Lecture 3B - Worms Flashcards
What are worms?
highly developed multicellular organisms which generally replicate outside of the human host (through the shedding of eggs typically in faeces)
What do worms that are parasitic in humans lead to?
great suffering on a global scale because they are hard to treat
Classes of worms?
roundworms (4,500 million infections globally)
tapeworms (175 million)
trematodes (250 million)
What do worms rely on the body for?
nutrition of the parasite at early stages of its life cycle
Where does the ascaris roundworm have an adult stage?
in the gut, which can shed eggs into the faeces
What happens to the ascaris worm eggs outside the gut?
they are fertilised and the embryonic form of the parasite is reingested
Where do the larvae of the ascaris worm go?
they hatch from the eggs inside the gut, they break through the gut wall and migrate through the blood stream to the lungs
What happens to the larvae once in the lungs?
the developing larvae are coughed up and swallowed, gain to reinfect the gut and grow to adult hood
Why do worms go to the lungs?
because of the very fine capillaries
they go via the hepatic portal vein because the blood from the gut goes there
What are roundworms known as?
nematodes
Intestinal nematodes?
often cause diarrhoea, itch and anaemia
How are intestinal nematodes acquired?
orally or through skin, transmitted by faeces
Strongyloids?
threadworm - can migrate to lungs
Trichuris?
whipworm - transmitted via the soil, if human faeces is used asa fertiliser and food isnt cleaned
Ascaris?
roundworm
migrates to liver, heart, lung and back to gut
some patients carry 1000+ worms, females worms can lay 200,000 eggs daily
Enterobius?
pinworm
Necator and ancylostoma?
hookworms - larvae can penetrate bare feet
Trichostrongylus?
mild intestinal symptoms but very common
Extraintestinal nematodes?
trichinella (trichinosis) and dracunulus (guinea worm)
Trichinella?
present in infectedmear, cysts in muscle
Dracunculus?
can grow up to one metre long in the skin
Larva migrans?
disease eruption can occur in a variety of tissues when invaded by larvae of roundworms
What are nemathelminthes?
roundworms which include the nematodes - includes roundworms like ascaris
What are platyhelminthes?
all flatworms
What are platyhelminthes divided into?
the cestoda (tapeworms like taenia)
the trematodes (flukes like sheep liver fluke)
What are extraintestinal nematodes?
thread like wormsn, 200-300microns long when adult and about one red blood cell wide when transmitted by an insect vector
What stage do extraintesinal nematodes have?
an insect stage in which the larvae develops
Where do injected larvae go
to specific tissues such as skin, lungs, lymphatics
- here they mature to adults (forming skin nodules)
What happens once extraintestnal nematodes mature?
after a sexual stage they produce microfilariae
What do the microfilariae do?
migrate to particular tissues depending upon the species involved, giving rise to pathogenesis as they mature to microlarval stage?
Wucheria bancrofti?
microfilarial blockage of lymphatic ducts leading to elephantiases
affects over 120 million people throughout the tropics and subtropics
Onchocerca volvulus?
larval migration to the eye causing river blindess
300 million at risk in sub saharan africa, parts of arabia and S america
27 million cases annually, 300,00 cases of permanent blindess
Treatment for onchocerca?
Ivermectin, but needs to be continued for 10-15 years as it only kills the larvae and not adult worms
evidence that doxycycline can kill adult worms
What is elephentiasis?
legs swell to a huge extent because the fluid cannot return due to blocked ducts
Treatment for wucheria?
Diethylcarbamazine can kill all forms of the worms in around 2 weeks
treatment more effective when used with ivermectin
Where do adult flukes mainly reside?
in blood (veins), gut or lungs
Life cycle of flukes?
complex, but essentially adult flukes produce eggs which become encysted when present in the liver or other tissues (bladder, lung, CNS)
What does reaction to presence of fluke eggs cause?
pathological changes in the infected tissue
What happens in schistosomiasis?
eggs are released via faeces or urine into water, where the parasite is taken up by snails, the snail then releases a form of larva (cercaria) which can penetrate skin and infect persons coming into contact with water
Schistostoma mansoni?
FLUKE
encysted eggs present in the liver can cause fatal cirrhosis
Fasciola hepatica?
sheep liver fluke - can also infect humans
Where is schistosomiasis most common?
transmitted by water
most prevalent in agriculture and fishing communities fro affected areas
What can infestation with schistosomiasis cause?
a variety of complications, mainly gut and urinogenital - but also include seizures, anaemia and renal failure
praziquantel is the preferred treatment
What can flukes penetrate?
the colon wall and make their way via the hepatic portal vein to the liver
what does infestation with fasciola cause?
jaundice amongst a variety of complications
causes cirrhosis and liver damage = jaundice
Tapeworms?
cestodes
flat segmented worms containing both male and female organs
Taenia solium?
pork tapeworm
pigs become infected by swallowing eggs present in the human faeces
What happens when humans ingest the uncooked pork?
the ingested eggs release larvae in the duodenum
the larvae are carried in the blood to muscle, CNS and the eye where get encysted and cause pain and neurological problems such as epilepsy
Where is taenia a problem?
Mexico, latin america and other countries in the southern hemisphere with uncooked meat
Epinococcus granulosus?
adult worms are found in the guts of dogs
they produce eggs (excreted in faeces) which can remain viable for up to a year
Where can epinococcus eggs be found?
in dog fur, on dog leads and on the tongues of infected dogs
What happens when epinococcus eggs are ingested?
they release larvae when in the gut and larval cysts can then be found in the liver and other tissues of humans and sheep
Cysts of epinococcus?
can be quite large (litres of fluid) and contain many immature larvae, causing major problems when they burst
How big are cestodes?
a few millimetres to 25 metres
What can the larval form of cestodes penetrate?
the gut wall and migrate to any internal tissues
typicall they affect the lungs and liver but can also affect the CNS
What can infected meat contain?
hundreds of larval cysts (taenia solium) which can infect consumers when eaten
the mouth of taenia solium hook into the gut wall so as to anchor the tapeworm
