Rapid and biologically safe diagnosis of African swine fever virus infection by using polymerase chain reaction.

In order to circumvent the need for infectious virus for the diagnosis of African swine fever (ASF), we established the polymerase chain reaction (PCR) technique for the detection of ASF virus (ASFV) DNA. A 740-bp fragment that originated from the conserved region of the viral genome was partially sequenced. From this sequence, four PCR primers and one oligonucleotide probe were designed and synthesized. A specific 640-bp PCR product was amplified by using oligonucleotides 1 and 5 as primers and extracts of the following samples as templates: organs and plasma obtained from ASFV-infected pigs, ASFV-infected cell cultures, and cloned DNA fragments containing the same conserved genomic region as that in the original 740-bp clone. No specific reaction products were observed in the corresponding controls. The identities of the PCR products were confirmed either by a second amplification with nested primers or by hybridization with a specific, biotinylated oligonucleotide probe. PCR proved to be a quicker and more sensitive method than virus isolation followed by the hemadsorption test when spleen and plasma samples from experimentally ASFV-infected pigs were tested. Furthermore, cloned virus DNA could be used as a positive control in the place of a live virus control. This is advantageous whenever the use of live virus is undesirable.