Helminths (Dustin) Flashcards
General description of helminths
Worms, Eukaryotes.
From 0.1 mm to 15 meters
Reproduce by producing eggs, using intermediate and final hosts
Usually they are parasites of the GI tract, but can infect other tissues and cause filiarisis
Typically produce eosinophilia, IgE elevation
2 types of infectious helminths, relevant morphology, their sexual reproduction pattern, their digestive tract development, and any sub-categories?
- Roundworms (nematodes): cylindrical, unsegmented body. Males are smaller/curved, females are larger/linear. Usually sexual reproduction. Have complete intestinal tract.
- Flatworms (platyhelminthes): Usually hemaphroditic but can have sexual reproduction. Incomplete or lack of digestive system. Can be trematodes (flukes) or cestodes (tapeworms)
What are some morphological features of flukes and tapeworms?
Flukes (trematodes): leaf-shaped, 2 suckers. Complex life cycle (in another card)
Tapeworms (cestodes): long worms consisting of several segments (proglottids, and sum of the segments is called strobila). Has suckers on scolex (head) and rostellum + hooks. Male and female genitals are formed in mature proglottids. Mature proglottids are basically a bag of eggs
What is the life cycle of trematodes?
- Egg
- Flagellated larva (miracidium)
- Saccular larva (sporocyst, in intermediate host)
- Redia: larvae in the GI
- Cercaria: final larva stage, infective. Can penetrate skin
Adult stage develops in final host.
Categorization of all the worms that are on the topic list
(I don’t expect to be able to recite all the names of the worms off the top of my head but this is just a refresher card to be able to group the species)
Cestodes: Taenia saginiata and solium, Diphyllobotrium latum, Hymenolepis nana, Echinococcus granulosus and multilocularis
Trematodes: Schistosoma mansoni japonicum and haemotobium, Fasciola hepatica, Paragonimum westermani
Nematodes: Trichinella spiralis, Enterobius vermicularis, Ascaris lumbricoides, Trichuris trichuria, Strongyloides stercolaris, Toxocara canis and cati, Hookworms (Ancylostoma duodenala and Necator americanus)
+Nematodes causing filiarisis: Loa loa, Wuchereria bancrofti, Dracunculus medinensis, Oncocerca volvulus
Which species of nematodes have only an intestinal phase in humans?
Which ones also have an extraintestinal phase?
Only intestinal: Enterobius vermicularis, Trichuris trichuria
Extraintestinal phases: Ascaris lumbricoides, Toxocara canis and cati, Ancylostoma duodenala, Necator americanus, Strongyloides stercolaris
Which species are the geohelminths? (no direct-human-human transmission; only through soil)
Infectious eggs develop in soil: Trichuris trichuria, Ascaris lumbricoides, Toxocara canis and cati
Infectious (filariform) larvae develop in soil: Ancylostoma duodenala, Necator americanus (hookworms). Strongyloides stercolaris.
Viviparous nematodes (release only larvae): Trichinella spiralis
Antihelminth drugs, based on taxonomy
Anti-nematode: albendazole, mebendazole, thiabendazole, levamisole, ivermectin
Anti-trematode or cestode: Praziquantel, Niclosamide
Taenia saginata: Location Morphology/Taxonomy Life cycle Disease Diagnostics Therapy
- “Beef Tapeworm” - found in Africa, South America, Eastern Europe
- Tapeworm (Cestode, Flatworm/Platyhelminth), 3-10m.
- Eat raw/undercooked beef (intermediate host) infected with cystericus larva -> larva form in SI -> develop to mature worms in 3 months (human definitive host) -> proglottids containing eggs released in stool -> ingestion by other cattle -> form cysts in cow muscle, brain, eye
- Usually asymptomatic, maybe GI upset. T. saginata not as bad as solium.
- Diagnostics: motile proglottids in stool
- Therapy: niclosamide, praziquantel
Taenia solium: Location Morphology/Taxonomy Life cycle Disease Diagnostics Therapy
- “Pork Tapeworm” - found wherever pork is raised
- Cestode, Flatworm/Platyhelminth, 2-5m. Hooks on proglottid heads.
