One hundred years of African swine fever: a tribute to R. eustace Montgomery.
This paper provides the first description of the disease as it occurred against the background of the way the settlers' pigs were farmed and traded. It describes the clinical signs and macroscopic pathology of natural and experimental cases. Pigs were raised either for home consumption or direct movement to a bacon factory and each outbreak occurred independently. Although circumstantial evidence suggested involvement of warthogs in the transmission of the disease to pigs, attempts to infect pigs by direct contact with warthogs consistently failed. However, inoculation of pigs with the blood of either warthogs or bush pigs that were experimentally infected, resulted in infection of the domestic pigs for up to or a little longer than two weeks post infection of the wild pigs. The second part of the paper described investigations into immunity to the disease in domestic pigs. Efforts to produce immunity through the use of serum against classical swine fever obtained from England failed to protect pigs against the East African virus. A pig that was immune to the classical swine fever virus developed severe clinical signs and died when inoculated with the East African virus. However, limited experiments with serum from one pig that survived infection with the East African virus as well as serum from bush pigs did not demonstrate protection in inoculated pigs from subsequent infection with the East African virus. Using heated virus, Montgomery found that one pig inoculated with the virus that had been heated to the temperature required to destroy the virus was immune, but pigs inoculated with virus heated to below the virus death point developed chronic forms of the disease that resembled classical swine fever. Similar chronic forms of ASF have been described elsewhere particularly in the Iberian Peninsula after the 1960 incursion and were ascribed to naturally attenuated viruses. However, this phenomenon has rarely been observed in other endemic areas. Vaccination of pigs with inadequately attenuated ASF virus is also likely to have played a role. Since the initial attempts by Montgomery to immunize pigs against ASF, great efforts by researchers in many countries have gone into developing a safe, efficacious vaccine but the results so far have largely been disappointing. In recent times considerable progress has been made particularly towards identifying promising candidates for a vaccine against the East African ASF virus currently circulating widely in Europe and Asia, but despite the available technology today which is beyond anything that Montgomery could have dreamed of, the truth is that a broad spectrum, guaranteed safe and efficacious vaccine against ASF in all its epidemiological scenarios has not become a reality. Therefore one hundred years after the discovery, the world is still grappling with the ASF virus. Thus the struggle continues on all fronts.