Comparative Parasitology 67(2) 2000 - Peru State College

Table 1. Infectivity and distribution of Echinostoma trivolvis in jirds.
Group
A
B
C
D
E
F
Day
postinfection
5
8
10
12
15
17
No. of
exposed
(infected)
jirds
7 (7)
7 (7)
7 (7)
7 (5)
7 (1)
7 (0)
* I = anterior; II = middle; III = posterior.
t Not significant.
Mean (± SE)
No. (%) of worms
recovered
14.1 ± 2.4 (35.4)
13.6 ± 2.2 (33.9)t
4.3 ± 0.9 (10.7)
1.7 ± 1.8 (4.3)
0. 1 ± 0.4 (0.4)
0
ological, histochemical, and electron microscopical
studies of the intestines of jirds infected
with E. trivolvis were also carried out.
Materials and Methods
Metacercarial cysts of Echinostoma trivolvis were
obtained from the kidney and pericardial sac of laboratory-infected
Biomphalaria glabrata (Say, 1816)
snails. The worm strain was previously described by
Fujino and Fried (1993a). Forty cysts were fed via a
stomach tube to each jird, and 7 jirds were lightly
anesthetized with ether and killed by cervical dislocation
at days 5, 8, 10, 12, 15, and 17 postinfection
(p.i.). Six groups of untreated control jirds, 7 per
group, were also killed on the same days as the infected
hosts. The jirds were starved for about 12 hr
prior to necropsy to avoid food residue in the intestine.
The intestine was removed and opened longitudinally
to determine worm location. The worms were counted,
and their distribution was recorded in the small intestine,
which was divided equally into anterior, middle,
and posterior regions, and in the cecum and colon plus
rectum. Where applicable, Student's /-test was used to
analyze differences between means, and P < 0.05 was
considered statistically significant.
For histological samples, pieces of intestine (2 cm
long) located 10 cm anterior to the cecum, corresponding
to the middle jejunum to ileum, were excised and
fixed for 3 hr in Carney's fixative. The samples were
dehydrated with an ethanol series and embedded in
paraffin. Histological sections 5ixm thick were stained
with periodic-acid Schiff for goblet cell mucins. Mucosal
mast cells were stained with alcian blue (pH 0.3)
and safranin O. All counts were expressed as the number
of cells per villus-crypt unit (VCU) (Miller and
Jarrett, 1971) for goblet cells and cells per 10 VCU
for mast cells. Thirty to 50 VCUs were analyzed per
host. Logarithmic transformation of data: geometric
means (antilog of mean log of data) was performed.
For comparison of the cell counts, goblet cell numbers
were multiplied 10 times as for the mast cells. This
transformation tends to stabilize variance and to normalize
such data.
For scanning electron microscopy (SEM), the intestinal
tissue from jirds infected with E. trivolvis at 8
FUJINO ET AL.—EXPULSION OF ECHINOSTOMES 237
No. of worms located in the:
Small intestine
Total (I II III)1 Cecum
97 ( 4 49 44)
90 (30 21 39)
30(13 8 9)
10 ( 3 4 3)
1(1 0 0)
0
1
4
0
1
0
0
Colon +
rectum
and 10 days p.i. and control tissues were excised from
the upper ileum, opened longitudinally with fine needles,
and pinned on small rubber boards in physiological
saline. The intestinal debris was removed by gentle
flow of saline forced over the surface with a pipette.
After a brief rinse in 0.1M sodium cacodylate buffer
(pH 7.4), the specimens were fixed for 3 hr with 3%
glutaraldehyde, postfixed for 3 hr in 0.1 M osmium
tetroxide (pH 7.4), and then dehydrated in an ethanol
series. The material was dried in a carbon dioxide critical-point
drying apparatus (Hitachi HCP-2, Tokyo, Japan),
coated with palladium in a Hitachi E 1030, Tokyo,
Japan ion sputter, and examined in a Hitachi s-
450 SEM, Tokyo, Japan at 10 kV. For transmission
electron microscopy (TEM), the material was prepared
as described for SEM procedures in Fujino and Fried
(1993a). Ultrathin sections stained with uranyl acetate
and lead acetate were viewed in a JEOL JEM 1210
electron microscope operating at 80 kV.
Results and Discussion
Infectivity and worm recovery data are presented
in Table 1. All jirds were infected with
E. trivolvis at days 5, 8, and 10 p.i., and this was
confirmed by fecal examination under the microscope.
By day 12 p.i., 5 of 7 jirds were infected,
but only 1 was infected by day 15 p.i.
Worm recoveries were 35.4% and 33.9% at days
5 and 8 p.i., respectively, and this difference was
not statistically significant. The recovery data
dropped to 10.7% at day 10 p.i., fell markedly
to 4.3% by day 12 p.i., and finally to 0.4% by
day 15 p.i. Most worms were expelled between
days 10 and 15 p.i., and all were expelled by
day 17 p.i. Most worms were found in the middle
to posterior part of the small intestine at day
5 p.i. The worms moved mainly anteriad to the
middle of the small intestine by day 10 p.i. Such
an anteriad worm shift was reported previously
in ICR mice infected with E. trivolvis at day 21
p.i. (Weinstein and Fried, 1991). In the present
Copyright © 2011, The Helminthological Society of Washington
1
0
0
1
0
0