An Introduction to Parasites

Question 1

What are the main groups of parasites ?

Answer 1

• Protozoa
• Helminths
• Arthropods

Question 2

What category does Malaria fall into and explain its life cycle ?

Answer 2

Protozoa - caused by plasmodium species which a mosquito vector

• Sporozoites are injected under the skin the mosquito
• They travel through to blood to the liver where they mature
• They then re-enter circulation as merozoites
• These invade and destroy RBC’s using them to multiply
• Sexual forms are taken up by mosquito

Question 3

What category does amoebic dysentery fall into and explain its life cycle ?

Answer 3

Protozoa - caused by Entamoeba Hystolytica

• Trophozoite ingests red cells by pseudopodia
• Diarrhoea with blood/pus
• Protozoal cysts in stool samples
• Liver abscesses in late disease

Question 4

What category does Leishmaniasis fall into and explain its life cycle ?

Answer 4

Protozoa - caused by several species

• Cutaneous or muco-cutaneous leishmaniasis causes skin/mucosal ulceration
• Visceral Leishmaniasis causes fever, weight loss and hepato-splenomegaly
• Spread by sandfly bites

Question 5

What category do Nematodes fall into and explain its life cycle ?

Answer 5

Helminths - caused by Ascaris Lumbricoides

• Ingested eggs enter circulation
• Embryos hatch and pass through lungs
• Enter stomach and move to small intestine as adults
• Ova seen on microscopy of stool samples
• Often asymptomatic
• Can cause Loefller’s Syndrome (Accumulation of Eosinophils in lungs)
• Mass of worms can block bile duct

Question 6

What category do Trematodes fall into and explain its life cycle ?

Answer 6

Helminths - caused by Schistosomiasis

• Eggs excreted in urine or faeces
• Miracidia released in fresh water
• Penetrate the body of a snail as an intermediate host
• Cercaria emerge from snail 4-6 weeks later
• Penetrate human skin
• Migrate through lungs to liver