134
Contagious Abortion of Cattle, Sheep and Goats
[VOL. XVIII, PART III
As before, however, the factor of congestion complicates this picture. During the monsoon
buffaloes cannot be grazed and they are consequently standing in congested cowsheds, sometimes
for weeks at a stretch. The influence of congestion may perhaps be eliminated by comparing this
result with the records of farm 2, page 131, which, besides carrying the herd of Brucella-infected
cattle already discussed, keeps a herd of closely co-habiting buffaloes. 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. Thus the two environments may be
compared as follows :—
Environment
Climate . . . . . .
Disposal of animals . . . . . .
Source of infection . . . . . .
Result . . . . . .
Farm 2
Sunny and dry . . . . . .
Congested
.
.
.
.
.
.
Very great
.
.
.
.
.
.
No epidemic . . . . . .
Farm 3
Overcast and humid
Congested
Ample
Pandemic
The above data, surely suggest that, in buffaloes at least, rainfall plays a considerable part in
the dissemination of Brucellosis.
Without wishing to labour the point several other Brucella epidemics in buffaloes offer support-
ing evidence. Another dairy farm (4), situated in a dry healthy climate, purchased several buffaloes
from a humid, Brucella-infected locality. These animals aborted shortly after arrival, but up-to-
date there has been no rapid spread of Brucellosis to the remainder of the herd. This record holds
an entirely new significance, for, it is possible to suppose that the buffalo requires for its infection a
strain of Brucella that has been adapted to these animals by passage—a hypothesis which might
account for the failure of transmission in farm 2. But in this case buffaloes themselves are bringing
a presumably adapted strain to a disease-free herd and yet transmission does not occur.
In another farm (5), there was a major epidemic of Brucellosis in cows during the normally dry
summer of 1940, whilst the abortion rate in a co-habiting herd of buffaloes remained average for
their class. In July 1942, however, there was an exceptional monsoon, which coincided with a
second major epidemic in cows and which was immediately succeeded by a major epidemic in buffaloes.
The inference, here, is self-evident. The year 1942, moreover, was remarkable for a heavy monsoon
throughout India, and several reports were received of abortion epidemics amongst Punjab village
buffaloes ; in some cases these outbreaks were associated with the rains. Another report was received
from a private farm in charge of an American veterinarian, who, unprompted by the writer, stated
that the buffalo abortion was associated with the exceptional rainfall.
These records all lead to the same conclusion and it is tempting to accept the simple explanation
that in disseminating the disease amongst buffaloes, at least, a fluid vehicle is more satisfactory than
a dry one. In this respect the buffalo's habit of wallowing requires consideration, and, at first sight,
it might seem to be the key to the problem. On closer investigation, however, it appears that the
period of the year when it is essential for buffaloes to wallow is during the dry heat of April, May
and June, at which time water is everywhere short and the few available small tanks and ponds are
grossly congested with animals. Later, during the rains, wallowing is still widely practised, but the
animals are dispersed over a far wider expanse of water. If, therefore, the fluid of the wallow is the
vehicle of transmission Brucella epidemics would be worse in dry summers when the liquid would
be most concentrated, whilst, assuming a one or two month transmission and incubation period,
abortion epidemics should commence in May or June rather than August, or September.
It seems, then, that the vehicular action of water may not be the explanation. It is possible
for instance that the rainfall and restriction of animal movements may result in a loss of resistance,
a supposition which is in part supported by the buffalo's peculiar liability to abort as the result of