Worms

Question 1

What are the main different types of Helminths?

Answer 1

There are 3 main classes of Helminths

1. Cestodes (tape worms)
2. Trematodes (flukes) (incl. schostosoma)
3. Nematodes (Roundworms (incl. Hookworm, Strongyloides9

Question 2

What are the different shapes of the 3 classes of Worms?

Answer 2

1. Cestodes (tapeworm) –> Flat, can be long
2. Trematodes –> Flukes (small, plane)
3. Nematodes (roundworms) –> cylindrical

Question 3

What are the most important Cestodes?

Answer 3

1. Beef and pork tape worms (human worms)
2. Echinococcus - dog tape worm

Question 4

What are the main lifcycles of the pork and beef tapeworm?

Answer 4

Ultimatet host ist Human

Human infected faeces –> ingested by pigs/pork –> cysts in animals –> hedge in humans (usually GI tract). NO cysts in human normal life cycle

NOTE: if humans have cysts –> humans will have eaten human faeces (is the pig in the life-cycle)

Question 5

What is Echinococcus? Why does it clinically usually cause more problems than pork and beef tapeworms?

Answer 5

Echinococcus is a dog worm (Cestode) with sheep as intermediate hosts

The Lifecycle is the same as Pork and beef tapeworm, but with the dog as ultimate host

Are problematic if humans accidentally become intermediate host –> cyst formation (cysts are the problematic things that kill people)

Question 6

What is the main management of Tapeworm infection?

Answer 6

1. Of worms: Praziquantel (for humans and dogs)
2. Of cysts: difficult (as drugs don’t penetrate)

Prevetnsion: hygiene, de-worm dogs, cull foxes

Question 7

What is the main epidemiology of schistosomiasis?

Answer 7

Differnt sub-types with high prevalence in

Mainly in sub-saharan africa and parts of Brazil and south-east asia (south east asia now almost extinct)

Question 8

What are the main signs and symptoms of schistosomiasis?

Answer 8

1. Acute infection: skin reaction
2. incubation period –> with hedging in blod (4-8 weeks) –> fever, cough malaise
3. chronic infection (depending on site involved)

Bladder: haematuria, dysuria (+ increased bladder squamous cell carcinoma)

Hepatic. hepatosplenomegaly
Lungs, brains

Question 9

How is Schistosomiasis diagnosed?

Answer 9

Microscops of urine of stool (visualisation of the eggs)

Serology (antibodies against adult worms)
Biopsy of cysts (can be present)

Question 10

Explain the life cycle of schistosomiasis

Answer 10

1. Humans (definitive host) excrete eggs in urine or faeces
2. Eggs hedge in water into miracidia which penetrate into fresh-water snails
3. Snails produce sporocyst that replicate asexually into cercadia.
4. Cercadia are in water and can penetrate human skin again if in contac with humans
5. Worms edge in blood
6. Sexual reproduction of worms in bloodstream and migration + lie eggs in target organs (liver, bladder)

Question 11

What is the main treatment and prevention of schistosomiasis?

Answer 11

Treatment:
Is very easy: praziquantel

Prevention:
Is hard:
Kill snails
Destroy snail habitat
Mass treatment
Interrupt transmission: no swimming, no washing etc

Question 12

What are the most imporant sub-groups of Nematodes?

What is their main route of transmission?

Answer 12

Nematodes = Roundworms such as
Hookworms
Ascarids
Strongyloides

Question 13

What are the main helminths transmited through soil?

What is their main mechanism of entry?

Answer 13

Usually differnt types of roundworms (Nematodes)

• Ascaris lumbricoides – ingested with food
• Trichuris trichiura – ingested with food
• Hookworm – transdermal infection
• Plus: Strongyloides stercoralis – transdermal infection

Question 14

What are the main mechanisms/ causes of disease that infections with roundworms cause?

Answer 14

Very common and hugh burden of disease

Usually in GI system but can have other phases

• Migration (ascaris, hookworm and strongyloides)
• Intestinal obstruction (ascaris)
• Malabsorption and blood loss (all of them)
• Psychological distress

Question 15

What is Ascaris? What is the routte of transmission?

Answer 15

Ascaris = big big nematode with very big global burden of disease

Transmited through soil (from fecal ingestion of eggs) –> migration through body

Question 16

What helminth is the only helmintth that is capeable of auto-infection?

Answer 16

Strongyloides
–> therefore burden not related to dose, as can replicate within human

Question 17

What are filariasis?

How do they cause disease?

Answer 17

Filariasis is a sub-group of nematode infections spead by blackflies and moquitoes

Some diseases caused by these include

• river blindess
• loa loa
• elephantasis

Cuase disease via eitther 1) impaired lymphatic drainage (elephantiasi)
or 2) via miicofiliae (river blindness)

Question 18

What is myiasis?

Answer 18

Parasitation of human flesh by fly larvae

Question 19

What are the most common causes of eosinophilia?

Answer 19

Non-parasitic (most common) (incl. atopy, drug allergies, malginancies)

But the following parasites caus eosinophilia

• Soil transmitted helminths esp. strongyloides
• Schistosomiasis
• Filaria
• Leaking hydatid cysts