Acanthocephalan parasitic disease in fishes

1. Acanthocephala:
A diverse group
The spiny / Thorny – headed worm
Tiple Jayanta Subhash
AAH 2019-22-06

2. Introduction
 Acanthocephalans are endo parasitic worms
comprising approximately 1100 species
 Acanthocephala is an important but a minor
group of parasites that shows characteristics
similar to that of rotifers.
 Adult members of this group are present and
mostly feed on the intestinal walls of fresh and
marine water fishes all over the world
 Juveniles of other species occur in the
viscera, especially the mesentery and liver of
fishes that act as paratenic hosts.

4. Classification
 Kingdom ; Animalia
 Phylum ; Acanthocephala
 Class ; Palaeacanthocephala
 Order ; Echinorhychida
 Family ; Echinorhynchidae
 Genus ; Acanthocephalus

5.  It is believed that approximately 1150 species
of Acanthocephalan parasites exist within the
four orders:
 Neoechinorhynchidea
 Echinorhynchidea
 Aporhynchidea
 Gigantorhynchidea.

6.  Acanthocephalus acutispinus
 Acanthocephalus acutulus
 Acanthocephalus alabamensis
 Acanthocephalus anguillae
 Acanthocephalus anthuris
 Acanthocephalus balkanicus
 Acanthocephalus breviprostatus

7.  Acanthocephalus bufonis
 Acanthocephalus clavula
 Acanthocephalus correalimai
 Acanthocephalus kubulensis
 Acanthocephalus lucidus
 Acanthocephalus lucii
 Acanthocephalus lutzi
 Acanthocephalus madagascariensis

8.  Acanthocephalus minor
 Acanthocephalus nanus
 Acanthocephalus opsariichthydis
 Acanthocephalus parallelcementglandatus
 Acanthocephalus prallelotestis
 Acanthocephalus paronai
 Acanthocephalus pesteri

9. Morphology
• Bilaterally symmetrical and dioecious, pseudocoelomate
worms.
• Characterized by a spined proboscis that is invaginable
and retractable into sacular proboscis receptacle.
• Attachment to the host intestine is by proboscis.
• Patterns of hooks and proboscis are of taxonomic
importance.
• The neck is the unarmed region behind the proboscis-
usually short and inconspicuous- some genera it is
extremely elongated and may be inflated.

10. • The reminder of the body is trunk- in some species
bears tegumental spines- which may enhance the
attachment to the host intestine.
• All the ontogenic stages lack alimentary canal- a
genital pore is the only visible opening.

11. Proboscis

12. Click to add Text
• Conspicuous internal organs are those of the reproductive system.
• Male- there are two testes- followed by one to eight cement glands.
• Ovaries fragment early in the development to form ovarian balls-
which float free in the pseudocoelom.
• As development proceeds, pseudocoleom fills with eggs- Eggs are
passed through a funnel-shaped uterine bell to a slector apparatus- which
allows only fully-formed eggs into the uterus.

13. • Other eggs are directed back to the pseudocoelom through a series of canals
and pores.
• Female system terminates in a vagina, regulated by a vaginal sphincter,
which discharges through a genital pore.
• Most do not possess an excretory system- Protonephridial organs discharge
through ducts that for males enter the vas deferens and for females enter the
uterus

14. Life Cycle
 Acanthocephalans have complex life cycles, for both
developmental and resting stages.
 Requires vertebrate as definitive hosts and
arthropods as intermediate hosts
 For development to occur, the eggs when released
from the female containing the acanthor are ingested
by an arthropod, usually a crustacean.

15.  Inside the intermediate host, the acanthor is released
from the egg and transforms into an acanthella
 Acanthella then penetrates the gut wall and
transforms into the infective cystacanth stage (cyst) in
the body cavity.

16. Acanthor
Amphipod carrying
cystacanth

18.  This stage after eaten by a suitable final host
develops into a mature adult, or by a paratenic host,
in which the parasite again forms a cyst.
 When consumed by a suitable final host, a fish, the
cycstacanth removes its cyst wall, everts its
proboscis, pierces the gut wall and then feeds, grows
and develops its sexual organs.

19.  This juvenile or cystacanth is the infective
stage for a definitive host.
 After mating, adult male uses the excretions of
its cement glands to plug the vagina of the
female, to prevent subsequent matings from
occurring.
 Embryos develop inside the female, and the
life cycle repeats.

21. Intercalated hosts
• When cystacanths of some species are ingested by
vertebrates that are unsuitable as definitive hosts, they
penetrate the intestine and localise in extra-intestinal sites.
• They remain as cystacanths in these paratenic hosts.
• Predator definitive hosts acquire acanthocephalans from
prey animals that serve as paratenic hosts.
• Fishes are important paratenic hosts for (Corynosoma)- of
marine birds and mammals-infecting acanthocephalans.
• Post-cyclic transmission: In some species transmission of
adult worms from one definitive host to another occurs due
to ingestion.

