helminths Flashcards
What is a key difference in the lifecycle of nematodes and platyhelminthes?
Nematodes get bigger through their lifecycle but cestodes and trematodes look different at all stages in life cycle.
What does dioecious mean? Which helminths are?
Separate sexes
all nematodes and schistosoma species
What are DALYs?
Disability Adjusted Life Years
It is a measure of overall disease burden, expressed as the number of years lost due to ill-health, disability or early death.
Which STH has the biggest health burden?
Ascaris lumbricoides
What is MDA?
Mass drug administration (MDA) is the administration of a treatment to every member of a defined population or every person living in a defined geographical area (except those for whom the medicine in contraindicated) at approximately the same time and often at repeated intervals.
Life cycle of Ascaris lumbricoides
- Adults reside in small intestine, eggs in faeces
- eggs mature in external environment
- embryonated eggs ingested from soil/ contaminated food
- L3 larvum hatch and penetrate gut wall, migrate to lungs via bloodstream
- migrate up trachea and swallowed back into the gut where they mature
treatment of nematodes
albendazole/mebendazole
Life cycle of Trichuris trichuria
- Unembryonated eggs passed in faeces
- Eggs mature in external environment
- Embryonated eggs are ingested
- Larvae hatch in small intestine
- Adult worms embed into well of caecum and large bowel
Diagnosis of trichuris
stool microscopy or colonoscopy
Life cycle of Hookworm species
- Eggs in faeces
- develop in external environment into filariform larvae
- penetrate skin ‘ground itch’
- bloodstream transport into lungs
- migrate up trachea and swallowed by gut
- adult worms develop in SI
Life cycle of Enterobius vermicularis ‘pinworm’
- Eggs on perianal skin
- Maturation on skin surface
- Scratching - picks up eggs on hands/ bed linen
- Ingestion of embryonated eggs by same host ‘auto-infection’ or another host
- larvae hatch in SI
- Adult worm in caecum
- Adult females migrate out through anus to lay eggs on skin
Diagnosis of Enterobius
Scotch tape method, peri-anal swab, lookunder microscope
What are the different life cycles of Strongyloides stercoralis
Free living worm in environment, direct parasitic life cycle in host, autoinfection cycle
Diagnosis of strongyloides
larvae in faeces or sputum, concentrate stool, charocoal cultures, antibody detection, pcr
Which infection is more intense- Ascaris or Trichuria?
Ascaris - higher egg count in faeces (200,000 per day) compared to Trichuria (20,000)
In Ascaris larvae enter bloodstream and migrate to lungs
in trichuris larvae hatch in SI and embed into caecum.
Name the cestode species
Taenia saginata–‘beef tapeworm’ Taenia solium–‘porktapeworm’ Diphyllobothrium latum–‘fish tapeworm’ Hymenolepis nana –‘dwarf tapeworm’ Echinococcus spp.
What is the general morphology of cestodes?
tapeworm with scolex (head) with hooks or suckers for attachment and proglottids (segments). they’re hermaphrodite
Generalised cestode life cycle
- Adults in small intestine
- Proglottids break off which hold eggs
- Eggs shed in faeces
- Ingestion by intermediate host
- Develop into metacestode (juvenile)
- Definitive host ingests metacestode
Which cestode does not require an IM host?
Hymenolepsis nana
What drug is used to treat cestodes?
Praziquantel
How do you acquire D.latum?
Ingestion of raw or undercooked fish
What IM hosts are there of D.latum?
- cyclops ‘water flea’
2. fish
Brief life cycle of D.latum
- Eggs released in faeces
- Hatch into ciliated larvae in freshwater
- Cyclops ingest
- Fish ingest cyclops
- Definitive host eats fish
- Adult worm in small intestine
What parasite causes cystercicosis?
Taenia solium
What are the main differences between T.solium and T.saginata?
T.saginata: eggs do not infect humans, only cysticercus infective to humans, only adult worm present
T.solium: Eggs do infect humans, cysticercus AND egg is infective to humans. Adult worm AND juvenile cysts present
How can you prevent infection with Taenia?
