Parasites

Question 1

What is a definitive host?

Answer 1

Either harbours the adult stage of the parasite or where the parasite utilizes the sexual method of reproduction

Question 2

What is the intermediate host?

Answer 2

Harbours the larval or asexual stages of the parasite

Question 3

What is a paratenic host?

Answer 3

Host where the parasite remains viable without further development

Question 4

What are the 4 subclasses of protozoa?

Answer 4

Flagellates
Amoeboids
Sporazoans
Trypanosomes

Question 5

What are the 2 types of Helminths and their 2 subclasses?

Answer 5

Platyhelminths (Flatworms)

• Cestodes (Tapeworms)
• Trematodes (Flukes)

Nematodes (Round worms)

• Intestinal Nematodes
• Tissue Nematodes

Question 6

What causes Ascariasis?

Answer 6

Intestinal nematode,

Ascaris lumbricoides

Question 7

How does Ascaris lumbricoides infect humans?

Answer 7

Ingestion of eggs from faeces

Eggs hatch and burrow through intestinal wall, travel in the blood to the lungs. From the alveoli they travel up the trachea and then down into the stomach and intestines.

More than 1 billion affected worldwide

Question 8

How does Ascariasis present clinically?

Answer 8

Few worms = asymptomatic, but more:

Lung migration:
Loefflers syndrome - dry cough, dyspnea, wheeze, haemoptysis, eosinophilic pneumonitis

Intestinal Phase:
Malnutrition
Migration – into hepatobiliary tree and pancreas
Intestinal obstruction

Question 9

What drug is used to treat Ascariasis and what is its mechanism of action?

Answer 9

Albendazole

Prevents glucose absorption by worm
Worm starves-detaches-passed PR

Question 10

What kind of Platyhelminths are the Schistosoma spp.

Answer 10

Trematodes/Flukes

Question 11

Where is Schistosomiasis mainly found?

Answer 11

Africa

Snails are the intermediate host for Schistosoma spp.

Question 12

What is seen clinically in infections with Schistosomiasis haematobium?

Answer 12

Urinary (S. haematobium)

• Haematuria
• Bladder fibrosis and dysfunction
• Squamous cell carcinoma of bladder

Question 13

What is seen clinically in Schistosomiasis?

Answer 13

Swimmers itch - rash at point of entry

Katayama fever - systemic reaction weeks later

Chronic Schistosomiasis

Question 14

Schistosomiasis caused by: 
S. mansoni; 
S. intercallatum, 
S. japonicum; 
S. mekongi 
may also have what symptoms?

Answer 14

Portal Hypertension

Liver cirrhosis

Question 15

How is Schistosomiasis treated?

Answer 15

Praziquantel

Question 16

Hydatid disease is caused by what?

Answer 16

Echinococcosis is caused by a cestode (Tapeworm) found in sheeps and dogs

Echinococcus granulosus
- cystic

Echinococcus multilocularis
- alveolar

Question 17

How does Hydatid disease present clinically?

Answer 17

Cysts: 70% liver, 20% lungs
May remain asymptomatic for years, 
Mass effect
Secondary bacterial infection
Cyst rupture- hypersensitivity

Question 18

Which species of Plasmodium causes the most severe Malaria?

Answer 18

Plasmodium falciparum

P. vivax, P. ovale and P. malariae al cause milder forms of Malaria.

Question 19

What do plasmodium spp. use as their vector?

Answer 19

Anopheles - a genus of mosquito

Question 20

How does malaria present clinically?

Answer 20

Parasites rupture red cells, block capillaries and cause inflammatory reaction

Fever & Rigors 
Cerebral malaria 
Renal failure 
Hypoglycaemia
Pulmonary oedema
Circulatory collapse
Anaemia, Bleeding and DIC

Question 21

How is Cryptosporidiosis spread?

Answer 21

Cryptosporidium parvum and Cryptosporidium hominis

Faecal-oral spread

Human-Human, animal reservoir (cattle, sheep, goats)

Question 22

How does Cryptosporidiosis present clinically?

Answer 22

Watery diarrhoea with mucus (no blood)
Bloating, cramps, fever, nausea, vomiting

Incubation 2-10 days (usually 7)
Lasts up to 2 weeks

Can be severe in old, young and immunocompromised

Question 23

What is the treatment for Cryptosporidosis?

Answer 23

Nitazoxanide