88
Incidence of Equine Strangles in India
Examination of Tables II and III
The data have been analysed in two ways :
A. Omitting October, November and March in
the Punjab and May and November at Ahmednagar
as being months when climatic characters are
likely to be less fixed, the year was divided into
seasons and the incidence figures for these months
totalled as shown in Table III. The Punjab
seasons taken were (i) July to September, a moder-
ately wet warm period ; (ii) December to February,
the cold season; (iii) April to June, the hot dry
season. At Ahmednagar, (i) June to October,
months of high rainfall and humidity; (ii) De-
cember to April, a dry period with a distinctly
lower mean minimum temperature than June to
October.
Table III shows, firstly, that in the Punjab the
attack rate is invariably lower from July to Sep-
tember than at any other time, though at Mona
and Sargodha, as stated, this may not mean
much. Secondly, the difference between the
percentage figures, 57.3 and 38.0, for Mona and
Sargodha for the periods December—February
and April—June respectively is statistically
significant. Similarly, in the totals for the stud
farms there is a significant difference between the
percentages, 24.8 and 34.6, 34.6 and 40.6, and
34.9 and 65.1, respectively. The suggestion,
therefore, is that strangles is mainly a disease of
colder months.
B. Mr. Suprakas Sen has examined the monthly
attack rate from another angle. For each depot
and stud farm, the attack rates of the different
months, calculated from the total number of
cases admitted during the period covered, have
been examined and the months, in which the
percentages of affected animals do not differ
significantly from the highest one, have been
grouped. The result of this approximate method
of analysis is summarized thus :
Periods of maximum prevalence of strangles
Mona
Sargodha
Probynabad
Coleyana
Renala
Ahmednagar
Horses
Mules
Horses
Mules
Feb.—Mar.,
Jan.—Feb.,
Dec, April,
March
Feb.—April
April
Feb.—April
Jan.—April
June, and Oct.
June
May
An analysis of mortality rates by a similar
method shows that strangles mortality was promi-
nent at,
Mona in horses, February—March
„ „ mules (*), January, March—May
Sargodha in horses, January, March—May
„
„ mules (*), January—May
Coleyana (*), January—March, May, June
[(*) Calculations made from very small numbers and
hence only approximate]
Where no mention is made, the mortality rate
at different parts of the year do not differ.
Hence, from this method of analysis also it
seems that the period, February to April, is most
prominent for the development of strangles.
Two points are to be mentioned in connection with
Tables II and III. (1) At Renala, 1938 was a phenomenal
year in which 262 cases of strangles were recorded, in fact
nearly all the young stock. Of these, 52 cases occurred in
April and 68 in May. There is no suggestion that weather
conditions were responsible, and the Estate Manager has
no explanation to advance. (2) At Probynabad, high
figures for strangles cases are recorded in 1924 (May and
June, 71), 1923 (June, 44) and 1932 (June, 16). It is
interesting that May 1924 had the highest rainfall recorded
at Montgomery station in 29 years, viz. 1.62" or nearly
five times the average, the next highest being May 1923
with 1.29". May 1924 also showed the lowest average
maximum temperature in the 29 years, viz. 94.7°F.
(average 104.0°F.), while the minimum for this month was
also low, viz. 71.5°F. (average, 76.2°F.).
A further point to be noted concerns Coleyana. In 1943
strangles was prevalent at a rather unusual time of the
year ; between May and September there were 76 cases of
which 20 occurred in July, 30 in August and 11 in Sep-
tember. Most affected animals were under two years but
a few were four to six years old. No weather conditions
could be held responsible , and in fact, it has been noted
that, with a high incidence at Coleyana, the attack rate at
Renala nearby might be low, and vice versa. Probably,
the main contributing circumstance of the 1943 deviation
was the low incidence over several previous years.
Examination of local meteorological data
The meteorological data so far dealt with have
been monthly average figures recorded at stations
some miles from the depots and farms. While these
suffice to show the climatic trend of the areas, they
may fail to bring out the full relationship of weather
conditions to the disease. In an attempt to
study the matter more closely, daily records of
rainfall and air temperature were obtained from
the depots themselves and from a local recording
station close to Coleyana and Renala. From these
records, charts were prepared, on which were
also inserted, where available, the daily admissions
of strangles cases. In order to economize space,
only selected portions of these charts are re-
produced. The outbreaks in Figs. 7 (Mona) and 8
(Sargodha) began in December and were over in
May. Both appear to show an association be-
tween low minimum temperature and the onset
of outbreaks. It should be noted, however, that in
outbreaks starting earlier in the autumn this asso-
ciation may not be observed.
In order to test this point further, correlation
coefficients for case admissions and minimum air
temperature were worked out. The coefficients
proved to be negative and significant for Mona
and Sargodha, negative but not significant
for Coleyana. (They were: Mona —0.128*,
* The coefficients for Mona and Sargodha, though signi-
ficant and therefore suggestive, are small and should not be
relied upon