154
Transmission of Pasteurellosis by the Fleas
Out of the 34 samples examined, 15 were
positive. As would be expected the proportion
of fleas found infected decreases with time since
the last infective meal. More samples examined
within 24 or 48 hours after the infective feed were
positive than later.
EXCRETION OF P. boviseptica IN THE FAECES OF
FLEAS
Eskey and Haas [1940] determined the pre-
sence or absence of infection in the fleas by in-
oculating their faeces into guinea-pigs. The role of
infected faeces in transmission from animal to ani-
mal or from animal to man by the rubbing of faecal
droplets into abrasions or wounds has been pointed
out by several investigators. In the present
experiments the infectivity of six faecal samples
was determined by cultural examination. Three
samples collected from infected fleas at the time
of their second feed after 24 hours fasting were
negative, while two out of three samples collected
after 48 hours fasting were positive.
EXPERIMENTS
TO
DETERMINE
WHETHER
INFEC-
---- CAN OCCUR BY INOCULATION OF INFECTIVE
FAECES THROUGH WOUNDS ARISING FROM BITES
OF HEALTHY FLEAS
Sample of infected faeces was collected from
about 200 fleas at the time they were used for
a second feed after 24 hours fasting. The sample
was found positive on cultural examination after
it had been allowed to remain at room temperature
for 24 hours. In the second part of the experiment
about 100 healthy fleas, previously fasted, were
allowed to bite healthy rabbit for one hour on
a closely clipped area on its belly and a suspension
of the infected faecal sample was then rubbed into
the bites with a pestle. The movements of the
rabbit were then restricted so that the area could
not be licked. The rabbit died after 24 hours
of pasteurellosis.
DISCUSSION
Out of the 15 experiments using a virulent
Pasteurella strain in rabbits, 12 gave positive
results and under these conditions evidently very
few fleas were necessary for transmission.
In young buffaloes, eight transmission experi-
ments were negative, one was positive and two
must be put as doubtful. Since the method em-
ployed with buffaloes was the same as with rabbits,
there appears to be no reason for the failure with
buffaloes unless the vectors were incapable of in-
oculating a sufficient number of organisms. If
this is so the species of fleas used must be consi-
dered an inefficient vector. From cultural exa-
mination of infected batches of fleas which have
taken an infective meal it seems likely that only
a certain proportion of fleas are capable of imbibing
infection. According to Eskey and Haas [1940]
only 38 per cent of X. cheopis and 20 per cent of
D. montanus became infected in spite of multiple
infective feeds. On the other hand, Douglas and
Wheeler [ 1943 ] who determined the percentage
of infected fleas by cultural and histological ex-
amination report that 96 per cent of these species
became infected. Douglas and Wheeler, however,
consider that the efficiency as a vector of a given
species of flea is not solely determined by the
proportion of fleas infected but is dependent on
the multiplication of bacilli in the alimentary
canal of the insect. It would be of some interest
to ascertain the percentage of infectivity in C. felis
and also whether P. septica multiplies in its alimen-
tary canal.
Daubney, Hudson and Roberts [1934] have
shown that pasteurellosis could be experimentally
transmitted in mice and rabbits. So far, the
experiments recorded here corroborate their find-
ings. Mehra [1943] reports a heavy mortality
amongst rodents in a locality where an outbreak
of haemorrhagic septicaemia occurred and also
the presence of a large number of fleas in the
burrows of rats. He further showed by ex-
perimental field investigations that the fleas trans-
mit the disease through their bites, but if, as
suggested above, the inefficiency of C. felis as a
vector is established, there remains little or no
doubt that the flea in question, which in-
cidentally is the common flea found on cattle
and young buffaloes, cannot be held responsible
for outbreaks of haemorrhagic septicaemia. As
an alternative vector, X. cheopis, the common
rat flea, which has been proved to be efficient
in human plague, suggests itself. However, even
if this flea is proved to be equally efficient in the
case of haemorrhagic septicaemia, it would be dif-
ficult to incriminate it, since this species is not
normally found on cattle. And assuming that it
may occasionally attack cattle, it would then have
to be ascertained whether rodents carry the organ-
isms in question. It is of interest in this connec-
tion to note that Neumann [1903] isolated a
supposed representative of the Pasteurella group
from a wild rat. Smillie [1920] also encountered