8
Rinderpest Immunisation with Goat Virus
actions in buffaloes, however, and the evidence that virus occurs in the blood
and nasal secretion we feel that it would be dangerous to be unduly com-
placent regarding this aspect of the problem.
THE EFFECT OF THE SIZE OF THE DOSE OF VIRUS
As indicated in the introduction many workers attach some importance
to the size of the dose and endeavour to reduce the severity of the reaction
in buffaloes by giving half the cattle dose. They often maintain that this
purpose is effected by so doing. Instructions for use of the Burma desiccated
goat spleen virus recommend greater dilution for use in buffaloes than in
cattle. The idea is not entirely new as in 1917 Schein used a similar proceed-
ing for the double inoculation of cattle and buffaloes in Indo-China to obtain
if possible some regularity of reaction and to avoid undue severity or compli-
cations. Schein used 1 c.c. of virulent blood diluted 1 in 100 with a variable
dose of serum. The method, however, does not appear to have been generally
accepted or utilised. Experience with experimental infection and double
inoculation with bovine virus would not lead one to expect that as crude a
variation of the infecting dose as 0.5 c.c. of blood or spleen suspensi n for
buffaloes as opposed to 1 c.c. for cattle would have any regular effect on
the resulting reaction. Our experiments have borne out this anticipation
(Table II). Thus, of three buffaloes vaccinated with 0.25 c.c. spleen suspen-
sion two died, while of three vaccinated with 0.5 c.c. again two died and in
this case the third animal appeared to have been immune before the experi-
ment. The tables in general bear out the contention that the size of the
dose affects but little the course of the reaction. If, however, dilution is
carried further and a dose bordering on the minimal infective dose is arrived
at then some modification of the resultant reaction appears to occur. Some
authors maintain that a dose approximating the M.I.D. will result in a
lengthening of the incubation period and perhaps enhance the chances of
recovery. Our experience supports this view but regularity of reaction can-
not be relied on by this means and death from rinderpest has occurred with
as small a dose as 0.001 c.c. of goats blood (Table II). The short series of
buffaloes receiving 0.1 c.c., 0.01 c.c. and 0.001 c.c. may be worth recording
in greater detail. There appeared to be some lengthening of the incubation
period with the animal receiving a dose of 0.1 c.c. which showed no marked
symptoms until the tenth day and with the animal which received 0.01 c.c.
as he also showed little until the ninth day. In the case of the animal which
received 0.001 c.c., however, symptoms commenced on the sixth day and
death occurred on the nineteenth ; in fact the temperature chart of this animal
is very closely parallel to the control animal which received 5 c.c. of the same
goat's blood. Even if in the majority of cases a very small dose increases
the length of the incubation period it is by no means assured that such a
prolongation does make for a greater recovery rate or a happier convales-
cence. There is also the disadvantage that failure to infect and so immunise
may be the result of such an endeavour and the length of life or activity of
a virus may be prejudiced under field conditions. A convenient working
dose, many times the minimal, therefore appears best for field inoculations.