Helminth Parasites (3/10)

what causes trichinosis?

any species of trichinella parasite

most common species in artic bear and walrus meat: T nativa

raw meat

general features of helminths

worm

usually large (0.3mm-25m long)

grotesque

categories: nematodes, trematodes, cestodes

what is the difference between nematodes, trematodes and cestodes?

nematodes: roundworms, separate sexes

trematodes: flukes, separate or hermaphroditic

cestodes: tapeworms, hermaphroditic

what is the life and transmission cycle of helminths?

complete life cycle: fertilized egg (embryo), larval, adult stages

sexual reproduction

intermediate 2ndary host: larval developement

definitive final host: adulthood and mating

basic helminth life cycles (source and route of infeciton)

source: contaminated food, soil, water, infected animals

route: oral, penetration of skin

5 basic cycles: see table in notes

What is the relationship between worm infections and the human population?

The number of worm infections is greater than the number of humans.

What are common helminth infections in children in rural tropics and subtropics?

Schistosomiasis, filariasis, hookworm disease, ascariasis, and onchocerciasis.

What are the common helminth infections found in developed nations?

Pinworm and trichinosis.

What are some factors contributing to continuing helminth infections?

Use of human excrement for fertilizer, eating raw meat or fish, and exposure of bare feet in contaminated soil or water.

symptoms of helminth infection

enlargement of organs, hemorrhage, wt loss, anemia

how do worms migrate in helminth infections?

with enzymes to liquefy and penetrate tissues -- feeding, tissue dmg, blocked ducts and organs, toxic secretions, pressure

incomplete immunity of helminth infection

protective coverings, large, inaccessible, migration

diagnosis of helminth infection

eosinophilia: increased eosinophils, granular leukocytes which destroys worms

travel history

detection of eggs in stools, urine, or blood

how do we control helminth infections?

sewage treatment: no human feces as fertilizers, water treatment, no raw meat

chemotherapy: paralyze worms and interferes w metabolism

see table in notes

what are examples of nematode infections?

intestinal nematodes (cycle A): ascariasis

intestinal nematodes (cycle B): hookworms, strongyloidiasis, trichinosis

Tissue nematodes (cycle E): filariasis, bancroftian filariasis, river blindness, loa loa, dracontiasis

what are nematodes?

headless worms w smooth protective outer cuticle, periodically shed as the worm grows, sexes are distinct

abundant animal group, mostly not parasites

types: intestinal and tissue

50 species are human parasites

ascariasis and its life cycle

ascaris lumbricoides - intestinal nematodes cycle A

larva and adult in humans > embryonic eggs in feces > food contamination > oral entry > intestine > circulation > heart > lungs > throat > swallowed > SI > 200k embryos/d

Ascaris lumbricoides

Ascariasis

worms retain motility, do not attach

severe inflamm rxns mark migration

allergic rxns can occur

heavy loads can retard physical and mental development

What is the life cycle of hookworms?

Larvae burrow into skin > circulation > lung > throat > small intestine

What are common symptoms of hookworm infection?

Dermatitis, pneumonia, nausea and vomiting, pain, blood diarrhea, chronic fatigue, anemia

strongyloidiasis and symptoms

intestinal nematode cycle B

threadworm infections

blood diarrhea, liver enlarged, bowl obstruction, malabsorption

trichinosis

trichinella spiralis

intestinal nematodes cycle B

mammalian host, encysted larval form in muscles

human infection: raw meat from swine or bear

200k new cases in US

trichinosis symptoms

initial: fever, diarrhea, nausea, abdominal pains, sweating

2nd phase: intense muscle/joint pain, sob, eosinophillia > heart and brain dmg and death

how do you prevent trichinosis?

cook meat well, freezing kills worm larvae

freezing limitations for preventing trichinosis

cold resistant: T nativa in alaska bear and walrus meat, freezing artic meat will NOT kill larval cysts

bear or walrus meat needs to be cooked to gray color at 160F.

