Pathogenicity of an African swine fever virus strain isolated in Vietnam and alternative diagnostic specimens for early detection of viral infection

Hu Suk Lee,Ngoc Anh Bui,Tai-Young Hur,Long Hoang Tran,Duy Tung Dao,Sang-Ik Oh,Kyoung-Min So,Vuong Nghia Bui,Jae-Hee Roh,Minh Anh Kieu,Thanh Duy Le,Quang Huy Nguyen

doi:10.1186/s40813-021-00215-0

Abstract

BackgroundAfrican swine fever (ASF), caused by the ASF virus (ASFV), was first reported in Vietnam in 2019 and spread rapidly thereafter. Better insights into ASFV characteristics and early detection by surveillance could help control its spread. However, the pathogenicity and methods for early detection of ASFV isolates from Vietnam have not been established. Therefore, we investigated the pathogenicity of ASFV and explored alternative sampling methods for early detection.ResultsTen pigs were intramuscularly inoculated with an ASFV strain from Vietnam (titer, 103.5 HAD50/mL), and their temperature, clinical signs, and virus excretion patterns were recorded. In addition, herd and environmental samples were collected daily. The pigs died 5–8 days-post-inoculation (dpi), and the incubation period was 3.7 ± 0.5 dpi. ASFV genome was first detected in the blood (2.2 ± 0.8) and then in rectal (3.1 ± 0.7), nasal (3.2 ± 0.4), and oral (3.6 ± 0.7 dpi) swab samples. ASFV was detected in oral fluid samples collected using a chewed rope from 3 dpi. The liver showed the highest viral loads, and ear tissue also exhibited high viral loads among 11 tissues obtained from dead pigs. Overall, ASFV from Vietnam was classified as peracute to acute form. The rope-based oral fluid collection method could be useful for early ASFV detection and allows successful ASF surveillance in large pig farms. Furthermore, ear tissue samples might be a simple alternative specimen for diagnosing ASF infection in dead pigs.ConclusionsOur data provide valuable insights into the characteristics of a typical ASFV strain isolated in Vietnam and suggest an alternative, non-invasive specimen collection strategy for early detection.

Highlights

African swine fever (ASF), caused by the ASF virus (ASFV), was first reported in Vietnam in 2019 and spread rapidly thereafter
To address these knowledge gaps, we investigated the virulence and pathogenicity of ASFV strains from Vietnam by experimentally challenging pigs with ASFV
To the best of our knowledge, this is the first experimental viral infection study to evaluate the incubation time, clinical signs, viremia, and virus excretion patterns in pigs infected with an ASFV isolated in Vietnam that belongs to p72 genotype II [8]

Summary

Introduction

African swine fever (ASF), caused by the ASF virus (ASFV), was first reported in Vietnam in 2019 and spread rapidly thereafter. The rope-based oral fluid collection method could be useful for early ASFV detection and allows successful ASF surveillance in large pig farms. A previous study reported that the Chinese ASFV isolates are highly lethal to domestic pigs even at low doses of the virus and that the clinical signs start showing very early period during the course of infection [6]. Several molecular and pathological studies on ASFV-infected pigs from ASF outbreak farms were conducted to evaluate the characteristic lesions and examine the genetic properties of ASFV strains from Vietnam [10,11,12]. Because no virus inoculation studies have been conducted to evaluate the virulence and pathogenicity of ASFV isolates from Vietnam, the pathogenicity of these strains is not fully understood.

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Conclusion