256
Agglutination Test for Brucella Infection in Cattle
tionship to antibody production, serum-virus
neutralization and immunity reactions, than
the latter. It has already been demonstrated
that the chick embryo strain of encephalomye-
litis virus can be utilized for immunization
purposes far more effectively than the other
strams. But whether this is due alone to the
great concentration of the virus in the chick
embryo or to the concentration together with
a change in the character of the virus itself,
acquired by sojourn in the chick embryo, is at
present an open question.
One more virus disease may be mentioned
in concluding this short discussion, namely, in-
fectious equine anaemia, which has points of
special interest. It is a highly infective but
non-contagious disease,
septicaemia-like in
character, appearing in either an acute or chro-
nic form and marked by recurring febrile periods
which, in the early stages, take place at remark-
ably regular intervals of approximately 21 days
and are suggestive of a cycle not unlike that of
certain protozoan infections. The virus is
present and apparently multiplies in the circu-
lating blood and has no known special affinities
for cellular tissues. The minutest quantity of
blood will transmit infection and disease to a
healthy horse, and this, with other observations,
has led to the strong suspicion that an insect
host or vector is responsible for the natural
transmission of the disease.
Horses which recover from the disease, and
they are many, are apprently immune from
further attack but may carry the virus in their
blood for the rest of their natural lives and thus
become virus reservoirs. As an instance, a
horse which had recovered from the naturally
contracted disease when about five years of
age, lived the remainder of its life at one of our
research stations, passing 20 years of age. At
intervals during that whole period its blood
proved highly infective for horses and repro-
duced the typical disease. The fact that
apparently normal healthy horses may be and
frequently are carriers of infectious-anaemia
virus is not to be overlooked when horses are
used for the production of anti-sera intended
for either human or animal use.
Inability to infect any species of laboratory
animal or to propagate the virus of infectious
equine anaemia under laboratory conditions
has hindered the investigations we have carried
on for 25 years. But with improved methods
of study recently introduced and experience
gained with regard to susceptibility of mouse,
ferret and chick embryo to virus infections,
there are increasing possibilities of propagating
this virus in the laboratory and of studying it
to better effect.
Many other diseases in which the etiological
agent is filterable and ultramicroscopic occur
in North America. Many more, unknown on
the North American Continent, are frequent in
either Europe, Asia or Africa. These virus
diseases are just as important, economically,
as the diseases of known bacterial origin, with
which they have much in common. The view
that viruses are animate, particulate elements
and agencies appears to be well taken and
doubtless will be held until satisfactory evi-
dence to the contrary has been produced.
Their orderly classification, powers of multipli-
cation and adaptation, as well as other inher-
ent properties and affinities will for a consider-
able time to come hold the attention of virolo-
gists and, perhaps the interest and scrutiny of
geneticists.
THE STANDARDIZATION AND INTERPRETATION OF THE AGGLUTI¬
NATION TEST FOR BRUCELLA INFECTION IN CATTLE*
By W. L. HINDMARSH, B.V.Sc., M.R.C.V.S., D.V.H., Veterinary Research Station, Glenfield, N. S. W
THE Secretary of Section L has asked me to
lead the discussion on the subject of "What
constitutes a reaction to the agglutination test
for contagious abortion?" At first glance it
might appear that a certain degree of agglu-
tination and sedimentation of the bacteria
constitutes a reaction, but in the diagnosis of
infection the matter is by no means so simple.
It appeared to me, therefore, that a general dis-
cussion of the development of the test and the
various factors involved would be of some value.
Topley [1933] records that agglutination of
bacteria was first described by Gruber and
Durham in 1896. Grunbaum [1896], Widal
[1896] and Widal and Sicard [1897] recognized
the value of the test for the diagnosis of typhoid
*Reprinted from the Australian Veterinary Journal, Vol. XVI, No. 1, February 1940