Tioman virus, a paramyxovirus of bat origin, causes mild disease in pigs and has a predilection for lymphoid tissues

Abstract

Disease manifestation, pathology, and tissue tropism following infection with Tioman virus (TioPV), a newly isolated, bat-derived paramyxovirus, was investigated in subcutaneously (n = 12) and oronasally (n = 4) inoculated pigs. Pigs were either asymptomatic or developed pyrexia, but all of the animals produced neutralizing antibodies. The virus (viral antigen and/or genome) was detected in lymphocytes of the thymus, tonsils, spleen, lymph nodes and Peyer's patches (ileum), tonsillar epithelium, and thymic epithelioreticular cells. Virus was isolated from oral swabs but not from urine. Our findings suggest that the pig could act as an intermediate or amplifying host for TioPV and that oral secretion is a possible means of viral transmission.

FIG. 1.

Histology, IHC, and ISH of TioPV infection of pigs. (A) Intracytoplasmic TioPV inclusions within the epithelial cells of an infected pig tonsil (arrows). Hematoxylin and eosin, 40× objective. (B) Intranuclear inclusion in a TioPV-infected pig tonsil (arrows). Hematoxylin and eosin, 40× objective. (C) A Warthin-Finkeldey-type giant cell in the medulla of the thymus. Hematoxylin and eosin, 40× objective. (D) TioPV antigens in epithelial cells of a tonsillar crypt. Rabbit anti-TioPV antibody, chromogen 3,3′-diaminobenzidine, brown, counterstained with Harris's hematoxylin, 20× objective. (E) TioPV antigens in the epithelioreticular cells (arrows) of the medulla and within lymphocytes (arrowheads) of the thymus. Pig anti-TioPV antibody, chromogen 3-amino-9-ethylcarbazole, red, lightly counterstained with Mayer's hematoxylin, 40× objective. (F) Viral antigens in lymphocytes surrounding the periarterial lymphatic sheath of the spleen. Rabbit anti-TioPV antibody, chromogen 3,3′-diaminobenzidine, brown, counterstained with Harris's hematoxylin, 20× objective. (G) Viral antigens in the parafollicle of the lymph node. Rabbit anti-TioPV antibody, chromogen 3,3′-diaminobenzidine, brown, counterstained with Harris's hematoxylin, 20× objective. (H) ISH of TioPV in the thymus showing the viral genome in an epithelioreticular cell adjacent to Hassall's corpuscle. Chromogen nitroblue tetrazolium-5-bromo-4-chloro-3-indolyl-β-d-galactopyranoside, dark blue, 40× objective. (I) TioPV genome detected in epithelial cells lining a tonsillar crypt by ISH. Chromogen nitroblue tetrazolium-5-bromo-4-chloro-3-indolyl-β-d-galactopyranoside, dark blue, 40× objective. (J) Viral antigens in cell debris within a tonsillar crypt. Inset, ISH of TioPV in the cell debris within the crypt. Pig anti-TioPV antibody, chromogen 3-amino-9-ethylcarbazole, red, lightly counterstained with Mayer's hematoxylin, 40× objective; inset, chromogen nitroblue tetrazolium-5-bromo-4-chloro-3-indolyl-β-d-galactopyranoside, dark blue, 40× objective. (K) IHC positivity in circulating leukocytes (arrows). Rabbit anti-TioPV antibody, chromogen 3,3′-diaminobenzidine, brown, counterstained with Harris's hematoxylin, 40× objective.