Sheep infected and re-infected with orf virus
responded with lesions which evolved through classical
pox stages of papule, vesicle, pustule and scab. In
susceptible sheep they resolved within five weeks whereas
in re-infected sheep there was an accelerated response,
the lesions healing within three weeks.
Experiments were designed to correlate the roles of
humoral and cell-mediated immune responses with clinical
responses. Sera were analysed for changes in the levels
of total proteins, serum fractions, IgM, IgGl, IgG2 and
antibodies. Leucuocytes from infected and re-infected
sheep were also assayed for cell-mediated immune responses.
Changes in the total serum proteins of infected and
re-infected sheep, pre-challenge and post-challenge were
not significant. Contrarily, there were significant in¬
creases in the gammaglobulin levels in re-infected sheep
and slight increases in the levels in infected susceptible
IgM levels of infected and re-infected sheep were not
markedly altered. IgGl and IgG2, in contrast, increased
significantly after infection and re-infection. The in¬
creases correlated positively with orf antibody titres.
The rate of antibody production was significantly
slower in infected sheep than in re-infected sheep and the
titres attained were much lower in susceptible sheep than
in re-infected sheep.