Observations on the Infectivity of Parasitic Third-Stage Larvae of Uncinaria lucasi Stiles 1901 (Nematoda: Ancylostomatidae) of Northern Fur Seals, Callorhinus ursinus Linn., on St. Paul Island, Alaska

Abstract

Twelve fur seal pups, which had not nursed their mothers, were used in an infectivity experiment. Pups were exposed to parasitic 3rd-stage larvae of Uncinaria lucasi from belly tissues of fur seal bulls, bachelors, and pregnant cows, to determine maturation capability of the larvae. Hookworms were not recovered from the intestines of 3 pups receiving larvae from belly blubber of bulls, 6 pups receiving larvae from belly blubber of bachelors, and 1 nonexposed pup. Maturation of hookworms did occur in 2 pups exposed to larvae from a mixture of belly blubber, mammary tissue, and milk of pregnant cows. Parasitic 3rd-stage hookworm larvae from belly tissues of pregnant and "non-pregnant" fur seal cows averaged 938.1 and 802.1 micron long, and 34.1 and 31.5 micron wide, respectively; however, larvae from belly tissues of a fur seal bull, bachelors, 2-year-old males, male and female yearlings and pups, and Steller Sea Lion subadults averaged 640.5-732.0 micron long and 20.9-24.9 micron wide.

Epidemiology of hookworm (Uncinaria spp.) infection in New Zealand (Hooker’s) sea lion (Phocarctos hookeri) pups on Enderby Island, Auckland Islands (New Zealand) during the breeding seasons from 1999/2000 to 2004/2005

“…As described in northern fur seals (Olsen and Lyons 1965), free-living third-stage larvae would penetrate sea lions through the skin, lose their sheath, and stay in hypobiosis, or arrested development in the blubber or abdominal muscles only; they would then migrate to the mammary glands in lactating females (Lyons 1963). Lyons and Keyes (1978) hypothes ise d that a hormonal signal initiated the larval migration to the mammary cisterns but it has also been suggested that the decrease of immunocompetence, characteristic of preparturient females induced the larvae to resume their development and start their migration towards the glands (Anderson 2000).…”

“…in Juan Fernandez fur seals (Sepúlveda and Alcaíno 1993) and in California sea lions (Lyons et al 2000a). Several additional studies have compared measurements of larvae found in different tissues from animals of various ages (Olsen and Lyons 1965;Lyons and Keyes 1978;Sepúlveda and Alcaíno 1993;Lyons et al 2003). Larval sizes varied considerably depending on both the host's age and the tissue sampled, with larvae from the mammary glands of lactating females being longer than those found in the blubber of other adult fur seals.…”