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

Abstract

Background: 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.

Objective: 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.

Methods: 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.

Results: 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.

Conclusions: 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.