Comparative Parasitology 67(1) 2000 - Peru State College

(Latreille, 1804) Brandt and Ratzeburg, 1831, a
terrestrial isopod (Schmidt and Olsen, 1964;
Nickol and Dappen, 1982). Cystacanths of this
acanthocephalan species also have been reported
(Nickol and Oetinger, 1968) from the mesenteries
of short-tailed shrews, Blarina brevicauda
(Say, 1823) Baird, 1858, in New York state.
When cystacanths of P. cylindraceus were
discovered in the viscera of short-tailed shrews
of eastern Nebraska, a study to assess the significance
of these parenteral forms was undertaken.
The distribution of extra-intestinal forms
among shrews and other co-occurring mammals
was determined, infectivity of isopod-borne cystacanths
to shrews and other co-occurring mammals
was studied, and infectivity of mammalborne
cystacanths to robins was tested.
Materials and Methods
Acquisition and maintenance of P. cylindraceus
Gravid female worms obtained from robins and starlings
in Lancaster County, Nebraska, were stored a
maximum of 3 mo in tap water at 4 C. To infect isopods,
egg suspensions were prepared by pulverizing
stored worms in tap water. Each suspension was examined
microscopically to ensure the presence of fully
developed eggs.
A laboratory colony of isopods (A. vulgare) was
maintained in covered plastic containers (32.5 X 17.5
X 9.0 cm) provided with 2 to 3 cm of soil, pieces of
broken clay pots for shelter, a sponge moistened regularly
to maintain humidity, and potato slices for food.
Large pieces of potato were used to maintain humidity
in some containers in place of the moistened sponge.
These pieces of potato were allowed to sprout, and
isopods were observed feeding regularly on the shoots
as well as the potato itself.
To obtain laboratory-reared cystacanths, isopods
less than 9.5 mm long (see Nickol and Dappen, 1982)
were removed from the colony and held without food
for 36 hr, after which they were allowed to feed on
potato slices over which a suspension of P. cylindraceus
eggs in water had been spread. Exposure was in
covered wells (3.5 cm diameter X 1.() cm deep) imprinted
on a plastic plate. Fresh egg suspension was
added to the potato slices after 24 hr. Except to add
egg suspension, isopods were left undisturbed in the
dark. After 36 to 48 hr of exposure, isopods were removed
and isolated in a separate culture. Before use,
cystacanths were allowed to develop at least 70 days
in the isopods to ensure infectivity (Schmidt and Olsen,
1964).
Survey of mammals
Mammals at 13 sites located within 4 townships
(North Bluff, Oak, West Lincoln, and Yankee Hill) in
and around Lincoln, Nebraska, were surveyed to determine
locations at which parenteral infections occur
and to determine which species harbor cystacanths in
nature. Mammals were trapped with medium-sized
COADY AND NICKOL—PLAGIORHYNCHUS CYLINDRACEUS IN SHREWS 33
Sherman live traps baited with a mixture of peanut
butter and oats, and all mammals caught were examined
for P. cylindraceus cystacanths.
Laboratory exposure of mammals
To determine susceptibility to P. cylindraceus cystacanths,
mammals of 6 species, collected at sites from
which P. cylindraceus was absent in previous surveys,
were administered cystacanths orally. The mammal
species exposed were short-tailed shrews; European
mice, Mus musculus Linnaeus, 1758; hispid pocket
mice, Perognathus hispidus Baird, 1858; wood mice,
Peromyscus leucopus (Rafinesque, 1818) Thomas,
1895; deer mice, Peromyscus maniculatus (Wagner,
1845) Bangs, 1898; and 13-lined ground squirrels,
Spermophilus tridecemlineatus Mitchill, 1821.
To expose mammals, laboratory-reared cystacanths
were pipetted to the back of the throat of lightly anesthetized
(methoxyflurane) animals. Following exposure,
each animal was placed into a receptacle lined
with clean, Ian-colored paper toweling for observation
and recovery. After the animal recovered from anesthesia,
it was returned to its normal housing. The recovery
receptacle then was examined for cystacanths
that were not ingested by the animal. The white cystacanths
were highly visible on the paper towels, making
possible an accurate determination of the number
administered.
Mammals were housed in standard mouse cages fitted
with wire tops, water bottles, paper towels for nesting
and shelter, and wood shavings. All nonsoricids
were fed commercial hamster and gerbil food and observed
to ensure that they were eating. Short-tailed
shrews were provided additionally with a block of untreated
wood (5 X 10 X 15-25 mm) and a small clay
flower pot. The wood absorbed excess oil from the
shrew's fur and provided shelter. The shrews deposited
feces regularly within the flower pots, which were removed
easily and cleaned. Shrews were fed 5 adult
cockroaches, Periplaneta americana (Linnaeus, 1758)
Burmeister, 1838, from a laboratory colony at each of
3 daily feedings.
Survey and susceptibility of isopods
A survey was conducted to determine what isopod
species inhabit sites from which the infection was determined
to be present in shrews. Isopods were collected
by hand for 1 hr at night by flashlight, identified,
and examined for cystacanths.
To investigate the extent of intermediate host specificity,
isopods of 3 terrestrial species (Armadillidium
nasatuin Budde-Lund, 1885, A. vulgare, and Metoponorthus
pruinosus (Brandt, 1833) Budde-Lund, 1879)
were exposed to eggs of P. cylindraceus. All of these
isopods were collected within Lancaster County, Nebraska.
Peromyscus feeding trials
Deer mice (P. maniculatus) were offered isopods (A.
vulgare) as prey to determine the likelihood of their
consuming an intermediate host in nature. After having
food withheld for 4 hr, each of 6 deer mice was presented
20 isopods of assorted sizes for a period of 2
hr in 10-gallon aquaria. The bottom of each aquarium
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