Midterm 1 Flashcards
Wucheria Bancrofti
- filarial nematode
- cause of elephantiasis
Unusual within the nematodes because: - have 2 hosts (including an insect vector)
- don’t produce eggs but instead microfilariae
- the microfilariae are what blocks up the vessels and causes the swelling
Wucheria Bancrofti Life Cycle
- Mosquito takes a blood meal from a human and L3 larvae enter the human (L3 larvae are the infective stage)
- L3 larvae develop into adults and adults are present in the human lymphatic system
- There are both male and female adults that sexually reproduce and produce microfilariae which can migrate within the lymphatics and the peripheral blood stream
- The microfilariae travel into the peripheral blood stream only at night to limit encounters with the host’s immune compounds and to be present when the mosquitos are active and likely to pick them up (Mosquitos are active at night time and they are biological vectors for W. Bancrofti)
- Mosquitos take a blood meal, picking up the microfilariae (L1 stage)
- The microfilariae develop into the infective stage L3 within the mosquito and migrate to the mosquito proboscis
- Mosquito takes a blood meal from human, injecting the infective L3 larvae into the human.
Filarial nematode
Guinea Worm Life Cycle
- Copepod eats L1 larvae in the water 2. L1 larvae undergoes molts to become the infective L3 larvae 3. Human drinks unfiltered water containing copepods that house the infective larvae. Or humans eat fish or amphibian that had consumed the copepod 4. Larvae are released within the human when the copepods die 5. The larvae penetrate the host’s stomach and intestinal wall and mature into adults. Separate males and females will sexually reproduce 6. Fertilized female migrates to the skin and causes a blister and L1 larvae will be discharged through the blister.
- About 1 year until the female emerges from the host’s foot.
Tissue-dwelling nematode and filarial nematode.
Dogs can be definitive hosts as well.
Guinea Worm
Dracunculus - Causative agent of dracunculiasis
Long-thread like worm
Tissue-dwelling nematode and filarial nematode
Whirling Disease
Caused by Myxobolus
Myxobolus Lifecycle
- Myxospores of the parasite are released from the cartilage of an infected fish
- Myxospores are ingested by an annelid (ex tubifex tubifex) and extrude polar filaments to attach to the intestinal mucosa
- Germ cell within the myxospora migrates to the intestinal epithelium where it undergoes asexual and sexual reproduction
- Diploid organism forms and undergoes cell division to give rise to a single triactinomyxon
- Triactinomyxons (hooked spores) are released in the feces of the annelid and enter the water column
- Fish (or amphibians, reptiles, mammals) get infected when the triactinospore polar filaments attach themselves to the fish skin (typical fish are salmonids)
- Sporoplasm penetrates the fish and undergoes asexual reproduction and in the epidermis and then migrates thought the CNS to the cartilage
- The parasites feed on the cartilage
- After 80 days or so, the parasite differentiates again the myxospore arises
Trematode 3 Host Lifecycle
- Egg released into the environment and develops into the miracidium larval stage 2. The miracidium infects a mollusk host and develops into a sporocyst 3. The sporocyst then develops into rediae in which cercariae leave the host and enter the next host (usually the disease vector). 4. Within the next host, the cercariae will encyst as metacercariae (this can also be cercariae encysting as metacercariae on vegetation). 5. The vertebrate definitive host will eat the metacercariae by ingesting the disease vector or consuming the vegetation that have metacercariae. 6. Parasite settles in the digestive tract or lungs/liver of the host and develops into a hermaphroditic adult 7. Adult lays eggs which are expelled from the host and the lifecycle rebegins
Schistosomes
The causative agent of schistosomiasis. Very devastating.
TREMATODE with only a 2 host life cycle -
1. Cercariae exit the snail, and actively seek out their vertebrate host (they have eye spots and can swim)
- Enter the vertebrate host via penetration and develop into schistosomulae - circulation - and then into adults - no metacercariae stage. May be bc large vertebrate hosts are unlikely to be eaten by another host.
