J.
A.
IDNANI
219
reached because no animals infected with the
virulent strain of rinderpest virus lived beyond
10 days.
An experiment was made to test the role of
breath as transmitting agent in a closed atmos-
phere without direct transpiration. A hill bull
artificially infected with line E rinderpest virus
was allowed to breathe in the closed trevis
within a length of six feet on the sixth day
after inoculation. The infected animal was
removed after six hours and a healthy bull was
secured in its place and detained for 15 minutes.
This animal developed typical rinderpest and
died on the 12th day.
Less virulent strain
The strain used was the line D virus, men-
tioned above. The first experiment was com-
menced on the fifth day at a distance of six
feet, the exposure lasting six hours. The
healthy animal so exposed remained unaffected
for the next 26 days and was then re-exposed
to an infected animal on the sixth day under
similar conditions. No reaction ensued during
the following 13 days and the animal reacted on
test. Evidence confirming these findings was
obtained in three other experiments with line D
virus. In the first two of these, two healthy
bulls were exposed, one on the fifth and one
on the sixth days, while a third was exposed
daily from the sixth to the ninth day. The
exposure in all cases was for six hours at six
feet, but no transmission occurred and all
experimental animals reacted on test.
Goat-adapted strain
In view of the large-scale vaccinations against
rinderpest being carried out in India with goat
vaccine' virus, the infectivity of the expired air
of a bull inoculated with goat virus was tried.
A healthy animal was exposed to an infected
bull daily from the sixth to the ninth day for a
period of six hours at a distance of six feet.
The disease was not transmitted and the exposed
bull later proved susceptible. Similar results
were obtained in two more such experiments,
although in one case the distance was reduced
to four feet.
DISCUSSION
Certain viral and bacterial diseases of man and
animals, such as influenza, tuberculosis, con-
tagious pleuropneumonia of bovines and distem-
per of dogs, are known to be communicable
through the nasal chambers and preventive
measures in such diseases primarily consist of
segregation of victims. Of the many problems
that confront the veterinary worker in the field
there is none so important as that of the spread
of disease and a thorough knowledge is necessary
of the means by which dissemination takes
place. In the case of rinderpest, experimental
evidence brought out in this paper, shows that
expired air of infected animals can play a part
in spread and may explain the contact infections
recorded in the literature. This finding further-
strikes a note of caution to those engaged on
researches of a similar nature to avoid vitiation
of their experiments by this hitherto unknown
route.
Such conditions, it must be admitted, as have
made it possible to prove the role of breath as
a transmitting agent in rinderpest, are perhaps
unobtainable in all outbreaks of the disease,
but it cannot be denied that in most of the rural
areas in India cattle are housed in narrow enclo-
sures and through lack of proper understanding
of animals hygiene, sick animals are frequently
kept together with the rest of farm stock, thus
facilitating dissemination of disease.
The differing behaviour of the virulent and the
two less virulent strains of virus raises the
much discussed question of dose and virulence
as factors in the successful implantation of a
virus on susceptible tissue.
The existence of three factors, viz., distance,
period of exposure and stage of the infected
animal, which determine whether transmission
is or is not successful, at any rate in the case
of line E virus, supports the view that much
diffusion of the infective agent takes place in
the air currents between an infected and a
healthy animal. The problem of the degree of
subinfective dosage required to initiate an infec-
tion is worthy of assessment, but for financial
reasons even a preliminary test to compare the
virulence of line D virus with that of line E
virus in terms of minimum infective dose has
been withheld for the time. The present small
investigation was limited to the question of
whether rinderpest can be shown to be easily
communicable by the expired air of infected
animals. Now that this has been established,
the examination of details can be undertaken as
facilities permit.
Much work has been done to explain airborne
infections of man. Thus Dudley [1928], in
defining the infective range of droplets expel-
led from the nose or mouth, states that some of
these droplets are visible and contain many
cells and hundreds of bacteria, while others are
of microscopical dimensions with only a single
cell and one or two bacteria. Heavy particles
drop to the ground within two or three feet as
the propulsive force of expiratory effort ceases,
but smaller droplets may remain suspended for
some time according to the atmospheric humidity