Ultrastructure of interlamellar Henneguya exilis in the channel catfish.

TLDR: Ultrastructural aspects of interlamellar Henneguya exilis infections in channel catfish are reported and evidence suggests that host cellular cytoplasm as well as interstitial material is taken in by plasmodia.

Abstract: Ultrastructural aspects of interlamellar Henneguya exilis infections in channel catfish are reported. The plasmodium wall of this form differs from that of other species in that it is composed of two outer unit membranes which give rise to a zone of numerous pinocytic canals. Single-membraned canals appeared to be a stable feature of the wall while double-membraned canals are interpreted as those actively carrying out pinocytosis. Evidence suggests that host cellular cytoplasm as well as interstitial material is taken in by plasmodia. Plasmodium wall integrity, aggregation of parasite ectoplasmic components, numbers of pinocytic canals, and number of mitochondria proximal to the wall vary among different plasmodium profiles and may be related to plasmodium maturity. The parasite causes extensive hyperplasia of basal cells, which in turn replaces most other cell types found in noninfected gill filaments. Cytoarchitectural differences between basal cells of noninfected filaments and basal cells adjacent to plasmodia include significantly shorter microfilament bundles in the latter.

Figures

FIGURE 1. Light micrograph of 1 ,um thick Epon section through the distal portion of a catfish gill filament infected with interlamellar H. exilis. Gill lamellae are completely absent as are the characteristic capillary beds and some cell types that characterize the noninfected filament. Profiles of plasmodia (P) are surrounded by compact layers of cells, while the remainder of the filament is filled with dendritic cells, probably derived by hyperplasia of basal cells which reside between lamellae of normal filaments. The long arrow points to a relatively "immature" plasmodium while the short arrow points to a "mature" plasmodium containing a large number of spores (see Observations and Discussion). Toluidine blue, X 150.

Full text

-(4$01(27.%$!0 1* (-".+--(4$01(27.%$!0 1* (-".+-
(&(2 +.,,.-1-(4$01(27.%$!0 1* (-".+-(&(2 +.,,.-1-(4$01(27.%$!0 1* (-".+-
.'- -.473!+(" 2(.-1  /$01(-2'$(.+.&(" +"($-"$1

+20 1203"230$.%-2$0+ ,$++ 0+20 1203"230$.%-2$0+ ,$++ 0
$--$&37 $6(+(1$--$&37 $6(+(1
(-2'$' --$+(-2'$' --$+
 291' 291'
(++( ,300$-2
 0& -2 '$0 /$32("1
.'- -.470
-(4$01(27.%$!0 1* (-".+-
)) -.473-+$#3
.++.52'(1 -# ##(2(.- +5.0*1 2'22/1#(&(2 +".,,.-13-+$#3!(.1"() -.47
 02.%2'$ 0 1(2.+.&7.,,.-1
300$-2(++( , -# -.47.'-0+20 1203"230$.%-2$0+ ,$++ 0
$--$&37 $6(+(1
(-2'$' --$+
 291'
.'- -.473!+(" 2(.-1

'22/1#(&(2 +".,,.-13-+$#3!(.1"() -.47
'(102("+$(1!0.3&'22.7.3%.0%0$$ -#./$- ""$11!72'$ /$01(-2'$(.+.&(" +"($-"$1 2
(&(2 +.,,.-1-(4$01(27.%$!0 1* (-".+-2' 1!$$- ""$/2$#%.0(-"+31(.-(-.'- -.473!+(" 2(.-1!7
- 32'.0(8$# #,(-(120 2.0.%(&(2 +.,,.-1-(4$01(27.%$!0 1* (-".+-

