130 STUDIES ON FOOT-AND-MOUTH DISEASE [Vol. XXVII, Part IV
received polyvalent vaccine prepared from all the three standard strains of the foot-
and-mouth-disease virus. The animals were kept under observation for one week
following vaccination and the nature of reaction was studied. The reaction was
practically of the type as was noted in the hill bulls in the laboratory tests. About
a dozen animals showed local swelling that persisted for more than a week. All
the animals were feeding normally and well during the period of observation.
Natural outbreak
A natural outbreak of foot-and-mouth disease occurred among the young stock
on the Farm at the end of March, 1953. As the disease showed a tendency to spread
among the young animals and calves, the Farm authorities aphthised all the young
stock to lessen the duration of the outbreak. During the investigation in the latter
half of April, 1953, it was observed that the infection was prevalent among the young
stock only. The disease had not spread to adults, particularly the cows as they
were housed in sheds away from the young stock.
This outbreak afforded an opportunity to assess the value of the vaccination
which had been carried out on February 11, 1953. During the course of the outbreak
on the Farm, daily observations and careful examination of all the animals was made.
It was noticed that of the vaccinated group comprising 236 animals only two calves
contracted a mild form of the disease while as many as 210 out of the 400 unvaccinated
animals suffered from the disease. Unfortunately, the type of virus responsible
for this outbreak could not be determined, as intimation of the occurrence of the
disease was received late and the material collected for the isolation of the virus
proved non-viable. However, the efficiency of the vaccine in preventing the disease
is proved beyond doubt on account of the occurrence of this natural outbreak of the
disease only about 2½ months after vaccination.
The second experimental trial of the concentrated crystal violet vaccine, biva-
lent type 'O' and 'A' was made at the Tisco Farm, Jamshedpur, and animals ranging
between the age-group of 9 months to 3 years were taken up for vaccination. Half
the total number of the young stock was vaccinated and the other half was kept as
healthy controls so that in the event of a natural outbreak of foot-and-mouth disease
it would be easy to assess the value of the vaccine. A total number of 117 animals
of the representative breeds of cattle—Sindhi, Hariana, Jersey and Murrah buffaloes—
on the Farm were vaccinated with 5 cc. each subcutaneously on February 18, 1954.
The post-vaccination reaction in the animals was satisfactory.
The first immunity test to find out the degree and duration of immunity was
carried out on January 3, 1955 and the second one on September 12, 1955.
The results of these tests are presented in Table II.
It will be observed that in both these tests, vaccinated animals under test did
not show any reaction. In the first immunity test 3 out of the 4 controls reacted
typically showing primary lesions in the mouth and a rise of about 2ºF in body
temperature. In the second immunity test the reaction to the challenge observed
in all the four controls was also typical.
The results of these tests indicate that there was evidence of adequate immunity
for a period of 17 months and 25 days or say nearly 18 months following vaccination.