Replication and virulence in pigs of the first African swine fever virus isolated in China

ABSTRACT

African swine fever (ASF) entered China in August 2018 and rapidly spread across the entire country, severely threatening the Chinese domestic pig population, which accounts for more than 50% of the pig population worldwide. In this study, an ASFV isolate, Pig/Heilongjiang/2018 (Pig/HLJ/18), was isolated in primary porcine alveolar macrophages (PAMs) from a pig sample from an ASF outbreak farm. The isolate was characterized by using the haemadsorption (HAD) test, Western blotting and immunofluorescence, and electronic microscopy. Phylogenetic analysis of the viral p72 gene revealed that Pig/HLJ/18 belongs to Genotype II. Infectious titres of virus propagated in primary PAMs and pig marrow macrophages were as high as 10^7.2 HAD₅₀/ml. Specific-pathogen-free pigs intramuscularly inoculated with different virus dosages at 10^3.5–10^6.5 HAD₅₀ showed acute disease with fever and haemorrhagic signs. The incubation periods were 3–5 days for virus-inoculated pigs and 9 days for contact pigs. All virus-inoculated pigs died between 6–9 days post-inoculation (p.i.), and the contact pigs died between 13–14 days post-contact (p.c.). Viremia started on day 2 p.i. in inoculated pigs and on day 9 p.c. in contact pigs. Viral genomic DNA started to be detected from oral and rectal swab samples on 2–5 days p.i. in virus-inoculated pigs, and 6–10 days p.c. in contact pigs. These results indicate that Pig/HLJ/18 is highly virulent and transmissible in domestic pigs. Our study demonstrates the threat of ASFV and emphasizes the need to control and eradicate ASF in China.

KEYWORDS:

• African swine fever virus
• virus isolation
• animal study
• pig
• transmission

Acknowledgements

We thank Dr. Linda K. Dixon and her team at The Pirbright Institute for technical discussion. The manuscript was written by D.Z. and Z.B; experiments and data analysis were performed by D.Z., R.L., X.Z., F.L., J.Z., X.L., L.W., J.W., J.Z., X.W., Y.G., and X.H; and the study was designed by D.Z., X.H and Z.B.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the the National Key R&D Program of China [grant numbers 2018YFC1200600, 2016YFC1202305], and the grant from the State Key Laboratory of Veterinary Biotechnology Program [grant number SKLVBP201801].