Identification of a novel Neorickettsia species in a Kemp's ridley sea
turtle with granulomatous nephritis and development of a quantitative
PCR assay
Abstract
An adult male Kemp’s ridley was found dead on the coast of Kenedy
County, Texas in August 2019 with bilateral severe, diffuse
granulomatous nephritis. Pan-bacterial 16S rRNA gene PCR and amplicon
sequencing of affected tissue indicated the presence of a
Neorickettsia. Neorickettsia is a genus of obligate
intracellular Alphaproteobacteria that are transmitted by digenean
trematodes. For further characterization, primers were designed to
amplify and sequence the groEL gene. Phylogenetic analysis found
that the organism was distinct from other known species to a degree
consistent with a novel species. Immunohistochemistry using an antibody
directed against a Neorickettsia surface protein showed bacterial
clusters within the renal granulomas. A species-specific quantitative
PCR was designed, and detected the organism within the liver and colon
of the index case. A qPCR survey of grossly normal kidneys
opportunistically collected from additional stranded sea turtle kidneys
detected this organism in five of 15 Kemp’s ridley turtles, two of nine
green turtles, and neither of two loggerhead turtles. Recognition of
this novel organism in an endangered species is concerning; additional
work is underway to further characterize the potential of this organism
as a pathogen of sea turtles.