Emergence of African swine fever in Bangladesh: key findings from an outbreak investigation.

Background: African swine fever (ASF), caused by the African swine fever virus (ASFV), is a significant transboundary animal disease characterized by severe hemorrhages and high mortality in pigs. It poses substantial socioeconomic threats to the global pork industry. This study reports the first in-depth investigation of ASF in Bangladesh, focusing on the clinicopathological observations in naturally infected pigs and the molecular detection of ASFV.

Case presentation: On August 28, 2024, an outbreak occurred on a farm in the Panchagarh district of Bangladesh, which housed 230 indigenous pigs, 210 of which were found dead suddenly. Clinicopathological observations were conducted to assess the tissue changes and confirm the presence of the virus. Postmortem examinations were performed on selected animals and tissue samples, including spleen, lungs and liver, were collected from four pigs for laboratory analysis. Real-time polymerase chain reaction (qPCR) was conducted on the collected samples to detect the presence of ASFV at the molecular level, targeting the B646L gene encoding the p72 capsid protein. Clinically, the pig exhibited high fever (41-42 °C), anorexia, marked dullness, respiratory distress and lethargy. A severe bloody nasal discharge (epistaxis) was also noted, which followed death. Gross pathological findings included red hepatization of the lungs with edema, severe hemorrhagic splenomegaly, and a congested hemorrhagic liver. Histopathological examination of the lungs revealed widespread pneumonia, with predominant infiltration of alveolar macrophages. The spleen exhibited massive multifocal necrosis, while the liver showed significant hepatocellular necrosis, portal hepatitis, macrophage infiltration, and the presence of intracytoplasmic inclusion bodies. All four samples tested positive for ASFV by qPCR.

Conclusions: Since the initial outbreak, no detailed investigation of African swine fever (ASF) has been documented in Bangladesh. This field investigation, therefore, represents the first comprehensive report in the country. Continued in-depth studies, including genomic characterization of the virus and systemic surveillance of the pig population, are essential for the effective control and prevention of ASF in Bangladesh.