ORIGINAL RESEARCH Quantitative and qualitative morphologic, cytochemical, and ultrastructural characteristics of blood cells in captive Asian water monitors Chaleow Salakij 1 , Jarernsak Salakij 2 , Kreangsak Prihirunkit 1 , Naul-Anong Narkkong 3 , Pornchai Sanyathitiseree 2 , Kwanjai Kranjanapitukkul 4 Departments of 1 Pathology, and 2 Large Animal and Wildlife Clinical Sciences, Faculty of Veterinary Medicine, Kasetsart University, Kamphaengsaen, Nakorn Pathom, Thailand; 3 Faculty of Science, Central Instrumentation Units, Mahasarakarm University, Maha Sarakarm, Thailand; and 4 Zoological Park Organization of Thailand, Dusit, Bangkok, Thailand Key Words Blood cells, cytochemistry, eosinophil, reptile, Varanus salvator Correspondence C. Salakij, Department of Pathology, Faculty of Veterinary Medicine, Kasetsart University, Kamphaengsaen, Nakorn Pathom 73140, Thailand E-mail: fvetcls@ku.ac.th DOI:10.1111/vcp.12183 Background: The Asian water monitor (Varanus salvator) is the most com- mon monitor lizard in Thailand. Reported data regarding hematology and morphology of blood cells for this species are scarce. Objectives: The objective of this study was to assess routine hematologic variables and characterize the morphology, cytochemical staining, and ul- trastructural features of blood cells in the Asian water monitor. Methods: Blood samples from 55 monitors (22 males and 33 females) were obtained for a CBC. Cytochemical staining (Sudan black B [SBB], peroxi- dase [PO], a-naphthyl acetate esterase [ANAE], and beta-glucuronidase [BG]), and scanning and transmission electron microscopy were performed using standard methods. Results: Determined mean (range) hematologic results of all monitors included PCV 0.32 L/L (0.20–0.44 L/L), HGB 106 g/L (62–157 g/L), WBC 15.9 9 10 9 /L (4.0–34.0 9 10 9 /L), heterophil 6.3 9 10 9 /L (1.5– 17.1 9 10 9 /L, azurophil 2.6 9 10 9 /L (0.7–9.5 9 10 9 /L), basophil 0.1 (0.1– 0.5 9 10 9 /L), lymphocyte 6.8 9 10 9 /L (0.5–13.1 9 10 9 /L), and monocyte 0.2 9 10 9 /L (0.04–1 9 10 9 /L) counts. Heterophils and basophils stained strongly positive with SBB, ANAE, and BG. Heterophils contained 2 types of granules, round SBB-positive and PO-negative granules, and electron- dense, large rod-shaped granules. Gamonts of Hepatozoon sp. were found in <1% RBC of 43 monitors. There was no significant difference between hematologic variables in Hepatozoon-positive and -negative monitors. Conclusion: Heterophils in Asian water monitors may also function as eo- sinophils based on cytochemical and ultrastructural features. The quantita- tive results may be used as base for further studies in healthy and diseased Asian water monitors. Introduction The Asian water monitor (Varanus salvator) is a large monitor lizard found throughout much of southern Asia, from Sri Lanka through Southeast Asia to the Moluccas. 1 It is the most frequently encountered mon- itor lizard in Thailand included in the category “Reserved wild animals” and listed in the Act of Ani- mals Protection and Conservation of Thailand since 1992. The determination of normal blood variables in a population serves as a reference for monitoring the health status, and is an essential tool for conservation efforts of such reptilian species. The circulating blood cells in reptiles are grouped into RBCs, WBCs, and thrombocytes. Notable species differences in reptile WBC cells include the morphology of heterophils and eosinophils. 2 Cytochemical stains are a standard tech- nique routinely used in veterinary laboratories for the identification of WBC lineage. 3 Data documenting the morphology, cytochemistry, and ultrastructure of blood cells of the Asian water monitor are scarce. Some morphologic studies on blood cells of a few lizards have 538 Vet Clin Pathol 43/4 (2014) 538–546 ©2014 American Society for Veterinary Clinical Pathology Veterinary Clinical Pathology ISSN 0275-6382