A NEW DISEASE OF FOWLS IN INDIA 109
The virus contained in this material has been maintained for over a year at
the laboratory by passage occasionally through fowls, and the reactions exhibited
in fowls injected with it have been identical in every respect with those provoked by
mouth-washings.
REPRODUCTION OF THE DISEASE.
A very large number of healthy fowls has been utilized during the course of the
work undertaken at this Institute, but examination of 113 records of birds used in
a series of 56 direct passages, where virus in the form of filtered mouth-washings
was employed, will serve as an indication as to the extent to which country-bred
fowls are susceptible to this affection. The number of fowls actually used in this
series was greater than 113, but all records of fowls which were destroyed in the
course of the experiments for various reasons, and where complications interfered
with the normal progress of the disease, have been excluded from the present note.
The results of experimental observation upon these 113 fowls may be summarised
as follows:—
Reacted and died........96 fowls or 85.0 per cent.
Reacted and recovered........11 fowls or 9.7 per cent.
No appreciable reaction.......6 fowls or 5.3 per cent.
The following Table shows the days after virus injection on which the 96 fowls
referred to above first exhibited symptoms, and the days also on which death
occurred.
|
— |
Days after injection of virus |
||||||||||||||||||||
|
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
13 |
14 |
15 |
16 |
17 |
18 |
19 |
20 |
|
|
Number of fowls showed first symptoms . |
0* |
0 |
12 |
30 |
30 |
15 |
3 |
2 |
0 |
0 |
2 |
1 |
0 |
0 |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
|
Number of fowls died . |
0* |
0 |
2 |
20 |
24 |
17 |
9 |
8 |
3 |
2 |
3 |
3 |
2 |
0 |
0 |
1 |
1 |
0 |
0 |
1 |
0 |
It will be seen from the above table that in artificial infection the incubation
period is between 2 and 14 days although by far the largest number of birds
developed the disease within 5 days of inoculation, so that virtually the incubation
period can be said ordinarily to be from three to five days, since only seven fowls
showed a " delayed reaction " from the 6th to 14th days, and the 12 reactions
which occurred as early as the second day nearly all took place at one period
during the sub-inoculations, indicating a distinct increase in virulence at that time
due to rapid passage. The average period of incubation was just over 3½ days.
* 10th day, or day of injection of virus.
Average (1) incubation period, 3.55 days; (2) duration of illness, 1.55 days.