306
'Lahore Canine Fever' and 'Tick Fever' of dogs
A dog was, accordingly, inoculated with a pure strain of T. evansi and destroy-
ed at the point of death, after showing a syndrome typical of the infection.
The lesions of this disease affect chiefly the haematopoietic tissues, liver, spleen
and bone marrow, and are consequent on a rapid destruction of erythrocytes in
the circulating blood, with a profound secondary anaemia not clinically unlike
that seen in a pure P. gibsoni infection. The spleen and liver were markedly
enlarged and the bone marrow hyperaemic. Sections of these tissues, stained
by Heidenhain failed to show any of the bodies described. Similarly, tissues
of the hill bull which had succumbed to a Babesia infection were examined with
negative results. It appears, therefore, that these bodies are specific for
' Lahore Canine Fever' and. artificially produced P. gibsoni infection, and as
ring forms of P. gibsoni are so frequently absent, or at least not found, in such
infections, one is led to question whether these bodies do not represent a phase
in the development of the life-cycle of P. gibsoni. When the infrequency, or
complete absence of parasites from the circulating blood is considered in rela-
tion to the development of a type of anaemia indicating early involvement of
the haemopoietic tissues, it appears a natural assumption that P. gibsoni is
essentially a parasite of the reticulo-endothelium of the haematopoietic tissues.
The appearance, of P. gibsoni in the circulating blood would, in these circums-
tances, be regarded as fortuitous. This is an aspect of the problem, however,
which further protozoological study alone can decide. Suffice to say that in
Puppy No. 15 which was inoculated with emulsion prepared from spleen of
Puppy No. 12 in which ring forms of P. gibsoni could not be found and these
bodies were numerous, a typical infection resulted, in which P. gibsoni was
found.
DISCUSSION
The literature on ' tick fever ' due to P. gibsoni is small, little work has
been done on the pathology and practically none on the histopathology of the
disease. In spite of this, it is difficult to explain the confusion which has existed
in the correct interpretation of a disease possessing the syndrome of ' Lahore
Canine Fever.' This is a disease showing striking evidence of haematopoietic
involvement, similar to that encountered in an authentic case of ' tick fever '
and yet there has been, on the part of previous investigators, a reluctance to
classify this disease as ' tick fever ' due to P. gibsoni.
There appear several reasons for this. Sufficient attention has not been
paid to the fact that, in true ' tick fever ' the presence of P. gibsoni in the cir-
culating blood is extremely erratic. It may be found only once or twice during
an extended attack of disease, or not at all. In Patton's [1910] original note
on the subject, he drew attention to the periodicity of the infection present in
the erythrocytes and Symons [1926-27] in the protocols of his excellent publica-
tion, clearly indicated the infrequency of parasites in the natural disease.
It appears to have been assumed that, because in the allied infection due to
P: canis, in which the blood always contains parasites in increasing numbers
throughout the course of the disease, the same observation must be true of a
P. gibsoni infection.