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Summary The apparent infectivity of certain arboviruses is increased by the action of specific antisera prepared in domestic fowls when assayed on chick embryo fibroblast (CEF) monolayers or the chorioallantoic membrane of the developing chick embryo. Of the viruses tested, Murray Valley encephalitis (MVE), West Nile (WNV) and Japanese encephalitis viruses from Casals group B, and Getah virus from group A demonstrate this enhancement, but Sindbis and SFV from group A do not. The virus plaque count is increased by up to 12 times the control plaque count, depending on the potency of the antiserum. Enhancement could not be demonstrated with rabbit or mouse antisera to MVE on the CEF monolayer, nor with fowl antiserum on PK‐2a cells or in suckling mice. Cross enhancing activity could be demonstrated between viruses within group B (MVE and WNV), but not between viruses from different groups (MVE and Getah). Preliminary work indicates that 19S antibody is involved, as well as antibody not susceptible to depolymerisation with mercaptoethanol.
R.A Hawkes (Sat,) studied this question.