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. 2024 Sep 28;12(10):1114.
doi: 10.3390/vaccines12101114.

Genotype II Live-Attenuated ASFV Vaccine Strains Unable to Completely Protect Pigs against the Emerging Recombinant ASFV Genotype I/II Strain in Vietnam

Nguyen Van Diep  1 , Nguyen Van Duc  1 , Nguyen Thi Ngoc  1 , Vu Xuan Dang  1 , Tran Ngoc Tiep  1 , Viet Dung Nguyen  2 , Thi Tam Than  3 , Dustin Maydaniuk  4 , Kalhari Goonewardene  4 , Aruna Ambagala  4 , Van Phan Le  3   5
Affiliations

Genotype II Live-Attenuated ASFV Vaccine Strains Unable to Completely Protect Pigs against the Emerging Recombinant ASFV Genotype I/II Strain in Vietnam

Nguyen Van Diep et al. Vaccines (Basel). .

Abstract

Background: African swine fever virus (ASFV) continues to spread globally, causing severe economic losses to pig farmers. Vietnam licensed two live attenuated vaccines based on the ASFV strains ASFV-G-ΔI177L and ASFV-G-ΔMGF to control the ongoing ASF outbreaks. In 2023, newly emerging highly virulent recombinant ASF viruses (rASFV I/II) containing genetic elements from both p72 genotype I and II ASF viruses were reported from Northern Vietnam. Objective: This study evaluated whether the two vaccine strains were able to protect the pigs against the emerging rASFV I/II strain VNUA/rASFV/TN1/23. Results: Pigs vaccinated with ASFV-G-ΔMGF or ASFV-G-ΔI177L, when challenged with rASFV I/II, succumbed to the infection, or developed signs of chronic ASF. Conclusions: The findings from this study show that both vaccine strains that are licensed and used in Vietnam are unlikely to protect pigs from the emerging highly virulent rASFV I/II. This complicates the ongoing efforts to control ASF in Asia and globally and emphasizes the urgent need for a novel vaccine that can effectively protect pigs from the rASFV I/II.

Keywords: ASF; ASFV-G-ΔI177L; ASFV-G-ΔMGF; emerging; live-attenuated; rASFV I/II; vaccine.

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Conflict of interest statement

Authors Nguyen Van Diep, Nguyen Van Duc, Nguyen Thi Ngoc, Vu Xuan Dang, Tran Ngoc Tiep were employed by the company AVAC Vietnam Joint Stock Company. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Daily rectal temperatures of pigs (#11–16) inoculated with ASFV-G-ΔI177L (104 HAD50 IM per pig) before (A) and after (B) challenge with rASFV I/II (103 HAD50 IM per pig). The dates pigs were found dead or euthanized as they reached the humane endpoint are marked with an arrow. DPV = days post-vaccination. DPC = days post-challenge.
Figure 2
Figure 2
Daily average cumulative clinical scores (CCS) of the pigs that received ASFV-G-∆I177L, ASFV-G-ΔMGF, or PBS before and after the challenge with the rASFV I/II strain. DPV = days post-vaccination.
Figure 3
Figure 3
Swelling of tarsal joints (arrows) of pigs #14 (A) and #11 (B) that survived the rASFV I/II challenge.
Figure 4
Figure 4
Daily rectal temperatures of pigs (#17–23) inoculated with ASFV-G-ΔMGF (104 HAD50 IM per pig) before (A) and after (B) the challenge with rASFV I/II (103 HAD50 IM per pig). The dates pigs were euthanized are marked with an arrow. DPV = days post-vaccination. DPC = days post-challenge.
Figure 5
Figure 5
Daily rectal temperatures of control pigs (#5–10) inoculated IM with a sterile PBS (A) and challenged with rASFV I/II (103 HAD50 IM per pig) (B). The dates pigs were found dead or euthanized are marked with an arrow. DPV = days post-vaccination. DPC = days post-challenge.
Figure 6
Figure 6
Viremia was detected in individual pigs following inoculation with ASFV-G-ΔI177L (A), ASFV-G-ΔMGF (B), or sterile PBS (C) followed by the rASFV I/II challenge. The samples with detectable levels of ASFV viral genome were further tested to differentiate the genotype II (G2) vaccinated strains vs. the recombinant challenge virus strain (G1). DPV = days post-vaccination.
Figure 7
Figure 7
Detection of ASFV genomic material in nasal swabs collected from individual pigs following inoculation with ASFV-G-ΔI177L (A), ASFV-G-ΔMGF (B), or sterile PBS (C) followed by the rASFV I/II challenge. DPV = days post-vaccination.
Figure 8
Figure 8
Serum anti-ASFV antibody levels in individual pigs following inoculation with ASFV-G-ΔI177L (A), ASFV-G-ΔMGF (B), or sterile PBS (C) followed by the rASFV I/II challenge.
Figure 9
Figure 9
Gross pathological lesions observed in pigs that received ASFV-G-ΔI177L (A–E), ASFV-G-ΔMGF (F–I), and died/were euthanized after the rASFV I/II challenge. (A) Subcutaneous hemorrhage and hematoma in the left pinna, (B) consolidated lungs, (C) congestion in the gastric mucosa, (D) splenomegaly, (E) ulceration at the gastroesophageal junction, (F) hemorrhagic mesenteric lymph nodes, (G) hemorrhages in the ear, (H) hemorrhages in the tonsil, submandibular lymph nodes, and superficial inguinal lymph nodes, and (I) hemorrhagic submandibular lymph nodes.
Figure 10
Figure 10
Gross pathological lesions observed in pigs #14 (A–F) and 11 (G–I) that received ASFV-G-ΔI177L and survived the rASFV I/II challenge. (A) Swollen left hock joint (arrow) and dermatitis under the neck, (B) Dermatitis with necrotic and denuded skin, (C) Increased synovial fluid in the left hock joint, (D) Necrotic lymphoid tissues of the ilea-cecal valve, (E) Hemorrhagic lymph nodes, (F) Gastric ulcers (arrows), (G) Swollen hock joint, (H) Increased synovial fluid in the hock joint, (I) hemorrhagic submandibular lymph nodes.
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