238
Respiratory
Diseases of the Horse
already ( 1887 ) perfectly familiar with the strepto-
cocci. Ostertag [1908, cit. Mitscherlich, 1941]
also isolated gram-negative ' diplo-streptococci'
from the lungs of horses affected with brustseuche.
It can be concluded from the work of Mitscherlich
[ 1941 ], which will be discussed later, that there is
a gram-negative diplo-streptococcus which is patho-
genic for the horse and which in some ways resembles
a true streptococcus. It grows best in a medium
containing blood- or serum. On blood agar plates
dry pin-point colonies surrounded by hæmolytic
zones are produced, and a, flocculent deposit, leaving
a clear supernatant, fluid, is formed in 1 per cent,
serum broth. Continued cultivation is difficult and
cultures usually die out. It is not pathogenic for
guinea-pigs, but usually kills mice in from one to
five days, and necrotic fecci were sometimes observed
in the liver. It would appear that this organism
has several points of resemblance to the Neisseria
group of organisms, which includes the meningo-
coccus and gonococcus, as described by Topley and
Wilson [ 1936 ].
Despite the foregoing discussion, streptococci
were the ultimate cause of the pneumonia in the
series of cases reported by M'Fadyean [ 1938], and
recent work in this country and abroad has clearly
demonstrated the important part played by group
' C' streptococci in respiratory and other diseases
of the horse. Lignière's conclusions that pastenrella
organisms were the primary cause of equine
contagious pneumonia has already been mentioned.
Webb [ 1909 ] isolated pure cultures of pastenrella
organisms from the lungs of horses and donkeys
dying from pneumonia, but the clinical history of
the outbreaks suggests that the virus of contagious,
equine pneumonia was the primary ætiological agent.
The extensive researches of Bemelmans [ 1921 ]
indicate that, whilst pasteurella organisms may be
isolated from cases of infectious pneumonia, diplo-
streptococci, staphylococci or pseudo-pyocyanca are
found more frequently.
It appears that under varying conditions of time
and place any of the above organisms may complicate
the virus infection of contagious pneumonia. It is
therefore not surprising that there was great con-
fusion at a time when bacterial classification had not
been standardized, and in the early accounts it is
difficult to decide with any certainty which organism
is actually being described.
INFECSTIOUS CATARRH
(Equine infectious bronchitis, epizootic laryngetracheites,
epizootic cough, Hoppegarte cough, Brussels disease,
skalma)
Waldmann and Köbe [ 1936 ] described a highly
infectious virus disease characterized clinically by
a dry, strong cough as its chief symptom, and
pathologically by lesions of bronchitis and peri-
bronchitis. In horses kept under good conditions
the disease usually ran its course as a pure virus
infection, but when the preliminary symptoms were
overlooked, and animals were not specially cared
for, serious complications, such as broncho-pneu-
monia and pleurisy, occurred, due to invasion of the
lungs by streptococci, sometimes followed by death.
Horses were infected by the intranasal inoculation
of lung filtrates and the disease was also transmitted
to pigs and cattle. Recovered animals showed at,
least a partial immunity. Oprescu [ 1938 ] des-
cribed a similar disease which could be trans-
mitted by the subcutaneous inoculation of
blood.
It is probable that infectious catarrh is similar
to the condition known to the older German writers
as skalma, and apparently various types of the
condition are now prevalent amongst German army
horses. Mitscherlich [ 1941 ] studied an outbreak
affecting 176 out of 240 horses. He states that this
disease can be differentiated from :
(1) Strangles by the presence of purulent nasal
catarrh and the infrequency of lymph-node swellings
and abscess formation.
(2) Brustseuche: in this disease there is a
longer incubation period, a more prolonged fever
and usually a red-brown nasal discharge and dull
areas in the lungs. At autopsy there is a serious
effusion and a thick fibrinous deposit on the pleura
which is not seen in respiratory catarrh.
(3) Influenza, in which there is a marked morning
recession of the fever, swelling of the conjunctiva,
œdema of the breast and intestinal catarrh.
Blood taken during the febrile stage produced the
disease when inoculated intravenously into another
horse, but both the early serous and the latter
' grey-white ' nasal discharge failed to cause the
disease when introduced into the nasal cavity of a
horse. Staphylococci were isolated from the serous
nasal discharge, but when once it has assumed the
characteristic grey-white colour gram-negative diplo-
streptococci were found in about 50 per cent of the
examinations. This organism was also isolated
from the lungs of four horses which died of broncho-
pneumonia. Bacillus abortus equi was also isolated
from one of the cases and staphylococci from each of
the others. A pure culture of the grain-negative
diplo-streptococcus produced purulent rhinitis in a
horse which nad just recovered from a simple virus
infection. It was concluded that this organism, the
chief characteristics of which have already been
described, was the most important secondary bacteria
invader and that it is probably similar to an organism
isolated by the early workers from cases of
brustseuche. Traub [ 1941 ] isolated group 'C
and Seeleman [ 1941 ] groups ' C ' and ' D ' strep
tococci from cases of this disease.