22. Click to add Text
An egg eaten by an arthropod
hatches into an acanthor,
develops into an acathella,
becomes a juvenile (which may
progress to a cystacanth), and
is eaten by the final, vertebrate
host in which it becomes adult
Within the invertebrate host,
the acanthor is liberated from
the egg, bores through the gut
wall, and develops into an
acanthella
The acanthella then
becomes a juvenile. The
vertebrate host becomes
infected by eating the
arthropod intermediate
host.

23. Enhanced transmission
• Eggs of several species possess filaments that
entangle in aquatic vegetation- apparently anchor
them in the habitat that occupied by their intermediate
hosts.
• Transmission enhanced by behavioural modification of
intermediate hosts.
• Three-spined sticklebacks (Gasterosteus aculeatus)
preferentially consume infected prey when given a
choice between equal numbers of infected and
uninfected amphipods.

24. Host-Parasite Relationships
1 ; Site selection
• After ingestion by the definitive host, cystacanths are activated
and attach to the wall of the small intestine.
• Many species apparently remain at the activation site and
develop to maturity.
• Others migrate and localize in specific regions of the intestine .
• Several factors, including physiological differences along the
alimentary tract maximization of sexual congress have been
implicated in site specificity.
• In most cases, however, it is unknown whether differences in
sites occupied result from differences in sites of activation,
differential mortality or emigration by the parasites.

25. Host-parasite Relationships
(Course of infection)
• Shortly after infection, proboscis is surrounded by necrotic
tissues- becomes haemorrhagic and inflamed after a few
days.
• Species which penetrate deeply (Acanthocephalus
anguillae), inflamed tissues around the anterior part of the
worm is dominated by monocytes and macrophages-
• Maturing into epitheloid cells- an outer belt of connective
tissue appears
• This chronic stage results in the fibrous nodule visible in
the outer surface of the intestine.

26. • Species that do not penetrate deeply (Acanthocephalus
lucii) move about in the intestine and change their point
of attachment before the connective tissue response
results in nodules.
• Copulation in the definitive hosts occur within 24 h of
infection
• For most species, egg production starts between 4-8
weeks after infection. (At peak production a pig infecting
acanthocephalan produces about 260,000 eggs per
day).

27. • Male worms have shorter life span- Death of males and
subsequent loss from the host may begin shortly after
copulation.
• Most of the parasites of poikilothermic host live about
one season.

28. Attachment

29. Clinical signs
 No visible external symptom to determine infection .
 Worms ( about 10- 20 mm ) have been observed extending from the
rectum in moribund fishes .
 The attachment site, because of the hooks present, causes damage to
the intestinal epithelia & become a foci of secondary infection.
 Discoloration of viscera and enlargement of intestine often observed in
heavily infected fish.
 It also cause blockage of the lumen and hence ,affects the digestive &
absorptive capacity of animal .

30. Acanthocephalan in host intestine

31. HOST IMMUNE RESPONSE
Cellular :
Goblet-cell hyperplasiya occurs in Acanthocephalan infection .
Apart from this increased number of immune cells ( eosinophils
,neutrophils, leucocytes, monocytes) damages Acanthocephalan
tegument .
Humoral :
Activation of plasma cells in the inflammatory tissue around the
proboscis

32. Histopathology
• Acanthocephalans embed their spiny proboscis into the
mucosal epithelium
• Attachment is frequently between villi.
• At the site of attachment, cells are destroyed and
fibroblasts, lymphocytes and macrophages are
mobilized below the lamina propria, where fibrinous
inflammation resulting in an increased amount of
connective tissue, causes thickening.
• Worms of deeply penetrating species often possess very
long necks and bulbous proboscis which anchor them
deep within the gut wall.

33. • A fibrotic tunnel is formed- this terminates in a capsule,
covered by serosa and mesentery, which protrudes
several millimeters into the coelomic cavity.
• Sometimes these capsules persist as conspicuous
fibrinous nodules on the external surface of the
alimentary canal, or proboscis perforates the capsule to
emerge free into the coleom or penetrate liver or other
organs (A. anguillae in gold fish)

34. Diagnosis & treatment
• Diagnosis of intestinal acanthocephalan infection can be
made from wet mounts of intestinal tract
• The species are identified mainly by the arrangement of
hooks on the proboscis
• Proper treatment methods have not developed yet
• Detection of anti- mortem faeces of host
• But bath treatment in highly concentrated salt solution for
prolonged time generally done
• Drug : loperamid , doses of 50 mg/kg administration for 3
consecutive days is effective .

35. REFERENCE
1. P. T.K. Woo , Fish Diseases and Disorders,
volume 1 : Protozoan and Metazoan infections ,second edition
2. Ronald J. Roberts , Fish Pathology ( third edition )
3. Marcogliese, D.J (1994) Aeginina longicornis , new intermediate
host for Acanthocephala
4. Schmidt , Gerald D.( 1971) The Journal of Parasitology

36. THANK YOU