- Eat raw/undercooked pork (intermediate host) infected with cystericus larva -> larva form in SI -> develop to mature worms in 3 months (human definitive host) -> proglottids containing eggs released in stool -> ingestion by other pigs -> form cysts in pig muscle, brain, eye
- Usually asymptomatic, maybe GI upset or cysterceri may damage muscles, eyes, or CNS (neurocysticercosis from ingesting eggs in water contaminated by pig feces, NOT by ingesting larva in meat).
- Diagnostics: motile proglottids in stool
- Therapy: niclosamide, praziquantel
Diphyllobothrium latum: Location Morphology/Taxonomy Life cycle Disease Diagnostics Therapy
- “Fish tapeworm” - northern climates, places where raw fish is eaten
- Cestode, Flatworm/Platyhelminth. 13m (largest flatworm)
- Consume raw fish -> larvae mature in SI -> eggs released in stool, get into water -> embryo ingested by crabs (first intermediate host) -> procercoid larva -> migrates to muscles of fish (second intermediate host) -> plerocercoid larva in fish, later eaten by human.
- Usually symptomless, may have diarrhea or deficient B12, megaloblastic anemia
- Diagnostics: lidded eggs present in stool
- Therapy: niclosamide, praziquantel
Hymenolepis nana: Morphology/Taxonomy Location Life cycle Disease Diagnostics Therapy
- “Dwarf tapeworm” - 5cm
- Worldwide, mostly tropical regions
- No intermediate host. Spread by dirty hands. Ingest infectious eggs -> cystericoid and worm develop inside -> proglottids detatch -> eggs released -> present in stool -> re-infection bc hundreds of worms in GI tract.
- Usually asymptomatic
- Diagnostics: ova in stool
- Therapy: praziquantel, niclosamide
What are the two Echinococcus species?
- Morphology/Taxonomy
- Definitive and intermediate hosts
- Life cycle
- E. granulosus and E. multilocaris
- Cestode, Flatworm/Platyhelminth. 2-6mm.
- Definitive hosts usually dogs/other carnivores (e.g. foxes, cats), intermediate are herbivores that dogs/ wolves/ foxes eat (e.g. sheep). Humans = rare accidental intermediate hosts
- Dogs release eggs in stool -> intermediate hosts take up eggs -> larva hatch in intestine and spread in tissues -> dogs eat infected intermediate animal
What are the two Echinococcus species?
- Difference between the two species
- Disease
- Diagnosis
- Therapy
- E. granulosus and E. multilocaris
- E. granulosis final host is dogs, intermediate are sheep, cattle, swine or human. Makes hydatid cyst. E. multilocularis final host is fox, intermediate hosts are rodents or humans. Has smaller spongy cysts which only invade liver (E. alvolaris)
- From GI, larva invade mucosa -> hematogenous spread -> form hydatid cysts in brain, liver, lungs. Cysts bursting can cause anaphylactic reaction
- Diagnosis: serology. Cysts: CT, MRI
- Therapy: surgical resection, benzimadazoles
Fasciola hepatica: Morphology/Taxonomy Life cycle Disease Diagnostics Therapy
- Sheep Liver Fluke (Trematode, Flatworm)
- Eggs develop to miracidia larvae in water -> in intermediate host (snails) transform to sporocyst -> redia -> cercaria. Cercaria move to plants or crustaceans. In definitive host (normally sheep, cattle; rarely human): cercaria ingested -> invade intestinal mucosa -> spread to liver -> adult helminth develops. After fertilization, eggs get in bile and released in stool.
- Hepatomegaly, hepatitis, bile duct obstruction, jaundice. May also infect eye, brain, lungs, skin.
- Diagnosis: egg detection in stool or bile
- Therapy: Benzimidazole, Praziquantel
Paragonimus westermani: Morphology/Taxonomy Life cycle Disease Diagnostics Therapy
- Chinese lung fluke (Trematode, Flatworm)
- Eggs develop to miracidia larvae in water -> in intermediate host (snails) transform to sporocyst and cercaria -> spread to crab. In definitive host (human): cercaria ingested in crab meat -> invade intestinal mucosa -> spread to lung -> adult helminth develops. Cough up the eggs then swallow them -> feces contains eggs.