Mass chemotherapy with praziquantel, improve sanitation, reduce carriage in intermediate hosts (animals: vaccinate, treat, remove from sewage areas), meat inspections, cook meat well
Name the liver flukes
Fasciola hepatica, Opisthorchis viverrini
Describe life cycle of the liver flukes
- Eggs released into environment
- Miracidia hatch from eggs and penetrate intermediate host (water snails)
- Amplification by asexual reproduction in snail
- Cercariae released
- Metacerciae encyst on plants (Fasciola) fish (Opisthorcis)
- Ingestion by humans/cattle/sheep
- Excystment in duodenum
- Penetrate gut wall and migrate to liver where they become an adult fluke
treatment of Fasciola hepatica
triclabendazole
What’s the difference between Fasciola hepatica and Fasciolopsis buski?
Fasciola adult flukes reside in billiary ducts in the liver, Fasciolopsis adults reside in intestinal mucosa in gut.
What is the name of the lung fluke?
Paragonimus westermani
Describe the life cycle of Paragonimus westermani
- Eggs in faeces (when swallowed) or sputum
- Miracidia hatch and penetrate water snail
- cercariae released
- Metacercarie encyst on crustacean (crab)
- Ingestion of crabmeat by definitive host (human/cat/dog)
- Adult fluke resides by airways
Describe general life cycle of Schistosomes
- Eggs passed in faeces (mansoni) or urine (haematobium)
- Miracidia hatch and penetrate snail
- cercariae released
- penetrate skin of waders/bathers ‘swimmers itch’
- cercariae lose tail ‘schistosomulae’ and migrate through circulation
- paired adult worms in venous plexus (blood) of gut (mansoni) or bladder (haematobium)
What is the difference in life cycle of S. mansoni and S. haematobium
In haematobium parasite resides in blood vessels of urinogenital system, invades bladder and enters urine-linked with bladder cancer.
In mansoni, parasite resides in blood vessels of gut and passes out in faeces.
Why is the development of an RDT important for schistosomiasis?
- to identify species
- where the tissue eggs are
- how many worms-infection increases with number of eggs
What are the symptoms of schistosomiasis?
abdominal pain, diarrhoea, blood in stool, liver or spleen enlargement, blood in urine (haematobium)
Treatment for all flukes
schisto: praziquantel and albendazole
paragonimus: praziquantel
fasciola: triclabendazole
opisthorchis: praziquantel and albendazole
Methods of control for schistosomes
MDA of praziquantel to interrupt transmission, snail control, improve sanitation, health education
life cycle of trichinella spiralis
- larvae infested in undercooked meat
- larvae released in stomach
- adults in SI
- females release larvae that enter lymph/ blood (cause cell death of heart cns kidney lover lungs)
- larvae encyst skeletal muscle
- larvum matures in skeletal muscle /nurse cell
describe life cycle echinococcus
- eggs released in animal faeces
- ingest by sheep
- cystic lesions in solid organs (liver and lungs)
- ingestion by canines of cysts of sheep
humans are accidental hosts
where do hydatid cause problems
liver
brain
lungs
main method of control for helminths
mda of benzimidazole drugs once or twice a year, donated by pharma
control of opisthorchis
encourage proper cooking of fish targeted or mass chemotherapy-repeated doses as part of an integrated campaign health education improved disposal of human faeces limit use of faeces as fertiliser snail control
intermediate hosts of schistosomes
Bulinus- haematobium
biomphalaria-masoni
apart from faecal smear what other lab based diagnostic methods could be used to detect taenia
detection of proglottids
coproantigen tests
swab around anal akin
concentration method for stool
other techniques more sensitive than direct wet mount of faeces
formal ether concentration technique
kato kaz
describe kato kaz technique
faeces passed through mesh to remove large particles
portion of sieved sample transferred to hole of a template on a slide
template removed and sample covered with cellophane covered in glycerol- glycerol clears faecal material around the eggs
