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'Lahore Canine Fever' and 'Tick Fever' of dogs
degree of resistance exhibited by pariah crosses is noted. The resistance to
infection and the likelihood of recovery can be computed, within reasonable
limits, on the basis of the percentage of pariah blood in the cross. There are
strong grounds for suspicion, therefore, that pariahs are the natural sources
of infection.
A definite seasonal incidence exists in ' Lahore Canine Fever.' The
smaller incidence occurs during the beginning of the hot season, i.e., from the
middle of March to the end of May and the greater towards the end of the hot
weather, i.e., from the middle of September to the first or second week in
November. Very few cases have been encountered in the real hot season.
This interesting observation immediately afforded a clue in the investiga-
tion. The periods noted synchronise with the two tick seasons, and it very
quickly became obvious that ticks were of important significance in the spread
of the disease. The first question that naturally presented itself seemed legiti-
mate—Is this disease ' tick fever' ? The answer, on available evidence,
appeared negative. Routine examination of blood films was consistently
negative in the great majority of cases. As this constituted, at the time, the
sole available criterion on which to formulate a diagnosis, a negative diagnosis
of ' tick fever ' was made and the etiology sought elsewhere.
It must be mentioned, however, that in a few cases, presenting identical
clinical symptoms, a diagnosis of ' tick fever ' (P. gibsoni infection) was made.
This finding immediately led to the question—Are all cases of clinically com-
parable canine fever referable to one etiological factor, P. gibsoni, and is the
natural deduction tenable that blood film examinations of suspected cases are
an unreliable means of determination of infection ?
The main purpose of this paper is to produce evidence that' Lahore Canine
Fever ' is, in actual fact,' tick fever ' (P. gibsoni infection), in a form that can
only be diagnosed with extreme difficulty, and to show that the accepted
methods of diagnosis by routine blood film examination are unreliable.
Mention must be made of the earlier experimental work and attempts to
reproduce the disease in young pariah pups by blood transmission from diseas-
ed dogs. These experiments were unsuccessful, owing to the relative insuscep-
tibility of such experimental subjects, as has already been stated. The injec-
tion of even large quantities of blood failed to reproduce the disease and it was
presumed therefore that:—
(a) the disease is not inoculable, and
(b) the disease is not ' tick fever '.
That this was a premature and unwarrantable presumption is suggested on the
grounds that, in a true P. gibsoni infection the blood is not uniformly infective.
Although the animal from which the blood is taken is known to be a positive
clinical case, there are phases of the disease when parasites are certainly not
present in the blood, (See Charts) and the failure to transmit infection to sus-
ceptible animals—and earlier experiments were done on pariah dogs—can
easily be explained. Even in direct transmissions with blood known to contain