Abstract
In a previous report, 1 the results of immunizing farm flocks with fowl pox vaccine prepared from entire chick embryo were described. The vaccine consisted of a composite of the chorio-allantoic membrane, yolk, yolk sac, albumen, embryo proper, and fluids from previously inoculated embryos that showed gross lesions on the chorio-allantoic membrane. While a high concentration of virus was noted in the chorio-allantoic membrane, the presence of virus in other parts of the embryo was also demonstrated. 2 The dehydrated vaccine was suspended 1-100 in tryptone broth and applied by the 3-stick method in 35 healthy farm flocks, comprising 25,164 chickens. Nine days after inoculation, more than 6000 birds, approximately one-fourth of the vaccinated birds, were observed with 95.85% showing takes. Forty-three days after inoculation, 71 culled chickens from 3 of the flocks were brought to the Laboratory and artificially exposed to fowl pox virus by the feather follicle method. Eighty-eight and seven-tenths per cent proved refractory.
The present note concerns an observation on the duration of the immunity produced by entire embryo vaccine. Seventy-one birds selected from 4 of the flocks were exposed, one year subsequent to vaccination, on the patagium by the 3-stick method to fowl pox virus in a 1-100 suspension in tryptone broth. The exposing virus was of the same strain as that use for vaccination, but consisted of the chorio-allantoic membrane which represents a greater concentration of virus than the entire embryo vaccine. The artificially exposed chickens were given three inspections at weekly intervals for lesions of fowl pox following exposure. Results of the exposure are noted in Table I.
Out of the 71, 3 susceptible birds were encountered. These were from the same flock.
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