Hematology, morphology, cytochemical staining, and ultrastructural characteristics of blood cells in king cobras (Ophiophagus hannah)

Background-King cobras (Ophiophagus hannah) have been captive-bred at Queen Saovabha Memorial Institute since 1996 to supply venom for antivenom production. Hematologic tests would be useful for evaluating the health of the snakes, however, basic hematologic data and morphology have not been described for this species. Objective-The purpose of this study was to determine basic hematologic values and evaluate light microscopic, cytochemical, and electron microscopic characteristics of king cobra blood cells. Methods-Blood samples from 13 wild-caught and 15 captive-bred king cobras were collected into EDTA from the ventral caudal vein. A CBC was done using standard methods. Significant differences between groups were determined using t-tests. Cytochemical stains (periodic acid-Schiff [PAS], Sudan black B [SBB], alpha-naphthyl acetate esterase [ANAE], acid phosphatase [AcP], and beta-glucuronidase [beta-glu]), and scanning and transmission electron microscopy were done using standard techniques. Results-Eighteen snakes (64.3%) were positive for Hepatozoon infection. Hepatozoon organisms were detected nearly twice as frequently in wild-caught (11/13) as in captive-bred (7/15) snakes. Total WBC, azurophil, and lymphocyte counts were higher and fibrinogen concentration was lower in Hepatozoon-positive snakes. Captive-bred snakes had higher RBC values, lower azurophil, heterophil and punctate reticulocyte percentages, and higher lymphocyte numbers compared with wild-caught snakes. Lymphocytes were the most commonly observed WBCs, and stained positive with PAS, ANAE, AcP, and beta-glu. Azurophil granules stained positive with SBB, PAS, and ANAE. Heterophils were the largest WBCs; their granules stained with SBB, ANAE, and beta-glu. Basophil granules stained with PAS, SBB, ANAE, and beta-glu. Thrombocytes were strongly positive with PAS. Transmission electron microscopic examination revealed organelles within all WBCs except eosinophils and revealed the gamonts of Hepatozoon sp in RBCs and azurophils. Conclusions-These results provide comparative hematologic data and a guide for identification of blood cells in wild-caught and captive-bred king cobra snakes. Hepatozoon infection was relatively common, but was not associated with severe hematologic abnormalities.