THE JOURNAL
OF
PARASITOLOGY
Vol.
62,
No.
6,
December
1976,
p.
975-981
ULTRASTRUCTURE
OF
INTERLAMELLAR
HENNEGUYA
EXILIS
IN
THE CHANNEL
CATFISH
William
L.
Current and
John
Janovy,
Jr.
School
of
Life Sciences
and
Cedar
Point
Biological
Station,
UN-L,
Lincoln,
Nebraska
68588
ABSTRACT: Ultrastructural
aspects
of
interlamellar
Henneguya
exilis
infections
in
channel catfish
are
reported.
The
plasmodium
wall
of this form differs from
that of
other
species
in
that it is
composed
of
two
outer
unit
membranes which
give
rise to a
zone
of
numerous
pinocytic
canals.
Single-mem-
braned canals
appeared
to be a stable feature
of
the wall
while
double-membraned canals
are
interpreted
as
those
actively
carrying
out
pinocytosis.
Evidence
suggests
that host
cellular
cytoplasm
as well
as
interstitial
material is taken
in
by
plasmodia.
Plasmodium
wall
integrity,
aggregation
of
parasite
ectoplasmic
components,
numbers
of
pinocytic
canals,
and number
of
mitochondria
proximal
to
the
wall
vary
among
different
plasmodium
profiles
and
may
be
related to
plasmodium
maturity.
The
parasite
causes
extensive
hyperplasia
of
basal
cells,
which
in
turn
replaces
most
other cell
types
found
in
noninfected
gill
filaments.
Cytoarchitectural
differences
between
basal cells of
noninfected filaments
and basal
cells
adjacent
to
plasmodia
include
significantly
shorter
microfilament
bundles
in
the
latter.
Seventeen
species
of
Henneguya
have
been
reported
from several families
of North Amer-
ican
freshwater fishes
(Hoffman,
1967).
Henneguya
species
have been
implicated
as
causative
organisms
of
infectious
disease
re-
sulting
in
significant
losses to
the
catfish
farming
industry
(McCraren
et
al.,
1975).
Seven different
Henneguya
disease manifes-
tations
in
channel catfish
are
now
recognized.
One
of these in which
parasites
begin
their
development
among
basal
cells between
gill
lamellae,
the
interlamellar
form, causes
seri-
ous losses
among
immature
fish
(McCraren
et
al.,
1975).
Meyer (1969)
reported
epi-
zootics of this form which
resulted in losses
of
95%
of
fingerlings.
Additional concern
over
the
interlamellar
infection
stems
from
reports
that
infected
fish are
less tolerant than
healthy
fish
to
handling
and
treatment
with
parasiti-
cides. The
interlamellar
form
is
apparently
spreading
in the
south-central United States
due
to
unrestricted sale and
transport
of
in-
fected fish
(McCraren
et
al.,
1975).
This
study
concerns some
ultrastructural
aspects
of the
interlamellar form
of
Henneguya
exilis. The
plasmodium
wall
structure,
inter-
actions between
the
plasmodium
and
adjacent
basal
cells of
the
host,
and
apparent
parasite-
induced
cytoarchitectural
rearrangements
of
basal cells
are
reported.
This is
the
first
re-
port
of the
ultrastructure of
this form
of H.
exilis
infection.
Received for
publication
29
January
1976.
MATERIALS AND
METHODS
Infected
fish
were
collected
by
gill
netting
from
Lake
Ogallala
and
Lake
Keystone,
Keith
County,
Nebraska,
the
lakes
nearest
the
Univer-
sity
of
Nebraska
Cedar
Point
Biological
Station.
Data
presented
in
this
paper
were derived
from
a
single
infected
channel
catfish,
Ictalurus
punc-
tatus
(Rafinesque),
about 6
lb in
weight,
collected
26
June
1975,
in
Lake
Keystone.
Infected
and
uninfected
gill
filaments
were
ex-
cised,
fixed
for
2
hr
at room
temperature
in
3%
(v/v)
glutaraldehyde
in 0.1
M
phosphate
buffer
(pH
7.4),
and
processed
for
electron
microscopy
according
to
the
methods
of
Janovy
et al.
(1974).
Silver-gray
sections
were
cut with
glass
knives
on a
Porter-Blum
MT-1
ultramicrotome,
mounted
on
150-mesh
Formvar-coated
grids,
stained with
uranyl
acetate and
lead
citrate,
and
viewed
and
photographed
with
a
Philips
EM
201
electron
microscope.
The
distal
portion
of one filament
was
serially
sectioned
for
light
microscopy
in
order to
deter-
mine
the
number
and
orientation
of
plasmodia
within
the
filament.
Epon
sections
1
,um
thick
were taken at 12
,um intervals
and
stained with
0.5%
toluidine
blue
in
1%
sodium
borate
prior
to
examination.
The
parasite
was
identified
as
Henneguya
exilis
Kudo
1929,
based
on
spore
measurements
and
morphology,
geographical
location,
and
host
spe-
cies.
The
infection
type
was
established
on
the
basis of
criteria
given
in
Minchew
(1972)
and
McCraren et
al.
(1975).
Basal
cells
were char-
acterized
ultrastructurally by
their
prominent
bundles
of
elongate
microfilaments,
desmosomal
junctions,
and
interdigitating
pseudopodia.
Terminology
used for
life
cycle
stages
in
this
study
is in
agreement
with Lom
and
de
Puytorac
(1965)
and Lorn
(1969).
"Mature"
spores
were
identified
as
those which
exhibited
very
electron-
dense
cytoplasm
surrounded
by
an
extremely
electron-dense
shell and
elongate
polar capsules
975

