J. B. POLDING
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India, where brucellosis is common in village cattle. Thus, of 405 sheep and goats bled in 15
towns of south India, 11 (2.5 per cent) were positive : of 250 tested in 11 towns of north India,
none was positive.
DISSEMINATION
The channels by which Brucella leave and re-enter their host are well known. The point to be
noted is that, although these parasites are considered obligatory, in favourable circumstances they
will survive outside the host and be available for dissemination. In this part of the paper an at-
tempt is made to indicate the conditions governing this dissemination in a continent, where extreme
cases give opportunities for comparison not often seen elsewhere. Throughout north-west India,
there is daily scorching sunshine from April to October, natural shade is rare, and the total annual
rainfall is one inch or less. In the south, conditions are the converse, temperatures vary little around
blood heat, the atmosphere and land surface are moist, while natural shade is everywhere more com-
mon and for fairly long periods the sky is overcast. However, this survey has shown that brucellosis
is enzootic in the south and rare in the north-west. The inference is that sunshine and dryness are
inimical to Brucella, or conversely that equable temperatures, humidity and shade favour their sur-
vival. Certain less general observations support this premise. Earlier in this paper, the decrease
of brucellosis on the Punjab grantee farms was noted. These farms lie in a semi-desert tract and
for the most part their indigenous stock live and calve out-of-doors. It is possible that this is an
example of self-elimination of brucellosis due to animals living in dry, sun-lit surroundings. By
contrast, there are three farms in Assam, a region enduring a heavy and protracted monsoon and
lying within the bi-seasonal rainbelt. The animals of these farms are similar in type and origin to
those of the grantee herds, yet in 1941 the incidence of reactors amongst them was 20 per cent, whilst
their abortion rate varied from 2 to 6 per cent per annum.
In another indigenous herd of the Punjab (farm I), the mean annual abortion rate during the
climatically normal period 1930-1935 was 1.27 per cent of several thousand pregnancies, while during
the entirely rainless period 1936-1939 the rate was only 0.66 per cent. Here, another important
consideration arises, for during the rainless years the stock could not be grazed but had to be stall-
fed in congested corrals. The result of this over-crowding was a severe epidemic of tuberculosis.
It appears, therefore, that conditions of congestion, sufficient to produce an air-borne respiratory
infection due to a relatively resistant organism, resulted in a decrease of Brucella infection during a
period of constant sunshine and extreme dryness. Thus congestion as a factor in the spread of bru-
cellosis may be secondary to excess of sunlight.
In contradistinction to these observations in the classical outbreak noted in Tables IX and X
(farm 2). Here again atmospheric humidity was negligible and sunlight was more or less conti-
nuous. Congestion also was extreme, the animals never being out of the farm compound. The
contradictory results of farms 1 and 2 may perhaps be explained on the grounds of hygienic condi-
tions. On farm 1, aborting animals were segregated and gross infective materials, such as the pla-
centa, were quickly destroyed. On farm 2, no such precautions were taken and general cleanliness
was lacking.
In cows, therefore, it appears that, provided gross sources of contagion are removed, the steri-
lizing effects of sunlight are sufficient to suppress the remaining minor sources, even when conges-
tion is great; conversely, where animals are dispersed, hygiene becomes of less importance and the
effects of sunlight are paramount. Village cattle on the whole graze over wide areas and dispersion
thus counteracts the lack of hygiene, but here again sunlight probably plays a major part in sup-
pressing the disease.
There are, however, other aspects of the effect of climate on the dissemination of Brucella,
namely humidity and rainfall, but while the possible importance of moisture is well illustrated by
the restriction of indigenous brucellosis to the humid tracts of India, it is even more sharply em-
phasised by some aspects of the epidemiology of brucellosis in buffaloes.