Diversity, impacts and diagnosis of pathogenic parasites in sea turtles from Queensland, Australia

Chapman, Phoebe (2017). Diversity, impacts and diagnosis of pathogenic parasites in sea turtles from Queensland, Australia PhD Thesis, School of Veterinary Science, The University of Queensland. doi:10.14264/uql.2017.413

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Author Chapman, Phoebe
Thesis Title Diversity, impacts and diagnosis of pathogenic parasites in sea turtles from Queensland, Australia
School, Centre or Institute School of Veterinary Science
Institution The University of Queensland
DOI 10.14264/uql.2017.413
Publication date 2017-03-16
Thesis type PhD Thesis
Supervisor Paul C. Mills
Mark Flint
Rebecca J. Traub
Thomas H. Cribb
Myat T. Kyaw-tanner
Total pages 156
Total colour pages 2
Total black and white pages 154
Language eng
Subjects 0707 Veterinary Sciences
0602 Ecology
Formatted abstract
Parasitism is a significant cause of stranding and mortality in endangered sea turtles. Two
parasites in particular (or groups thereof) have been noted for their impacts on green sea
turtle populations. The first are the spirorchiid blood flukes, which inhabit the circulatory
systems of their host. The second is the eimeriid coccidian Caryospora cheloniae, a
systemic parasite affecting a number of organs. Diversity among these organisms is poorly
explored, and is almost certainly greater than currently recognised. The parasites and their
associated diseases fluctuate both temporally and spatially in terms of prevalence and
severity, however, the factors driving these fluctuations are poorly understood. A variety of
questions remain unanswered in terms of the epidemiology and relative pathogenicity of
the different parasite species. Of particular interest are brain lesions, which have been
associated with both parasites and in some cases lead to neurological deficiency and
subsequent mortality. Difficulties in finding answers to these questions is compounded by
a lack of reliable, fast and quantitative ante- and post-mortem diagnostic tools for either
parasite, which restricts their investigation.

In order to catalogue local species and assess diversity, adult spirorchiid flukes were
collected during post-mortem examination of deceased sea turtles and characterised by
molecular and morphological means. Eleven distinct species or genotypes were identified,
comprising a mix of previously described and novel species or variants. Samples were
also collected from green sea turtles that died during a coccidiosis related mass mortality
event in south east Queensland and northern New South Wales. While only one species of
coccidian (C. cheloniae) had been previously described, molecular characterisation of the
organism implicated in the outbreak revealed two distinct coccidian genotypes, which has
significant implications for diagnosis and management.

Spirorchiid ova have been associated with granulomatous lesions in a wide range of host
tissues. However, it has not been possible to identify spirorchiids beyond the genus level
based on morphology, which has frustrated any attempts to identify the species or variants
responsible for severe lesions. In this thesis, a molecular approach was used and a
terminal restriction fragment length polymorphism (T-RFLP) assay was developed to
detect and identify individual species within the often mixed assemblages of ova in turtle
tissues. This assay proved to be a more specific and sensitive alternative to traditional
microscopic detection methods. Through correlation with histopathology and gross
pathology, the tissue tropisms, relative occurrence and pathogenicity of each species were
investigated. The most common species (Neospirorchis Genotype 2) was found in 96% of
samples, encompassing tissues from all organs sampled. On average, a greater number
of spirorchiid species were detected in tissues where lesions were present, and numbers
increased along with the severity of lesions. The age, sex or body condition of the host did
not show an effect, however, age was found to be a significant factor in the diversity of
spirorchiid infections in some other organs.

Distinct tissue tropisms were evident for the two coccidian genotypes. The first and most
common genotype was found in gastrointestinal, brain and lung tissues, with associated
encephalitis and enteritis. The second was detected in kidney and thyroid tissue, again
with an accompanying inflammatory response. The two species are therefore likely to have
different impacts on their host, and this must be considered in epidemiological
investigations and development of diagnostic tools.

In order to explore options for future ante- and post-mortem diagnostics, TaqMan qPCR
assays were developed to detect and quantify both Neospirorchis spp. and Caryospora
spp. infections. These assays were able to be run as a single tube multiplex reaction, and
reliably detected both parasites in tissue samples. This provided an efficient and cost
effective means of differentiating between two parasitic infections that may present with
similar neurological signs. Given that the data collected using the T-RFLP assay indicated
that spirorchiids (most notably the Neospirorchis) are almost universally present in
stranded turtles, the relative quantitative data provided by these assays will be central in
ascertaining the factors that induce severe inflammatory responses to infections.

This study has uncovered diversity among important turtle parasites, investigated the
epidemiology and pathology associated with infections, and has contributed two important
diagnostic tests to the investigation and management of these significant causes of
disease and mortality in green sea turtles. Moving in to the future, these tests will make
important contributions to the investigation of disease outbreaks, understanding of disease
epidemiology and pathology, and the relationship between disease and environmental
factors – objectives that have been beyond the capability of previously existing methods
and tools.
Keyword Marine turtle
Chelonia mydas
spirorchiid
coccidia
Neospirorchis
Caryospora
diversity
DNA
pathology
diagnosis

Document type: Thesis
Collections: UQ Theses (RHD) - Official
UQ Theses (RHD) - Open Access
 
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Created: Tue, 07 Mar 2017, 09:11:56 EST by Phoebe Chapman on behalf of Learning and Research Services (UQ Library)