Follicle-sinus complexes in muzzle skin of domestic and wild animals as diagnostic material for detection of rabies

Abstract

We previously reported a novel diagnostic method using follicle-sinus complexes (FSCs) in the muzzle skin for postmortem diagnosis of rabies in dogs. However, whether this method works in other animal species remains unclear. Here, FSCs were collected from a wolf, a red fox, 2 bats, and a cat, and examined for the presence of viral antigen, viral mRNA, and viral particles. Viral antigen and viral mRNA were confirmed in Merkel cells (MCs) in FSCs of all species. Electron microscopy performed using only samples from wolf and cat confirmed viral particles in MCs of FSCs. These results suggested that this novel diagnostic method using FSCs might be useful for detection of rabies not only in domestic but also wild animals.

Keywords: Merkel cell; follicle-sinus complex; postmortem diagnosis; wild animal.

Fig. 1.

Viral antigens were concentrated in a part of the outer root sheath of the follicle-sinus complexes at the level of the ring sinus. a: wolf, b: cat, c: red fox, d: bat. HS: hair shaft, OS: outer root sheath. Immunohistochemistry. Bar=100 µm.

Fig. 2.

Transverse sections of follicle-sinus complexes (FSCs) in the muzzle skin of wolf. CAM 5.2 (green, 2a), viral antigen (red, 2b), and double-positive signals (merged images, yellow, 2c), and CK 20 (red, 2d), viral antigen (green, 2e), and double-positive signals (merged images, yellow, 2f) are visible in a part of the outer root sheath of FSCs. OS: outer root sheath, RS: ring sinus. Immunofluorescence staining. Bar=50 µm.

Fig. 3.

Positive signals (arrowheads) of in situ hybridization appear in the cytoplasm of Merkel cells of wolf follicle-sinus complexes (FSCs). In situ hybridization. HS: hair shaft, OS: outer root sheath. Bar=100 µm (insert, bar=25 µm).

Fig. 4.

Three matrix structures (*) and viral-associated structures are observed in the cytoplasm of Merkel cells of follicle-sinus complexes of wolf. N: nuclear. Transmission electron microscopy. Bar=2 µm.

Fig. 5.

Bullet-shaped viral particles (arrowhead) are observed in the rough endoplasmic reticulum of Merkel cells of follicle-sinus complexes of wolf. Mi: mitochondria, N: nuclear. Transmission electron microscopy. Bar=500 nm.