Qualitative and quantitative methods for estimating Spirorchiidiasis burden in sea turtles.

Area of Science:

• Veterinary Parasitology
• Marine Wildlife Health
• Helminthology

Background:

• Blood fluke (Spirorchiidae) infections, specifically *Hapalotrema mistroides* and *Neospirorchis* sp., are increasingly reported in Mediterranean loggerhead sea turtles (*Caretta caretta*).
• Assessing parasitic burden severity typically relies on post-mortem lesions, with limited standardization for evaluating parasitic load via tissue egg counts.
• Standardized methods are needed to quantify spirorchiid eggs in host tissues and feces for accurate disease assessment in sea turtles.

Purpose of the Study:

• To standardize and validate methods for quantifying spirorchiid eggs in loggerhead sea turtle feces and spleens.
• To compare egg counts obtained from different quantification techniques (modified McMaster vs. chemical digestion) in spleen tissue.
• To assess the correlation between fecal and splenic egg burdens and evaluate the diagnostic utility of copromicroscopy for *in vivo* assessment.

Main Methods:

• Fecal and spleen samples from 105 loggerhead sea turtles from the northwestern Adriatic Sea were analyzed using sedimentation-flotation techniques.
• Molecular methods were employed for unequivocal identification of spirorchiid species.
• Egg quantification utilized a modified McMaster method for feces and spleen, and chemical digestion for spleen samples; Spearman's rho test assessed correlations.

Main Results:

• Strong correlations were observed between splenic egg counts for *Hapalotrema mistroides* using the modified McMaster method and chemical digestion, validating the McMaster technique.
• High concordance between fecal and spleen qualitative examination for *H. mistroides* suggests copromicroscopy's utility for *in vivo* diagnosis.
• Weak correlations between fecal and splenic egg counts indicate that fecal burden may not reflect disease severity; low concordance for *Neospirorchis* sp. suggests limited organ embolization.

Conclusions:

• The modified McMaster method provides a reliable quantitative assessment of *Hapalotrema mistroides* eggs in loggerhead spleen tissue, though a multiplying factor is needed when comparing with chemical digestion results.
• Qualitative fecal examination is a valuable tool for *in vivo* diagnosis of *H. mistroides* infections in loggerhead sea turtles.
• Fecal egg counts are not indicative of disease severity, and lower concordance for *Neospirorchis* sp. warrants further investigation into its infection dynamics.