The ecology of Echinococcus multilocularis (Cestoda: Taeniidae) on St. Lawrence Island, Alaska. II. Helminth populations in the definitive host.

The helminths of 1,579 arctic foxes from St. Lawrence Island were investigated by standard methods. The foxes, obtained mainly during the winter from fur trappers, harbored 22 species of helminths. Four of those were trematodes, viz., Maritrema afanassjewi Belopol'skaia, 1952, Orthosplanchnus pygmaeus Iurakhno, 1967, Plagiorchis elegans (Rudolphi, 1802) and Alaria marcianae (LaRue, 1917), each of which occurred in a single host. Two species of cestodes, Diphyllobothrium dendriticum (Nitzsch, 1824) and Mesocestoides kirbyi Chandler, 1940, were uncommon (in 2.7 and 1.3% of the foxes, respectively). Taenia polyacantha Leuckart, 1856 and Echinococcus multilocularis Leuckart, 1863 were present in about 80% of the foxes, and Taenia crassiceps (Zeder, 1800) in less than 10%. The specimens of Taenia spp. from the autumn-winter sample were usually destrobilate. In about 2% of the foxes, acanthocephalans of six species occurred. Four of those, of the genus Corynosoma Lühe, 1904, were common in marine mammals of the region; a fifth, Corynosoma clavatum Goss, 1940, has been reported previously only from marine birds of the Southern Hemisphere; and the sixth, Polymorphus cf. minutus (Goeze, 1782), has been found widely in waterfowl of the Northern Hemisphere. Of the nematodes, Sobolophyme baturini Petrov, 1930, Cylicospirura felineus (Chandler, 1925), and Physaloptera sp. were rare (with each in only one to three foxes). Trichinella nativa Boev et Britov, 1972 and Crenosoma vulpis (Dujardin, 1844) were uncommon (1.5 and 4%, respectively). The nematodes most often present were Toxascaris leonina (von Linstow, 1902) (89%) and Uncinaria stenocephala (Railliet, 1884) (40%). Several of the rare to uncommon helminths probably were transported to the island by foxes immigrating from the adjacent continents via the pack ice.

Life shortening in mice exposed to fission neutrons and gamma rays. VI. Studies with the white-footed mouse, Peromyscus leucopus.

Some of the studies on late effects of neutron and gamma radiation previously carried out with the C57BL6 X BALB/c F1 hybrids of Mus musculus have been repeated with the white-footed mouse, Peromyscus leucopus, a cricetid rodent of a different subfamily, with differing physiological characteristics and a different spectrum of pathologies. Among the more important findings were the following: For both species, the life shortening per rad at low doses of either radiation was the same percentage of the life span. The limiting values of the relative biological effectiveness for life shortening from all causes of death were about the same for the two species, ranging from 8 to 16, depending on the method of calculation. Fractionated neutron exposures failed to produce significant life shortening in Peromyscus over that observed at single doses. Tumor-related deaths accounted for at least 70 to 75% of the radiation-specific excess mortality in Peromyscus.

Life shortening in mice exposed to fission neutrons and gamma rays. V. Further studies with single low doses.

Data are presented on the mean after survival of female B6CF1 mice exposed to single doses of neutrons (1 to 40 rad) or gamma rays (22.5, 45, and 90 rad). For gamma-ray exposures and for neutron exposures up to 10 rad, the dose-response curves are indistinguishable from linear; higher neutron doses produce significant departures and linearity. Consequently, in these data, an upper limit of the relative biological effectiveness (RBE) exists for life shortening from all causes of death after single neutron exposures; this value is 15.0 +/- 5.1. The RBE depends on the cause of death, ranging from 2 to 5 for lymphoreticular tumors to 23-24 for lung tumors.

Life shortening in mice exposed to fission neutrons and gamma rays. IV. Further studies with fractionated neutron exposures.

When mice were exposed to a total dose of 240 rad of fission neutrons divided into two, four, or six fractions given at 1-week intervals, more life shortening was observed than was seen after a single exposure. Maximum life shortening was observed with four fractions, although the value for six fractions was not significantly lower. Much of the augmentation effect was attributable to an increase in early deaths during the first 200-300 days after exposure, although differences persisted throughout the lifetime of the animals. The changes in life shortening were associated with changes in the distribution of causes of death; however, decrementation of the populations for any given specific cause of death failed to eliminate completely the differences in mean aftersurvival time.