J. A.
IDNANI
217
membrane with infected materials. Hutyra
and Marek [1938] suggest that "the infectivity
of the expired air is at least questionable".
In this paper are described a series of experi-
ments to test the infectivity of the expired air
of bulls inoculated with rinderpest.
METHODS AND MATERIALS
To produce optimum conditions under which
expired air from an infected animal would be
inhaled by a healthy one a wooden trevis was
improvised to secure the experimental animals
(Fig. 1). At each end a sliding trap door was
provided to secure the animals by the neck, so
that they could be made to stand facing each
other. The neck trap at one end was movable
so that the distance between the animals could
be adjusted as required. The whole structure
was covered with tarpaulin to allow reasonable
ventilation.
Prior to experimentation, all animals used
were trained to stand in the trevis without
fidgeting for six hours with an interval of two
hours for food and rest.
The viruses used were (a) a highly virulent
field strain, termed line E, (b) a strain, termed
line D of lower virulence and (c) a low virulent
goat-adapted strain. Line E was obtained from
an outbreak in a Village near Mukteswar in
1939, and it has since been maintained by
monthly passage through the medium of spleen
tissue collected on the fifth day after inocula-
tion. In the interval the virus is stored in the
refrigerator. The mortality among hill bulls
treated with this strain is over 90 per cent.
Line D has been maintained at the Institute for
about twenty years and now causes approxi-
mately 12 per cent deaths. The goat-adapted
strain was evolved at this Institute in 1927 by
implantation of rinderpest virus of bovine origin
on the foetal tissues of pregnant goats and then
recovering from maternal blood.
After exposure in the experiments, each bull
was kept in a chuppur for individual isolation.
The influence of relative humidity as a factor
in the transmission of rinderpest by breath was
investigated. It was found that the difference
between the relative humidity of atmosphere
outside and inside the trevis was 10 per cent
when a normal bull was exposed; but when a
bull infected with the virulent strain was allow-
ed to breath for six hours the difference was 6
per cent. With a bull infected with the less
virulent strain the difference was 8 per cent.
TRANSMISSION EXPERIMENTS
Hall [1935] in a series of tests carried
out to campare the virulence
of
blood
with that of nasal secretion taken at the height
of temperature found that whereas the mini-
mum quantity of blood capable of causing infec-
tion at that time was 0.002 c.c., nasal secretion
in 1/10th of that amount was infective. At this
Institute blood for experimental purposes is taken
on the fourth day after inoculation, if the tem-
perature reaction is typical. The first transmis-
sion experiment was therefore commenced on the
fourth day after inoculation. On this day a
healthy bull was exposed for three hours to an
infected animal at a distance of ten feet. No
reaction ensued during the next 13 days. The
same animal was then re-exposed to another
infected bull on two consecutive days (4 and 5)
for four and six hours respectively, the distance
between the two being reduced to five feet. Five
days after the second exposure a rise in its
temperature was recorded and the animal sub-
sequently showed
symptoms of
rinderpest.
These experiments showed that rinderpest can
be transmitted by the breath and that in the
first trial the exposure was too short or the dis-
tance too long (Table I).
In the next attempt a healthy bull was
exposed to an infected animal on the fourth and
fifth days for four and six hours respectively at
a distance of ten feet. No infection occurred
and the healthy bull later proved susceptible to
test with virulent blood. This result indicates
that the distance between sick and susceptible
animals has something to do with the dissemi-
nation of cattle plague. At a further trial at
a distance of eight feet between a healthy and
an infected animal on the fourth day after in-
oculation, the disease was not transmitted after
an exposure of six hours.
After these preliminary trials, an investiga-
tion was designed to limit the three factors, viz.
stage of fever, period of exposure at which
rinderpest can be transmitted through expired
air, and distance. As to the stage of fever
it is known from many tests with virus-producers
that the first rise of temperature occurs on the
third day. Healthy bulls were therefore expo-
sed—from the third to the sixth day, exposure
and distance being kept constant, viz. at six
hours and six feet (Table I),