Parasite Lifecycles

Question 1

What is the lifecycle of Ascaris?

Answer 1

1. Adults in the s. intestine of humans
2. Mating and eggs laid, released into faeces
3. Eggs develop into embryonated eggs
4. Eggs swallowed by host
5. Larvae enter blood via intestinal mucosa
6. Carried to the lungs by circulation
7. Coughed up and swallowed

Direct nematode roundworm

Question 2

What is the life cycle of Necator americanis?

Answer 2

1. Adults in s. intestine
2. Eggs released in faeces
3. L2 in soil eat bacteria
4. L3 infective, negatively geotrophic
5. Bores through human skin
6. Travels to the lungs via circulation
7. Coughed up and swallowed

Direct nematode hookworm

Question 3

What is the Toxocara canis lifecycle?

Answer 3

1. L2 activated by pregnancy in host
2. Puppies infected in vitro and milk
3. L2 migrate through liver to the lungs
4. Migrate to the trachea and the gut
5. Develop into L4 larvae and adults
6. Release eggs in faeces
7. Eggs activated by O₂ and moisture
8. Become embyronic and infective
9. Injested by host
10. Can cause blindness in humans

Dog roundworm/nematode

Question 4

What is the lifecycle of Enterobius?

Answer 4

1. Adults in l. intestine
2. Lay eggs in perianal area
3. Eggs released in faeces
4. Eggs ingested
5. Larvae hatch in s. intestine

Pinworm nematode/roundworm

Question 5

What is the lifecycle of Dracunculus?

Answer 5

1. Humans ingest water with copepods
2. L3 released when copepods die
3. Penetrate gut wall and enter tissues
4. Mate, males die and females enter limbs
5. L1 hatch in blisters on skin
6. Released in water and eaten by copepods
7. Develops through to L3

Indirect guinea worm/nematode

Copepod vector

Question 6

What is the lifecycle of Onchocera?

Answer 6

1. Adult worms in subcutaneous nodules
2. Birth microfilaria which circulate skin
3. Uptaken by blackfly when blood feeding
4. Microfilaria pentrate fly thoraic muscles
5. Develops to L3 and moves to proboscis
6. Released in human skin when fly feeds

• Indirect nematode causing river blindness*
• Vector is blackfly*

Question 7

What is the lifecycle of Wucheria and Brugia?

Answer 7

1. Adults in subcutaneous nodules
2. Birth microfilaria which circulate blood
3. Day: deep veins. Night: near surface
4. Uptaken by mosquito when it feeds
5. Penetrate midgut and develop in muscles
6. L3 migrates to proboscis
7. Enter skin when mosquito feeds

*Indirect nematode causing lymphatic filariasis

Vector mosquito*

Question 8

What is the lifecycle of Trichinella?

Answer 8

1. Adults in s. intestine
2. Larvae deposited in mucosa of gut lining
3. Travel to muscles via circulation
4. Form nurse cell cyst
5. Encysted larvae ingested by predator#

Nematode

Question 9

What is the lifecycle of Taenia saginata?

Answer 9

1. Adults in human s. intestine
2. Eggs releaces in faeces
3. Eggs ingested by cattle
4. Duodenum digests, oncosphere forms
5. Penetrate gut wall and enter blood
6. Form cysticerci in muscle tissue
7. Cystercerci ingested by human

Question 10

What is the life cycle of Diphyllobothrium latum?

Answer 10

1. Adult develops in human s. intestine
2. Eggs released in faeces
3. Eggs embryonate in water
4. Onchosphere forms, eaten by copepod
5. Procercoid larvae develop
6. Fish eats copepod
7. Plerocercoid develops, human eats fish

Question 11

What is the lifecycle of Echinococcus?

Answer 11

1. Adults in dog s. intestine
2. Faeces released in faeces
3. Harbivore ingests eggs
4. Onchosphere penetrates gut wall
5. Hydatid cysts form
6. Cyst ingested by dog
7. Protoscolex forms, then scolex
8. Attaches to intestine

Question 12

What is the lifecycle of Prostoma?

Answer 12

1. Adults in toad urinary bladder
2. Oncomiracidia passed out as frog breeds
3. Crawl over wet skin and enter nostrils
4. Initial development in respiratory tract
5. Mature in bladder, during hibernation

Question 13

What is the life cycle of Schistosomes?

Answer 13

1. Adults in blood vessels of bladder/gut
2. Eggs released through faeces/urine
3. Miracidium hatches, penetrates snail
4. Forms sporocyst
5. Forms redia
6. Forms cercaria, free-swimming
7. Penetrates human skin, enters blood

Question 14

What is the life cycle of Fasciola hepatica?

Answer 14

1. Adults in bile duct of liver
2. Eggs via bile released in faeces
3. Miracidia hatch in damp pasture, swim
4. Find snail host, form sporocyst
5. Form redia
6. Form cercariae, released from snail
7. Metacercariae encyst on grass, ingested

Question 15

What is the lifecycle of Dicrocoelium dendriticum?

Answer 15

1. Adults in sheep bile duct
2. Eggs released via bile in faeces
3. Miracidia ingested by snail
4. Form sporocyst
5. Form redia
6. Form cercariae, released as slime ball
7. Ant ingests, metacercariae encysts inside
8. Ant’s jaws fused at night, fixed to grass
9. Eaten by sheep

Question 16

What is the lifecycle of Entamoeba?

Answer 16

1. Adults in human gut
2. Can invade other organs through blood
3. Cysts in faeces
4. Ingested

Question 17

What is the life cycle of Acanthamoeba?

Answer 17

1. Facultative parasite in FW/soil
2. Can infect eyes from contact lens

Question 18

What is the life cycle of Naegleria?

Answer 18

1. Very rare faculative parasite
2. Water forcefully entering nostrils
3. Severe brain infection

Question 19

What is the life cycle of Apicomplexans Eimeria?

Answer 19

1. Sheep eats sporulated oocyst
2. 4 spprozoites released, enter gut cells
3. Schizogony occurs, merozoites released
4. Asexual life cycle
5. Merozoites can form micro/macrogametes
6. Fertilisation forms zygote
7. Unsporulated oocyst ejected in faeces
8. Sporogony forms sporolated oocysts

Question 20

What is the life cycle of Plasmodium?

Answer 20

1. Sporocytes from mosquito into blood
2. Sporozoite penetrates liver cell
3. Hypnozoites remain in liver
4. Exoerythrocytic schizogony
5. Forms merozoites, penetrate RBCs
6. Form schizonts
7. Erythrocytic shizogony
8. Forms merozoites