Spirorchiid trematodes or blood flukes are intravascular parasites that have been implicated as a significant cause of stranding and mortality in marine turtles worldwide.1-6 Spirorchiids have been a recurring health concern in Florida largely due to observations of heavily infected individuals in the stranding population and an uncertain role in at least one mass mortality event.3,5 Although studies of spirorchiidiasis comprise a significant portion of the marine turtle disease literature, much of this work has been biased towards chronically ill turtles and basic information is sparse or completely lacking from many regions, including Florida. Thus, understanding of spirorchiids and their impact on marine turtle health is at best vague and very incomplete. The objective of these studies was to assess the significance of spirorchiidiasis and characterize associated disease in stranded Caretta caretta and Chelonia mydas by examining the following factors: spirorchiids as a cause of death or contributing cause of death; diversity and prevalence of spirorchiids; associated pathological lesions; and relationships between parasitism and species, host size class, and nutritional condition at stranding. Methods targeting the recovery and identification of spirorchiids were applied in combination with standard necropsy techniques. Considerable effort was expended to include animals that died with acute insults to more closely approximate the host-parasite relationship in the free-ranging population. Significance of parasitism in necropsied turtles was classified as absent, incidental, contributory to death (one of multiple problems), fatal infection, or undeterminable based on intensity of infection, the organ/tissue affected, severity of pathological lesions, and any demonstrable relationship to cause of death. A total of 89 C. caretta and 59 C. mydas recovered by the Sea Turtle Stranding and Salvage Network from November 2004 through January 2008 were included. Total prevalence of spirorchiid infection was 96% for C. caretta and 89% for C. mydas, and included the spirorchiid genera Neospirorchis, Hapalotrema, Learedius, and Carettacola. Pathological lesions associated with spirorchiids and sites affected included neurological infections, endarteritis of small and large arteries, thyroiditis, thymitis, and ulceration/ischemia of the enteric mucosa associated submucosal and arterial egg emboli. Significant relationships between some forms of spirorchiidiasis and turtle size class, as well as species differences, were observed. Most infections in both turtle species were regarded as incidental, although spirorchiidiasis was classified as causal or contributory in 12.9% of C. caretta strandings, and contributory in 2.7% of C. mydas strandings. Notably, a large proportion of examined turtles had either large numbers of parasites/eggs and/or notable pathological lesions with no apparent relationship to the identifiable cause of death. This latter group included turtles in comparatively robust nutritional condition. The findings from this study provide essential information on the diversity of spirorchiids found in Florida marine turtles, prevalence, and the spectrum of organs affected and associated pathological lesions, which is relevant to disease/mortality studies, epidemiology, and rehabilitation. Furthermore, spirorchiid data collected from turtles that died of known, acute insults identified several areas of needed study with regard to potential health implications in the turtle host, and cautions against over-interpretation of significance in individual cases.
The authors thank Karrie Minch, Rhonda Bailey, Sue Schaf, Ed DeMaye, Kim Sonderman, Nashika Brewer, STSSN participants, and the Florida rehabilitation network for invaluable assistance with stranded turtles. Partial funding provided by Awards 2003-0206-011 administered by National Fish and Wildlife Foundation, NA06NMF4720005 administered by the National Oceanic and Atmospheric Administration, and grant number 06-017R from the Florida Sea Turtle Tag Grants program.
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