J. R. HADDOW AND J. A.
IDNANI
47
From Table II it will be observed that all adult fowls vaccinated proved to be solid-
ly immune for five months. In tests at longer intervals the immunity appeared to be
waning. In chicks, the period of complete immunity was two to three months after which
the results were variable.
At this point in the work it became evident that other methods of vaccination, referred
to below, were likely to be more immediately profitable, hence this particular line of work
was dropped. It may be said, however, that the advantages of the gel vaccine are that it
can be applied safely to fowls or chicks without interference with health or reduction of
egg-laying ; on the other hand, the gel is troublesome to prepare and, since it does not keep
well, its use, particularly in India, must obviously be limited to organized poultry farms ad-
jacent to well-equipped laboratories.
IIA. PIGEON PASSAGED VIRUS
Various workers have commented on the fact that pigeons can be infected with Ranikher
disease, but attempts to carry on the virus in this species have failed after three or four
passages.
One of us (J. R. H.) had carried out experiments earlier in collaboration with Iyer
(unpublished), and from one of these, it appeared that further passages, though uncertain,
might be more successful than was previously thought possible. We have now examined
further the possibility of fixing the virus in pigeons. The previous failures may perhaps be
attributed to a low virus content in pigeons dying in earlier passages before the virus is
fixed, and also to the use of adult pigeons. Hence, we used material from young, 4 to 5
months old, pigeons destroyed just after the height of febrile reaction, and, as an added
precaution, we inoculated eggs from each pigeon passage in order to secure large quanti-
ties of virus.
The first attempt, using strain R1, failed at the second passage, but a second attempt,
using strain R 10, was successful. The virus recovered from the first passage was passaged
twice in eggs and thence directly in pigeons until the ninth passage when it died out.
Revived with egg-passaged material from the seventh pigeon passage, it was again success-
fully continued by direct passage. Up to about the twentieth passage, reactions in pigeons
were late (6 to 9 days) and a number survived or were rapidly improving at the time of
destruction. From the twentieth passage onwards the virus appeared to be fixed, the
reaction appearing in 3 to 5 days and being in all cases severe and invariably fatal. Periodic
test results are given in Table III.
TABLE III
Inoculations with pigeon passaged virus
Passages
11—50
51—100
101-180
No. of
fowls
22
32
6 (chicks)
135
47 (chicks)
Result
died, 6 reacted and recovered, 7 no reaction—immune.
3 died, 3 reacted and recovered, 26 no reaction—immune.
1 died , 3 reacted and recovered, 2 no reaction-immune.
11 died, 25 reacted and recovered, 99 no reaction-immune.
21 died, 3 reacted and recovered, 23 no reaction—immune.
As only small numbers of fowls were inoculated in the first two groups of passages, the
results are not reliable enough to permit drawing firm conclusions. In the third group,
however, several batches, each of 25 birds, were inoculated, and the results in these cases
give a clear indication of the degradation in virulence which has occurred during many
pigeon passages. Contrary to our observations on viruses degraded in other ways, it was
noted that as virulence decreased, the incubation period grew longer. Ultimately, the
incubation period had extended from the normal 3 or 4 days to 7 to 9 days, and, as might be
anticipated, the immunity conferred is more slowly achieved, viz., after 4 to 5 days as
compared with 48 hours with other strains. The total losses incurred in using pigeon virus
as a vaccine amount to 12 to 16 per cent of birds inoculated, i.e. 8 per cent mortality
plus 4 to 8 per cent of reactors permanently maimed. The pigeon virus is not suitable for
vaccinating chicks.