Newcastle disease vaccination: the use of live virus after inactivated vaccine

Abstract

The use is described of Beaudette's Roakin strain live virus intra-ocularly on fowls previously vaccinated with an aluminium hydroxide adsorbed formalinized chick embryo vaccine. Good response to this combination was recorded from three months after using the killed vaccine. When the virus was applied per wing-web, a reliable percentage of reactions only took place when the interval between the two vaccines was five months or more. Experiments determining (1) the most effective routes of application of the live virus, (2) the optimum dilutions of the live virus, (3) the interval necessary between the use of the inactivated and the live virus for the intra-ocular and wing-web routes of application of the live virus and the effect on the egg production are described. Allantoic fluid, infected with Roakin strain virus, having an embryo Ld 50 of not less than 10⁻⁸ was diluted 1/10 in 50 per cent. glycerine-saline containing 1/8,000 crystal violet. The crystal violet was incorporated to colour the vaccine and so to facilitate its application. One drop of this diluted virus was applied intra-ocularly with an eye-dropper. Experiments conducted indicate that the intra-ocular route of application of the live virus is superior to the intranasal. The use of live virus after killed vaccine was characterised by absence of the drop in egg production which usually follows live virus immunization in susceptible fowls. In field tests conducted five large flocks, totalling 25,000 laying hens and 49,000 young stock (one to five months old) were vaccinated satisfactorily with a combination of these two vaccines. The severe effects of the live virus on egg production was controlled. Two small control susceptible flocks of 38 and 183 laying hens showed a total drop in egg production of 50 per cent. and 24 per cent. respectively, when they were treated with live virus in the same manner. One flock of 500 immunized with 0•5 c. c. of locally prepared adsorbed killed vaccine and vaccinated with live virus per eye, one month later, showed a good H.I. response without a drop in egg production. Response to the live virus was judged on the production of a serum H.l. titre higher than 1/160. Where good reactions occurred more than 50 per cent. showed a titre of 1/1,280 or higher. The use of the Roakin strain following an inactivated adsorbed vaccine after an adequate period, is recommended as a safe method of vaccinating permanently laying hens and younger stock. The use of the virus per eye does not set up a local inflammation or an increase in mortality.