ABSTRACTS
115
After the ground refuse screenings had been subjected to the processes of
digestion, germination studies were made on the weed seeds voided in the manure
and none of them were found to be viable. (I. K.)
Newcastle Disesase Immunisation with Live Virus. BEAUDETTE, F. R. BIVINS, J.
A. and BARBARA R. MILLER (1949). The Cornell Veterinarian XXXIX,
302-334
THE authors have reviewed the literature rather critically and in great detail
and conclude that so far no safe method has been evolved for the use of viru-
lent active virus as such or for its attenuation by storage, drying or tissue culture
to enable the same to be used as a safe vaccine. But other methods such as
passage in embryonating eggs, or in ducks, hamster or sheep brain have given
encouraging results.
The authors' experiments were based on the presumption that it is possible
to come across a naturally low virulent or apathogenic strain, which could be
used for immunization without having to be modified, if a large number of strains
of Newcastle disease virus were examined. With this in view the authors studied
105 strains of their previous collection. All these strains were first tested on
five birds each and all but nine strains were discarded as unsuitable. A strain
was regarded as unsuitable if it caused a single death or paralysis. Eight out of
the nine were again tested on 42 to 50 birds each and only one was found to be
quite safe and satisfactory. This strain was first used for immunization of 2884
chicks at 30-36 days old by 'Stick' and intramuscular methods with a loss of
1.73 per cent from all causes. Of these 578 birds were challenged with a virulent
strain, which produced cent per cent mortality in controls, by intramuscular
and intranasal instillation methods 15 to 23 days after vaccination and only one
died of Newcastle disease. This bird was vaccinated with stick method and
challenged by intranasal instillation. Another lot of 8715 chicks were vaccinated
with a loss of 1.64 per cent from all causes. In a third series of vaccination a
total of 83,059 birds from 25 days to young layers were vaccinated in 20 commercial
farms with a loss of 1.82 per cent. This rather high loss was due to a heavy
mortality in one of the farms due to some intercurrent disease and if this was
eliminated the loss would be only 1.09 per cent.
An incident is recorded where 710 chicks between 37 to 41 days old got in-
fection with the vaccine strain as a result of housing in rooms which were not
disinfected and the mortality was 13.94 per cent. This high mortality was
attributed to the infection taking place through the respiratory tract. This
incident reveals that vaccinated birds are a source of infection for a time. To
confirm this the authors conducted experiments and it was proved that a certain
percentage of contact susceptible birds do get a silent infection and become resis-
tant to virulent virus.
The other observations made by the authors are (1) the proper age for vacci-
nation is just when the chicks are four weeks old as by this time the parental
immunity, i.e., the passive immunity derived from the immune parent, is lost
and the chicks become susceptible, (2) that vaccination of chicks even after the