Investigation of the First African Swine Fever Outbreak in a Domestic Pig Farm in Hong Kong

Figures

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  Figure 1. Map of the farm buildings and floor plan of Building #11 where the initial outbreak was detected. (a) The map of the farm and its surroundings are depicted. The sheds where the ASF-related incidents occurred are indicated in the sequence of events by stars. (b) The floor plan of the finisher pig “index” shed in Building #11, containing 16 pens, is depicted. (c) Health conditions of pigs housed in Building #11. A few pigs presented mild skin reddening and nasal discharge on Day 5.

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  Figure 2. Clinical signs and gross lesions of pigs suspected of ASFV infection. On Day 7, (a) pigs with diffuse reddening of pinnae and (b) a dead pig with purplish-blue discoloration on the tips of the pinnae were found in Building #11. On Day 13, (c) a recumbent pig with diffuse reddening of pinnae and (d) conjunctivitis was found in Building #12. Gross lesions, including (e) mild splenomegaly (round edges of the spleen) with congestion and (f) mesenteric lymph node enlargement and hemorrhages, are shown.

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  Figure 3. Timeline of the ASF events and outbreak investigation in the domestic pig farm.

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  Figure 4. Post-mortem examination of index ASFV infected pig. Left panels: gross findings of index pig on day 0. (a) Skin lesions of multiple well-demarcated irregular patches (black arrows) are slightly raised and often with a rim of red to brown discoloration. (b) Pulmonary congestion and diffuse pulmonary edema (red arrows: prominent interlobular septa). (c) Splenomegaly with mildly round edges and congestion (red arrow). (d) Renal lymph node hemorrhages. Right panels: histopathological examination of index pig on day 0. (e) Multifocal to coalescing edema in the alveolar spaces and the interlobular septa (lung, H&E, 40X). (f) Bronchus-associated lymphoid tissue necrosis and fibrinonecrotic alveolitis/vasculitis (lung, H&E, 400X). (g) Lymphoid necrosis (spleen, H&E, 400X). (h) Necrotic focus with hemorrhage (pancreas, H&E, 100X). (i) Necrotic epidermis and suppurative infiltrate with fibrin thrombi in the blood vessels in the superficial dermis (skin, H&E, 100X). (j) Vasculitis and spilling of inflammatory cells to the adjacent cerebral parenchyma (brain, H&E, 400X).

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  Figure 5. Phylogenetic analysis of the full-length genome of ASFV Hong Kong isolate (HK202103; GenBank accession: OK358852). The combined nucleotide alignment for 121 orthologs is used to build the tree. The branch length shows the nucleotide substitution rate. The bootstrap values from 1000 replicates are indicated on each node. The complete tree with all available full-length genome sequences from GenBank used for the analysis is provided in Supplementary Figure S3.

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  Figure 6. Potential risk factors and routes of ASFV introduction into the outbreak farm. High-risk and low-risk factors are indicated with solid and dashed lines, respectively. Adapted from Pfeiffer et al. [38]. Abattoir (A) main abattoir. Abattoir (B) minor abattoir.