73
SECTION VII.
(A).—Rainfall and Surra.
The question as to what conditions influence the early or late advent of Surra in horses, is one of
especial interest and importance, both from a practical and scientific standpoint. It is only in Govern-
ment and private establishments, however, where careful records are collected concerning disease, that
details can be obtained, from which deductions of any value can be drawn. In 1890, efforts were
made in this Laboratory to compile statistics, with a view to determine what effect is produced on the
appearance of the disease, by the varying amount of rainfall in different years. At present we have
obtained statistics for the past ten years, with regard to the date on which the disease first made its
appearance at the stables of the Bombay Tramway Company, together with the records of rainfall
during the same period.
TABLE XXII.
Showing the monthly rainfall in Bombay for the years 1888—1897, with the dates of Surra outbreaks, and the
number of horses attacked in each Surra season at the Bombay Tramway Company's Stables.
Months.
January
...
February ..
March ...
April
May...
...
June
...
July
August
September
October
November...
December ..
Total Rainfall
year.
Total Rainfall
1st May to
of outbreak
Surra.
No. of horses
tacked in
year.
...
...
...
...
...
...
...
...
...
...
...
...
for
from
date
of
at-
each
1888.
Inches.
l.85
0.02
0.10
...
...
15.76
22.47
11.43
4.92
18th
0.11
1.16
...
57.82
54.69
14
1889.
Inches.
...
...
...
...
0.67
19.89
30.15
10.32
14th
2.71
3.80
...
...
67.84
61.97
47
1890.
Inches.
...
...
...
0.01
0.06
24.55
21.34
10.61
6.45
6th
0.58
1.25
0.13
64.98
63.56
2
1891.
Inches.
...
...
0.20
...
...
13.99
32.48
6.94
13th
22.53
1.04
...
...
77.18
66.50
1
1892.
Inches.
...
...
...
...
0.11
13.30
23.86
36.56
12th
18.73
1.89
0.67
...
95.12
84.87
15
1893.
Inches.
...
0.14
...
0.02
6.30
21.47
20th
16.14
13.57
7.52
0.45
1.63
0.22
67.46
39.41
11
1894.
Inches.
0.22
...
0.06
0.01
...
16.87
26.16
11th
8.40
12.04
3.08
...
0.01
66.85
44.09
10
1895.
Inches.
...
0.07
.....
...
0.08
17.84
18.04
15.97
2nd
11.91
3.62
0.06
...
67.59
52.02
17
. 1896.
Inches.
...
...
...
9th
0.26
28.02
36.44
30th
20.77
1.62
0.01
0.53
...
87.65
85.49
19
1897.
Inches.
0.01
...
...
...
...
14.40
30.19
13.82
20.60
2.51
26th
...
8l.53
81.52
3
Remarks.
9th May 1896. One case of Surra
most unusual.
20th July 1893. 3 horses attacked:
1 Australian, 1
Arab, 1 Persian.
30th
August Regular outbreak
1896.
commenced.
26th November Three Australians
1897.
at Parel stables.
Flies very
troublesome.
Average annual rainfall for ten
years.
73.40inches.
Average for ten years.
67.35 inches.
Average death rate from Surra for
ten years.
13.9.
As will be observed on reference to the above table, the most common months for Surra to appear
(6 times out of ten) were September and October, twice it appeared in August, and once in July and
November respectively ; when a rainfall of 6.3 inches fell in Bombay in May 1893, three horses were
attacked on the same day, viz. 20th July. It was then considered that the disease might be accounted
for by the hæmatozoon or its resting form having escaped the great heat during the month of May,
and so have retained its vitality, so that its power of re-producing the disease would be increased by the
earlier rainfall and the outbreaks of Surra thus occur sooner. But in 1896 a sporadic case of Surra
occurred amongst the same stud, consisting of some 700 horses on the 9th of May, a most unexpected
occurrence, as up to that time only one animal (Australian, No. 65, owned by a private individual) had
been observed with the disease, and that was contracted in the districts. From the first of the previous
November until May 9th, 1896, only 0.06 of an inch of rain fell, and that was in the first mentioned
month. Consequently here we have undoubted proof, confirmed by microscopic examinations of the
blood of the animal, that Surra may appear in Bombay in the hottest part of the year, when no rain
has fallen for six months. In ten years one animal out of 139 attacked with Surra developed the disease
in the month of May, but the annual outbreak at these stables which carried away 17 horses did not
occur until September, October, November of the same year towards the end of the monsoon season.
On the other hand, it is a well established fact that in the great majority of years during which an
excess of rain falls, the most severe outbreaks of Surra occur. In support of this statement the follow-
ing outbreaks may be brought forward. During 1894 heavy rain fell on several successive days in
September in the Ahmedabad, Baroda and neighbouring districts, thousands of equines succumbed to
Surra during the October and November following, over an area of 400 square miles, and by order of
Government the horse-fair at Ahmedabad was abandoned for a period of two years.
NOTE.—The large numbers in the rain columns denote the date on which the first case of Surra appeared.
B 2204—19