Parasitology (2) Flashcards
(18 cards)
What are helminths?
1) Worms
2) Largely compared to protozoa and prokaryotes
3) Relatively complex
4) Life cycles involve no. of stages with distinct changes in morphology
5) Sexual reproduction usually involves production of eggs
What are the 3 classifications of helminths?
1) Roundworms e.g., Hookworm - Ancylostoma duodenalis
2) Tapeworms e.g., Taenia saginata, beef tapeworm
3) Flukes e.g., Fasciola hepatica, liver fluke
What can helminths infect in humans?
1) Intestine - Ascaris lumbricoides, Schistosoma mansoni
2) Liver - Fasciola hepatica, Echinococcus multilocularis
3) Bile duct - Clonorchis sinensis
4) Lymphatic system - Wuchereria bancrofti
5) Lungs - Paragonimus westermani
6) Skeletal muscle - Trichinella spiralis
What is hookworm?
1) Infection acquired when larval worm in contaminated soil burrows through skin (usually bare foot)
2) Eventually leads to severe and chronic anaemia
What is the life cycle of hookworm?
1) Infective larvae found in contaminated soil
2) Penetrate host’s skin, enter small blood vessels and thus main circulation
3) Larvae travel to the heart, through cardiac blood supply to lungs
4) Coughed up and swallowed
5) Enter intestinal tract and migrate to small intestine
What happens in the small intestine when a hookworm has infected a patient?
1) Grow in size and develop into mature adult worms
2) Adult female worms up to 15mm long and males about 10mm
3) Attach to gut wall using sharp ‘teeth’ and suck membrane and blood from host’s blood vessels
4) Produces anticoagulant to reduce clotting of host’s blood
5) At least half of blood taken in passes through worm’s digestive tract but is not metabolised and passes out again undigested
6) So worm has to continually feed and continually migrate to fresh sites on host’s intestinal wall
How long can hookworm’s live for?
1) Adult worms can live for 10 years inside hosts if undetected
2) Cause severe anaemia due to blood ingested by worm and bleeding at ‘old’ sucking sites
How does a hookworm reproduce inside a host?
1) Usually each host is infected with more than 1 worm
2) If male and female present, they mate
3) Female produces fertile eggs, each containing a ‘rhabditiform’ larva
4) Eggs fall into intestine and thus are excreted with faeces
What happens when a hookworm egg hatches?
1) As long as the egg reaches damp, warm soil surface, it starts to hatch
2) Goes through an series of developmental stages to form a filariform larva
3) Process takes 7-10 days
4) Filariform larva wait for suitable host to arrive
5) Can survive for several months but often die after a few weeks from desiccation and exposure to sunlight
What are possible preventions and treatments for hookworm?
1) Easily preventable disease, wear shoes
2) Can treat with anthelminthic drugs (mebendazole, albendazole), iron tablets etc.
3) Not everybody has same ‘worm burden’, but if re-infected, tend to acquire a similar no. of adult worms
What is the lab identification for hookworm in a faecal sample?
1) Concentration method (e.g., formol-ether)
2) Wet preparation - small pea-sized amount emulsified in saline, cover slip on top, no need for stain as eggs are clearly visible if present
What is taenia spp?
1) In humans - adult tapeworms in intestine
2) Infection often asymptomatic but can cause - abdominal pain, nausea and vomiting, change in appetite, weight loss
What is the life cycle of Taenia saginata?
1) Fertilised eggs in grass eaten by cow
2) In intestine - egg hatches
3) If it is in right environment of correct host, will release oncosphere
4) Using the hook and digestive enzymes, penetrate gut wall and move into blood circulation
5) Spread around body of cow - most destroyed, those that survive migrate to muscle tissue
6) Develop into larvae - cysticerci, 1 cysticerus
7) Grow and divide (asexual reproduction) inside a cyst, lodged in muscle
What happens when a human eats an infected cow with Taenia saginata?
1) Eating undercooked infected beef, moves larvae to small intestine
2) Cysticerus senses correct environment; ‘evaginates’ (larval worm pops out), stimulated by bile salts
3) Using suckers on its head, worm attaches to gut wall, grows and develops into adult
How does Taenia saginata reproduce?
1) Hermaphrodite - all male and female reproductive organs in each proglottid so self-fertilisation or cross fertilisation possible if worms close together
2) Mature eggs present in segments at end of the worm’s body
3) Fall off into host’s gut
4) Each proglottid contains thousands of eggs - in gut, proglottid starts to dry out and eggs released
5) They are excreted in faeces individually
6) If human faeces containing eggs reaches area where cattle are grazing, cycle starts again
What is the lab identification for taenia saginata in a faecal sample?
1) Look for cysticerci by eye
2) Detection of eggs
3) Concentration method (e.g. formol-ether)
4) Wet preparation - small pea-sized amount emulsified in saline, cover slip placed on top, no need for stain as eggs are clearly visible if present
What is the lab diagnosis for T. solium and T. saginata?
1) Eggs of T. solium and T. saginata identical
2) Can use PCR to distinguish but can use: proglottids, count no. of branches
3) Scolex if someone has passed a whole worm
What is the treatment for Taenia?
Praziquantel
