MARCH 1948] RAM NARAIN MOHAN AND SYED MAHMUD ALI 9
YEAR TO YEAR VARIATION IN MORTALITY
The extent of annual mortality due to anthrax as recorded in the reports of the Department from
1897-98 to 1944-45 has been briefly summarized elsewhere. It is seen that the annual figures of these
48 years show a very great variation, viz., from nil to a maximum of 2,555, working to an average of
under 450 deaths per year. This variation remains almost as patent when it is considered in relation
to total mortality in livestock and even after allowing for fluctuations due to seasons and random
causes. The extent of variation seems too great and irregular to be satisfactorily explained as due
to direct influence of any climatic or other environmental factors. The three periods which stand
out more or less prominently associated with heavy mortality are considered below.
(i) The year 1899-1900 recorded 804 deaths due to anthrax against 40 in the preceding and
339 in the succeeding years, and the total mortality in the three-year period from 1899-
1900 to 1901-02 was 1,436.
(ii) The heaviest annual mortality ever experienced was recorded during 1917-1919 (4,238
deaths in two years).
(iii) An extended period of eight years from 1934-35 to 1941-42 recorded an average annual
mortality of 1,310 in bovines and about 50 in other animals.
The periods noted above do not bear any relationship with each other and it is difficult to imagine
that the heavy mortality experienced in them was primarily related to any natural factors. It seems
likely that the occurrence of large epizootics and consequent heavy mortality are chiefly due to
spread of infection by means which are well appreciated by animal epizootiologists. The fact that
these periods have occurred at intervals of about 18 years may not be of any significance.
Regional distribution
Some idea of the regional distribution of anthrax in Bengal can be gained by considering (i) the
number of years during which anthrax outbreaks have occurred in the different districts, (ii) the
mortality figures of different districts, and (iii) the number of outbreaks occurring in different districts
during 1937-1946.
The past years have shown wide difference in these respects. Generally speaking, the extent to
which a particular district has been affected with anthrax seems to have been largely governed by its
area and livestock population. Nevertheless, even after allowing for such factors, certain districts
do seem to have been affected somewhat more than the others. Dacca stands out as the most heavily
affected district. Moreover, it is in this district that the disease has often spread to goats and also
to human beings. The other districts in which the incidence has been comparatively high in the past
few years are Midnapore and Murshidabad in West Bengal, and Tippera, Noakhali and Mymensingh,
flanking the banks of the Brahmaputra in East Bengal. In the Gangetic delta in south Bengal, the
districts of Khulna and Bakarganj have occasionally experienced heavy mortality—that occurring
in 24-Parganas in 1917-1919 has already been noted. In the remaining districts, the incidence has
been low and very irregular. The central Bengal districts have been affected the least.
USE OF SERUM AND VACCINE
Both serum and vaccine have been used in the past, the former in affected villages and the latter
generally in unaffected villages in areas affected with larger epizootics of the disease. In 1936, anthrax
spore vaccine was obtained from Burma and was used extensively in the field after a preliminary test
for its safety. In 1937, anthrax spore vaccine manufactured at the Indian Veterinary Research
Institute became available. In preliminary tests, this vaccine was found to produce in a proportion
of animals inflammatory swellings at the seat of inoculation and some general systemic disturbance.
Such reaction, however, was seldom alarming and the vaccine was pronounced safe for general use.
From 1936-37 to 1939-40, a total of 22,466 bovines, one equine and 421 other animals (sheep and goats)
were vaccinated. Anti-anthrax serum has been used every year to protect thousands of animals dur-
ing outbreaks. During 1945-46, when a new brew of the spore vaccine became available from the
Indian Veterinary Research Institute, in addition to routine use of serum and vaccine by the district
staff, these products were specially used in two selected herds. These two tests are described below.
B