JOHN
FRANCIS
241
knowledge on the subject'. Pillers and others (1934)
also discussed the difficulty of differentiating strangles
from the various catarrhal affections of horses.
Beller and Traub [ 1941 ] noted that strangles
and infectious catarrh might occur together in the
same horse and after a very careful study put
forward the interesting suggestion that they are
both primarily due to the same virus and that the
different symptoms are due to different secondary
invaders or predisposition of the horse. Rexroth
[ 1941 ] as a result of clinical and pathological
investigations, supported this view.
Lührs [ 1933 ], whilst admitting that no one can
mistake true epidemic equine influenza, states that
there are many outbreaks of disease which one cannot
easily classify, and Law [ 1902 ], who was obviously
familiar with the epidemic disease, says that in
the slighter cases the lesions are often confined to
the anterior part of the respiratory organs which are
congested and red, the lesions may extend to the
bronchi. In human medicine there are similar
differences between epidemic and sporadic influenza,
and, although in some outbreaks influenza ' A ' or
'B' virus can be identified, in other clinically identical
outbreaks no virus can be isolated.
It would appear that, whilst the main clinical
entities—strangles, infectious catarrh and influenza
-can be recognized, we still do not know whether
they are caused by closely allied or distinct viruses.
SUMMARY AND CONCLUSIONS
An attempt has been made to assess the evidence
concerning the ætiology of the equine respiratory
diseases, and it is tentatively concluded that con-
tagious pneumonia is a distinct entity primarily
due to a virus. There is no doubt that viruses are
also responsible for outbreaks of infectious catarrh
and influenza, and probably also of strangles.
It appears possible that strangles and infectious
catarrh are both primarily due to the same or a
similar virus, and there is no evidence which proves
beyond doubt that the virus of influenza is distinct.
In any of the above diseases the uncomplicated
virus infection may pass almost unnoticed, although
producing immunity to subsequent infection.
Climatic conditions and methods of management,
however, have a great influence on the course of the
disease; under adverse circumstances, a variety of
bacteria may produce serious complications, and
there is little doubt that individual animals may
develop more or less characteristic symptoms when
suffering from a simple bacterial infection.
The results reported by Stableforth [ 1939 ],
Hignett [ 1940], Hignett and King [ 1940], as well
as other workers abroad, has demonstrated the value
of the sulphonamide group of drugs in the treatment
of pneumonia. The apparent specific action of
heosalvarsan and the sulphonamide group cannot,
however, be accepted as evidence that bacteria are
the primary ætiological agents. Methods of im-
munization, if they could be evolved, might be
effective and economical.
During the last great war it would appear that
research was carried out by a few enthusiasts, but
Edwards [ 1935b ] has said that the need for a trained
research cadre attached to the R.A.V.C. was ap-
parently not realized until the end, and it never came
into being ; a great opportunity to investigate the
respiratory disease of the horse was lost.
Knowledge concerning the viruses, hæmolytic
streptococci, methods of drying and preserving
biological materials, and the technique of investi-
gating respiratory diseases has greatly improved
since the last war. It is also felt that one of the
three methods which have been used to prepare
swine-fever vaccine [ see Francis, J. 1941 ], two of
which have also been successfully used in the control
of rinderpest, might very well be adapted particularly
for the preparation of an equine influenza vaccine.
In this disease, and possibly also in infectious
catarrh, virus is known to circulate in the blood.
It appears, therefore, that if the need arose, and
the necessary facilities were granted, an efficient
research cadre working in conjunction with clinicians
could do much to clarify our knowledge of equine
respiratory diseases and possibly evolve methods of
specific immunization. One gains the impression
that the clinical and pathological investigations
which are being carried out by the German Army
veterinary services are of a high standard. It is
pleasing to note [ J.A.V.M.A. 98: 254 ] that progress
is being made, at the U.S. Army Veterinary Corps
Laboratory, Front Royal, in the study of various
respiratory diseases of the horse and that vaccines
against influenza and strangles are being developed.
I am indebted to Dr J. T. Edwards for assistance
in the preparation of this article. I should also
like to thank the staff of the Imperial Bureau of
Animal Health and the library at Weybridge for
assistance in obtaining references and literature,
and Lieutenant-Colonel R. H. Knowles for permis-
sion to use the library at the R.A.V.C. Laboratory.
REFERENCES
Anon. (1941). " Equine Influenza, a Virus Disease"'
J. Amer. Vet. Med.. Ass. 98 : 82
Arnold, T. E. (1931). "Strangles". J. Ryl. Army Vet.
Corps 3 : 65-74, 109-119
Arnold, T. E. (1933). "Strangles, Principals of Causation
and Control ". Ibid. 5 : 6-15
Bazely, P. J., and Battle, J. (1940). " Studies with Equine
Streptococci ". Aust. Vet. J. 16 : 140-146
Beller, K., and Traub, E. (1941). "Present Position of
Investigation into Infectious Catarrh ". Zeit, Veterinark
53 : 88-97. (Abst. Vet. Bull. 12 : 374)
Bemelmans, E. (1921). " A Comparison between Human
Influenza and Equine Contagious Pneumonia". Rev.
Gen. Med. Vet. 30 : 337-391, 444-462. (Trans. J.A.V.M.A .
61 : 646 ; 62 : 52)
K 2