Platyhelminthes - Schistosoma Flashcards
Name and briefly describe the 4 major groups of Platyhelminthes
Trematoda - Parasitic flukes
Monogenea - Parasitic flatworms with 1 generation
Cestoidea - Tapeworms
Turbellaria - Free-living flatworms
What is known about the evolutionary origins of the Platyhelminthes?
They appear to all have a common ancestor, but Turbellaria is not considered a proper “Class”
In general, the platyhelminthes are ____ symmetrical
bilaterally
How is body symmetry related to cephalization?
Bilaterally symmetrical organisms tend to move in a forward direction, so it makes sense to have most sensory structures at the anterior end
The concentrated nervous tissue at the anterior end of a platyhelminth is referred to as
Ganglion
Briefly describe the structure of the platyhelminthes
Flattened. No circulatory system, nervous system running along entire body. Move via cilia and have protonephridia for filtration. Connective tissue called parenchyma. Reproduction usually hermaphroditic.
Platyhelminthes may secrete solid mucus pellets called ______
Rhabdites
How does the prevalence of sexual vs asexual reproduction influence effectiveness of parasitic infection?
Some organisms can reproduce asexually in their host and can build up to lethal levels through that
Briefly describe the structure of Trematodes
Very closely related to freeliving species. Most are hermaphroditic though some have separate sexes. Gut is highly diverticulated into many branches. Have a muscular pharynx and oral sucker. Many also have a ventral sucker (aka Acetabulum)
Briefly describe the female reproductive system in Trematodes
A single ovary where gametes are produced. Can be round or highly lobulated. This leads to an oviduct, then a union of the vitelline ducts (where yolk cells come from). This leads on to a tube lined with “gland cells”, and then the uterus. This is where the egg starts to maturate. The female gonopore is the exit point to the external environment
The fact that Trematode yolks come from Vitelline ducts means they are a _____ group
Ectolecithal
Briefly describe the male reproductive system in Trematodes
Consists of testis leading to vas efferens. Where many vas efferens meet it is called the vas deferens. At the end is the ejaculatory duct and finally the gonopore. The gonopore has an intromittent “cirrus” that can be retracted
Fasciola hepatica is otherwise known as _____, and it is the basis on which we study trematodes
the Giant liver fluke
The vitellaria of trematodes are divided into many subdivisions called _____
Follicles
Most flukes are ______ tissue parasites
Solid-tissue
Some flukes transfer through 3-4 different hosts in their lifetime. Briefly describe this
Usually start in a mollusc, moving from one kind to another, one or more other invertebrates (arthropods typically), and then 1 or 2 vertebrate hosts (usually fish)
Opisthorchis sinensis is otherwise known as ______
Chinese liver fluke
The gut of O. sinensis is diverticulated into ______ structures called _____
2, caecae
Vitellaria in trematodes are sometimes _____ distributed, meaning they are in the center of the body
Equatorially
The eggs of all flukes must stay in a _____ environment
moist
The first stage of a fluke is called a ______. Describe its appearance
Miracidium.
Has a ganglion, highly organized structures. Has a ciliated outer layer (usually a pair of cilia on each cell). Have “germline” cells, which will eventually become gonads.
Can swim around in the water.
How does the miracidium larva escape from a fluke egg?
Operculum of the egg pops open and and miracidium swims out
In aquatic situations, fluke miracidium larvae seek out their host. How do they do so and what happens after?
Look at skin biochemistry (usually of a snail), and dig inside of the skin. After this, the miracidium undergoes metamorphosis into a Sporocyst.
Name and describe the second stage in fluke development
Sporocyst - Loses cilia and absorbs nutrients directly from host (no gut). Start to divide asexually (within itself - more like internal budding). Adult-like characterists develop after a few generations
Name and describe the third stage (juvenile) in fluke development
Redia - develops after 2-3 cycles of sporocyst asexual production. Has a gut, protonephridia, proper sex tissues. Can form more Redia within itself (asexual reproduction). After a while the next juvenile (Cercaria) develops).
Name and describe the fourth stage (second juvenile) in fluke development
Cercariae. Usually have a tail and exit the host (usually a mollusc) by leaving the skin and search for the next host (usually aquatic), typically develop into a metacercarium before infection host
What do Cercariae stage juvenile flukes do when they enter a host?
Usually drop their tail and encyst in muscle. This causes the “metacercarium” to develop
The outer body wall of flukes is referred to as the ____
Tegument
How do cercaria of Opisthorchis senensis seek out their preferred fish host?
They respond to light. They sit on the bottom sediment and quickly swim up if light is blocked. If they reach the surface without hitting a fish they just float back down to the bottom
TRUE OR FALSE: Cercaria generally have the same body plan between all flukes
False, some have swimming tails, some don’t. Some have cilia, some don’t. They all vary quite a bit
Briefly describe the structure and function of the fluke tegument.
Consists of distal and inner zone.
Distal is a continuous, multmitochondrionated structure with small spines and invaginated crypts to increase surface area.
Inner zone consists of large “cytons” (embedded in parenchyma tissue) connected to the outer zone via internuncial processes (cytoplasmic streams).
The tegument absorbs some amino acids and glucose from the host with some excretion of nitrogenous waste. Protects the body from host immune response.
How can the tegument help flukes avoid immune response?
