Parasitic infections

Question 1

Two types of parastic organisms that cause disease?

Answer 1

1. Protozoa: UNICELLULAR EUKARYOTIC
2. Helminths: MULTICELLULAR EUKARYOTIC - parasitic worms

• Protozoa and helminths are usually endoparasites = live inside the body

Question 2

Different routes of parasitic infection transmission

Answer 2

1. Contaminated food
2. Contaminated water
3. Walking bare feet
4. Bug bites
5. Sexual contact
6. Close contact with infected pets
7. Lack of hygiene

Question 3

Lifecycle of the malaria parasite

Answer 3

• Caused by P. falciparum (75%) and P. vivax (20%) = parasitic protozoans
  1. Female Anopheles mosquito transmits sporozoite to human host
  2. Sporozoites infect liver cells/hepatocytes and mature into schizonts, which rupture and release merozoites
  3. After initial replication in liver, the parasites undergo asexual multiplication in the erythrocytes
  4. Merozoites infect RBCs and initiate a series of asexual multiplication cycles that produce 8 to 24 new infective merozoites
  5. Now, the cells burst and the new infective cycle begins
  6. Other merozoites develop into immature gametocytes
  7. Gametocytes are ingested by an Anopheles mosquito during a blood meal
  8. The parasites multiplication in the mosquito is known as the sporogonic cycle
  9. While in the mosquitos stomach, the gametocytes fuse generating zygotes, the zygotes become motile and elongates which invade the midgut wall of the mosquito where they develop into oocysts
  10. The oocysts grow, rupture, and release sporozoites which make their way to the mosquito’s salivary glands
  11. Inoculation of the sporozoites into a new human host perpetuates the malaria life cycle!

Question 4

Symptoms of malaria

Answer 4

• Begin 8-25 days following an infection
• Initial manifestations are flu-like
  Headache
  Fever
  Shivering
  Joint pain
  Vomiting
  Haemolytic anaemia
  Jaundice

Question 5

Treatment of malaria

Answer 5

• Antimalarials (treatment or prevention)

1. Quinolones: block parasite detoxification of heme
   - E.g. quinine, chloroquinine, amodiaquine, mefloquine, primaquine
2. Anti-folates - folic acid metabolism
   - Sulfonamides, pyrimethamine, proguanil, chlorproguanil
3. Artesmisin (new) - Generation of free radicals that alkylate and oxidise proteins and lipids within infected RBCs
   - Artesunate, artemether, dihydroartemisinin

Question 6

African trypanosomiasis:

1. Causative species
2. Transmission route
3. Signs and symptoms
4. Treatment

Answer 6

1. Causative species
   - TRYPANOSOMA BRUCEI
   - Parasitic disease
2. Transmission route
   - Bite of an infected tsetse fly
3. Signs and symptoms
   - Stage 1 (1-3 weeks after bite)
   Fevers
   Headaches
   Itchiness
   Joint pain
   Parasite found in peripheral circulation

• Stage 2 (weeks to months after bite)
  Parasite crosses blood-brain barrier and infects CNS
  Confusion
  Poor concentration
  Numbness
  Trouble sleeping
  Untreated infection eventually leads to coma and death

4. Treatment
   - Pentamidine
   - Suramin
   - Melarosoprol
   - Eflornithine
   - Nifurtimox

Question 7

How is Leishmaniasis transmitted?

Answer 7

Bite of certain type of sandflies

Question 8

How is toxoplasmosis transmitted?

Answer 8

• Toxoplasma gondii
• Eating poorly cooked food
• Exposure to cat faeces
• Mother to child

Question 9

Soil-transmitted helminthiases symptoms

- Commonly used drugs?

Answer 9

• Usually no symptoms

- Heavy infections:
Abdo pain
Diarrhoea
Blood and protein loss
Rectal prolapse
Physical and cognitive growth retardation

• Drugs
  Albendazole
  Mebendazole

Question 10

Life cycle of Ascariasis (round worm)

Answer 10

1. Adult worms live in the lumen of the small intestine
2. Eggs in faeces
3. Embryonate/fertilised eggs mature to infective form
4. Swallowed by human
5. Larvae hatch
6. Invasion of intestinal mucosa
7. Portal circulation
8. Systemic circulation to lungs
9. Larvae maturation in the lungs
10. Penetration of alveolar walls
11. Ascend bronchial tree to throat
12. Swallowed
13. Go to small intestine where they develop into adult forms

Question 11

Transmission of onchocerciasis (RIVER BLINDNESS)

Answer 11

Bites of infectied simulium blackflies, which breed in fast-flowing streams and rivers

• Onchocerciasis is a major cause of blindness in many African countries