36
Respiratory Diseases of the Horse
The question of secondary bacterial invasion is somewhat confused. M'Fadyean [1938]
assumed that the organisms isolated by Schutz [1887] and used in his attempts to produce
brustseuche were typical streptococci. This appears to be incorrect, for an examination of the
original artical shows that the organism was a gram-negative bacterium which often occurred
in pair and was usually encapsulated. Friedberger and Frohner [1908] also state that the
' diplo-bacteria ' of Schutz are gram-negative. It can be concluded with reasonable certainty
that these were not pasteurella organisms. Nocard and Leclainche [1903] say that although
the organism was originally described as gram-negative, it is now known to be gram-positive.
This cannot be accepted, however, because his article on strangles [Schutz, 1888] makes it quite
clear that he was already (1887) perfectly familiar with the streptococci. Osterag [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 pathogenic for the
horse and which in some ways resembles a true streptococcus. Its 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 focci 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, and 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. Ligniere's conclusions that pasteurella organisms were the primary
cause of equine contagious pneumonia has already been mentioned, Webb [1909] isolated pure
cultures of pasteurella organisms from the lungs of horses and donkeys from pneumonia, but the
clinical history of the outbreaks suggests that the virus of contagious equine pneumonia was the
pirmary ætiological agent. The extensive researches of Bemelmans [1921] indicate that, whilst
pasteurella organisms may be isolated from cases of infectious pneumonia, diplostreptococci,
staphylococci or pseudo-pyocyanea 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 confusion 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.
INFECTIOUS
CATARRH
(Equine infectious bronchitis, epizootic laryngetracheites, epizootic cough, Hoppegarte cough,
Brussels disease, stnalma.)
Waldmann and Kobe [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
peribronchitis. 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-pneumonia 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 trasmitted
to pigs and cattle. Recovered animals showed at least a partial immunity. Oprescu [1938]
described a similardisease which could be transmitted by the subcutaneous inoculation to blood.
It is probable that infectious catarrh is similar to the condtion 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