16
THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY. ] VII, I
description of Theileria mutans.
Previous to this, Theileria parasites in
India used to be designated as " small piroplasms ", as distinguished from B.
bigemina or " large piroplasms ", the presence of any of these forms in blood
smears being held to " indicate infection with the causative agent of tropical ' red-
water ' " [Edwards, 1925]. About the same time, Cooper, working at this Insti-
tute, discovered certain structures, indistinguishable from Koch's blue bodies,
in the lesions of bulls that had died after inoculation with rinderpest virus, these
lesions presenting a resemblance to those of East Coast Fever, the blood picture in
these fatal infections having been later characterized by Edwards [1930] as follows :
" Almost 100 per cent of the cells were invaded, often with numerous parasites,
and in some cases the elongated bacillary forms of piroplasms were frequent or
even preponderated, instead of the oval form usually found almost exclusively
in the latent type of infection". Structures, similar to those discovered by
Cooper, have since been not infrequently encountered in this country, both in the
blood and organ smears from acute cases of natural theileriasis in cattle, the
parasite concerned in all such cases having been believed to be T. mutans, which,
as is well known, is of widespread occurrence in the blood of cattle in India. The
conditions under which this species of parasite, which is normally innocuous for the
bovine species, attains the status of a virulent variant for these animals have
been the subject of speculation, and the view has been tentatively advanced that
the parasite might "gain special pathogenic properties in the body of a highly
susceptible host'' [Edwards, 1925], this possibility being suggested by the fact that
Brumpt, in Paris, succeeded in exalting an Algerian strain of T. mutans by passag-
ing it through French cattle that were normally free from infection with this
parasite. It would appear that this was the only position that could be taken at
the time concerning the identity of the parasite, particularly in view of the fact
that all attempts to transmit the disease experimentally were consistently nega-
tive, this being held to be suggestive of the existence of a "carrier" infection in the
majority of the cattle population in, this country.
Since the foregoing observations were published, however, the position in
regard to bovine theileriasis in different parts of the world has passed through a
series of vicissitudes and the problem has now attained a degree of complexity
which is perhaps not shared by any other protozoan disease of animals. In India
itself, a mass of new facts has come to light necessitating a revision of the view
previously advanced in regard to the specific identity of the parasite
involved in fatal cases of theileriasis in cattle. One salient fact that has emerged
out of the controversy that has centred, round the question of the identity of these
parasites is the unreliability of their morphological features as an indication of the
extent of their pathogenicity. As pointed out by Sergent and his collaborators
[1927], the actual pathognomonic element in theileriasis is the presence of the
plasma bodies, so that the question of the specific identity of the theileria parasites
themselves assumes a position of only secondary importance. On the other hand,