Histopathological findings
Microscopic lesions of cases 1-8 were tabulated in Table 2. All eight
cases showed haemorrhage with variable severity in the splenic tissue
(Fig 3a-c). In 3/8 pigs (cases 20, 58 and 59), severe haemorrhage
replaced the red pulp parenchyma and many tissues surrounding the
lymphoid follicles, rendering the evaluation of necrotizing tissue
difficult. In the liver tissue, the hemorrhagic lesion was seen in
different levels of severity in 6/8 cases. The mild cases showed focal
haemorrhage in zone 2, and severe cases showed multifocal to more
extensive haemorrhages (Fig 3d-f). In the tonsillar tissue, all cases
did not show any obvious significant changes in the tonsillar
morphology, and the lymphoid follicles were easily identified in low
magnification (x40, light microscope, field number 18) (Fig 4a). In
higher magnification, apoptotic tissues, characterized by numerous
nuclear debris and karyorrhexis, were more intense within the diffuse
lymphoid tissue (T-cells area) compared to the lymphoid follicles (Fig
4b-c). Extensive necrosis or haemorrhages were not seen in all cases. In
the lymph node tissue, sinus haemorrhages, apoptotic bodies and necrosis
were remarkable in all cases (Fig 5a). Like the tonsil, lymphoid
follicles were easily identifiable in the lymph node tissue.
In the lung tissue, interstitial pneumonia was seen in all 8 cases.
Mononuclear inflammatory cell infiltration increased the thickness of
the interstitium (Fig 5b). In many cases, pulmonary intravascular
macrophages were easily detectable in the small blood vessels and
capillaries. No prominent alveolar macrophages were seen in all cases.
Pulmonary oedema was seen in 5/8 cases, while pulmonary congestion (3/8)
and haemorrhage (2/8) were uncommon. In the brain tissue, meningitis
(8/8) and perivascular cuffing (5/8) were characterized with 2–4 layers
of mononuclear cells with frequent apoptotic bodies or nuclear
karyorrhexis (Fig 5c). Rarely, neutrophils were found in the meninges
among the mononuclear cell infiltration. Severe congestion of the
meningeal capillaries was common, but haemorrhages were subtle and not
present in most of the cases. Perivascular cuffing was commonly
accompanied with swollen endothelial cells. Glial nodule was absent in
all cases.
In the cardiac tissue, epicardial and myocardial haemorrhage was seen in
3/8 cases (Fig 5d). The haemorrhagic areas were sometimes infiltrated
with aggregates of mononuclear inflammatory cells. Microscopically,
haemorrhagic lesions were seen in various locations of the
gastrointestinal tract tissue. Case 58 showed haemorrhage in the lamina
propria of gastric tissue with oedema in the submucosal layer (Fig 5e).
Case 18 showed multifocal haemorrhages in the outer muscularis layer of
the small intestinal tissue (Fig 5f). Case 19 showed haemorrhages in the
deep lamina propria, dilated capillaries with congestion, and oedema in
the submucosa layer of large intestinal tissue (Fig 5g). In the renal
tissue, all cases showed haemorrhage in the renal pelvis (Fig 5h), but
only cases 57 and 59 showed oedemas in the area. Petechial haemorrhages
of the renal cortex were seen in 5/8 cases, with the lesion occasionally
extended into the capsular surface (Fig 5i). The haemorrhagic lesion was
absent in the renal medulla. Multifocal interstitial nephritis was seen
in 5/8 cases.