Helminths

Taenia spp. (Tapeworms)

Definitive host is vertebrates including humans
scolex attaches to intestinal wall using suckers and hooks
proglottids form continuously behind scolex and mature as they move downward
tapeworm absorbs nutrients directly through its surface because it has no digestive tract
gravid proglottids contain fertilized eggs and may break off and exit in feces
some species form cysts in muscle tissue of intermediate hosts and infection occurs from undercooked meat

Taenia identification

Scolex with suckers and sometimes hooks
long chain of proglottids
gravid proglottids appear dense and filled with eggs
cysts in muscle contain a single larval scolex

Schistosoma mansoni (Blood fluke)

Causes schistosomiasis
life cycle includes a freshwater snail as intermediate host
eggs released in human urine or feces infect snails and develop into larval stages
free swimming cercariae penetrate human skin and enter bloodstream
adults reside in blood vessels and females produce large numbers of eggs daily
eggs cause most damage by triggering inflammation in liver and spleen
disease can cause abdominal swelling
anemia
and susceptibility to other infections

Schistosoma identification

Adult worms show male with groove holding female
cercariae are free swimming larvae with forked tails
eggs have characteristic lateral spine

Trichinella spiralis

Causes trichinosis
adults live in digestive tract and females release live larvae into bloodstream
larvae migrate into skeletal muscle and form cysts
infection causes muscle pain due to toxins released
commonly transmitted through undercooked pork or wild game
encysted larvae resistant to drug treatment
prevention depends on thoroughly cooking meat

Trichinella identification

Cysts visible in muscle tissue containing coiled larvae

Ascaris lumbricoides (Human giant roundworm)

Causes ascariasis
only host is humans
eggs shed in feces and remain viable for years
infection occurs from ingesting eggs in contaminated food or water
larvae hatch in intestine
migrate into bloodstream
travel to lungs
move up trachea
are swallowed
and return to intestines to mature
adults attach to intestinal wall and feed on blood and fluids
may reach up to 14 inches long
light infections asymptomatic
heavy infections cause diarrhea
vomiting
and discomfort
treatment with anti helminthic drugs is effective

Ascaris identification

Large roundworms
eggs thick walled and oval
adults long and cylindrical living in intestine