Follicle sinus complexes (FSCs) in muzzle skin as postmortem diagnostic material of rabid dogs

Immunohistochemical detection of virus antigen in the nasal planum of rabid dogs

The rabies virus is one of the most neurotropic of all viruses infecting mammals. During the terminal phases of infection, the virus spreads to peripheral tissues, including the skin. The external skin of the nose, called the nasal planum, is a sensory organ where numerous nerve bundles and terminal nerves are distributed. Therefore, the nasal planum is expected to serve as a postmortem diagnostic material. However, the distribution of rabies virus antigens in the nasal planum in rabid animals has not yet been studied. In this study, the nasal planum was obtained from 45 rabid dogs. In all rabid dogs, the viral antigen was detected in the peripheral nerve tissues, Merkel cells, and squamous cells. The viral antigen in the epidermis exhibited three patterns: first, a diffuse positive pattern from the basal layer to the squamous layer; second, a reticular positive pattern along the cell membrane in the squamous layer; and third, a basal layer pattern of the epidermis. In the dermis, viral antigens were detected more often in lamellated corpuscles just beneath the rete pegs. These results suggest that the nasal planum could serve as a useful alternative source for postmortem diagnosis in rabies endemic countries.

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

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.

Statistical analysis of the usefulness of follicle-sinus complexes as a novel diagnostic material for canine rabies

In the present study, follicle-sinus complexes (FSCs) were harvested from the muzzle skin of 123 dogs with suspected canine rabies, and the sensitivity and specificity of FSC analysis were compared with those of brain tissue immunohistochemistry analysis. In the FSCs, viral antigen was detected from Merkel cells. Sensitivity was 97.3%, specificity was 100%, and the coefficient κ was 0.88. These results reconfirm that FSCs are very useful for the postmortem diagnosis of canine rabies, and suggest that 5 FSCs can yield results that are almost equivalent to those derived from brain tissue analysis in rabid dogs.