Genetic Characterisation of African Swine Fever Virus in Outbreaks in Ha Nam Province, Red River Delta Region of Vietnam, and Activity of Antimicrobial Products Against Virus Infection in Contaminated Feed

Abstract

Introduction: African swine fever (ASF) was officially reported in Vietnam in February 2019 and spread across the whole country, affecting all 63 provinces and cities.

Material and methods: In this study, ASF virus (ASFV) VN/Pig/HaNam/2019 (VN/Pig/HN/19) strain was isolated in primary porcine alveolar macrophage (PAM) cells from a sample originating from an outbreak farm in Vietnam's Red River Delta region. The isolate was characterised using the haemadsorption (HAD) test, real-time PCR, and sequencing. The activity of antimicrobial feed products was evaluated via a contaminated ASFV feed assay.

Results: Phylogenetic analysis of the viral p72 and EP402R genes placed VN/Pig/HN/19 in genotype II and serogroup 8 and related it closely to Eastern European and Chinese strains. Infectious titres of the virus propagated in primary PAMs were 10⁶ HAD₅₀/ml. Our study reports the activity against ASFV VN/Pig/HN/19 strain of antimicrobial Sal CURB RM E Liquid, F2 Dry and K2 Liquid. Our feed assay findings suggest that the antimicrobial RM E Liquid has a strong effect against ASFV replication. These results suggest that among the Sal CURB products, the antimicrobial RM E Liquid may have the most potential as a mitigant feed additive for ASFV infection. Therefore, further studies on the use of antimicrobial Sal CURB RM E Liquid in vivo are required.

Conclusions: Our study demonstrates the threat of ASFV and emphasises the need to control and eradicate it in Vietnam by multiple measures.

Keywords: African swine fever virus; Sal CURB; Vietnam; pig; virus isolation.

Fig. 1

Detection of ASFV in a field sample of spleen tissue. A – HAD assay of the spleen homogenate; B– the real-time PCR amplification of the p72 gene

Fig. 2

Phylogenetic analysis of VN/Pig/HN/19 based on its partial p72 (A) and EP402R gene encoding the CD2v protein (B) genes. Numbers along branches indicate bootstrap values >70% (1,000 replicates). The black triangle indicates the ASFV isolate from this study. Scale bars indicate nucleotide substitutions per site

Fig. 3

(A, B). The combination of feed with the Sal CURB RM E Liquid, Sal CURB F2 Dry or Sal CURB K2 Liquid and 1×105/mL HAD₅₀ of VN/Pig/HN/19 strain one, three, and seven days post inoculation. Values represent mean and standard deviation results from three independent experiments. Significant differences compared to control are denoted by * for P < 0.05 and ** for P < 0.01

Fig. 4

(A, B). The combination of feed with the Sal CURB RM E Liquid, Sal CURB F2 Dry or Sal CURB K2 Liquid and 1×105/mL HAD₅₀ of VN/Pig/HN/19 strain one, three, and seven days post inoculation. Values represent mean and standard deviation results from three independent experiments. Significant differences compared to control are denoted by * for P < 0.05 and ** for P < 0.01