Can take host tissue and molecules into their tegument and the invaginations in it - causing less recognition of the fluke as a pathogen
Within the tegument, flukes have a layer of ____ muscles with a _____ layer of muscles beneath them
Circular, longitudinal
Schistosomes are unique from other trematodes in that they…
Have no redia stage and are dioecious
Adult males of the genus Schistosoma has a structure called the ______, unique among trematodes. What is the purpose and why is it different from other trematodes?
Gynecophoral canal. It is a groove in the male in which the female must sit in order to reproduce. Schistosoma spp. are the only dioecious trematodes
What is Schistosomiasis?
A group of diseases that are 2nd behind malaria in parasite related tropical disease in the world. It is endemic in many areas of the tropics and sub tropics. Largely a juvenile disease.
Describe the life cycle of Schistosoma worms
Eggs passed in either feces or urine, miracidium hatches. and infects a snail. Develops into sporocyst then in cercaria, which leave the snail tissues to swim in the water. They find their host based on keen sense of “smell/taste” - basically find amino acids associated with skin secretions of definitive host. Tail free cercaria are called Schistosomules, and they enter circulation and mature mostly in portal blood (liver or intestine). Male or female adults must find each other, where they rapidly grow and undergo reproduction
Describe the difference between eggs of Schistosoma mansoni, Schistosoma japonicum, and Schistosoma haematobium. If the organism is a complex, indicate so.
S. mansoni: Elongated with a large spine at one end
S. japonicum: Relatively round eggs with no spine
S. haematobium: Round eggs with a large spine at the end of the shell
S. japonicum miracidia infect ____ snails
Oncomeania
S. mansoni miracidia infect ____ snails
Biomphalaria
S. haematobium miracidia infect _____ snails
Bulinus
S. haematobium largely infects the ____ portal system and ____
Liver, urinary bladder veins
S. mansoni and S. japonicum largely infect the ____ portal system. Indicate which one infects the small/large intestines
intestinal.
S. mansoni - Large intestine
S. japonicum - Small intestine
Schistosoma parasites feed on….?
Blood - erythrocytes
What causes symptoms during schistosomiasis infection?
As eggs move throughout the body, inflammation occurs and tiny lumps surround each egg (granulomas), and this can back up blood vessels, puncture capillaries, cause scar tissue formation, generate autoimmunity. IT can cause the intestines to stop working properly as well.
What symptoms do Schistosoma parasites induce
On top of granulomas formed around eggs in the bladder, kidney, or intestines, they can also cause autoimmune responses that result in degradation of the walls of those organs
Briefly describe the internal and external structure of the female Schistosoma spp.
Oral sucker followed by Bifurcated gut, which leads to cecae and finally intestine. Have a weak ventral sucker.
Egg shell formation in Schistosoma spp. occurs in the ______
Mehlis’ gland
Briefly describe the internal and external structure of the male Schistosoma spp.
Have a more muscular esophagus than the female (for eating blood), and the muscular contraction of the male allows the attached female to take in blood more efficiently. Have multiple testes connected by vasa efferentia to vas deferens.
S. mansoni occurs in what countries?
Africa, Eastern Mediterranean, Caribbean, South America
S. japonicum parasites occur where?
South-East Asia, Western pacific
S. haematobium occurs where?
Africa, Eastern Mediterranean
How did the completion of the Aswan High Dam in Egypt affect the rates of Schistosomiasis?
Snail host populations went up a lot (due to year-round flooding and low-lying waters)
What is the risk behaviour associated with coming in contact with Schistosoma spp.?
Water contact with skin exposure
What are S. japonicum risk factors?
Because it is zoonotic, entering water that has had contact with infected sheep, goats, etc, can result in infection
What is the most effective Schistosomiasis drug?
Praziquantel
What has historically been used for Schistosomiasis treatment?
Trivalent antimonials
How does Praziquantel affect Schistosome worms
Affects the integrity of the integument and appears to cause worms to go into permanent muscle contraction spasms
Spines are often present in the tegument of trematodes. Which of the trematodes studied in class has significant spines?
Schistosoma spp. have oral and ventral suckers densely surrounded by spines. Female Schistosomes have anteriorly directed spines no their posterior ends
How is the nervous system arranged in flukes?
Orthogon (ladder-like), with longitudinal cords connected by transverse rings along the body. Miracidia and cercariae generally have far more sensory structures (ex. tangoreceptors, eye spots) than adults as they need to find the next host quickly
Approximately how many people per year are infected with Schistosomiasis? How many of those develop symptoms? What about severe complications.
Over 200 million per year, with 120 million symptomatic and 20 million of those suffer severe consequences
How long has Schistosomiasis been around and what was the telltale historical symptom?
Has been around since before 1200 B.C., characterized by bloody urine.
____ is the only New World Schistosoma species
S. mansoni
Where was S. japonicum discovered and how is that related to its distribution?
Discovered in Japan. Distributed across China, Taiwan, Philippines, SEA
Of the three major Schistosoma species, which are complexes and which are standalone species?
S. mansoni: Single species
S. japonicum: Complex
S. haematobium: Probably a complex
TRUE OR FALSE: Schistosoma species have no pharynx
TRUE
What physiologic reasons, other than sex, are there for the presence of the gynecophoral canal of the male schistosome
Male have more robust muscles for keeping down food, so when a female is inserted in the gynecophoral canal, she can eat more. On top of this, male’s muscles enables the pair to move into smaller veins where the female will deposit eggs
How does one become infected with Schistosomiasis
Skin contact with water that has had fecal contamination with schistosome worms
