Helminths Flashcards
What are the 3 categories of helminth?
Nematodes (roundworms), cestodes (tapeworms), trematodes (flukes)
What are the 3 common soil transmitted helminths?
- Ascaris lumbricoides (roundworm)
- Necator americanus & Ancylostoma duodenale (hookworms)
- Trichuris trichiura (whipworm)
How do helminths multiply?
Cannot multiply within the host. Eggs must be released from definitive host before reinfection can occur.
Ascaris lumbricoides lifecycle
- fertilised egg is shed into environment via faeces
- begins to develop into larvae inside of protective casing
- parasite is ingested by host and casing is dissolved in stomach
- larvae penetrate into bloodstream and migrate to the lungs
- grows and develops inside lungs, travels up trachea, and migrates to intestines where it can mate
Ancylostoma duadenales & Necator americanus life cycle
- eggs are released through faeces into the environment
- larvae hatch out of eggs in the soil
- infective larvae penetrate through skin of new host and travel through bloodstream to the intestine
What disease does Wuchereria Bancroft cause?
Lymphatic filariasis, resulting in elephantiasis
Wuchereria bancrofti life cycle?
- adults live in the human host lymphatic system
- adult females produce live sheathed microfilariae which are released into lymph and blood channels
- mosquito takes a blood meal and ingests microfilariae
- microfilariae sheds the sheath, penetrates the mosquito midgut, and migrates to thoracic muscles to produce infective larvae
- larvae migrate to mosquito head and proboscis
In what ways can hookworm be prevented?
- chemotherapy, stops transmission
- providing footwear
- Increasing sanitation
3 most common schistosoma species?
S. Haematobium (urogenital), S. japonium and S. mansoni (intestinal)
Life cycle of Schistosoma?
- Adult customers live inside venules within the bowel/rectum or bladder
- female produces eggs which penetrate through venules into the lumen of bladder or bowel, then are released through faesces/urine
- eggs hatch in water to release miracidia, which penetrate snail tissue
- sporocysts are developed into infectious cercariae
- cercariae is released by snail into water and is free swimming, so finds a host and penetrates the skin
- cercariae loses tail during penetration and become schistosomulae which migrate to portal blood in the liver to mature into adults
- paired worms migrate to bladder/bowel to lay eggs in venules
What side effects occur from schistosomes?
- blood loss from eggs penetrating the bowel/bladder tissue
- granuloma formation from eggs being swept away to other body parts
- neurological problems from eggs being lodged in the brain
What drug is available for schistosomiasis?
Praziquantel, needs an antibody response from the host
