ABSTRACTS
Prevention of ovine mastitis by the use of staphylococcus toxoid.
F. C. MINETT (1939). J. Comp. Path. 52, 167
R ECENT knowledge on the rôle of antitoxin in staphylococcal immunity had not
been exploited to ascertain if the course of infection in staphylococcus mastitis in
animals can be modified through prior intervention with toxoid. The author has, there-
fore, now tried to supply experimental data on the point. The sheep was employed as
the experimental animal for testing the extent to which specific toxoid treatment might
modify the course of acute staphylococcus mastitis and in order to gain experience of the
kind of toxoid that should be used and the antitoxin response likely to be aroused.
It is essential to note that the sheep for use in these experiments were selected after
a preliminary titration of their blood sera for natural staphylococcal α—antitoxin.
Only those with low titres of antitoxin were selected for experiment. In some experi
ments, however, sheep with higher antitoxin level were used for toxoid treatment, as it
was anticipated that the toxoid treatment might act as a secondary stimulus in such
sheep and so lead to a higher state of immunity.
Two types of toxoid were used for immunisation trials, a formalised toxoid and an
alum-precipitated toxoid. The toxoids were used subcutaneously and where two doses
were given, an interval of about 3 weeks was allowed. After an interval of about 10
days after injection of the first or second dose of toxoid, the treated animals along with
an adequate number of controls were tested for immunity by instilling into one or both
sides of the udder a mixture of toxin and living culture of a virulent staphylococcus. In
one experiment the interval was prolonged to about 3 months to see if immunity could
be demonstrated after that interval.
Samples of serum were collected from the experimental animals before coming under
experiment and again at intervals after treatment with toxoid and after administration
of the test dose, with a view to follow how the level of anti-toxin in these animals fluctuat
ed and how these fluctuations were correlated with the state of the resulting immunity.
In the article the results as regards these fluctuations are summarised in tabular form and
again illustrated graphically; also the degrees of resulting mastitis are illustrated dia¬
gramatically.
In all, five experiments were conducted and they were designed to test the relative
efficacy of the following methods of immunisation: (1) single large dose of formal toxoid ;
(2) two large doses of formal toxoid ; (3) single small dose of alum-precipitated toxoid ;
(4) two small doses of alum-precipitated toxoid ; (5) a single large dose of alum-precipi
tated toxoid; and (6) two large doses of alum-precipitated toxoid.
The following observations were made :—
(1) Following the injection of the test dose, control sheep took very little food
during the first three or four days. The day after injection they suffered
from some degree of lameness which persisted for a few days in some of
them. The udders were swollen and tense and many sheep suffered from
necrosis of the tissue and skin of the udder. A few even died or had to be
destroyed on humane grounds. But in animals submitted to treatment
with toxoid the general effects were reduced to a considerable extent.
Unprotected sheep with low antitoxin titre suffered more severely from the
test inoculation than those with higher titres.
(2) In some experiments there was a relationship between the size of the local
reaction following the test inoculation and the subsequently developed
serum titre. It was in the direct ratio in control sheep and in the inverse
ratio in the immunised sheep. Thus in the control group the local reaction
was largest in animals which later showed a high antitoxin response. In
the toxoid group the higher antitoxin response was associated with smaller
local reactions.
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