Further Indication of Viability of Larvae of the Hookworm (Uncinaria lucasi) for Several Years in Tissues of Northern Fur Seals (Callorhinus ursinus)

Abstract

Recently it was reported that parasitic thirdstage larvae of the hookworm, Uncinaria lucasi, lived definitely for 1 yr and probably for at least 4 yr in tissues of northern fur seals (Callorhinus ursinus) (Lyons and Bigg, 1983, J. Parasit. 69: 442-443). These data were obtained from fur seals in captivity. Earlier, research on northern fur seals, collected at sea during the annual migration to breeding grounds, indicated that parasitic third-stage hookworm larvae lived for at least 6 mo in their tissues (Lyons, 1963, PhD Dissertation, Colorado State University, Fort Collins, Colorado, 87 p.; Olsen and Lyons, 1965, J. Parasit. 51: 689-700). Further data are presented herein on life span of parasitic third-stage hookworm larvae showing that they were viable in tissues of 2 captive female northern fur seals for a minimum of approximately 6 yr. Two northern fur seal females (cows) were captured as yearlings on hauling grounds next to Tolstoi Rookery on St. Paul Island, Alaska in October, 1977 and taken directly to the Seattle Aquarium in Seattle, Washington. During the period of captivity, these 2 cows were kept in a sea water pool with 4 other northern fur seals; 1 female of the same age but captured a year earlier as a weanling, 2 bulls approximately 9 yr old but captured as apparent 2-yr-olds, and a 3-yr-old female which was born in captivity in Canada and put in the pool in December, 1981. In 1983, at about 7 years of age, the 2 cows captured as yearlings in 1977 gave birth to live pups. On June 27, 1 cow gave birth to a male pup and on July 3, another cow had a female pup. Prior to the birth of the present pups, other northern fur seal pups had not been born at the aquarium. Feces of both pups were positive for hookworm eggs when examined at 20 and 23 days of age for the male and at 23 days of age for female. Presence of hookworm eggs in the feces of the pups indicated that the origin of the infection was transmammary passage of parasitic third-stage larvae that had been in the tissues of their mothers for a minimum period of about 6 yr. It has been established that adult hookworms in northern fur seal pups originate from parasitic thirdstage larvae passed in the "first-milk" of females to their offspring (Lyons, 1963, loc. cit.; Olsen and Lyons, 1965, loc. cit.). Also, it has been shown that adult hookworms are present only in pups, not in older fur seals (Olsen, 1958, Tr. 23rd N. Amer. Wildl. Conf., 3-5 Mar., 152-175). Therefore, the hookworms in the pups born in the aquarium had to have stemmed from tissue stages of larvae acquired by their mothers before capture about 6 yr earlier. It is probable, but not provable, that the cows acquired the larvae in their tissues when they were pups; if so, this would mean that the larvae, passed through the mammary system to the present pups, had lived in tissues for about 7 yr. The fact that northern fur seal pups can be infected, by transmammary transmission, with larvae of U. lucasi capable of surviving for several years in tissues of cows, should be considered in management of these animals in captivity. Feces of pups, born in captivity to northern fur seals and other species of pinnipeds in which hookworms occur, should be examined for eggs of this parasite. This is because of the potential danger to the health of the pups posed by this parasitic infection. One report (Fiennes, 1966, Jour. Zool. 148: 341-362) indicates that the death of a 6-wk-old California sea lion (Zalophus californianus) pup, born to a female which was in captivity at least 16 yr (Pugsley, pers. comm., 1984), was due to hookworms. A few hookworm eggs, passed in feces of the male pup at 23 days of age, were observed to determine their fertility. Nine of the eggs were placed in drops of water on coverslips positioned over wells on a hanging drop slide. Developing from these eggs were 1 free-living third-stage larva and 6 firstor second-stage larvae. An additional free-living third-stage larva was hatched from an egg in a small amount of feces and water