MI: Worms

Question 1

What are 3 main types of helminths and some examples?

Answer 1

Cestodes (tapeworm)

• Hydatid
• Pork / beef / fish tape worm

Trematodes (Flukes)

• Lung, liver, intestinal
• Blood (schistosoma)

Nematodes (Roundworms)

• Hookworms
• Ascarids
• Stongyloides

Question 2

Describe the tapeworm lifecycle

Answer 2

Question 3

What are hyatids?

Answer 3

Dog tape worm (echinococcus)

• Dog and foxes are definitive hosts
• Encyst in liver, lungs
• Complications due to cyst rupture or mass effect

Question 4

Describe the lifecycle of hyatids?

Answer 4

Question 5

How are cestode infections diagnosed?

Answer 5

Visualisation, serology and imaging

Question 6

How are cestode infections treated (tapeworm and hyatid)?

Answer 6

PAIR - puncture, aspiration, injection, reaspiration

Question 7

Describe the lifecycle of schistosomiasis

Answer 7

Lifecycle

• Cercariae invade human skin when in contact with contaminated water.
• Worms develop in venous plexus
• Eggs excreted in faeces or urine
• Hatch into miracidia, which parasitise snails
• Snails release cercariae

Adult schistosomes lay eggs

• Migration of eggs through bladder or bowel causes damage
• Retrograde passage of eggs into the liver causes “cirrhosis”

Question 8

Where is schistosomasis endemic to?

Answer 8

Africa, SE asia, South America

Question 9

How is schistosomiasis diagnosed?

Answer 9

Microscopy - seeing the eggs

• Urine - S. haematobium
• Stool - S. mansoni, S. japonicum

Serology

Biopsy

Response to treatment

Question 10

Treatment of schistosomiasis

Answer 10

Praziquantel

Prevention (hard) - kill snails, education (no swimming or washing)

Question 11

What are 4 soil-transmitted helminths?

Answer 11

• Ascaris lumbricoides
• Trichuris trichiura
• Hookworm
• Strongyloides stercoralis

Question 12

Ascaris lifecycle

Answer 12

Ingested with food

Question 13

How many people affected in Ascaris in world

Answer 13

1 billion

Question 14

Describe the lifecycle of strongyloides

Answer 14

Only helminth capable of autoinfection

• Larvae invade skin
• Mature into adult pinworms in the small bowel
• Eggs produced, hatch into rhabtidiform larvae
• These mature into filariform larvae (infectious)
• These can autoinfect via perianal skin

Question 15

How do strongyloides cause damage?

Answer 15

Generally asymptomatic

• Hyperinfection
• Larva currens
• Malabsorption

Question 16

How is strongyloides treated?

Answer 16

Ivermectin

Question 17

What is filariasis?

Answer 17

Nematode infections spread by blackflies and mosquitoes

Categories according to the worm tropism

• Lymphatic filariasis (Wuchereria, Brugia)
• Subcutaneous filariasis (Onchocerciasis, Mansonella, Loa loa)
• Serous cavity filariasis (Mansonella, Dirofilaria)

Adult worms release larvae (microfilariae) taken up by vector

Question 18

How does tissue damage occur in filariasis?

Answer 18

• Adult worms: lymphatic filariasis (elephantiasis, scrotal swelling), also oncho (nodules)
• Microfilariae: Onchocerciasis (depigmentation, river blindness)

Question 19

How is filariasis diagnosed?

Answer 19

• Microscopy - blood film, skin snips
• Serology (ELISA)
• Imaging - find adult worms (USS dance sign)

Question 20

How is filariasis treated?

Answer 20

Combination of ivermectin and diethylcarbamazine (DEC) with albendazole

Question 21

Describe the lifecycle of filariasis

Answer 21

Question 22

What is myiasis?

Answer 22

Asphyxiate larve by covering wound with vaseline

Question 23

What is this?

Answer 23

Ginea worm - only worm that comes out your leg

Question 24

Worms coming out of febrile child?

Answer 24

Nematode (ascaria) - does not like heat

Question 25

What is this?

Answer 25

Dog hookworm - Someone stepped in sand infected with dog poo - Dog hookworms cannot migrate properly so remain local to invasion site

Question 26

Describe 2 main parasite screening investigations.

Answer 26

- Microscopy - Serology

Question 27

What is commonly seen on FBC in helminth infection?

Answer 27

Eosinophilia