Abstract

Many recent studies have sought to optimize the fecal flotation procedure and other diagnostic techniques in veterinary parasitology, as a means of improving the detection of helminth eggs in domestic species.^1,2 It is unclear, however, whether these efforts in optimization are applicable to parasite species of marine origin given adaptations of these parasites to the marine environment. Since parasitism is a common comorbidity in stranded pinnipeds, verification of these diagnostic procedures is clinically important. We hypothesized that the helminth eggs of pinnipeds would have different specific gravities than those of terrestrial domestic mammals; in part, because of the potential implications of a marine environment on the eggs. Fecal samples were collected from twenty-seven live or necropsied pinnipeds that stranded and were brought to The Marine Mammal Center (Sausalito, CA) for rehabilitation between March 14 and August 12, 2015. There were 10 males and 17 females, including 22 California sea lions (Zalophus californianus), 2 harbor seals (Phoca vitulina), 2 elephant seals (Mirounga angustirostris), and 1 Guadalupe fur seal (Arctocephalus townsendi). Stranding locations represented 8 coastal California counties, ranging from Sonoma to Los Angeles (approximately 500 miles of coast). Five age cohorts were represented, including 14 adults, 4 subadults, 3 juveniles, 1 yearling, 2 weaners, and 4 pups. Modified double centrifugal flotations were carried out on 1 gram samples, and sediments were examined.³ Sugar-gradient modified centrifugation flotations were performed on ten samples to determine the specific gravity (SpG) of helminth eggs.³ Results showed trematode, ascarid, and cestode eggs were detected in 14/27 (52%), 10/27 (37%), and 4/27 (15%) individuals, respectively. Trematode eggs per gram (EPG) ranged from 1 to too numerous to count (TNTC), whereas ascarid counts ranged from 3–482 EPG. Since trematode egg counts were TNTC and cestode eggs are not typically quantified, only ascarid egg counts were analyzed statistically. Normality of the data was assessed, and non-parametric statistical approaches were used to compare ascarid egg counts between groups (Mann Whitney U test). There was no significant difference in ascarid counts based on sex or age class (p<0.05). While ascarid eggs typically had a SpG of 1.00–1.15, the ascarid eggs from 2/7 (29%) individuals had a broader range of SpG, extending from 1.05–1.27. Trematode eggs consistently had a high SpG of 1.15–1.27, and 4/9 (44%) individuals had a SpG ranging from 1.05–1.27. Although eggs representing all 3 parasitic groups were found in the sediments examined, egg counts were surprisingly lower than expected. In conclusion, it was determined that the SpG of trematodes and ascarids is similar to that seen in terrestrial hosts,³ and a flotation media with a SpG>1.25 may be most appropriate for use in marine species. Further studies on parasites of marine mammals and diagnostic approaches focused on the detection of helminth eggs from these hosts are necessary in order to better understand these populations and the factors that influence their health.

Acknowledgements

The authors would like to thank The Marine Mammal Center for providing samples and demographic information on individual animals, as well as the Colorado State University Veterinary Diagnostic Laboratories for use of facilities and equipment. The study was funded, in part, by a grant from the National Center for Veterinary Parasitology (NCVP).

* Presenting author
+ Student presenter

Literature Cited

1.  Dryden MW, Payne PA, Ridley R, Smith V. 2005. Comparison of common fecal flotation techniques for the recovery of parasite eggs and oocysts. Vet Ther. 6(1):15–28.

2.  Greenwald RJ. 2007. Centrifugation versus simple flotation. J Am Vet Med Assoc. 231(3):375–376.

3.  David ED, Lindquist WD. 1982. Determination of the specific gravity of certain helminth eggs using sucrose density gradient centrifugation. J Parasitol. 68(5):916–919.