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Occurrence and Spread of Fowl Cholera in India
organisms, both virulent and avirulent, from the
mucous membranes of apparently healthy animals.
Hughes and Pritchett [1930] could not produce
the disease by the oral administration of virulent
Past. aviseptica in capsules and found that the
usual channel of infection was through the upper
respiratory tract. Webster [1924, 1 and 2],
working with rabbit pasteurellosis, found that
preceding an outbreak, there was a fall in resis-
tance due to adverse environment, and a cor-
responding rise in the number of the organism
which ultimately led to an outbreak of the disease.
It would appear from the existing work that the
more resistant are not affected, those less resistant
become carriers, while hypersusceptible birds die
of infection.
EXPERIMENTAL
An outbreak of fowl cholera provided the
opportunity to study certain epizootiological
aspects of the disease. This occurred in the
Institute farm which is self-contained as no
eggs, chicks or fowls are brought from outside,
and every possible precaution is taken to prevent
the introduction of diseases. The disease broke
out in 1940 in a group of 40 cockerels causing
the death of six only. The source of infection
was undetermined. A further outbreak occurred
in two adjoining pens in mid-summer, 1941,
with sporadic cases over a period of a month.
Out of a flock of 2,000 birds, only 11 died.
The organisms recovered were of the 'blue
colony' type [Hughes, 1930] associated with
enzootic fowl cholera. The recurrence of the
disease on the farm, the type of organisms re-
covered, the insignificant morbidity and mortality
and the course of the outbreak led us to suspect
the existence of carrier fowls in the flock, such
a possibility being in accord with the findings
of Manninger [1921], Van Es [1937] and Shook
and Bunyea [1939]. Therefore, soon after the
second outbreak, it was decided to examine
the flock for the presence of carriers.
METHODS
(1) Agglutination test. The rapid whole-blood,
stained-antigen method, employed by Shook
and Bunyea [1939], was tested using serum from
fowls and rabbits previously immunized with
Past. aviseptica. The serum had a titre of 1/320.
Crystal violet-stained antigens of homologous
and heterologous strains were used. The re-
action was unsatisfactory and the results were
not clear-cut. However, the strains of fowls
cholera used by us were perhaps not quite suit¬
able for the test.
(2) Bacteriological. Webster [1924, 1] working
with rabbit pasteurellosis, and Pritchett et al
[1930] working with fowl pasteurellosis, recovered
the organisms from carriers by culturing the
upper respiratory tracts.
Preliminary tests were conducted to standardize
the technique. The following methods for obtain¬
ing material from nasal passages of fowls were
compared: (a) nasal washings obtained by syring
ing the nose with saline or broth; (b) swabbing
the nasal cavity with dry cotton swabs; and (c)
swabbing the cavity with a wet cotton wool
swab. Nasal washings invariably gave a profuse
growth of contaminating bacteria. Swabs and
especially wet swabs gave better results and
isolated colonies of Pasteurella could easily be
obtained.
With regard to culture media, Webster and
Baudisch [1925] showed that the growth of
Pasteurella was more profuse under a reduced
oxygen pressure and on media with a trace of
rabbit blood or an iron compound with strongly
catalytic properties. Schütze and Hassanein
[1929] also got better results by adding smal l
amounts of blood or sodium sulphite. A test
was therefore run to compare routine laboratory
media and certain other enriched media. The
following were used: (a) nutrient agar, (b) plain
broth, (c) agar with 5.0 per cent ox blood, (d)
agar with 1.0 per cent ox blood (e) agar with
0.5 per cent sodium sulphite, (f) agar with haemo
lyzed rabbit blood, (g) Fielde's medium, and
(h) peptone broth with 10.0 per cent inactivate
ox serum.
Serum broth gave thicker growth than plain
broth. The counts on nutrient agar were si gni ¬
ficantly lower. All the other enriched media
gave uniformly good results, with little difference
in counts. As to the relative value of liquid
and solid media, swabs from the nasal cavity
were sown as follows: (a) into a tube of broth
which was incubated for 24 hours at 37ºC. and
then plated, (b) into a tube of broth, which was
incubated for one hour and then plated, and
(c) on to a blood-agar plate. Initial incubation
in the liquid medium invariably led to an over
growth of contaminants. Direct sowing on blood
agar gave discrete colonies from which Pasteurella
colonies could be easily picked.