152
Transmission of Pasteurellosis by the Fleas
TABLE I
Bacteriaemia in rabbits after P. septica infection
Rabbit
1
2
3
Time
after
inocula-
tion
(hour)
3
4
5
6
7
9
11
14
16
10
12
14
Body
temperature
(ºF.)
102.6
102.2
102.6
103.6
102.4
105.0
105.2
105.4
101.2
104.0
104.0
103.4
Micros-
copical
examina-
tion
Negative
„
„
„
„
„
Positive
„
„
„
„
„
Organisms
per c.c. of
blood (in
thousands)
0.1
0.2
1.9
11.5
2.3
5.1
150.0
3500.0
303000.0
96.0
2700.0
30600.0
From Table I, it is seen that the organisms
begin to appear in the circulation about four hours
after inoculation, the bacteriaemia becoming in-
tense after 11 hours and persisting till death. The
bacteriaemia is of progressive type, its intensity
being in inverse relation to the interval before
death. As would be expected, microscopical
examination of blood smears in the initial stages
is not dependable, but the presence of bipolar
organisms in smears indicates an intense bacteri-
aemic condition. The blood may contain before
death an enormous number of bacteria, e.g. more
than 300 million per c.c. Any suctorial insect
feeding on such an infected animal till death would
thus certainly infect itself very heavily.
Handling of fleas. Fleas were collected from
local pariah dogs by combing or hand-picking.
Enclosed in cloth bags surrounded by cotton wool
and kept in cigarette tins at room temperature,
the fleas survived for 24 to 36 hours. Those kept
in flasks, with plenty of hair from dogs and pieces
of filter paper, survived in a fasting condition for
five days or more at 22ºC. and relative humidity
80 to 90 per cent.
Before the feed, fleas were fasted for at least
12 hours in the first few experiments, the fleas
were fed on small closely clipped areas of the skin
along each side of the belly, both the donors and
receptors being held in position under an inverted
funnel of convenient size. In later experiments,
however, this method was abandoned, since it
was found unnecessary when the fleas were hungry.
The fleas were placed on the donors when the
latter were showing numerous bipolar bacteria
in the blood, and were left till half-an-hour
after the donors death. The infected fleas were
then collected, fasted for 6 to 48 hours, and then
placed on the receptors. They were kept under
a funnel to make sure that they fed and were then
finally allowed to remain on the receptor till death
or otherwise.
Specimens of fleas which had fed on infected
donors were examined at times for Pasteurella.
For this purpose, some ten fleas were taken at
random after completing the feed and were kept
at 22ºC. and relative humidity 80 to 90 per cent
until the remainder of the batch was used for a
transmission experiment. The sample fleas were
then washed with alcohol, dried and ground in a
mortar with saline and serial dilutions plated
in serum agar. Supposed Pasteurella colonies
were picked and tested in mice. Specks of faeces
from infected fleas were examined by a similar
method.
TRANSMISSION EXPERIMENTS IN RABBITS
Fifteen experiments were made in three series.
In the second and third series, the fleas collected
were used in successive experiments, as long as
there were any fleas surviving and positive trans-
missions were appearing. In the first series, there
was a single experiment with 250 fleas. The
second series was started with 450 fleas, and fleas
were used in the five experiments in batches of
450, 75, 34, 16 and 7 respectively. The third
series was started with 200 fleas, and there were
nine experiments, the number of fleas used being
200, 61, 25, 14, 7, 5, 4, 2, and 1. The first experi-
ment (first series) gave negative result, although
the fleas from the donor were proved by culture
to contain Pasteurella. In the second series, the
first four experiments were positive, while that
with seven fleas was negative. In the third series,
all experiments were positive except the last where
only one flea was used.
EXPERIMENTS IN YOUNG BUFFALOES
Transmission from one buffalo to another is
usually impracticable for various reasons. It
is extremely difficult to collect the infected fleas
from a buffalo donor after death, as they abandon
the host and hide in debris or crevices in walls,
etc.; and one has to depend solely on the chance
of infected fleas coming out again and biting the
receptor which is accommodated in the same room.
The use of disinfectants has to be avoided, other-
wise vectors will be killed, and it is thus difficult
to avoid the possible infection of the receptor