Dipetalonema odendhali (Nematoda: Filarioidea) from the Northern Fur Seal, with a Description of the Microfilaria

Abstract

Dipetalonema odendhali Perry, 1967, is reported from the northern fur seal (Callorhinus ursinus) from St. Paul Island (Pribilof Islands), Alaska, and compared with specimens taken from the California sea lion (Zalophus c. californianus). Microfilariae are described. Samples of blood were taken from 130 fur seals, including twelve, 8-week-old pups. Microfilariae were not found in samples from the pups, but were present in 83% of 118 samples from fur seals over 3 years of age. The species of filarioid nematode infecting the northern fur seal, Callorhinus ursinus (Linnaeus, 1758) has not been determined to date. V. B. Scheffer (1965, pers. comm.) wrote: 1949 I collected a fur seal (Callorhinus ursinus) spleen on St. Paul Island [Pribilof Islands], Alaska, and sent it to John T. Lucker, Bureau of Animal Industry, who found in it larval filariids which he could not identify. In 1950 I sent 100 fur seal hearts and 100 salted, dried diaphragms to the BAI to be examined for filariids and trichinids; none was found. We found microfilariae in blood of a fur seal killed in Seattle Zoo on 7 February 1958 .... In 1963, our veterinarian Mark C. Keyes found microfilariae in the blood of 35 of 40 subadult male fur seals on St. Paul Anderson (1959) examined five poorly preserved adult filarioids-four from the USNM Helminthological Collection and one from Ontario Research Foundation-from Alaskan northern fur seals, and assigned them tentatively to Dipetalonema spirocauda (Leidy, 1858), pending examination of better specimens. Three were from subcutaneous tissue, one from the testicular sheath, and one from the upper colon. Delyamure (1961) reported microfilaremia in fur seals in Soviet waters. In 1961 E. T. Lyons (pers. comm.) found pieces of adult filarioids and microfilariae in samples of blubber, fur, and skin from fur seals-adult or subadult, and, also, immature-on St. Paul Island. In July and August 1967 the authors collected blood samples and adult filarioid worms from Received for publication 23 July 1970. * Present address: Department of Veterinary Science, University of Florida, Gainesville, 32601. fur seals killed on St. Paul Island, Alaska, during the summer harvest of the fur seals for their p lts by personnel of the Bureau of Commercial Fisheries, U. S. Fish and Wildlife Service. The identification of the species of filarial worm infecting the northern fur seal and the description of the morphology of the microfilaria were the objectives of this investigation. Information was also obtained on the incidence of infection among fur seals. MATERIALS AND METHODS A necropsy of 5 adult fur seals was performed for the collection of the adult filarioids. Also, 28 male gonads with scrotal skin but no bacula, and 25 bacula with some tissue and skin at the base of the prepuce were examined. Fur-seal skins from the previous day's harvest, after soaking in seawater 24 hr, were stripped of their blubber by the workers at the processing plant. The authors collected this blubber from about 250 3to 4-year-old bulls and 50 cows, and examined it for filarioids at the laboratory. Ninety female and 9 male adult filarioids were collected. These were refrigerated overnight in Ringer's solution, and then fixed in hot 70% isopropyl alcohol, ethyl alcohol being unavailable. For microscopic examination they were cleared and mounted in lactophenol. Samples of blood were obtained from 106 adult and subadult fur seals and 12 captive pups about 8 weeks old. Approximately 3 ml of blood from the heart of each fresh kill were collected into a vial containing EDTA. Peripheral blood was collected from the live pups. Two thick and 2 thin films were made from each sample within 3 hr of collection, and also 1 ml of blood from each sample was added to 10 ml of 2% formalin. Whole blood was used for films except for specimens from 10 bulls, for which serum from 10 ml of blood per animal was used (Coffin, 1953). One of the 2 slides per fur seal was fixed in absolute methyl alcohol within 3 hr after making the films. Stain-