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Some of the curves would appear to be influenced in this way. and epidemic die down, one or other may even disappear.
The epizootic
When such has occurred it will be seen that in these temporarily plague freed areas, the epizootic is the first to make its reappearance, and the rat plague is followed by a recurrence of human plague within a week or a fortnight.
It has been said that one or other of these outbreaks may disappear. The lessons which one learns from these curves are that it is possible to have an absolute disappearance of the epidemic.
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Sanitary efforts appear so far to be highly successful in regard to the removal of human plague. With the epizootic, the matter is unfortunately otherwise. survey of the curves will show a drop of the epidemic to zero. The epizootic falls. at the same time. The fall may be considerable, but it rarely reaches zero.
These results impress upon us the fact that it is the infected rat which we have to cope with, and that no matter how far reaching our cleansing operations and stamping out system" of human plague benefit us, the root of the evil still remains in the shape of infected rats.
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Among the Health Districts of Hongkong, it would appear that the sanitary success obtainable in any one district is in a great measure vitiated by the condition of affairs in neighbouring districts. One district may be thoroughly cleansed and freed from all plague infection, yet in the course of a few days, such labour and expense are lost, owing to the incoming infection which possibly exists in the immediate surroundings.
Viewing, in the first place, the general chart for 1902, it strikes one that some possible connection exists between rat plague and human plague.
The epizootic is much in excess of the epidemic. Fluctuations in the one are followed by fluctuations in the other.
The epizootic appears in advance of the epidemic. An interval of a week or a fortnight usually elapses. So far as the results of the general chart for 1902 are concerned, it would be a mistake to hastily conclude that the one is the cause of the other that rat plague is the cause of human plague.
I approached the subject for 1902 with a perfectly open mind. I was quite prepared to find rat plague had nothing to do with human plague, and would not have been surprised to find man the cause of the epizootic.
The general chart shows us then, that there is a geral resemblance of the epidemic curve to that of the epizootic. The only thng which strikes one is that it commences a week later, and that rises and falls in the epizootic curve are usually followed by similar fluctuations in the epidemic curve. In fact the number of acute rises in the epizootic curve is frequently followed by a similar number of rises in the epidemic curve.
This is certainly true of the earlier stages of outbreak. In order to examine more closely the course and relations of such curves it will be advisable to divide these up into different stages:
(1) The Initial stage.
(2.) The Fastigium.
(3.) The Defervescence.
(4.) The Subsequent history of the curves.
The Initial Stage of the Epizootic. In all the districts of Hongkong the epizoo- tic was existent on the 8th April. Only two districts form the exception, in which its onset was unexplainably delayed, namely, in districts Nos. 5 and 10. In these the epizootic appeared in the middle of April.
For the year 1902, owing the fact that the examinations were not commenced until the beginning of April, it is impossible to say more than that rat plague was existent. It was apparent that in some districts, the epizootic was present for some considerable time previous to the commencement of the examinations. others, however, it was certainly absent.
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