On September 2, 2025, a collaborative team from the Vietnam National University of Agriculture and the Canadian Food Inspection Agency published a new study in the international journal Pathogens, reporting the pathological characteristics of a newly emerged recombinant African swine fever virus (ASFV genotype I/II) in Vietnam.
This study revealed the high pathogenicity and rapid transmission of this recombinant virus, posing new challenges to existing vaccine control systems.
Research Highlights
· The first experimental confirmation: The newly emerged Vietnamese recombinant strain, VNUA/rASFV/HD1/23 (genotype I/II), possesses extremely potent virulence, with a 100% lethality within 4–10 days.
· Dose determines life or death: The 10⁴HAD₅₀ group died an average of 5 days, while the 10² group survived only 7.75 days. Viral load is positively correlated with the speed of onset.
· Enhanced pathological profile: a "triad" of splenic infarction, pulmonary edema, and renal hemorrhage, with microscopic evidence of vascular collapse and lymphocyte depletion.
Public Health Alert: This strain is completely resistant to both genotype II live vaccines currently available in Vietnam, rendering herd immunity barriers virtually non-existent.
High Cross-Border Risk: The strain is highly homologous to the recombinant strain detected at the China-Russia border during the same period, suggesting the formation of a "China-Vietnam-Russia" transmission corridor.
On September 2, 2025, a collaborative team from the Vietnam National University of Agriculture and the Canadian Food Inspection Agency published a new study in the international journal Pathogens, reporting the pathological characteristics of a newly emerged recombinant African swine fever virus (ASFV genotype I/II) in Vietnam.
This study revealed the high pathogenicity and rapid transmission of this recombinant virus, posing new challenges to existing vaccine control systems.
Research Highlights
· The first experimental confirmation: The newly emerged Vietnamese recombinant strain, VNUA/rASFV/HD1/23 (genotype I/II), possesses extremely potent virulence, with a 100% lethality within 4–10 days.
· Dose determines life or death: The 10⁴HAD₅₀ group died an average of 5 days, while the 10² group survived only 7.75 days. Viral load is positively correlated with the speed of onset.
· Enhanced pathological profile: a "triad" of splenic infarction, pulmonary edema, and renal hemorrhage, with microscopic evidence of vascular collapse and lymphocyte depletion.
Public Health Alert: This strain is completely resistant to both genotype II live vaccines currently available in Vietnam, rendering herd immunity barriers virtually non-existent.
High Cross-Border Risk: The strain is highly homologous to the recombinant strain detected at the China-Russia border during the same period, suggesting the formation of a "China-Vietnam-Russia" transmission corridor.
Figure 1. Daily average rectal temperature (°C) of ASFV-infected and uninfected pigs (control group)
Figure 2. Average clinical scores of ASFV-infected and uninfected pigs
2. Viral Detection: Viruses can be detected in oral fluid earlier than in blood.
· Virus in blood (viremia): Viruses were detectable within 3 days in the 10³ and 10⁴HAD₅₀/mL groups, while some pigs in the 10²HAD₅₀/mL group required 6 days.
· Virus in oral fluid: Viruses were detectable within 2 days in the 10⁴HAD₅₀/mL group (earlier than in blood), while those in the 10³ and 10²HAD₅₀/mL groups required 4 and 5 days, respectively, suggesting that oral fluid can be used as an early monitoring sample.
Table 1. Detection of African swine fever virus genomic material in oral fluid
3. Pathological Features: Typical Acute ASF Lesions
· Gross Lesions (present in 100% of pigs): Splenomegaly with infarction, hemorrhagic and enlarged lymph nodes, and tonsil congestion; 92% of pigs presented with pneumonia and renal hemorrhage, and 58% presented with intestinal hemorrhage.
· Histopathology: Splenic white pulp showed structural destruction, congestion, and hemorrhage; lymph node lymphocytes were significantly decreased with necrotic cell debris; lungs were congested and edematous, with alveolar effusions; and renal vasodilation and congestion were observed.
Table 2. Summary of gross lesions in pigs inoculated with VNUA/rASFV/HD1/23 strain
Figure 3. Gross pathological lesions in pigs infected with VNUA/rASFV/HD1/23
(A) Infarction (red circle) and splenomegaly; (B) Mesenteric lymph node hemorrhage (red circle);
(C) Pulmonary inflammation and edema; (D) Tonsillar congestion;
(E) Inguinal lymph node enlargement and congestion (black arrow);
(F) Mandibular lymph node enlargement and congestion (red arrow); (G) Gastric mucosal congestion;
(H) Renal pelvic hemorrhage (green circle); (I) Numerous petechiae on the renal cortical surface.
Figure 4. Histopathological lesions (A1–F1) are microscopic comparison specimens of the spleen, tonsils, inguinal lymph nodes, lungs, stomach, and kidneys, respectively.
4. Pathogenicity Comparison: Comparable to Globally Highly Virulent Type II Strains
The pathogenicity (onset rate, mortality rate, and pathological lesions) of this recombinant strain is consistent with highly virulent type II strains worldwide, such as the 2007 Georgian strain and the 2018 Heilongjiang strain from China, and existing vaccines offer no protection.
Summary
This study reveals for the first time the potent pathogenicity and pathological characteristics of a new recombinant ASFV in Vietnam, emphasizing the need to strengthen early detection, optimize diagnostic methods, and accelerate the development of new vaccines against recombinant viruses. The prevention and control of African swine fever has entered the "recombinant era," and international cooperation and scientific response are urgently needed!
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