J. F. SHIRLAW AND P. R.
KRISHNA
IYER
201
Vaccination with Assam 16th generation 'culture virus'. Workers on the problem of immunity
are generally agreed that vaccination by 'culture virus' is the most satisfactory method of control
of the disease in the field. The method depends on the fact that continued subculture of the organism
results in gradual attenuation, a stage in attenuation being reached at which the inoculation of sus-
ceptible cattle is harmless, although productive of immunity. The culture so attenuated retains
its immunizing properties through a considerable number of generations until, finally, these are
lost or weakened to such extent as to be of little value. Workers in Africa [Hayes, 1926 ; Walker,
1922; Bennett, 1932; and others] have found that the use of culture virus earlier than the 16th
generation is dangerous, occasionally producing fatal reactions. Culture virus older than the 73rd
generation is of diminished potency and, therefore, of little value save in protecting specially sus-
ceptible herds when, of course, it must be employed. Between these stages of attenuation there is
said to be little variation in immunizing values, although Bennett [1932] states that earlier cultures
give a more satisfactory immunity than later. The method depends for its success in great part,
however, on the relative susceptibility of cattle populations in any given area and the strain of the
vaccine used. Even in countries where the disease is widely prevalent, a common procedure in the
use of the vaccine is inadvisable. For example, Henderson [1929] found in Nigeria that the local
strain of virus was not safe until the 177th generation culture. Stewart [1935] observed that
cattle of the Gold Coast the second generation of the Sudan culture virus was safe, whereas the 67th
generation had no immunizing value. The development of immunity produced by this method is
slow. Purchase [1939] found that with relatively large suitably-spaced double doses of 11th—
47th generation culture, immunity was established 36-44 days after vaccination, whereas, in animals
given only 1 c.c. of the same vaccine immunity tests failed at the 72nd and 85th day 'Only at
the 106th day could any degree of immunity be shown in animals vaccinated with 1 c.c. and in these
cases the degree of immunity was not comparable'. Le Roux [quoted by Purchase, 1939] states
that it is not so much the breed of cattle, per se, as the local environment which affects the reactions,
and this point of view is supported by Curson and Thornton [1936] who failed to discover any cor-
relation between the different breeds and their reported reaction to culture vaccine.
The 16th generation Assam 1 culture was tested in six cattle, each receiving 2 c.c. subcutane-
ously at the point of the shoulder; two animals reacted badly and died and in the others there
was no reaction. The four survivors were tested for immunity along with one control 145 days
later, the test dose being 5 c.c. homologous virus subcutaneously at the point of the shoulder. The
control reacted severely and died, whilst the vaccinated animals showed no reaction and were thus
solidly immune. The results indicate that the 16th generation Assam 1 culture is unsafe as a vaccine
in the hill cattle selected for the test but that animals which can withstand such vaccination are
solidly immune.
Vaccination of cattle with Assam. Australian and African culture vaccines. This test was carried
out in 28 cattle disposed in seven batches for each vaccine under test, viz.:
Assam 1
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Australian 264
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Australian 264
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Australian 173
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Kenya Narok
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Kenya V4
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Kenya ML
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Rhodesian R
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20th
63rd
73rd
72nd
55th
24th
11th
44th
generation culture,
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6 cattle
3 „
4 „
3 „
3 „
3 „
3 „
3 „
B 2