4
Studies on Newcastle (Ranikhet) Disease Virus
Diagnosis
Because of its similarity in several respects to a number of other fowl
diseases, the diagnosis of Ranikhet disease is not easy. Bacteriological examin-
ation and fowl sub-inoculation tests are essential for a differential diagnosis.
The symptoms of fever, inappetance, somnolence, gastro-enteric disturbance
and paralysis of the legs and wings are seen also in fowl cholera, fowl typhoid,
fowl plague, spirochaetosis, and a variety of other diseases. Fowl plague
seems to be one of the diseases to which Newcastle disease has several points
of resemblance and the demonstration of immunological differences between
the two diseases seems necessary for a positive diagnosis.
Burnet and Ferry [1934] made comparative filtration studies between
Newcastle disease and fowl plague viruses, and showed that the two viruses
were independant, the Newcastle disease virus being larger than that of fowl
plague. Further, they produced evidence as a result of their experiments using
the technique of inoculation of the chorioallantoic membrane of the developing
chicken embryo to show that fowl plague and Newcastle disease viruses were
distinct entities. The Newcastle virus was found to be more resistant to photo-
dynamic inactivation by methylene blue solution than fowl plague.
Etiology and nature of the virus
The etiological agent of Newcastle disease has been shown by Doyle
[1927], Burnet and Ferry [1934] and a number of other workers to be a
filterable virus.
In studying the nature of the virus, Doyle [1927] selected mouth
exudate for filtration experiments, as being most suitable. That most
workers have found the saliva of infected fowls to be the best medium for
these studies may be accounted for by the fact that the virus is intra-cellular
in the tissues and that it is difficult to release the virus from the cells.
Picard [1933], in his attempts to loosen the virus completely from the cell-
structure through osmosis, exposed the organ emulsion to the influence of a
9 per cent salt solution.
Topacio [1934] successfully cultivated the virus for 31 generations over a
period of 112 days in a medium consisting of chicken-embryo tissue and plasma.
The culture-virus did not appear to differ from the natural virus in its ability
to set up an active immunity, as shown by the susceptible fowls immunized
with the former resisting the injection of the latter. In some of the experi-
ments the cultures were contaminated. The virus was, however, freed from
contamination by filtration ; a certain amount of contamination did not appear
to interfere with the viability and multiplication of the virus.
Farinas [1930] reported that the virus, as determined by cataphoresis, was
negatively charged. This has been confirmed by the author.
Under natural conditions it is unlikely that the virus will remain viable
for any great length of time [Iyer, 1939]. Owing to the rapid dissemination of
infection and the almost 100 per cent mortality, not very long after the infec-
tion has gained entrance into the animal body, instances of persistence of in-
fection are uncommon in localities where the rearing of fresh birds is sus-
pended for a time. Under experimental conditions, the virus, as contained
in the organs such as liver and spleen, can be conserved in the refrigerator for
about six months in 50 per cent glycerine.