What is the redia stage?
redia. a larval stage of liver fluke which develops from the sporocyst larva. It possesses a mouth, suctional pharynx and simple gut, and gives rise to secondary rediae or to carcaria larvae.
What is sporocyst larva?
The sporocyst larval stage occurs in the life cycle of Fasciola hepatica which is a parasitic trematode. It is commonly called as liver fluke and it belongs to the class Trematoda and phylum Platyhelminthes. The parasite completes its life cycle in two hosts which are snails and sheep.
What is metacercariae larva?
Definition of metacercaria : a tailless encysted late larva of a digenetic trematode that is usually the form which is infective for the definitive host.
Where is cercaria found?
A cercaria develops inside a snail, which is its first intermediate host, then it emerges and has a short free swimming life in the water. To prepare for morphological study, place snails in small dishes containing clean water in one (Fig.
What is Hexacanth larva?
Hexacanth is the larval stage of Taenia which are released when eggs are hatched. The hexacanth then develops into cysticercus or metacestode phase in voluntary muscles. The early cysticercus absorbs nutritive substance from host tissues and grows in size.
What does sporocyst mean?
1 : a case or cyst secreted by some sporozoans preliminary to sporogony also : a sporozoan encysted in such a case. 2 : a saccular body that is the first asexual reproductive form of a digenetic trematode, develops from a miracidium, and buds off cells from its inner surface which develop into rediae.
What is cercaria larva?
A cercaria (plural cercariae) is the larval form of the trematode class of parasites. It develops within the germinal cells of the sporocyst or redia. A cercaria has a tapering head with large penetration glands. It may or may not have a long swimming "tail", depending on the species.
What is miracidium larva?
The miracidium is a ciliated, nonfeeding larva (Fig. 9.18). Under favorable conditions, it escapes from the eggshell, usually through the operculum, into the environment. The miracidium is elongated and covered with flattened, ciliated epidermal plates.
What is meant by Encystment?
: to enclose in or as if in a cyst an encysted tumor. intransitive verb. : to form or become enclosed in a cyst protozoans encysting in order to resist desiccation. Other Words from encyst. encystment \ -ˈsis(t)-mənt \ noun.
What is Redia and cercaria?
Definition of redia : a larval form of a digenetic trematode (such as a liver fluke) that is produced within a sporocyst, has a mouth, pharynx, and gut, and contains cells which give rise to other rediae or to cercariae — see also redial entry 3.
What do you mean by cercaria?
Medical Definition of cercaria : a usually tadpole-shaped larval trematode worm that develops in a molluscan host from a redia. Other Words from cercaria. cercarial \ -ē-əl \ adjective.
What is the cercaria stage?
Cercaria: After about six to seven weeks within the snail (first) intermediate host, the sporocyst finally gives rise to the cercaria. This is a more developed larva, resembling the adult echinostome with a collar of spines at the anterior end, but also having a strong tail, which it loses before adulthood.
Where does redia ingest?
As the redia moves through the host’s tissues, it actively ingests host cells. Digestion of the cells takes place in the lumen of the cecum. Some rediae augment these intestinal feedings by secreting hydrolytic enzymes to the exterior and lysing surrounding host cells.
How many bud-like projections does a redia have?
They eventually escape from the sporocyst through the molluskan tissue and migrate to the digestive gland. Each redia is elongate and normally possesses two or four bud-like, antero- and posterolateral projections, the ambulatory buds (or procruscula) ( Fig. 9.20 ). As their name implies, the ambulatory buds facilitate movement ...
What are the two intermediate hosts of trematodes?
Fish-borne trematodes have a complicated life cycle with two intermediate hosts. Starting from a human host, the adult worms deposit fully developed eggs; the eggs are then passed to the environment through the feces, and they must get into water to hatch and infect their first intermediate host, a freshwater snail. After being ingested by a suitable snail, the eggs release miracidia, which undergo several developmental stages in the snail: as sporocysts, redia, and cercariae. The snail intermediate hosts for Opisthorchis are Bithynia goniompharus, B. funiculata, and B. siamensis. Parafossarulus manchouricus often serves as a first intermediate host for C. sinensis, and snail hosts also include other Bithynia, Tarebia, Alocinma, and Bulimus spp. Once inside the snail's body, the miracidium hatches from the egg and parasitically grows inside of the snail, where it develops into a sporocyst that houses the asexual reproduction of redia, the next stage. The redia house the asexual reproduction of free-swimming cercariae. This system of asexual reproduction allows for an exponential multiplication of cercaria individuals from one miracidium. Once the redia mature, having grown inside the snail body until this point, they actively bore out of the snail body into the freshwater environment and seek out fish. Cercariae are released from the snail and then penetrate freshwater fish—the second intermediate host ( Cyclocheilichthys and Puntius spp., Hampala dispar ), encysting as metacercariae in the muscles or under the scales. Once inside the fish muscle, the cercaria creates a protective metacercarial cyst with which to encapsulate its body. This protective cyst proves useful for when the fish muscle is consumed by a human or other host, such as a cat, dog, pig, or any other fish-eating mammal. The acid-resistant cyst enables the metacercariae to avoid being digested by the gastric acids and allows them to reach the small intestine unharmed.
What is the physical effect of rediae on mollusks?
On each side of the pharynx is a cephalic ganglion from which nerve fibers radiate. Flame cells occur in most rediae, terminating at the bladder (s) in either single or multiple excretory pores.
How long does it take for Metacercariae to reach the liver?
Most reach the liver within 6 days after excystment.
Where do miracidia develop?
When miracidia are fully developed within the eggs, the eggs hatch in water and the miracidia are liberated in water and swim to infect a snail host. The miracidia penetrate the tissues of the snail and localize in the hemocele where it becomes a sporocyst ( Blair et al., 1999 ).
Why is Fasciola Hepatica important?
Fasciola hepatica occupies a prominent place in parasitology because its life cycle was the first among digenetic trematodes to be completely elucidated, and that achievement has been the impetus for all subsequent investigations on life histories.
