A survey of leukocyte profiles of red-backed salamanders from Mountain Lake, Virginia, and associations with host parasite types

In this project, red-backed salamanders, Plethodon cinereus, were collected from the heart of their range (Mountain Lake, Virginia, USA), in an effort to document the typical, or baseline, leukocyte profile of this species in its natural state. From microscopic examination of thin blood films, we determined relative proportions of all leukocyte types and determined the ratio of neutrophils to lymphocytes, which is a useful index of stress levels. In addition, individuals were examined for three naturally occurring endoparasites: two gastro-intestinal (trematodes and a ciliated protozoan in the genus Cepedietta) and one in the blood (a Rickettsial bacteria). This allowed us to conduct statistical comparisons of leukocyte data across parasite infection groups. Of 36 salamanders, 11 (31%) had trematode parasites, 7 (19%) contained Cepedietta parasites, 6 (17%) were parasitized by Rickettsia, and 12 had no parasites. The most common leukocytes were lymphocytes (87.4%), followed by neutrophils (4.2%), monocytes (3.3%), eosinophils (2.6%), and basophils (2.5%). The average neutrophil/lymphocyte ratio for these salamanders was remarkably low (0.05) for an amphibian population. Statistical comparisons of leukocyte profiles among parasite infection groups indicated parasitized salamanders had twice as many circulating leukocytes as nonparasitized individuals, which could be considered an “inflammation response”. There was a slight but significant elevation in relative eosinophil abundance in parasitized salamanders. There were few differences in leukocyte subsets between parasite types, nor was there evidence of any proliferation of phagocytic cells in any parasitized individual.