Ultrasonographic assessment and ultrasound-guided biopsy of the retropharyngeal lymph nodes in Asian elephants (Elephas maximus)

Endotheliotropic herpesvirus causes a fatal disease in young Asian elephants, but there are no methods for identifying latent carriers of the virus. During the postmortem study of one female African elephant and three male and two female Asian elephants, a lymph node located bilaterally caudoventral to the parotid gland, approximately 1·5 to 5 cm below the skin, was identified as suitable for transcutaneous ultrasound-guided biopsy. An ultrasonographic assessment and two biopsies were performed on 39 Asian elephants, and these lymph nodes were classified ultrasonographically as active, inactive or chronically active. The calculated mean (se) volume of 10 active lymph nodes was 17·4 (6·9) cm3, and that of three chronically active lymph nodes was 10·6 (1·0) cm3, whereas the mean volume of 17 inactive lymph nodes was 3·1 (0·6) cm3. The presence of lymph node tissue in samples obtained by ultrasound-guided biopsy from three animals that were maintained under conditions that allowed for additional sampling was confirmed histologically. The DNA extracted from the lymphoid tissue and the whole blood of all the elephants was negative for endotheliotropic herpesvirus by PCR.