Intraerythrocytic rickettsial inclusions in Ocoee salamanders (Desmognathus ocoee): prevalence, morphology, and comparisons with inclusions of Plethodon cinereus

Abstract

Reports of an unusual intraerythrocytic pathogen in amphibian blood have been made for decades; these pathogens appear as membrane-bound vacuoles within erythrocytes. It is now understood that the pathogen is a Rickettsia bacteria, which are obligate intracellular parasites, and most are transmitted by arthropod vectors. In an effort to further understand the host range and characteristics of this pathogen, we examined 20 Ocoee salamanders (Desmognathus ocoee) from a site in southwest North Carolina for the presence of rickettsial inclusions and report the general characteristics of infections. Seven individuals (35%) were infected, and this level of prevalence was consistent with all other members of this genus examined to date. In contrast, infections within the genus Plethodon tend to occur in less than 10% of individuals, based on review of the literature. The difference could be related to the semi-aquatic nature of Desmognathus salamanders versus the completely terrestrial Plethodon. It is also possible that both groups are hosts to different types of rickettsial bacteria, since the inclusions found here only vaguely resembled those found recently in red-backed salamanders (Plethodon cinereus). Inclusions in Ocoee salamanders measured 4 µm in diameter on average, and most cells (88%) only had one inclusion. Of all infected individuals, inclusions occurred in approximately 3% of erythrocytes. Similar to that found in red-backed salamanders, infected hosts were significantly larger than non-infected. Future investigations into the nature of this unusual parasite of amphibians would help to further our understanding of its life cycle and transmission.