188
STUDIES IN IMMUNIZATION AGAINST FOWL POX [Vol. XXVIII, Pt. IV,
A second trial in baby-chick vaccination was made by Lubbehusen and Beach
[1937] in 15 groups comprising of several thousand chickens from day-old to 55
day-old. Their studies indicated that a satisfactory ' take ' in day-old chicks
induced immunity against fowl pox for a period of at least 18 months. These
findings were further supported by field observations. The results neverthe-
less lent support to the previous view that the rate of growth and resistance to
other diseases were adversely affected. Data indicated that a systemic reaction
followed in chicks vaccinated at 1, 13, 28 and 42 days, but the reactions
were progressively less severe as the age of the chicks increased. However, in
general, the retardation of growth was more than excessive mortality.
" The age limit of the bird at the time of vaccination (F. P. V.) is important.
In certain areas day-old chicks are vaccinated, but the severe systemic reactions
and high mortality rate following vaccination do not make birds of this age satis-
factory subjects of vaccination. " The preferable age for vaccination of chickens
is from 6 to 12 weeks according to Delaplane [1943] and from 8 to 10 weeks accord-
ing to Beaudette [1941]. As a rule, the chicken should be one month old. Chickens
should not be vaccinated within one month, and preferably two months before pro-
duction. However, " with pigeon pox vaccine this upper age limit for vaccination
is not important since the vaccine does not produce a systemic reaction following
its application. In young chicks, the age limit depends upon the feathering of the
bird since the vaccine is applied only by the feather follicle method. " [Charles
H. Cunningham, 1952.]
Preliminary studies were made in this Division in day-old chicks with
an egg-adapted fowl pox virus isolated in India [Iyer, Rao, and Thakral, 1953].
In these studies, among the vaccinates, neither growth retardation nor lowering
of resistance to intercurrent infection due to excessive reaction, was noticed as
was previously reported by other workers who used the F. P. scab virus for the
same purpose, while the immunity conferred was a durable one lasting for over
a year. Subsequent studies are reported in this paper.
Pigeon pox virus immunization
Doyle and Minett [1927] adapted fowl pox virus to the pigeon. For a decade
this strain of scab virus was incorporated in the Indian Veterinary Research Ins-
titute scab vaccine for controlling fowl pox in India. Presently the pigeon pox
scab virus is in use for this purpose, but the immunity is short-lived, breaking down
in about three months under natural conditions [I. V. R. I., Poultry Research Divi-
sion, 1950]. Glover [1939] observed that protection given by this virus was erratic.
Similarly Haig [1951] found the immunity response to vary while using an egg-
adapted P. P. V. strain. He reported that a moiety became refractory to challenge
with F. P. V. while in the other moiety, the response varied from 100 to 0 per
cent. The maximum antibody titer was reached in 10 days. In the Union of
South Africa, an egg-adapted P. P. V. vaccine is in use to immunize chicks from day-
old to four weeks old, while vaccination is carried out with F. P. V. in older chickens.