Studies of Newcastle Disease. II. Evaluation of Two Killed Newcastle Disease Vaccines

Abstract

N recent years the popularity of virus Newcastle disease vaccines has steadily increased, while the percentage of birds immunized with killed vaccines has decreased. This trend is due, in part, to the ease with which live vaccines can be administered, as well as to the early reports regarding the low-grade immunity engendered by the use of inactivated vaccines.' Although the present widespread use of live-virus vaccines has served to minimize the losses resulting from Newcastle disease, the inherent nature of products of this type limits the possibility of eventual eradication of the disease. For this reason, investigations of inactivated Newcastle disease vaccines have been continued. The authors have in the past completed two field studies dealing with the efficacy of inactivated Newcastle disease vaccines. Schoening et al.7 found that although vaccination with a formalin-inactivated, commercially produced Newcastle disease vaccine did not entirely prevent the disease, it enabled the vaccinated birds to withstand a severe exposure, with relatively few losses as compared with unvaccinated control birds. Legenhausen et al.6 have shown that an inactivated crystal violet vaccine was capable of stimulating a degree of immunity comparable to that resulting from the use of live virus vaccines under field conditions.