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Contagious Abortion of Cattle, Sheep and Goats [VOL. XVIII, PART III
more common, but for fairly long periods the sun is overcast altogether. But it has already been
shown that Brucellosis is endemic in the south and rare in the north-west (page 116). The simple
and understandable inference is, that sunshine and dryness are inimical to Brucella microbes, or
conversely that equible temperatures, humidity and shade are propitious to their survival.
Other more isolated observations corroborate these suppositions. On page 128 allusion has been
made to the decrease of Brucellosis on the Punjab Grantee Farms. These farms lie in a semi-dessert
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, sunlit surroundings.
In contrast to this, are the returns from three farms situated in Assam, a region which endures a
heavy and protracted monsoon and which, moreover, lies within the bi-seasonal rainfall belt of
India. The animals of these farms are of similar 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 is from
2 to 6 per cent per annum.
In another indigenous herd of the Punjab [farm (1)], the mean annual abortion rate during the
climatically normal period 1930 to 1935 was 1.27 per cent of completed pregnancies, whilst, during
the entirely rainless period 1936 to 1939, this rate was 0.66 per cent, i.e., a reduction by half. Here,
another important consideration arises, for, during the rainless years the stock could not be grazed
and 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-
born respiratory epidemic of a relatively resistant organism, resulted in a diminution of Brucella
infection during a period of constant sunshine and extreme dryness. Congestion as a factor in the
spread of Brucellosis, therefore, may be secondary to excess of sunlight and it seems likely that
Brucellosis is essentially not an air-born disease.
In contradistinction to this result, are the findings at a pinjrapole [farm (2)] situated on the arid
Deccan plateau. During 1941-42 this farm suffered an extremely violent epidemic of Brucellosis
and 77 per cent of the herd aborted. Here, climatic variation was negligible and sunlight was more
or less continuous. Congestion also was extreme, the animals never being out of the farm compound.
The contradictory results of farms I and II may perhaps be explained on the grounds of hygiene.
In farm (I) aborting animals are segregated and gross infective materials, such as the placenta, are
quickly destroyed. In farm (II), no such precautions were taken and general cleanliness was lacking.
In cows, therefore, it appears that, provided gross sources of dissemination are removed, the
sterilizing effects of sunlight are sufficient to suppress the remaining minor sources of infection, even
when congestion 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
bacterial dispersion, therefore, counteracts the lack of hygiene, so that, here again, sunlight plays a
major part in the suppression of contamination.
There are, however, other aspects of the effects of climate upon the dissemination of Brucella'
i.e., humidity and rainfall and the possible role played by moisture is very well illustrated by the
restriction of indigenous Brucellosis to the humid tracts of India, and especially by some aspects
Brucella epidemiology in buffaloes. Only one serious endemic of Brucellosis has been encountered
in buffaloes (farm 3). The abortion rate on this farm is shown in Table XXI and, for India, it is
undeniably excessive, possibly unique. In an attempt to explain this unusual incidence, many
environmental factors have been considered, but the only extraordinary influence that could be found
was the exceptionally heavy monsoon, amounting to 80 in. of rainfall in the period June to Septem-
ber. Table XXIII presents a statement of the percentage rates of abortion amongst susceptible
stock for each month of the year, the calculation being made from an aggregate of the returns for
five years. The head of stock that was adjudged susceptible to abortion in any one month was the
aggregate of animals carrying a foetus between five and nine months of age inclusively. This period
of term was selected after a study of Table XX.
A further study of the same Table, however
indicates that the liability to abort differs in the various months selected in the proportion of