128 STUDIES ON FOOT-AND-MOUTH DISEASE [Vol. XXVII, Part IV
Experimental vaccination
Small-scale laboratory experiments were conducted using various percentages
of virus content to test the value of the vaccine, monovalent type 'O'. The dosage
for all brews of vaccine was 5 cc. subcutaneously. Of the various experiments
carried out in this connection, two are dealt with in detail; the first one in which
the vaccine contained 15 per cent virus and the second with 10 per cent virus.
These vaccines were tested in batches of hill bulls and careful observations were
made on the reaction following vaccination. This consisted of a slight local
swelling lasting for 3 to 4 days, a general rise in the body temperature of about a
degree above the normal for a couple of days. Animals continued to feed normally
during the period. The nature of reaction in the vaccinated animals was
practically the same as seen with the usual dilute vaccine in spite of an increase in
the concentration of the virus. Details of the experimental work were recorded in
the annual report of the scheme [Gopalakrishnan, 1951].
Immunity test
Immunity test of the two batches of animals was carried out by the administra-
tion of live virulent virus type 'O' given intralingually in 4 tracks. The details of
the tests are given in Table I. In the batch of 8 animals vaccinated with the con-
centrated crystal violet vaccine containing 15 per cent virus only, 6 were available
for the immunity test, the other two died earlier of other causes. All the
six an mass were found immune when challenged with virus type 'O', 23 days after
vaccination. Five control animals receiving the virus alone, reacted severely while
one did not react, probably due to previous natural infection and consequent
immunity. In the other batch of 10 animals vaccinated with the concentrated crystal
violet vaccine containing 10 per cent virus content and challenged 27 days later, a
breakdown of immunity was observed in 4 animals. It was thus concluded that the
vaccine containing 10 per cent virus was not very satisfactory. It was, therefore,
decided to use a vaccine containing not less than 15 per cent virus for further experi-
mental trials.
Field trial of the vaccine
Since the laboratory tests with the vaccine containing 15 per cent virus were
satisfactory, both as regards the post-vaccination reaction mild and transient and
the, type of immunity which appeared to be adequate, arrangements were made to
undertake large scale field trial in an organised farm where facilities were available
for periodical observations and recording. The trial was carried out at the Govern-
ment of India, Cattle-cum-Dairy Farm, Karnal. As a practical test under natural
field conditions, half of the young stock of age-group between 9 months and 3 years,
were taken up for vaccination and about an equal number of the same age-group was
kept as unvaccinated healthy controls with the view that if there was a natural
outbreak of foot-and-mouth disease it would be easy to assess the value of the vaccine.
A total of 236 animals of the representative breeds on the Farm were vaccinated on
February 11, 1953. Bivalent vaccine, type 'O' and 'A' was given to 189 animals and 47