Sessional_Paper_1904 — Page 722

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The initial rise in rat plaque is usually a rapid me.

It commences with two, four, or six cases iu one week. The number is doubled or tripled during the next week, and the maximum of the epizootic is usually reached in about a month or six weeks after its commencement.

Such is the ordinary course of rat plague. Minor differences are found on going into detail, some of which are interesting.

Exception may be taken to the condition of affairs in district No. 3. The small number of cases of the epizootic and the epidemic during the initial stages, coupled with the preliminary organisation of the rat collecting staff must be held accountable for any apparent discrepancies. In district No. 4, the initial height of the epizootic reached its maximum within the month. A slight fall then took place, concurrently with a fall in the epidemic. This was succeeded by a second maximum in the height of the epizootic, which was reached exactly two months after the commencement of the outbreak.

A somewhat similar condition of affairs is found in districts Nos. 6 and 9.

The rise in the epizootic may be sudden, or by a series of weekly elevations. Sudden advents of rat plague are most frequently found. Gradual elevations with intervening depressions, are not common. In general the epizootic reaches a much higher level than the epidemic. In a few instances, the height of the latter approaches that of the former, but this is rare, so far as 1902 is concerned. In districts Nos. 9 and 10, both reach approximately the same level. In districts Nos. 5 and 6, this is also marked, but not to the same degree.

1a. The Initial Stage of the Epidemic.-In the general curve for Hongkong, there is a general rise to the maximal point. The epizootic curve reached its maximum within 5 weeks. The epidemic curve followed closely behind, reaching its maximum in 7 weeks, e.g., a fortnight later than rat plague. In contradistinction to the curve of the epizootic, the rise in human plague is accomplished by a series of elevations, followed usually by slight depressions. An explanation of this is hy no means obvious. Comparisons made with the rat plague curve, show elevations in the epidemic curve subsequent to a distinct rise in the epizootic.

Such elevations in human plague occur usually within a week or fortnight after the rise in epizootic plague. When we study the curves as detailed for each individual district, certain variations are found which give us a considerable amount of information in regard to the possible inter-relationship.

An examination of the Koeloon curve shows us how closely it resembles the general curve of Hongkong. The apex of the epidemic curve is reached a fortnight later than the maximum of the epizootic tracing. A break in the initial stage of the epidemic curve is observable. On looking for similar evidence in that of the epizootic, we find it in the shape of an elevation followed by a depression occurring about a fortnight earlier.

Very satisfactory curves are obtained in Districts Nos. 2, 5, 9 and 10.

In No. 2 the epidemic curve is broken and only reaches its maximum a week after the epizootic has risen beyond what to begin with looked like its ultimate maximum.

In No. 5 the epidemic curve appeared to be following the epizootic closely. The latter reached its maximum but fell suddenly. This sudden fall apparently had the effect of prolonging the low elevation of the epidemic curve even causing a slight depression. Subsequently the severe infection raised the epidemic, and the curve reached its maximum about a month after that of the epizootic.

The picture shmon us by Districts Nos. 9 and 10 could not be finer. The rise of the epidemic in both is gradual. The apex of the curve in both is reached a fort- night later than that of the epizootic.

In that of No. 9 the elevations and depressions in the epidemic curve compare admirably with all the variations found in the epizootic curve.

One would almost imagine that the second curve in its rise and fall, is too good to be true. Such an epidemic curve, occurring ten days or a fortnight after that of the epizootic, is, in my opinion, strong evidence of some extremely close ralation existing between rat plague and human plague. ·