The p H Stability of Viruses of Newcastle Disease and Fowl Plague

Abstract

Evaluations of the pH stability were made on 4 strains of the Newcastle disease virus, including the Hertfordshire strain (H) and 3 strains (11914, RO, and C) isolated from cases of "pneumo-encephalitis", and on the Dutch E. Indies strain of the fowl plague virus. A variant virus (Strain 4395) isolated from the plague virus was similarly studied. The source of the virus in all tests was the allanto-amniotic fluid of embryonated chicken eggs which had been infected 10-12 days after incubn. These materials were admixed 1 to 99 with parts of a buffer soln. with pH values of from 2 to 12. These mixts. or their dilutions in 1% peptone broth (pH 7.8) were held at 2-6 [degree]C until used. Infective virus was detected by its activity in 10- to 12-day eggs after intra-allantoic inoc. The pH of the mixts. was detd. by a glass electrode potentiometer. In the acid range, RO and C showed comparable stability, while 1 California strain was more resistant and was comparable to strain H. All 4 strains were similar in the presence of alkali after exposure for 1 hr., while infective virus of English and RO strains decreased in concn. after 1 day. For all 4 strains, after 1 hr., a maximal stability existed from pH 4 to 11, while survival was possible from pH 2 to 12; after 1 wk. a maximal stability occurred between pH 5 to 9, and virus survival was anticipated from pH 2 to 11. The plague virus survived in maximal titer, after 1 wk., from pH 6 to 11; the same stability was seen at various pHs for 1 hr., but at this time infective virus was still present at pH 5 and pH 12. The pH values of the virus-buffer mixts. drifted toward the pH of the virus material, but after 1 wk. this did not exceed 0.25 of one pH value in the extreme of the acid range or 0.5 of one pH value in the extreme of the alkaline range. The pH stability of the plague virus was compared with that of a variant virus isolated from it. The quantity of virus material to that of buffer was 1 to 9. The stability patterns of the infectivity of both of these viruses were essentially similar. The data show a close relationship among the 4 strains, a diversity between the virus of Newcastle disease and that of fowl plague, and a similarity between the fowl plague virus and a variant virus derived from it. The stability patterns are useful in the identification of the virus of Newcastle disease and of fowl plague.