A pathological study of the tongues of rabid dogs in the Philippines
During rabies virus infections, the minor salivary glands are one of the important organs for virus replication and excretion into the oral cavity. However, details of pathological findings and viral antigen distribution in the minor salivary glands remain poorly understood. In this study, we conducted pathological tests on the tongues of 71 rabid dogs in the Philippines; the minor salivary glands (von Ebner’s glands, lingual glands), circumvallate papilla, autonomic ganglia, and skeletal muscles were evaluated. Inflammatory changes were observed in the von Ebner’s glands of 20/71 dogs, in the circumvallate papilla of 10/71, and in the tongue muscle of 1/71. Conversely, no morphological changes were observed in the lingual glands and autonomic ganglia. Viral antigens were detected via immunohistochemistry-based methods in the cytoplasm of the acinar epithelium in the von Ebner’s glands of all 71 dogs. Virus particles were confirmed in the intercellular canaliculi and acinar lumen via electron microscopy. In the autonomic ganglia, viral antigens were detected in 67/71 rabid dogs. Viral antigens were detected in the taste buds of all 71 dogs, and were distributed mainly in type II and III taste bud cells. In tongue muscle fibers, viral antigens were detected in 11/71 dogs. No virus antigens were detected in lingual glands. These findings suggest that rabies virus descends in the tongue along the glossopharyngeal nerve after proliferation in the brain, and von Ebner’s glands and taste buds are one of the portals of virus excretion into the saliva in rabid dogs.
The authors would like to acknowledge the invaluable help of staff at the Research Institute for Tropical Medicine (RITM), Department of Health, Philippines for tissue collection from dogs and the permission to use these samples in the current study. This work was supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (Kakenhi No. 26450410), and a grant for scientific research from the KITASATO University, Heiwa Nakajima Foundation, and AMED/JICA, SATREPS, Japan.
Compliance with ethical standards
The samples are dog’s heads which are clinical specimens routinely submitted for rabies diagnosis in the rabies laboratory of the Research Institute for Tropical Medicine (RITM) in the Philippines.
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