H. R.
KAPUR
85
when infected lice were transplanted on a healthy bull but positive when an
emulsion of these was inoculated. Hornby [1926] succeeded only in a single
instance in transmitting rinderpest in East Africa through the bites of Glos¬
sina morsitans. Crawford [1933], in Ceylon, suggested that in the absence
of Glossina the larger biting flies might transmit the disease in India. Working
on this suggestion, Bhatia [1935] was the first to carry out experiments with
Tabanus orientis and Stomoxys calcitrans, using the interrupted method of
feeding. He conducted four experiments with T. orientis, feeding 6 flies in
the first, 8 in the second, 18 in the third with negative results and 36 in the
fourth where he claims to have succeeded in transmitting the disease. With
S. calcitrans, however, his findings were negative throughout. Sen and Abdus
Salam [1937] also report negative results with S. calcitrans. They made 411
experimentally engorged flies (fed singly) to bite a healthy animal over a
period of 23 days and 670 flies (fed en masse) in 6 days, thus bringing the
total to 1081 over a period of 29 days.
The experiments described in this article were carried out with the object
of obtaining an indication as to the extent to which transmission through
biting flies is possible under field conditions, the only species of fly used in
these experiments being T.orientis. The spread of a fly-borne disease
depends largely on the feeding habit of the vector and, since very little is
known about this habit in T. orientis, it was considered desirable also to deal
with this aspect of the problem.
MATERIAL AND METHOD
The flies were mostly secured from the pastures frequented by healthy
buffaloes every morning. They were kept in ordinary mosquito netting cages
and starved for 24-48 hours. A thick layer of absorbent cotton soaked with
water was kept on the roof of each cage and this in turn was covered over with
a damp cloth, in order to provide the flies with a constant supply of moisture.
During the day these cages were partly exposed to sunlight and a few dry
twigs were also placed in them in order to simulate the natural conditions
as far as possible.
After the lapse of the above-mentioned period their wings were clipped
half and they were then fed on a bull artificially infected with rinderpest. The
host, if quiet, was made to stand ; otherwise it was cast and properly secured.
An area about 6-in. × 6-in. on the back in the former and on the abdomen in
the latter case was shaved and wiped clean. The feeding of flies was always
conducted in shade. Six to ten flies at a time were left on the prepared site
and covered over with a glass beaker, a watch being kept to study their
behaviour.
An animal at the height of temperature reaction was selected for providing
the infective feed and used for four consecutive days for feeding the flies and it
was then replaced by another that had been injected with virus four days
previously. The flies that started feeding were allowed about one-and-a-half
to two minutes for the feed and then interrupted. When a fly had actually fed,
a large drop of blood appeared at the site of bite and it was then allowed to
complete its feed on a healthy bull which was kept close at hand. If, however,
B 2