endemic disease we suppose that the poison is either kept in existence by continued transmission from one case to another, or that it can subsist outside the human body in soil, water, or otherwise. The first mode of existence is that of a pure contagious disease, such as small-pox ; and it is plain that this mode of continued existence obtains, the case of plague also. It is not, however, clear that the second may not also be one of the modes of existence of plague which would then be a so called "miasmatic" disease like ague, as well as a contagious one. In India, for instance, the disease appears as if it depends on a poison in the soil, since it returns years after to the same spot, appearing in many villages simultaneously; and some morbid influence causes the death of animals (rats) which live under ground. Similar facts have been observed in China; and, if further inquiry should confirm the hypothesis, it would show that plague is (like anthrax or the "steppe murrain" of cattle) both miasmatic and contagious. If so, is no difficulty in supposing the disease to be carried by contagion to a distant part, and there to be established in the soil, for a longer or shorter period, as the conditions are more or less favourable. The adaptation of this hyphothesis would remove many of the difficulties attending the explanation of plaque epidemics, and to some extent reconcile the controversies of the last three centuries between the "contagionist" and "non-contagion list" schools. It has been maintained by the former that European epidemics have always been caused by the importation of the disease from its home in the East, by the latter that it arose on European soil in the same way as in Egypt or Syria.
In the case of an imported non-endemic disease, the only question which arises is how the importation is effected, -- which the disease may be brought by the air alone, whether by infected persons only, or whether also by objects which have been in close relation to infected persons. Transmission of the disease by the air cannot be pronounced impossible; and there are facts to show, that it is even probable with distances measured by yards, or possibly even hundreds of yards; but there is no evidence whatever that the disease has ever been carried by the air over distance measured by miles. Transmission of the disease by infected persons over longer or shorter distances, and from one country to another, is an established fact. Transmission by infected objects over great distances and from one country to another seems less clearly established. The last two cases must be separately considered.
1. It is clear that the first necessary condition to such transmission is contagion, or transference of the disease from the sick to the healthy. The existence of contagion is shown by such facts as these:-- when a case of plague breaks out in a house the other inmates are extremely likely to take the disease ; and even in severe forms the plague does not cease till it hast affected all or nearly all the household. This is indisputably an almost universal law. In the plaque of London in 1603 it was said the disease entered hardly any house but it seized all that lived in it. And in 1879, on the Volga, in one village, as was ascertained by Mr Colvill and the present writer, the plague attacked five houses containing thirty-three persons, all of whom except two took the disease and died. In this respect plague resembles typhus. In the next place the disease will spread from an infected house to persons who have close relations with it. Thus in the villages on the Volga it was noticed that after one family was affected cousins and relations by marriage were the next to be attacked.
Doctors and those visiting the house are also exposed to the risk, though in a less degree. In Vetlanka on the Volga three physicians and six surgical assistants died. On the other hand, doctors in some instances have singularly escaped from being attacked by the disease. In Egypt, in 1835, out of ten French physicians engaged one only died, nor was the immunity secured by any precautions. These experiences do not prove that the disease it not contagious, but they modify the exaggerated notions which have been held on the subject. The facts appear to be expressed by saying that it may undoubtedly be communicated from one person to another, but chiefly by breathing the air of the sick room, and this generally from prolonged not from momentary exposure, -- so the possibility of communication by chance meetings and similar contingencies may be disregarded. This view is that similar contingencies may be disregarded. This view is that of Dr Cabiadis and others who have studied plague in Irak [Iraq] where no doctor or assistant, with one exception, suffered from the disease. It is not inconsistent with the experience recorded in Egypt. But it is clear that the intensity of contagion varies greatly in different epidemics. Modern experience contradicts the belief formerly entertained that contract with plague patients was the only or even the chief means of acquiring the disease. Everything tends to show that the atmosphere immediately surrounding the patient is the most effectual conveyer of contagion, and more effectual in proportion as the poison is concentrated. Precisely the same relations are observed with regarded to typhus.
It has been disputed whether dead bodies convey infection of plague. Formerly the contagion from this source was greatly dreaded, and the task of burying thought to be specially dangerous dangerous. But the French in Egypt made more than a hundred post-mortem examinations without precautions and without harm. In Mesopotamia and in Russia no autopsies were made, but in the latter country some striking instances were noted engaged tin burying the dead themselves dying of the plague. On the whole both facts and analogy lead to be belief that the disease may be derived from touching or being near a dead body, but not that there is any special danger of infection from this source.
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