Porcine Circovirus 2-associated vasculitis in a young farmed wild boar
Emily Rätsep, Stéphanie Bourgon
Animal Health Laboratory, University of Guelph, Kemptville, ON (Rätsep), Vankleek Hill Veterinary Services, Vankleek Hill, ON (Bourgon)
AHL Newsletter 2021;25(4):12.
On a wild boar farm with a history of respiratory signs, 4 animals had complete hind limb paralysis and 5 more demonstrated some degree of weakness. Approximately 20 animals had been treated by injectable Ivomec 10 days prior for the perceived respiratory issue. On physical exam, rectal temperatures were normal, heart rate and respiratory rates were increased for all affected pigs, and increased lung sounds were noted. There were no associated central nervous signs (cranial nerve reflexes remained), and forelimb movement was intact in all animals. Pigs showing weakness or paralysis were treated with 5 mg of Dexamethasone 5 by intramuscular injection. One animal was found dead, two animals were euthanized by the owner, and one 6-month-old sow was euthanized by intracardiac injection with T-61 and was submitted for postmortem examination at the AHL in Kemptville.
Postmortem findings for the submitted sow included voluminous, dark red lungs that failed to collapse on opening of the thorax, petechial hemorrhages on the bladder and a focally extensive area of hemorrhage observed within a lumbar spinal cord segment (L3-4). No obvious cause of the spinal cord hemorrhage was observed. A viral cause of pneumonia was suspected based on the gross findings in the lungs.
Histologically, a marked lymphohistiocytic vasculitis was observed in multiple tissues, including the heart, bladder, colon, esophagus, tonsils, and kidney. Vasculitis was also apparent within sections of spinal cord associated with areas of hemorrhage observed grossly, and within the associated pia matter. Focally, the area of hemorrhage within the spinal cord resulted in significant disruption of the parenchyma and injury to the grey and white matter in this location (Fig. 1). Other than moderate pulmonary edema, no histological lesions were observed in the lungs.
The presence of vasculitis in multiple organs raised suspicion of infection with porcine circovirus 2. Lung submitted for viral PCR confirmed the presence of porcine circovirus 2 (PCV-2, positive with Ct 11.56) and viral infection was further confirmed by immunostaining for PCV-2 antigen within mononuclear cells in the vascular lesions in multiple tissues, notably spinal cord and lung (Fig. 2). All viral testing performed on this pig (as part of the OAHN swine small herd postmortem project) was otherwise negative.
There are several syndromes associated with infection by PCV-2 in domestic pigs, including postweaning multisystemic wasting syndrome or PMWS. These syndromes are now collectively known as porcine circovirus associated disease (PCVAD), and have been reported in both domestic pigs and farmed wild boar (1,2). Of these syndromes, vasculitis is considered the hallmark lesion of the more severe forms of PCVAD (3). In these reports, an acute lymphohistiocytic vasculitis was often accompanied by pulmonary edema (as was observed in this case). While lesions in the brain or spinal cord are only rarely observed (4), the presence of systemic vasculitis combined with a suspected direct cytopathic effect on these vessels by the PCV-2 virus (5) would explain hemorrhage in multiple organs, including spinal cord.
PCV-2 infection with vasculitis and subsequent spinal cord hemorrhage is the presumed underlying cause of the spinal cord lesion, thereby explaining the history of weakness progressing to paralysis in this pig. Though rare, it is worth considering the possibility of PCV-2 infection as a potential cause of neurological signs and paralysis in pigs, especially in those with a history of respiratory signs and wasting. In this case, a vaccination program was implemented on farm, with improvement reported in the breeding sows and piglets. AHL
Figure 1. Hemorrhage within the spinal cord white matter with disruption of the parenchyma and damage to axons (arrow). Lymphocytes and macrophages are present within the adventitia of an adjacent vessel in this area (arrowhead). H&E stain.
Figure 2. Porcine circovirus 2 infection in a pig. Spinal cord (2A) and lung (2B) with immunohistochemistry for PCV2. There is positive immunostaining of scattered endothelial cells (arrowhead) in the spinal cord, and within alveolar macrophages and perivascular/peribronchiolar mononuclear cells in the lung (arrows). Immunohistochemical staining for PCV-2 antigen, Nova Red chromagen
References
1. Gillespie J, et al. Porcine circovirus type 2 and porcine circovirus-associated disease. J Vet Intern Med 2009;23:1151-1163.
2. Vicente, J, et al. Epidemiological study on porcine circovirus type 2 (PCV2) infection in the European wild boar (Sus scrofa). Vet Res 2004;35(2):243-253.
3. Langohr IM, et al. Vascular lesions in pigs experimentally infected with porcine circovirus type 2 serotype B. Vet Pathol 2010;17(1):140-147.
4. Seeliger FA, et al. Porcine circovirus type 2-associated cerebellar vasculitis in postweaning multisystemic wasting syndrome (PMWS)-affected pigs. Vet Pathol 2007;44:621-634.
5. Resendes AR and Segalés J. Characterization of vascular lesions in pigs affected by porcine circovirus type 2-systemic disease. Vet Pathol 2015;52(2):497-504.