976
THE
JOURNAL
OF
PARASITOLOGY,
VOL.
62,
NO.
6,
DECEMBER
1976
FIGURE
1.
Light
micrograph
of
1
,um
thick
Epon
section
through
the distal
portion
of
a cat-
fish
gill
filament
infected with
interlamellar
H.
exilis.
Gill
lamellae
are
completely
absent
as
are
the
characteristic
capillary
beds
and some
cell
types
that
characterize the
noninfected
filament.
Profiles
of
plasmodia
(P)
are
surrounded
by
com-
pact layers
of
cells,
while
the remainder
of
the
filament
is filled
with
dendritic
cells,
probably
derived
by
hyperplasia
of basal
cells
which
reside
between lamellae
of normal
filaments.
The
long
arrow
points
to
a
relatively
"immature"
plas-
modium
while the
short
arrow
points
to a "ma-
ture"
plasmodium containing
a
large
number of
spores
(see
Observations
and
Discussion).
Tolu-
idine
blue,
X
150.
with
a
completely
formed
and identifiable
polar
filament
(Lorn
and de
Puytorac,
1965;
Schubert,
1968;
Lom,
1969).
All other
stages
were
con-
sidered "immature."
Measurements
of 50 microfilament bundles
were
taken from
10 basal
cells
in
infected
filaments
and
from
10 basal
cells in
noninfected
filaments,
and
Student's "t"
test was used
to
compare
the
dif-
ference
between their
means.
Measurements are
reported
as
mean
?
standard
deviation.
All
measurements
were
taken
from
negatives
of
known
magnification.
OBSERVATIONS
Infected
gill
filaments
In
longitudinal
sections the
interlamellarly-
infected
gill
filaments
appeared
swollen due
to
hyperplasia
of some cell
types
also
present
in
noninfected filaments.
Parasites
were seen
as
numerous
irregularly
shaped
or
subcircular
profiles
through
various branches
of
different
plasmodia
(Fig. 1).
Lamellae
of
infected
fila-
ments
were
fused
beyond
the
point
of
struc-
tural
recognition
and
some cell
types
charac-
teristic
of these
structures,
e.g.,
pillar
cells
and
endothelial
cells,
were
rarely
observed.
Branched
plasmodia
were
contained
primarily
in the
core
of
the
filament,
and
profiles
were
rather
uniformly
distributed from the
base to
near the
tip
of
the
infected
filament. At
light
microscope
magnifications,
fish
cells
ap-
peared
to be
arranged
in
compact
layers
around the
plasmodium
profiles
and the
fila-
ment
contained
large
numbers
of
loosely
packed,
dendritic
cells,
particularly
distal to
the
parasite
profiles
themselves
(Fig.
1).
These
light-level
observations
are
consistent
with
those of
Minchew's
(1972)
which de-
scribe
the "most
severe"
interlamellar
infec-
tions.
Ultrastructural
study
revealed
a
num-
ber
of
specific
features of
not
only
the
plasmodium
wall
but also
of
cells
immediately
adjacent
to
the wall.
Plasmodium
wall
The
plasmodium
was delimited
distally by
two
unit membranes
separated
by
a
0.016
to
0.019
[/m
space,
with
much
of
the
outermost
membrane
having
a
coat of
fine
granular
ma-
FIGURE
2.
Transmission electron
micrograph
of
the
plasmodium
wall
of
interlamellar
Henneguya
exilis and
adjacent
cells
of
the
host. The
plasmodium
wall consists
of
two unit
membranes
(PM)
and
a
zone
of
pinocytic
canals
(PI).
Proximal
to
the
zone
of
pinocytic
canals are
pinocytic
vesicles
and
numerous
mitochondria
with
branched,
tubular cristae
(M),
vacuoles
of
various
sizes
(V),
myelin
figures
(MY),
and
endoplasmic
reticulum
(ER).
Arrows
point
to
double-membraned
pinocytic
canals
through
which
basal cell's
cytoplasm
is
evidently passing.
Within the
basal
cell
(H)
is seen
the
nucleus
(HN),
bundles
of
microfilaments
(MF),
and
mitochondria
(M).
Host mitochondria
contain
saclike
cristae.
Interdigitated pseudopodia
of
basal
cells
are seen
in the
lower
right
corner.
X
28,000.

CURRENT
AND
JANOVY-ULTRASTRUCTURE
OF
HENNEGUYA
EXILIS IN CHANNEL
CATFISH
977
Pr,
7~~~~~~~~~~~~~~~~~~~~~~~,~
8~~~~~~~~~~~~~~.~
'

978
THE
JOURNAL OF
PARASITOLOGY,
VOL.
62,
NO.
6,
DECEMBER 1976
. . . ~ ~ ~ ~ ~ ~ ~ l
-~~~~~~~~~~~~~~~~~~~~~1
'f'
f
~~~~~W
i*7
Al