Anisakine nematodes are commonly found in pinnipeds, both free in the stomach and attached to the gastric mucosa³. Larval and adult anisakids have been shown to cause gastric ulcers in grey seals⁶, and rarely, gastric perforation². It is likely that both mechanical action and production of allergens by the nematodes are responsible for gastric ulceration and perforation⁴. Nematodes have also been found attached to the intestinal mucosa, suggesting that there may be an intestinal phase of development⁵.

There has been one report of gastric perforation resulting in peritonitis in several free living California sea lions (Zalophus californianus) caused by anaskids⁴.

Between January 1992 and December 1997, The Marine Mammal Center (Sausalito, CA) treated 47 stranded California sea lions that, upon necropsy, were found to have severe peritonitis resulting from gastric or intestinal perforations. All of the animals were moderately to severely underweight, and all but five were anorexic. Of these 47 animals, 38 (81%) were found to have small oval perforations (0.5cm-1cm long) of the proximal duodenum, 2-3cm from the pylorus. Five cases of peritonitis were caused by perforations more distally in the intestines, while only four of the 47 (8.5%) presented with gastric perforations. Nematodes were detected in the stomachs of all cases.

The worms recovered from the perforations were composed of both larval and adult stages of the genus Contracaecum. Morphological features such as size, external features and male spicule characteristics identified the specimens as C. corderoi Lent et Freitas, 1948, a species previously only reported from southern fur seals¹.

Infection was light in most cases, with less than 50 parasites per animal counted in all but 4 (8.5%) of the animals. Of the four with heavy parasite loads, two presented with gastric perforations and two with duodenal perforations. Histology confirmed the presence of nematodes in the areas of ulceration. Twenty-seven of the animals (57%) were female and 20 (43%) were male. Thirty-six (77%) were 1-2 years of age, seven were 3-4 years old, and the remainder were over 5 years old. The animals averaged 4.2 days in treatment before death (s.d. = 4.8 days, range = 0-20 days), suggesting that these perforations were the cause of stranding rather than a result of the stress associated with rehabilitation.

The finding of C. corderi as the primary cause of gastric perforations leading to severe peritonitis in Z. californianus leads to speculations concerning El Nino. Could the warm water fish species moving northward have introduced the aberrant C. corderi larvae into the food chain of the California sea lion causing this syndrome?

References

1.  Dailey MD, RL Brownell, 1972. A Checklist of Marine Mammal Parasites. In Mammals of the Sea, Biology and Medicine, ed. S. Ridgway, Charles Thomas Publisher, Springfield, Illinois, 528-589.

2.  Fiscus CH, GA Baines, F Wilke, 1962. Pelagic fur seal investigations, Alaska waters. U.S. Fish and Wildlife Services, Special Scientific Report on Fish, 475: 1-59.

3.  Geraci JR, DJ St. Aubin, 1987. Effects of parasites on marine mammals. International Journal for Parasitology, 17: 407-414.

4.  Lauckner G,1985, "Diseases of Mammalia: Pinnipedia", in Diseases of Marine Animals Volume IV Part 2, ed. O. Kinne, Biologische Anstalt Helgoland, Hamburg, pp. 683-772.

5.  Montreuil PL, K Ronald, 1957. A preliminary note on the nematode parasites of seals in Gulf of St. Lawrence. Canadian Journal of Zoology, 35: 495.

6.  Young PC, D Lowe, 1969. Larval nematodes from fish of the subfamily anisakinae and gastrointestinal lesions in mammals. Journal of Comparative Pathology, 29: 301-313.