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Meteorological Phenomena and Plague.
That plague has a seasonal prevalence is very marked in Hongkong and rend- ers it necessary to record and consider the chief meteorological data of the season during which the disease is epidemic.
The weather, apart from any influence it may have on the development of the plague bacillus, has a distinct effect on the habits of the people.
In the cold weather old clothes padded with cotton wool are brought out, often from the pawnshops, and worn. Also for the sake of warmth within the houses, windows are kept closed at night and proper ventilation is impossible; there is no sleeping in the open during the cold months.
With the advent of warn weather the men of the coolie classes largely sleep in the street or on roofs of houses. Rain, however, or even the likelihood of rain drives them back into their houses.
Houses are therefore most overcrowded during the cold weather and wet wea- ther and least so during hot dry weather.
Overcrowding does in all probability have a direct effect in spreading plague from person to person. It is not in the houses of the well-to-do that plague gen- erally occurs but in overcrowded dwellings of the poor.
The questions suggested by a consideration of the meteorological data of a plague epidemic are :-
I. How can the habits of the people changing as they do with the changes of weather increase or decrease the incidence of plague amongst them? II. Does the variation in the weather from season to season have any influence on the development of the virulence and parasitic habit of the plague bacillus ?
With regard to question I- Whatever may be decided to be the chief mode of entrance of the bacillus pestis through the skin, whether through accidental cuts or abrasions or the bites of insects, it is obvious that the more overcrowded a house is, the more chance will there be of infection spreading.
In my report on the 1903 epidemic I pointed out that plague was worst in those districts where the number of inhabitants per floor was largest.
The year 1904 also shews the samne coincidence. No. 9 Health District is the most overcrowded (per floor) in the City and it is in this district that the disease has been most prevalent.
Out of 320 cases occurring in the City to end of July, 139 are set down to this district. I do not propose therefore to deal further with this overcrowding question here.
The remains however the question of the clothing worn during the cold wea- ther. It is the custom of the Chinese labouring classes to pawn their winter clothing when the warm weather comes and to redeem it on the approach of winter. These garments are often padded with cotton wool and are therefore un- washable. They get very dirty and may well enough afford shelter to fleas.
That the flea may be concerned in the transmission of plague is not a new idea. Many workers have brought forward the theory that fleas play an important part in the transmission of plague, notably ASHBURTON-THOMPSON and TIDSWELL in Sydney and lately Captain LISTER, I.M.S.
ASHBURTON-THOMPSON and TIDSWELL have shewn that fleas from infected rats when triturated and injected into susceptible animals can produce plague. TIDSWELL has also shewn that certain rat flens will bite man.
Captian LISTER has found rat fleas on the human subject during a plague outbreak in a lodging house in India (Bombay ?); out of a total of 30 fleas taken from the inmates 14 (nearly 50 per cent.) were rat fleas. E. H. HANKIN in a paper, published in the Journal of Hygiene for January 1905, ou Plague Epi- demiology, suggests the possibility that fleas may only become capable of transmitting the disease after the lapse of a period varying from ten to twenty days or more from the date of their exposure to the infection.
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