- Adults (separate males and females) shed eggs into stool or urine
- Eggs hatch to release Miracidia which penetrate the snail tissue and develop from into sporocysts and then into cercariae which are released from the snail and into the water. (No rediae stage)
(Separate male and females - most trematodes are hermaphroditic)
Swimmer’s Itch
Caused by schistosomes (trematodes - platyhelminthes)
- Eggs are released in the feces of a duck. 2. Eggs hatch to release miracidia 3. Miracidia penetrate mollusc intermediate host 4. Cercariae (free-swimming) exit the mollusc host and they can either penetrate the skin of birds or the skin of humans (humans are accidental hosts) and the human gets swimmer’s itch.
Trichinella
- The larva get lodged in the muscle cell of a pig and then they turn into nurse cell
- Humans will eat the undercooked meat housing the encysted larvae (L1) 3. Larvae released in the small intestine 4. Adults mature in the small intestine and sexually reproduce 5. Larva deposited in the mucosa - into the circulation 6. Encysted larvae in the striated muscle of human.
Post-slaughter testing, freezing for strains that are not cold resistant
Tissue-dwelling nematode
Direct life cycle
The one host can act as both the definitive host because both sexual reproduction and asexual reproduction occur
Dicrocoelium
Trematode (Platyhelminthes)
Associated with zombie ants
Dicrocoelium Lifecycle
Trematodes - Platyhelminthes
- Cercariae developed in the mollusc/snail cause mantle to secrete slime which contains the cercariae and provides protection and ants are attracted to the slime 2. Ants eat the slime along with the cercariae 3. Cercariae penetrate the gut wall and encyst as metacercariae - although a few migrate to the brain and stimulate a behavioural change - cause them to migrate up to tops of grass blades and remain there overnight to favor consumption by grazing animals. 4. Grazing animal (cow) consume the ant along with the metacercariae 5. Vertebrate host (DH) becomes infected and eggs are shed in the feces 6. Eggs are ingested by a snail (IH) (miracidia - sporocysts - cercariae) 7. Cercariae released from a respiratory pore in a slime ball
Echinococcus
Platyhelminth - CESTODE - ‘tape worm’
- Adult in the small intestine of the definitive host (scolex used to attach)
- Production of embryonated eggs that come out in the feces
- Eggs are eaten by sheep, goats or swine –> eggs become oncospheres - oncospheres hatch and penetrate the intestinal wall of the sheep, goats or swine
- Encyst to become hydatid cyst in the liver, lungs
- Dog or other canid (DH) eat the intermediate host and the cysts along with them
- Proscolex forms from the cyst and grows to form an adult tape worm in the intestine of the definitive host (dog, canid)
If humans eat the eggs:
- Can get cysts in the liver and lungs
Echinostoma
Platyhelminth - TREMATODE
- Eggs passed in the feces of the definitive host (vertebrate like duck, rodent, human)
- Eggs hatch to form miracidia which seek out a snail host
- Miracidia penetrates snail host (Miracidia - sporocysts - rediae - cercariae). Cercariae exit the snail host
- Cercariae swim to find a second intermediate host (ie. Snail or frog) –> Cercariae encyst as metacercariae within this second intermediate host. (infective stage)
- Duck, rodent, or human eat the second intermediate host and the metacercariae exist in the GI tract and become adults in this definitive host’s intestine
- Sexually reproduce and release eggs into the feces. (Diagnostic stage)
Taenia Life Cycle
- Cattle and pigs (IH) can become infected by feeding on grass contaminated with eggs or gravid proglottids
- Oncospheres hatch from the eggs, penetrate the intestinal wall and circulate to the muscle of the intermediate host (IH)
- Oncospheres then develop into cysticerci in the muscle of the IH
- Humans get infected by eating the IH meat infested with cysticerci of Taenia (most common)
- Scolex attaches in the intestine and adult matures here, growing proglottids
- Eggs or gravid proglottids are shed and present in the feces of the human host.
Humans can also be infected by accidental ingestion of eggs through contamination of feces. In this case, larvae will develop within the human and can cause serious pathology –> disease is called cystercercosis
Taenia
Platyhelminthes - Cestodes
Cystercercosis
Caused by Taenia infection where humans accidentally ingest the eggs through contamination of feces. Here the larvae develop inside of the human and this can cause serious health problems, including adult onset seizures
Most commonly, when humans are infected by Taenia
Nematodes
Typically have a direct life cycle with only one host but the filarial nematodes have an insect vector and a vertebrate definitive host.
