L26: Blood Flukes Flashcards
What does the digestive tract of Trematodes consist of
fore gut and two cacea
Go in depth about whats in the foregut of treamtodes
- anterior mouth, pharynx, esophagus
- ingestion and assimilation
*The mouth surrounded by a muscular oral sucker for attachment and feeding
Go in depth about whats in the two caeca of treamtodes
- longitudinal blind tubes
✓ intestine-like
✓ variable length depending on trematode species
✓ Digestion and absorption of food occur in the caeca
What is the tegument in Trematodes
syncytium – a multinucleated tissue with no cell boundaries
What is the synticum made of
- outer zone – the distal cytoplasm which is bound by the
plasma membrane - An inner zone – the proximal cytoplasm
What is inner/outer zone of syncytium. What are they composed of
proximal cytoplasm / distal cytoplasm
Distal
* glycocalyx is a surface coat covering the entire plasma
membrane
* Surface invaginations function much like microvilli
* The glycocalyx and surface invaginations same
function as in cestodes
* Tegumental spines embedded in the distal cytoplasm and
project outward from the surface
Proximal
*It is connected to the distal cytoplasm by cytoplasmic bridges
* Contains nuclei, endoplasmic reticulum, Golgi complexes and
mitochondria
* involved in repair and maintenance of components of the
distal cytoplasm
Whare the zones of the muscular system. Other key muscle
subtegumental:
underlying tegumes of longi, circular and diagnotl layers
gastodermal
line cacare to help move food down
ventral scucker: contractile muscle fibres located mid verntrally for attachment, no opening here
What are general characteristrics of somoregulatory system
consits of protenephridia, a tubular system without opening made of flame cells
flame cells has flagella, remove excess water by creating hydrostatic pressure
flame cell open to terminal tubule tat converge from larger tubes leading to excretory bladder
duct of bladder opens to exterior of organism located posterioly
How can trematodes reproduce
✓ Self-fertilization in hermaphroditic worms
✓ Cross-fertilization in hermaphroditic worms
✓ Mating between 2 dioecious worms – this occurs ONLY in Schistosoma spp
Describe the male reproductive system
- Generally, includes 2 testes, 2 vas efferens, a common vas deferens, a cirrus, cirrus sac, seminal vesicle and the prostate gland
- Depending on the species, one or more of these components may be missing, in different size, or in a different position
- Schistosomes are multi-testicular
Describe the female reproductive system
Consists of a single ovary that forms ova
* Depending on the species, the ovary may be anterior/ posterior to, or between the testes
- Other components are the oviduct which comprises the ootype (where fertilization occurs), Mehli’s gland and vitelline glands
(both function to secrete the eggshell), uterus (a long, convoluted tube) and Laurer’s canal (in some species)
Draw the reproductive sytem
Male reproductive system of a digenetic trematode
Female reproductive system of a digenetic trematode
Describe trematode eggs
Eggs are ovoid, shelled and contain the embryo and other materials
- The typical eggshell is equipped at one end with a lid-like
structure, the operculum
✓ The operculum allows the larva to hatch - In species lacking an operculum (mainly schistosomes), the
eggshells rupture longitudinally when larva (miracidium) hatch - Hatching occurs only under precise conditions of temperature,
osmolarity and light - Specific size and structural characteristics of trematode eggs are
useful in diagnosis
What time of parasite are trematodes
obligate parasite
In general describe trematode life cycle
✓ 1st intermediate host is an invertebrate, almost always a mollusk (harbors larval stages)
✓ 2nd intermediate host includes fish/ arthropod/ another mollusk (harbors the encysted juvenile trematode)
✓ Definitive host is a vertebrate (harbors the adult trematodes)
What are the life stages of trematodes, describe them
- Miracidium – The 1st larval form that hatches from the egg. In most species it is ciliated and infects the 1st intermediate host
- Sporocyst – Metamorphoses from miracidium following loss of the cilia and other organelles
- Redia – The 2nd larval form that develops in the 1st intermediate host. This stage is absent in some species
- Cercaria – The 3rd larval form. It also develops in- & emerges from the 1st intermediate host.
