Hematologic and plasma biochemical reference intervals for health monitoring of wild Australian tree frogs

Abstract

Few hematologic and biochemical reference intervals for wild amphibians have been established. Reference values would aid in early detection of emerging infectious diseases, which are a significant problem for amphibian conservation efforts. We aimed to establish reference intervals for a wide range of hematologic and plasma biochemistry variables for 2 species of Australian tree frogs, describe morphologic features of leukocytes, and analyze the effects of season, year, and parasite status on blood values. Blood specimens were collected from reference populations of wild adult Australian tree frogs, Litoria caerulea and L infrafrenata, for analysis of hematologic (manual) variables, plasma biochemical (automated) analytes, and plasma and serum proteins using automated methods, refractometry, and electrophoresis. Inter- and intraspecies differences were found in L caerulea (n = 80) and L infrafrenata (n = 66) frogs for hematologic and biochemical variables. Intraspecies differences were largely associated with seasonal variations. In the dry season, both species had higher WBC counts, with higher lymphocyte counts in L caerulea and higher neutrophil counts in L infrafrenata, and uric acid concentrations. In the wet season, both species had higher glucose and potassium concentrations, L caerulea frogs had higher neutrophil counts, and L infrafrenata frogs had higher total protein, phosphorus, and sodium concentrations, AST activity, PCV, hemoglobin concentration, and RBC, thrombocyte, and basophil counts. Hemogregarines were identified in 19% of blood samples from L infrafrenata frogs; multiple hematologic and biochemical variables were altered in infected frogs. Wide interspecies and seasonal variations highlight the need to establish species- and season-specific reference intervals for amphibians. Hematologic and plasma biochemical reference values should be useful in assessing the health status and in detecting emerging diseases in wild amphibians.