8
Problem of Equine Strangles in India
this result has only been attained at the price of
much acute sickness and possibly severe setbacks
in bodily condition. Fortunately, on the other
hand, the population will not have been
much depleted by death, since strangles is not a
killing disease. The misfortunes that may befall
our batch of 60 horses will perhaps be aggravated
by the arrival at intervals of similar batches,
which, although distributed in other paddocks,
are still lodged within the area set apart for
segregation.
We may now add some comment on the above
hypothesis. The suggestion that most of the
animals in a group will soon become infected is
supported by the history of events at Mona and
Sargodha where the annual attack rate has tended
to be so high. Incidentally, by analogy with
what is known of scarlet fever a seasonal rise in
the carrier rate would be expected in the autumn
and winter months.
It has frequently been said that the increasing
prevalence and severity of cases during an epidemic
may be due to the increasing infectivity and viru-
lence of the parasite during its passage from host
to host. There is, indeed, some evidence for the
existence of special epidemic strains in some
streptococcus infections of man. These are
strains which are endowed with a highly-developed
power of spreading among susceptible people
and of killing them. There is also some evidence
of the sudden appearance of hypervirulent strains
in the case of normally slow-spreading streptococ-
cus epidemics in small animals. In the case of
strangles also some increase in infectivity (in-
vasiveness), together with some increased power
of causing tissue damage, cannot be ruled out
but on that point there is no information. How-
ever, environmental factors acting upon the
host, as well as the simple congregation of in-
fected and susceptible animals is well known to be
sufficient by itself to enable epidemics to progress,
so that it is unnecessary to look for special
properties in the parasite.
It has been suggested above that the streptococ-
cus of strangles in different animals may produce
a healthy carrier state, a simple nasal catarrh
or typical strangles. Possibly, ideas regarding
this are now changing, but we may note in the
first place the analogous cases of 'snuffles' in
rabbits. 'Snuffles' is the clinical term for a
common disease condition of rabbits, caused by a
pasteurella and associated with pus in the nasal
sinuses, and accompanied by nasal discharge and
sneezing. Webster [1924] has shown how healthy
rabbits, i.e. rabbits free from pasteurella, vary in
their response to the nasal instillations of the
same amounts of living cultures of the organism.
Such rabbits may show (a) no response, (b) a
'healthy' carrier state, (c) 'snuffles' or (d) pneu-
monia or death, the result of the experiment in the
individual animal depending on its resistance.
Since we are dealing here with a respiratory
affection, the analogy to strangles is apt. Still
more apt is the case of outbreaks of respiratory
streptococcus disease in man where the same
infecting agent may produce (a) a healthy carrier
state, (b) a feverish catarrh, (c) tonsilitis of
varying severity, and (d) scarlet fever. Recent
researches on equine affections in Australia by
Bazeley and Battle [1940] have provided some
direct proof in showing that at least some of the
streptococcus strains from simple catarrh are
identical by agglutination and other tests with
those from strangles. They isolated 457 strains
of haemolytic streptococci from 415 cases
of disease in horses. All these belonged to
serological group C of Lancefield and by aggluti-
nation could be split into five main types. Although
the authors find that the specific types of equine
streptococci do not always appear to be associated
with specific diseases, it may be noted that all the
strains from fresh strangles abscesses—45 in
number—and 58 of 260 strains from pure res-
piratory catarrh cases belonged to the same
agglutinative types. Incidentally, it may be
observed that a study of the factors involved in
the spread of 'snuffles' and of lymphadenitis in
guinea-pigs—a strangles-like disease which occurs
naturally in these animals and caused by group C
streptococci [Seastone, 1939]—might provide valu-
able data in connection with strangles in horses.
Control of strangles. The final point to be
considered is whether any particular steps can be
taken to reduce the incidence of strangles in the
depots or to reduce the severity of cases.
In the case of our particular problem, there are
two fundamental considerations: firstly, that it is
not a question of trying to eliminate the disease
altogether, and, secondly, that any practicable
means of immunization must await the outcome of
academic research.*
Here it may be pointed out that the problem of
streptococcus disease in human beings is recog-
*Recent work appears to have brought this desideratum
nearer. While it has been shown, for instance by Stamp
[1.936], that some degree of type-specific immunity
against haemolytic streptococci can be produced in rabbits
by the use of broth cultures killed by heat, Loewenthal
[1938] has pointed out that very young cultures, which
consist mainly of capsulated organisms, ought to be used
and that the heat for killing them must be very cau-
tiously applied. Bazeley [1940, 1942] in Australia has
now proved that by similar methods a vaccine can be
prepared from strangles streptococci. He has shown that
this vaccine is capable of affording some immunity to
mice, that a protective serum can be prepared by its use
in rabbits, and that it has definite immunizing power
in horses. The possibilities of successful immunization
are thus distinctly promising.