African swine fever (ASF) is a mostly fatal viral infection of domestic pigs for
which there is no vaccine available. The disease is endemic to most of sub-Saharan
Africa, causes severe losses and threatens food security in large parts of the continent.
Naturally occurring attenuated ASF viruses have been tested as vaccine candidates,
but protection was variable depending on the challenge virus. In this
study, the virulence of two African isolates, one from a tick vector and the other
from an indigenous pig, was determined in domestic pigs to identify a potential
vaccine strain for southern Africa. Neither isolate was suitable as the tick isolate
was moderately virulent and the indigenous pig virus was highly virulent. The latter
was subsequently used as heterologous challenge in pigs first vaccinated with a
naturally attenuated isolate previously isolated in Portugal. Although a statistically
significant reduction in death rate and virus load was observed compared with
unvaccinated pigs post-challenge, all pigs succumbed to infection and died.