160
Occurrence and Spread of Fowl Cholera in India
TABLE III
Virulence tests
Cultures
574
.
.
. .
836
.
.
.
.
102
.
.
.
56
.
.
.
.
95
.
.
.
.
861
.
.
.
.
2027 . . . .
104
.
.
.
.
947
.
.
.
.
654
.
.
.
.
509
.
.
.
.
Result of inoculation
Fowl
S
S
S
S
S D
in 24 to 42 hr.
Do
Do
S
S
S
Rabbit
S
S
S
S
S D
in 18 hr.
Do
S
D
in 18 hr.
Do
Do
NOTES.—S=Survived. D=Died.
In all cases where deaths occurred, Past. aviseptica was
isolated.
new lot of birds was examined. Four fowls
(1.4 per cent) were found to harbour the infection
of the 'blue-colony' type. As the previous
test gave 4.06 per cent of carriers, it would appear
that the conditions on the farm had been inimical
to the propagation of the micro-organism and
conducive to maintenance of an adequate level of
resistance in the flock.
DISCUSSION
From the above results, it can be seen that
carriers could be detected 21 months after the
last recorded death from fowl cholera. Though
the possibility that the carriers might have
originated from an entirely fresh introduction
of the disease is not ruled out. it is equally possible
that the condition may have been present during
the whole period since the last infection. This
existence of carriers explains the perpetuation of
infection in apparently clean farms. Efforts at
prevention and control cannot therefore be
expected to succeed, if traditional measures, such
as the disinfection of poultry houses, etc. and
isolation and killing of diseased individuals
(clinical cases), are solely employed. Elimination
of carriers is the only reliable method of control.
If the ratio of the carriers to clinical cases is
high, such preventive measures will only give
a false sense of security. The recovery from
apparently healthy individuals of virulent Pasteu-
rella, capable of killing fowls, constitutes a serious
potential danger to the flock. The position is
summed up by Van Es [1937]: 'In the light
of present day evidence it appears that the crux
of the problem (of fowl cholera) lies with the
recognition and elimination of the healthy
infection carrier'. Pritchett et al. [1930] concluded
from their work that such a procedure was both
effective and practical.
SUMMARY
A three-years' survey of the incidence of fowl
cholera in India suggests that fowl cholera occurs
far less frequently than is usually believed and
that widespread epizootics are not a feature of
the disease.
In one outbreak, the disease was observed t o
run a typically enzootic course. The presence
of carriers to the extent of 4.06 per cent among
apparently healthy fowls was established and
they were even found in seemingly unaffected
pens.
Pathogenicity tests showed that about one
quarter of the strains of Pasteurella isolated from
carriers were virulent for the fowl and nearly
one-half for the rabbit. Examination of another
lot of fowls from the same farm, 21 months after
the last clinical case of fowl cholera, again revealed
the existence of carriers to the extent of 1. 4
per cent.
ACKNOWLEDGEMENT
The authors are deeply indebted to Mr A. J.
Macdonald for advice and criticism.
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