Abstract

Beluga whales (Delphinapterus leucas) from the Cook Inlet area are one of five identified stocks in Alaska. The Cook Inlet stock has recently experienced a significant population decline and is under review for listing under the Marine Mammal Protection Act (MMPA). Aerial survey counts dropped from an estimate of 653 whales in 1994 to 347 in 1998. A subsistence hunt by native hunters and regular mass strandings are known causes of annual mortality. Since 1995, frozen and formalin fixed samples have been collected from hunted animals and from a few stranded animals. High prevalence of a nematode was identified within the kidney of Cook Inlet stock. The parasite resulted in a destructive fibrosing and eosinophilic reaction within the kidney. In samples submitted to the Alaska Veterinary Pathology Services for histologic and/or gross examination, seven of 11 harvested animals and two of five stranded animals had lesions due to this parasite with an overall prevalence of 56% (nine of 16). In most cases, the animals otherwise appeared to be in good condition. In one juvenile stranded animal, the lesions were quite extensive, possibly affecting renal function. Other lesions thought to be related to parasites included mineralized fibrovascular mesenteric masses containing degenerated parasites and eggs, larval migration tracts in mesenteric lymph nodes, eosinophilic and lymphocytic vasculitis, and intimal and adventitial proliferation of vessels in the gastrointestinal tract and kidney. In the Chukchi/Beaufort stocks along the northern shore of Alaska, a similar renal lesion with intralesional nematodes was seen in only one animal out of 19 animals examined histologically from Pt. Lay (n = 8), Pt. Hope (n = 8), Barrow (n = 2) and Kaktovik (n = 1). Similar lesions were not mentioned in beluga whales from the St. Lawrence Seaway.^6,2

This parasite has been identified as Crassicauda giliakiana, a spirurid nematode. Kikuchi (1995)³ described this parasite in a Cuvier's beaked whale and Arvy (1973)¹ provided a good description of the parasites of the cetacean kidney, including Crassicauda boopis and C. giliakiana. C. boopis has been more extensively described than C. giliakiana. It causes a similar lesion in the kidney of fin and other large baleen whales.^4,5 The proposed life cycle of C. boopis is that larva are ingested and then undergo a somatic migration, most likely along the mesenteric arteries. The larva enter the blood stream through the mesenteric artery lumen, go to the kidney, and mature to adults. The tail of the adult extends into the calyxes, with release of eggs and larva into the urine. The body of the adult is associated with a marked inflammatory response and the anterior end extends into the renal veins. The tissue response to the adult can result in obstruction of vessels draining the kidney and thrombi with thromboembolism to other organs, notably the lungs. Adult animals seem to be able to tolerate C. boopis quite well, however it is thought to be capable of causing mortality, particularly in calves and yearlings.^4,5

References

1.  Arvy L. 1973. The kidney, renal parasites and renal secretion in Cetaceans. In: Pilleri, G. (ed.). Investigations on Cetacea, vol. V. Institute of Brain Anatomy, University of Berne, Berne, Switzerland. Pp. 231-310.

2.  De Guise S, A Lagace, P Bland, C Girard, R Higgins. 1995. Non-neoplastic lesions in beluga whales (Delphinapterus leucas) and other marine mammals from the St. Lawrence. J. Comp. Pathol. 112: 257-271.

3.  Kikuchi S, Y Kazuno, M Kiryu, M Nakajima. 1995. Morphology of Crassicauda giliakiana (Nematoda; spirurida) from a Cuvier's beaked whaled Ziphius cavirostris. Jap. J. Parasitol. 44: 228-237

4.  Lambertsen R. 1986. Disease of the common fin whale: crassicaudiosis of the urinary system. J. Mammol. 67:353-366.

5.  Lambertsen R. 1992. Crassicaudiosis: a parasitic disease threatening the health and population recovery of large baleen whales. Rev. Sci. Tech. Off. Int. Epizoot. 11:1131-1141.

6.  Martineau D, A Lagace, P Beland, R Higgins, D Armstrong, LR Shugart. 1988. Pathology of stranded beluga whales (Delphinapterus leucas) from the St. Lawrence Estuary, Quebec, Canada. J. Comp. Pathol. 98: 287-311.