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STUDIES IN IMMUNIZATION AGAINST FOWL FOX [Vol. XXVIII, Pt. IV,
Experimental vaccinations were made by the authors in day-old chicks,
using egg-propagated pigeon pox virus (P. P. V.) and fowl pox virus (F. P. V.) of
similar origin, with a view to assess their respective antigenic values for protecting
chicks of early age. The work was prompted by the success obtained in immuniz-
ing older birds with egg-adapted F. P. V. [Rao et al., 1953] which forms the basis of
this study.
EXPERIMENTAL
Vaccination with F.P.V.
One group of 100 Rhode Island Red chicks and another group of 100 Barred
Plymouth Rock chicks were vaccinated when day-old with a modified fowl pox
virus which had undergone fifteen passages in the chorio-allantoic membrane (c.a.m.)
of the embryonated chicken egg. Control groups of similar numbers were reared
under the same conditions of feeding and management. A group of 25 healthy day-
old chicks of Barred Plymouth Rock breed was placed in contact with the second
group.
The vaccine was prepared from fresh membranes finely disintegrated and sus-
pended in buffered 25 per cent glycerine broth, pH 7.4, and used at 8 per cent and
4 per cent concentrations, for the first and second groups respectively. The chicks
were wing-banded and individually weighed prior to vaccination. The stab method
of inoculations, using the eye of a sewing needle with the bridge filed off, was used.
The first group was inoculated with the fresh 8 per cent vaccine by one stab in the
web of the wing. The second group was inoculated with the 4 per cent vaccine
similarly. All chicks in the experiment were fed a balanced diet, with skim
milk as protein supplement and adequate supply of greens and limestone grit. They
had access to sunlight daily, after two weeks of age. Sawdust was used as litter
and the chicks were brooded cold as is the practice during summer.
Individual weights of the chicks (excepting those left in contact) were recorded
on the first day when the chicks were wing-banded, and subsequently every fort-
night till they were 8 weeks of age, when they were placed in the yards inoculated
with a prophylactic dose of Newcastle disease vaccine.
The 'takes' of fowl pox vaccination were checked at 7, 10, 14 and 21 days and
their nature and secondary lesions, if any, were recorded. Post-mortems were
scrutinised for any direct or indirect influence of vaccination on mortality like
'runting' or unthriftiness due to secondary lesions on mouth or eye-lid, and throat
lesions due to pecking of unhealed scabs.
OBSERVATIONS
"Takes" and secondary lesions
Good takes were noticed from the sixth day onwards, reaching a maximum
of 100 per cent in the first group and 96 per cent in the second group on the
tenth day respectively. The takes appeared like pale yellow pearls and
later developed into plaques as big as split peas (Figs. 3 and 4). The scabs
are shed generally by the third week, but in a few cases in the first group they
persisted up to four weeks. Nine chicks out of 100 in the first group and 4 chicks
out of the 100 vaccinated in the second group developed a secondary lesion on the
beak. Seven out of the 25 in-contacts had secondary lesions distributed as follows :
beak—2, eyelid—2, angle of the mouth—3. All secondary lesions, however, healed
up normally, though poor growth was noticed in five of these that developed such
lesions.