microwaving ineffective

filariasis and life cycle and major species

filarial nematodes - tissue nematodes cycle E

long threadlike worms with a biphasic life cycle (betw humans and mosquitoes/flies)

major species: wuchereria bancrofti and oncocerca volvulus

brancroftian filariasis and symptoms

wuchereria bancrofti tissue nematodes cycle E (larva)

affects 90M ppl

symptoms: elephantiasis -- inflamm and blockageof main lymphatic channels > accum fluid

River blindness/onchocerciasis

onchocerca volvulus -- tissue nematodes cycle E

west african villages along rivers are breeding sites for black flies: 50% adults blind

what are symptoms of onchocerciasis

inflammation and granulomatous lesions

river blindness: invasion of eyes

loa loa and its treatment

african eye worm - tissue nematodes cycle E

transmit by fly

can be felt slithering beneath skin

treatment: pull worm out, diethylcarbamazine

dracontiasis

dracunuculus medinensis - tissue nematode cycle E

dragon worm found in India, Middle East, Central Africa

Cyclops: arthropod in still water

infection cycle of dracontiasis

ingestion of larva in cyclops > intestine > SC tissue > irritants > itching blisters (fireworm) > eruption in water > cyclops

What are the types of trematodes/fluke infections?

schistosomes (cycle D): blood flukes

liver and lung flukes (cycle D)

what are flukes?

trematodes, they are mostly flat

blood flukes/schistosomiasis

renal/kidney schistosomes cycle D

old disease: ancient Egypt, males menstruating

20 million infections (africa, SA, ME, Far east)

symptoms and control of blood flukes

fever, chills, diarrhea, cough

chronic: hepatomegaly, splenomegaly, bladder obstruction, kidney damage, blood in urine, brain damage

control: snail-eating fish

life cycle of blood flukes

infected humans > eggs > ciliated larva (miracidium) > snails > forked larva (cercaria) > human skin > circulation > liver > intestine > feces

stages: mircidium phase, cercaria phase released by snails and burrows into human host, EM of mating adult worms

liver and lung flukes

cycle D

sexual development in humans

intermediate hosts: snails

what causes liver and lung fluke infection?

infection by ingesting inadequately cooked or raw freshwater fish and crustaceans

life cycle of liver and lung fluke infections

larva hatch and crawl into the bile duct > mature and shed eggs into standing water > snails > cercariae > fish

morphology of cestodes

scolex: head - sucker no mouth

neck

strobila: ribbon composed of reproductive segments (proglottids)

beef tapeworm infection/taeniasis (lifecycle)

taenia saginata cestode/tapeworm infection cycle C

2k proglottids anchored by scolex with suckers

lifecycle: proglottid > egg > encysted larva in beef muscle > ingested

How are cows and humans infected by taenia saginata?

cows infected by ingesting in fields w proglottids or egg contamination

human infected by eating raw beef

what are symptoms of taeniasis?

mild abdominal pain and nausea

cystericercosis

swine tape worm: taenia solium - cestode/tapeworm infection cycle C

T. solium smaller than T. saginata

endemic in areas consuming raw/partially cooked pork

what makes cysticercosis severe form of taenia solium infection

tapeworm larvae migrate to diff tissue > form peculiar cysticerci > tissue dmg in heart eye and brain

What are the types of fish helminths infections?

anisakiasis - anisakis infection

tape worm Diphyllobothrium latum: great lakes, canada, alaska, human hosts

anisakiasis

anisakis larvae burrow into tissue

tingling sensation in throat few hrs after eating sushi

acute GI pain, cramp, vomit

expelled wo further symptoms

How do I avoid infection from sushi?

reputable sushi bar: chef pick out larvae

tuna and octopus, avoid salmon and haribut

freeze fish for 5 days at -20C

Summary of helminth infections

Nematodes:

- intestinal nematodies: hookworms, strongyloidiasis, trichinosis

- tissue nematodes: filariasis, bacroftian filariasis, river blindness

Trematodes: blood flukes - schistosomiasis, liver and lung flukes

Cestodes: beef, swine, fish infections