COCCIDIOSIS IN GREEN TURTLES (CHELONIA MYDAS) IN AUSTRALIA: PATHOGENESIS, SPATIAL AND TEMPORAL DISTRIBUTION, AND CLIMATE-RELATED DETERMINANTS OF DISEASE OUTBREAKS

Systemic Caryospora-like coccidiosis in a clutch of hatchling red-eared slider turtles (Trachemys scripta elegans)

Caryospora-like organisms (CLOs) form a clade of at least 11 genotypes of related coccidia that can cause epizootic mortality in marine turtles. The biology, transmission, host species range, and host cell tropism of these organisms are still largely unknown. The goal of this study was to characterize the host cell tropism, pathologic and ultrastructural features, and phylogeny associated with the first report of a mortality event due to CLO in the freshwater red-eared slider turtle (Trachemys scripta elegans). Sudden mortalities within a clutch of captive-raised red-eared slider hatchlings (n = 8) were recorded, and deceased animals had severe segmental to diffuse, transmural, fibrinonecrotic enterocolitis and multifocal to coalescing hepatic necrosis, among other lesions associated with numerous intracytoplasmic developing stages of intralesional coccidia. Among the different developmental stages, merozoites were ultrastructurally characterized by an apical complex. A pan-apicomplexan polymerase chain reaction (PCR) yielded a 347 bp-amplicon matching the Schellackia/Caryospora-like clade with 99.1% identity to the US3 strain from green sea turtles (Chelonia mydas) and 99.1% identity to Schellackia sp. Isolate OC116. Surviving hatchlings were treated with toltrazuril sulfone (ponazuril) but were subsequently euthanized due to the risk of spreading the parasite to other chelonids in the collection. The ponazuril-treated hatchlings (n = 4) had mild proliferative anterior enteritis, with few intraepithelial coccidia in one hatchling confirmed as CLO by PCR. This is the first report of Caryospora-like coccidiosis in non-cheloniid turtles, highlighting the relevance of this disease as an emerging highly pathogenic intestinal and extra-intestinal form of coccidiosis of turtles with potential cross-species infectivity.

First report of Caryospora sp. infection in free-living green turtles (Chelonia mydas) in Northeastern Brazil

Infection by Caryospora cheloniae has been reported to be responsible for green turtle strandings with high morbidity and mortality rates worldwide. Although studies have already shown the pathogenesis of these infections, many aspects of this protozoan are still poorly understood, including their life cycle and infection dynamics in free-living sea turtle populations. Due to the lack of information about the infection by this protozoan in sea turtles in Northeastern Brazil, our study aims to describe Caryospora sp. infection and its pathological findings in free-living Chelonia mydas found on the north coast of the Bahia state. Between 2018 and 2019, 64 specimens of green turtles were necropsied in partnership with Fundação Projeto Tamar; among these, 10 (1.56%) had oocysts morphologically compatible with Caryospora cheloniae in the evaluation of fecal samples and histopathological examination of intestinal samples. The infected animals were juvenile green turtles that were found stranded on the beaches of the north coast of Bahia. The pathological findings were restricted to the lower gastrointestinal tract, with different presentations and intensities. About 70% of the animals with coccidial infection exhibited erosive and ulcerative fibrinous enteritis. This is the first report of coccidiosis in green turtles on the north coast of Bahia.

Pharmacokinetics of ponazuril after administration of a single oral dose to green turtles (Chelonia mydas)

The coccidian protozoan, Caryospora cheloniae, has been associated with severe enteritis and encephalitis in immature farm-raised green turtles (Chelonia mydas) in the Cayman Islands, immature green turtles off the coast of Florida, and immature stranded sea turtles in Australia. An effective anti-coccidial drug that is both orally absorbed and well-distributed throughout the body is needed for treatment of turtles diagnosed with coccidiosis in rehabilitation facilities. Ponazuril is a triazine antiprotozoal drug that is approved in the USA for the treatment of another Apicomplexan, Sarcocystis neurona, and has also been successfully used in the therapy of other coccidian parasites. The objective of this study was to perform an oral dose-ranging pilot study (10–100 mg/kg of body weight ponazuril) in green turtles (N = 9), followed by oral administration of ponazuril at 100 mg/kg body weight (N = 8) to assess its disposition. Another goal of this study was to optimize the method of oral drug administration to green turtles. Plasma ponazuril concentrations were quantified using high performance liquid chromatography (HPLC). Standard compartmental models were fit to the data. Ponazuril was absorbed after oral administration at 100 mg/kg BW, with a maximum plasma concentration of 3.3 µg/ml. Dose-dependent pharmacokinetic parameters only weakly correlated with the dose rate, apparently due to considerable pharmacokinetic variability observed between turtles. Administration of ponazuril in gelatin capsules using a balling gun was deemed the least variable and most successful method of drug administration. Further studies are needed to evaluate the safety and efficacy of ponazuril in sea turtles with coccidiosis.