Blood Sucking Nematoda and impact in Swim bladder.

1. Anguillicoloides
crassus

2. Taxonomy

3. (a) European eel Anguilla anguilla, the
final host of A. crassus
(b) eel swim bladder of A. anguilla
showing a typical number of adult blood-
sucking A. crassus, which can cause
heavy infections and might hamper the
5,000 km long catadromous migration to
the Sargasso Sea.
(c) nematodes in swim bladder (opened
up and well supplied with blood)
(d) third-stage larvae of A. crassus,
isolated from a paratenic fish host

4. • Adult anguillicoloides are all
strictly parasitic to the eel genus
Anguilla.
• A. crassus is known to infect six
of the 15-20 eel species currently
described worldwide.

5. Diagnosis of Infection
1. moribund behaviour
2. reduced swimming performance
3. abnormal hanging near the surface
4. body emaciation
5. swollen abdomen
6. Anal redness

6. Life Cycle Of A.crassus
• The adult, ovoviviparous nematodes are
localized exclusively in the swim bladder of its
final host.
• The Stage L1 already developed in uterus.
• Each female lays several hundreds of thousands
embryonated eggs, containing the second larval
stage (L2)
• The L2 larvae leave the eel via the pneumatic
duct.
• Newly hatched second-stage larvae (L2) attach to
the substratum by their caudal extremity.
• After penetrating the intestinal tract of the first
intermediate host, the nematode develops its
third-stage larva (L3) within a few days.

7. Life Cycle Of
A.crassus
• different species of fishes, mollusks, insects, and
amphibians can be incorporated in the life cycle of A.
crassus as so-called Paratenic Host.
• Smaller eels get infected predominantly by feeding on
parasitized first intermediate (obligate) hosts, e.g.,
crustaceans.
• larger eels mostly prey on infective paratenic (facultative)
hosts, e.g., fish or amphibians.
• The time to metamorphosis into fourth- stage larvae (L4)
is temperature dependent, and may vary from 2-3 weeks
up to 3 months post-infection.
• After an average of 8–10 months, A. crassus reaches
sexual maturity and the life cycle restarts.

8. Larvae of A.crassus
• A.crassus L2 larvae
• Surrounded by their egg sheath and L1 cuticle.
• Hatching of L2 larvae from egg

9. • Paracyclops fimbriatus (intermediate host)
infected with larvae which are visible in the
abdomen
• L3 larvae dissected out of the intermediate host
Paracyclops fimbriatus 10 d after infection with
L2 larvae. Moulting has already taken place.

10. Sections of L3 larvae (1) in the submucosa of the swim bladder of eel Anguilla anguilla where they
pass during their migration to the swim bladder lumen

11. • The difference between L3 (1) and
L4 (2) larvae is clearly visible.
• The L4 larvae are considerably
larger and are stained darkly
• Nematode moulting from L4 larva to preadult. The L4 cuticle is
still surrounding the parasite and is visible at the head end of
the parasite (1)

12. X-ray of experimental eels
• X-ray scans were used to measure
the swim-bladder length (SBL)
• determine the actual swim-bladder
status.
• An eel with a large, uninfected
bladder (top),
• An eel with a medium-sized bladder
with visible parasites (middle)
• An eel with a small bladder with
minimal volume (bottom)

13. • Dissection of the swim-bladder, whole (top) and cut open
(bottom) showing 19 parasites of various sizes.
• Three levels of swim-bladder wall transparency, -thickness and
length showing a large, thin- walled transparent swim-bladder (top),
a medium-sized swim-bladder with a thicker wall (middle) and a
small thick-walled non-transparent swim- bladder (bottom).

14. Microphotographic sections of eel swimbladders
• Swimbladder of an uninfected eel, showing the
swimbladder lumen (SBL) and the structure of normal
swimbladder wall (SBW), with its four layers: the
innermost mucosa or epithelium (E), the muscularis
mucosa (M), the submucosa (SM), the serosa (S, the
outermost layer), and blood vessels (arrowheads).
• Section of a damaged swimbladder, showing a
migrating third-stage larva (L3 indicated by arrow),
and the considerable thickening and structural
changes in all four layers.

15. Histopathological changes in the swimbladder wall of the European
eel
CS = cutting surface,
E = epithelium
Mm = muscularis
mucosae Sm =
submucosa
S = serosa
• Swimbladder wall of an uninfected
swimbladder
• The smooth surface shows only
elevations of the blood vessel
• Swimbladder wall of an infected,
thickened swimbladder.
• The epithelium is characterized by
heavy folds
• blood vessels can only be seen at the
cutting line.
• All layers show thickening.

16. • Epithelium of an uninfected swimbladder;
• higher magnification reveals short
microvilli on top of the epithelium and
makes cell borders visible.
• Epithelium of an infected swimbladder;
• in thickened swim bladders the surface
shows folds and the cells have a bubble
shaped surface

17. Blh - basal labyrinth,
Bla = basal lamina,
C = collagen fibres,
Ca = capillary,
F = fibroblast,
Jc - junctional complex,
M = macrophage

18. Opened swimbladders with different damage degrees

19. Swimbladders along with the liver (L), gallbladder (GB) and intestine
(I)
(a) Healthy swimbladder showing adult worms inside, and visible
pneumatic duct (PO)
(b) degraded swimbladder showing overall shrinkage, and no worms
inside the few lumen remaining.

20. • In Germany, eel populations are infected already
from 65% to 90% with A. crassus (Deutscher
Bundestag 2004)

21. Protective/Control Strategies
• 24 h water bath with Levamisole at 2 mg/l was the most effective procedure. However, larval stages L3 and
L4 in the wall of the swim bladder are not affected by any medication
• Trichlorfon and Diflubenzuron proved to be effective in single-dose application at concentrations (e.g. 0.01-
0.02 mg/l) which are not dangerous to eels
• There is no available vaccine against A. crassus on the market

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24. THANK YOU