154
Brucellosis in India
Only one major endemic of brucellosis has been encountered in buffaloes (farm 3). Here the
annual abortion rate was 21 per cent of pregnancies over a period of six years ; this for India is cer-
tainly excessive, possibly unique. In an attempt to explain this unusual incidence, many environ-
mental factors have been considered but the only extraordinary influence discoverable was the ex-
ceptionally heavy monsoon, with 80 in. of rainfall during the period June to September. Table XI
presents a statement of the monthly abortion rates among susceptible stock, calculated from an ag-
gregate of the returns for five years. This shows that abortion-rate for the months November to
July varied little about a mean of 1.4 and although the population of susceptible animals steadily
increases from January to July, there is no corresponding increase in the abortion-rate. In August,
however, whilst the number of susceptible animals commences to decrease, the abortion-rate sud-
denly doubles and in September and October it is thrice the mean for the normal months of the year.
Thereafter, the rate returns to normal. Now as the period of transmission and incubation of the
disease is likely to occupy a period of 1 to 2 months, the critical period of increased infection-rate
causing the increased abortion-rate during August, September and October, commences in mid-
June and lasts into August. But in this period the abortion-rate, and therefore presumably the
bacterial excretion-rate, is constant, whilst the corrected number of susceptible animals does not
vary greatly round a mean of 1200 ; further the absolute number of abortions in July is the same as
in May. In other words donor and receptor influences do not vary sufficiently during this period
to account for the large increase of abortions in August, September and October, and this increase
must be explained by a change in environment which affects bacterial survival and transmission.
But in mid-June the climate changes completely from diurnal sunlight to total sunlessness and con-
tinuous rainfall and this suggests that either the absence of sunlight or the presence of moisture, or
both, favours the spread of brucellosis in buffaloes.
TABLE XI
Monthly incidence of abortion among buffaloes of farm 3
Month
January . . .
February . . .
March .
.
.
.
April .
.
.
.
May
.
.
.
.
June .
.
.
.
July
.
.
.
.
August .
.
.
.
September . . .
October . . .
November . . .
December . . .
Term of pregnancy in months, and the abortion-
liability ratio for each month
9
(3.5)
12
7
11
10
10
46
131
134
116
80
40
21
8
(3.26)
7
11
10
10
46
131
134
116
80
40
21
12
7
(2.75)
11
10
10
46
131
134
116
80
40
21
12
7
6
(1.75)
10
10
46
131
134
116
80
40
21
12
7
11
5
(1.0)
10
46
131
134
116
80
40
21
12
7
11
10
No. of
abortions
(5 years
aggre-
gate)
2
3
4
10
14
17
14
27
36
21
5
1
No. of
suscep-
tible
animals
124
154
314
567
909
1,021
1,377
1,184
861
517
269
162
Ratio of
column
7 to 8,
per cent
1.6
1.9
1.2
1.7
1.5
1.6
1.1
2.3
4.2
4.1
1.8
0.6
Figures in columns 2 to 6 number of animals pregnant at the term shown. Aggregate for five years.
Figures in column 8 = sum of the figures in columns 2 to 6, after application of the abortion-liability ratio, plus the
figure in column 7.
As before however the factor of congestion complicates the picture. During the
buffaloes cannot be grazed and consequently they stand in congested cowsheds, sometimes for weeks
on end. The influence of congestion may perhaps be eliminated by comparing this result with the
records of farm 2 above, which, besides carrying the herd of Brucella-infected cattle already dis-
cussed, keeps a herd of closely cohabiting buffaloes. It is remarkable that during the epidemic no
abortions occurred in buffaloes, despite their exposure to excessive infection from cows. Now on
each farm the factor of congestion is probably about equal, but on farm 2, as evidenced by the spread
in cows, the abundant sunlight was unable to destroy the infection, and the two environments may
be compared as in Table XII.