- Mesocercaria – Forms in the 2nd intermediate host but is only present when there is a 3rd intermediate host
- Metacercaria – Forms in the 2nd intermediate host, when present in the life cycle. It must be ingested by the definitive host
General characteristics of Schistosoma
blood flukes infect humans and animals
cause schistomiasis aka snail fever aka bilharziasis
How are schistosoma unique
✓ Their life cycle involves one intermediate host and one definitive host
✓ Cercaria infect the definitive host directly, by penetrating the body surface rather than by being ingested
✓ Adult worms parasitize the intravascular niche
✓ They are dioecious and sexually dimorphic i.e., male and female reproductive organs are in separate worms
Schistosoma male and female worms describe
The adult male is robust and possesses a ventral groove called the gynaecophoral canal
✓ The female worm is held in the gynaecophoral canal, permitting almost continuous mating
✓ They possess 5 to 9 testes
✓ The male genital pore opens ventrally, posterior to the ventral sucker
✓ Males lack a cirrus
female: smaller, slender, position of ovary depends on species
Life Cycle of Schistosoma Species
Schistosoma eggs are eliminated with the feces or urine, depending on
species
2. under appropriate conditions, the eggs hatch and release miracidia
3. Miracidia swim and penetrate specific snail intermediate hosts
4. In the snail, miracidia first develop through two generations of sporocysts
5. Cercaria are produced from the second generation of sporocysts, and these
are released from the snail into water
6. The infective cercariae swim, and penetrate the skin of the human host
7. Within the definitive human host, cercariae shed their forked tails, becoming
schistosomulae
8. Schistosomulae migrate via venous circulation to the lungs, then to the heart
9. They then migrate to, and develop in the liver, exiting the liver via the portal
vein system when mature
10. Male and female adult worms copulate and reside in the mesenteric venules.
S. japonicum is frequently found in the veins of the small intestine (A), while
S. mansoni occurs more often in the veins of the large intestine (B). Most
often, S. haematobium inhabits the veins of the bladder (C). Females deposit
eggs in the venules. Eggs move toward the lumen of the intestine (S. mansoni
and S. japonicum) and of the bladder (S. haematobium).
11. The eggs are eliminated with feces or urine respectively
What schistoma species are of medical importance
S. haematobium
S. manosoni
S. japonicum
Key characteristics of relevant schistomas species
S. haem:
humans are definitve, urinary, f drop 30 eggs deposited single
S.mansoni
humans are definitive, infects primates, intestinal schistom, 190-300 eggs deposited single
S.japo
many mammal definitive hosts, zoonotice, humans can become definite, most pathogenic, 3500 eggs deposited in clusters
Clinical presentation
stage 1:
localised dermatisits, self limited
stage 2:
katayma syndone, delayed hypersneisitve cause schistomule moves, toxic reaction, pulomonrary congestion, eosinophilia, self limited
stage 3
2 months-yrs after infection, due to granula formation around eggs
granulomas maybe be ectopic, blood stool, dysentery, hepatosplenomegaly and pulmonary hypertension, fatal
How does immune system evade schistosomes
molecular mimicry
Utilization of an immune resistant outer tegument
✓ Membrane alteration by coating the parasite tegument with host proteins
✓ The secretion of several potent proteases
✓ Production of specific immunomodulatory factors affecting immune cell functions
✓ Granuloma formation
Epidemiology of Schist
poor, rural
lack of hygine, agricutural, reacrational, near snails, using water for domestic things, eco turism
Africa, middle east for haem and mansoni
japo is in indo and philpipins
Schisto diagnosis
eggs in stool/urine
rectal biopsises, bladder/mucoal biopsy
immunodiagonostic for travellers
Schisto treatment
praziquantel disrupt integrity of teguments, expose paraity to host antibodies
antihistamines
antibioitics for secondary infection
Cercarial dermatitis
swimmers itch by schisto im aquatic birds/mammals
clinically distinct from schisto cause not caused by human shistomsomes
cause unnatural host cercarieae don’t go to blood stream but go to skin and destroyed by ost immune
allergernic substances releases => locallised inflammatory reaction
worldwide issue
