The application of tissue cultures in the study of vesicular
diseases of animals has been illustrated by reference to pig kidney
tissue cultures and the virus of foot-and-mouth disease.Investigation ^ras carried cut on the most suitable method of
producing monolayer tissue cultures from pig kidneys by the
trypsinisution technique and it was found possible to produce
monolayers in suitable quality and quantity. The monolayers were
used for titration of the virus of foot-and-mouth disease and study
was made of the factors affecting the formation of plaques on the
monolayers. It was found that the number, size and shape of the
plaques formed were affected by the state of the cells, the nature
of the overlay, the conditions of culture incubation arid the strain
of virus used. By adherence to a standard techhique and by
comparison of titrea obtained from assay of a standard virus on
different sets of cultures it was possible to obtain accurate and
useful results.Strains of the virus of foot-and-mouth disease, which had been
passaged through mice and chick embryos did not multiply or cause
eytopathogenic effect in calf and ox kidney monolayers to the same
extent as strains passagsci in cattle or in kidney cultures and It
was possible to correlate their behaviour with non-infactivity tests
in cattle. All strains of the virus tested grew in pig kidney mono¬
layers and caused cytopathogenic effect but gave rise to plaques
of varying size and shape. The plaques arising from the different
strains were compared and it was found that the relative number of
the different plaque sizes varied with the origin of the virus and that the plaque population changed on peerage in different
cultures or animals.The adsorption and multiplication of the virus was followed in
pig kidney cell euepensions and monolayers, It was found difficult
to infect all the cells after 30 minutes absorption with a high
input of virus. The latent period was found to be 2.5 - 3 hours
for cell suspensions and monolayers and at the end of that time
there was a rapid virus increase. The titra of the culture reached
a peak of 10(6.7)-10(7.5) pfu/ml at 6 - 8 hours after which it
remained constant for a period up to 18 hours and then fell
gradually,Virus grown in pig kidney monolayers was inactivated by
adsorption on aluminium hydroxide and treatment with 0,03 formalin.
The vaccine thus produced protected guinea pigs agniast challenge
with liomologous culture virus arid stimulated the production of
neutralising antibody. Investigatione were made into the optimum
time of virus harvest. It was found that vaccine made from virus
harvested 24 - 42 hours after infection of the monolaye -B, when the
cytopathogmic effect was complete, gave the best protection to
guinea pigs on challenge- The siae of challenge dose which
distinguished between different levels of protection,was found to be
104 guinea pig IX^q, and & tentative scheme for a potency teat was
put forward baaed on the dilution of vaccine protecting 5* the
guinea pigs from generalisation after challenge with 104ITjq of
virus.Pig kidney monolayer tissue cultures were also used &3 a means
of differential diagnosis of vesicular diseases and for the assay
of neutralising antibody.These findings ware discussed in relation to diagnosis,
identification and classification of outbreaks of foot-and-mouth
disease in the field and to the selection of virus strains for
preparation of attenuated and inactivated vaccines. The method of
virus titration by the plaque technique was discussed with regard to
vaccine production, fundamental virus research, plaque analysis of
strains and genetic studies. The importance of virus growth studies
and production of high tltre virus stocks was emphasised in relation
to virus-cell interactions and in relation to provision of suitable
material for biophysical, biochemical and biological investigations
on the virus