3 host lifecycles are rare in nematodes.
Ascaris
Nematode - Most popular parasitic worm infection worldwide
Gut-dwelling nematode, non-blood feeders
- Humans ingest the eggs (accidental feces contamination - oral)
- Larvae hatch from the egg and travel to the lungs where they mature
- Matured larvae get coughed up and swallowed
- In the intestine, they develop into adults and produce eggs
The eggs are very resistant to harsh conditions - problem for general sanitation efforts
What is the causative agent of river blindness?
Onchocerca - filarial Nematode
River blindness can be treated with ivermectin
Heligmosomoides polygyrus
Rodent parasite
Gut-dwelling, non-blood feeding
NEMATODE
Heligmosomoides polygyrus Lifecyle
Nematode - Gut-dwelling, non-blood feeding
- Eggs are passed in the feces of the rodent host
- Eggs hatch L1 larvae which molt to L2 which molt to L3
- L3 larvae are the infective larvae which the rodents consume
- L3 larvae penetrate the intestinal mucosa where the L3 molts to L4 which then develops into the adult
- The adult migrates out of the mucosa and into the intestinal lumen where it can then shed eggs that are released in the rodent’s feces.
Onchocerca Lifecycle
Filarial nematode - Causative agent of River Blindness
- Black fly injects L3 infective larvae into human
- Larvae travel to subcutaneous tissues and adults develop in subcutaneous nodules 3. Adults produce unsheathed microfilariae that are found in the peripheral blood, lymphatics, urine. 4. Blackfly takes a blood meal and ingests microfilariae 5. Microfilariae penetrate gut and migrate to thoracic muscles - develop to L1 to L3 which then migrates to the blackfly’s proboscis, ready to be inserted when the fly takes its next blood meal.
The microfilariae can travel to the ocular tissue and cause damage.
Haemonchus sp.
Gut-dwelling blood feeding - Nematode
Parasite of the stomach of ruminants
Haemonchus sp. Lifecycle
Gut-dwelling, blood-feeding nematode
Parasite of the stomach of ruminants
- Eggs are released from the feces of the ruminant and develop into L1 larvae in the feces.
- L1 molts to L2 in the feces
- L2 molts to L3 (infective) which migrates to pasture
- The L3 stage larvae are ingested by grazing ruminants
- L3 unsheaths to L4 which molts to L4 in the abomasum
- Adults have lancet - piercing structure - to piece holes in the abomasum to feed from the blood supply of the ruminants
- Eggs exit the host via feces.
Ancylostoma
Human hookworm
Gut-dwelling, blood-feeding NEMATODE
Eggs in the feces of the human
Actively penetrate the skin of the host before migrating to the lungs… this is unusual for a nematode.
Ancylostoma lifecycle
- Eggs in the feces of the human definitive host
- Rhabdiform larvae hatch from the eggs (L1 +L2)
- which then develop into filariform larvae (L3 infective stage)
- L3 Filariform larvae wait for the host to come by and actively penetrate the skin of the definitive (only) host.
- Larvae will migrate to the lungs where they develop into L4
- The larvae are then coughed up and swallowed. The L4 larvae mature into adults in the intestine
- Adults hook onto the intestine and feed on the blood supply
- Adults sexually reproduce and eggs will be present in the feces
Schistosome Lifecycle
- Cercariae exit the snail, and actively seek out their vertebrate host (they have eye spots and can swim)
- Enter the vertebrate host via penetration and develop into schistosomulae - circulation - and then into adults - no metacercariae stage. May be bc large vertebrate hosts are unlikely to be eaten by another host.
- Adults (separate males and females) shed eggs into stool or urine
- Eggs hatch to release Miracidia which penetrate the snail tissue and develop from into sporocysts and then into cercariae which are released from the snail and into the water. (No rediae stage)
Trematode - Platyhelminth
Ascaris Lifecycle
- Humans ingest the eggs (accidental feces contamination - oral)
- Larvae hatch from the egg and travel to the lungs where they mature
- Matured larvae get coughed up and swallowed
- In the intestine, they develop into adults and produce eggs - released into the feces
Gut-dwelling, soil-transmitted nematode. Non-blood feeding
