*Article* **Pathogenicity and Genetic Characterization of Vietnamese Classical Swine Fever Virus: 2014–2018**

**SeEun Choe 1,**†**, Van Phan Le 2,**†**, Jihye Shin 1, Jae-Hoon Kim 3, Ki-Sun Kim 1, Sok Song 1, Ra Mi Cha 1, Gyu-Nam Park 1, Thi Lan Nguyen 2, Bang-Hun Hyun 1, Bong-Kyun Park 1,4 and Dong-Jun An 1,\***


Received: 31 January 2020; Accepted: 26 February 2020; Published: 28 February 2020

**Abstract:** Here, we examined the pathogenicity and genetic differences between classical swine fever viruses (CSFV) isolated on pig farms in North Vietnam from 2014–2018. Twenty CSFV strains from 16 pig farms were classified as genotype 2 (sub-genotypes 2.1b, 2.1c, and 2.2). The main sub-genotype, 2.1c, was classified phylogenetically as belonging to the same cluster as viruses isolated from the Guangdong region in South China. Strain HY58 (sub-genotype 2.1c), isolated from pigs in Vietnam, caused higher mortality (60%) than the Vietnamese ND20 strain (sub-genotype 2.2). The Vietnamese strain of sub-genotype 2.1b was estimated to have moderate virulence; indeed, genetic analysis revealed that it belongs to the same cluster as Korean CSFV sub-genotype 2.1b. Most CSFVs circulating in North Vietnam belong to sub-genotype 2.1c. Geographical proximity means that this genotype might continue to circulate in both North Vietnam and Southern China (Guangdong, Guangxi, and Hunan).

**Keywords:** CSFV; genotype; virulence; E2 gene; phylogenetic tree
