helminths Flashcards
describe the lifecycle of the helminth, ascariasis
** note they are maturing and growing as this cycle continues
released eggs (from human) are embryonated in the soil (takes a few weeks)
human ingests eggs
eggs go thru the GI tract into the small intestine
larvae hatches in the small intestine and then enters the bloodstream (thru the intestinal walls - transdermal)
travels thru the bloodstream to the liver and then the larvae will use the liver cells to continue its development before going back into the bloodstream
they then migrate into the heart into the pulmonary circulation - from there, they can enter the lungs
once in the alveoli, they experience pressure (larvae are growing and alveoli is small) - so they escape from the alveoli into the lung tissue
they then migrate up the trachea and over the epiglottis where it is then swallowed back into the GI tract, small intestine… here they have matured
after sexual reproduction, eggs can be defecated
describe the lifecycle of the helminth, taeniasis
cysticerci (larval stage, encapsulated) found in the muscle tissue of beef, are ingested with raw/undercooked beef
the cysticerci are then released in the stomach from the muscle tissue (the cyst degrades, and the larval stage itself is released)
it travels down to the small intestine. the worms mature
the worms have a scolex, which has on it 4 suckers – used to adhere to the walls of the small intestine. from here it can migrate if it want
often, people are only infected with one tape worm due to competition as one tapeworm can grow up to 10 meters. the tapeworms are also aphroditic, meaning having both reproductive organs in each segment – segments called proglottids. gravid proglottids are fertilized segments (egg production is occurring)
proglottids break apart and pass in feces
cows ingest embryonated eggs. eggs then hatch into oncospheres which migrate to tissues and develops to cysticerci
describe parasitic metazoa
macroscopic, multicellular organisms
—- can vary in size from millimeters to meters in length
can be ecto/endoparasitic
includes helminths (worms) and arthropods (insects and arachnids)
what are the types of helminths?
nematodes
— non-segment roundworms (round bodies)
cestodes
— segmented flat worms (tape worms)
trematodes
— non-segmented flat worms
what are the mechanisms of entry?
fecal-oral
transdermal
— invasive to tissues
— e.g. thru feet
vector-borne
predator-prey
— consumption of carcass that contains parasites
what are some mechanisms of survival the helminth can take?
incorporation of host-serum proteins on surface – hide from immune response
inhibition of the complement system
secretion of anti-inflammatory molecules
avoiding direct contact with host tissue (e.g. living in the lumen of the small intestine – going thru gastrointestinal tract, bypasses the immune system)
pausing life cycle when host develops resistance (dormant stage e.g. cyst)
what type of parasite is ascariasis (ascaris lumbricoides)?
large nematodes (non-segmented roundworms)
obligate parasite
monoxenous (only one host)
parasitic infection occurs thru ingestion of eggs via fecal contamination of soil, foodstuffs, and/or water supplies
most prevalent helminth infection
can grow up to 30 cm
—– high burden of adult worms can cause potential complications, obstructing the stomach
what are the symptoms of ascariasis?
people rarely show any symptoms and if they do, usually mild abdominal discomfort
problems occur when disease is untreated or if there are other concurrent factors (e.g. malaria)
malaria causes fever, and fever makes the worms want to leave and they’ll try to escape out any way, causing person to choke and/or bowel obstructions
what is anthelmintic?
substance or drug that is used to treat infections caused by helminths
mechanisms of action include killing the parasites and/or expelling them from the host’s body
what are the anthelmintic treatments available?
albendazole
—- binds to beta-tubulin and disrupts microtubules
—- affects nutrients and energy acquisition for helminths
ivermectin
—- binds with high affinity to glutamate-gated chloride channels found in nerve and muscle cells of invertebrates, including nematodes and arthropods
—- causes nerve and muscle damage by paralyzing it, then, stomach peristalsis can kill them
what type of parasite is taeniasis (taenia saginata)?
large cestodes (segmented flatworms)
can grow up to 10 meters in length
obligate parasite
diheteroxenous (2 hosts)
cows become infected after feeding in areas that are contaminated with taenia eggs from human feces
humans can become infected with tapeworms when they eat raw/undercooked beef
what are the symptoms of taeniasis?
most people with tapeworm infections have mild symptoms or no symptoms
what is the treatment for taeniasis?
anthelmintic medication: praziquantel
— hypothesized to disrupt calcium homeostasis resulting in uncontrolled calcium ion influx
similar to other anthelmintics but targets calcium instead
what is endophagic and exophagic?
endophagic
— mosquitoes that feed indoors
exophagic
— mosquitoes that feed outdoors