- Cystic cavities in lung, bloody sputum, can be complicated by bacterial pneumonia. Can penetrate brain, spinal cord, heart -> lethal.
- Diagnosis: eggs in stool or sputum
- Treatment: Praziquantel
Schistosomes: Species Morphology/Taxonomy Location Life cycle
- S. mansoni (colon), S. japonicum (SI), S. haematobium (bladder; egyptian hematuria)
- Blood Fluke (Trematode, Flatworm)
- Mostly Africa or wetlands of other areas
- Eggs develop to miracidia larvae in water -> in intermediate host (snails) transform to sporocyst and cercaria -> penetrate human skin -> cercaria migrate through portal blood to liver -> mature -> migrate to different locations based on species. Pass eggs in feces (S. mansoni and japonicum) or urine (S. haematobium)
Schistosomes:
- Difference between species
- Schistosomiasis
- Diagnostics
- Therapy
- Intestinal Schistosomiasis: S. mansoni (colon) and S. japonicum (SI). Parasite in the mesenteric veins. Can destroy gut mucosa and result in GI hemorrhage.
- S. haematobium: bladder Schistosomiasis. Can form granulomas and calcification in bladder, risk of bladder cancer. Causes hematuria.
- Schistosomiasis: often symptomless, other effects depends on species. Acutely: dermatitis, fever, diarrhea, hepatomegaly, portal hypertension, jaundice. If chronic it can cause cirrhosis, high lethality.
- Diagnostics: eggs in stool or urine
- Therapy: Praziquantel
Ancylostoma duodenale and Necator americanus: Morphology/Taxonomy Location Life cycle Disease Diagnostics Therapy
- Hookworm, Nematode. 7-15 mm.
- Duodenale is old world hookworm (Europe, Africa, Asia), Americanus is new world and Africa.
- Geohelminth. Filariform larva penetrate skin -> migrate to lung -> migrates again and adult stage in SI. Eggs released in stool -> larva form in soil (first non-infectious, then infectious)
- Disease: feed of sucking blood from intestine, causing anemia and GI pain, malnutrition. Duodenale takes more blood than N. americanus. Pneumonia
- Diagnosis: eggs in stool
- Treatment: mebendazole, albendazole
Toxocara canis and cati: Morphology/Taxonomy Location Life cycle Disease Diagnostics Therapy
- Nematodes. Dog/cat zoonotic infection. 10-20cm. Egg is round, has rough surface
- Worldwide
- Dog/wolf or cat is final host. Eggs released from their GI -> larva formation in 3-4 weeks (geohelminth) -> larvae ingestion by human (usually children) -> enter SI -> larvae migrate -> liver, brain eye. Larvae can’t mature in human.
- Disease: usually symptomless. Can have granuloma formation, blindness (ocular larva migrans), fever, pneumonia, myocarditis, encephalitis.
- Diagnosis: serology, detection in tissue
- Therapy: Tiabendazole
Trichinella spiralis: Morphology/Taxonomy Location Life cycle Disease Diagnostics Therapy
- Nematode, “Pork Roundworm”
- Worldwide
- Ingest pork infected with encysted larvae -> develop to adults in SI -> enter circulation, disseminate to any organ -> larvae form cysts in muscles (dead-end in humans)
- Disease: trichinosis. Acute enteritis, myalgia, fever, periorbital edema. Can damage myocardium or brain
- Diagnosis: serology, finding larvae in muscle biopsy
- Treatment: Tiabendazole
Enterobius vermicularis Morphology/Taxonomy Location Life cycle Disease Diagnostics Therapy
- “Pinworm,” nematode. Male 2-5mm, female 10-13mm.
- Worldwide, mostly spread between children
- Geohelminth. Ingest eggs -> larva in SI -> moves to perianal region, matures to adult. Eggs are laid in perianal region, spread via dirty hands (can be autoinfection)
- “Pruritus ani” - itching occurs at night.
- Detection: eggs on tape strip put on anus
- Therapy: mebendazole
Strongyloides stercoralis: Morphology/Taxonomy Location Life cycle Disease Diagnostics Therapy
- Nematode
- Typically tropical, but also Eastern Europe and Mediterranean
- Geohelminth filariform larvae enter skin -> migrate to lung -> swallowed and mature in GI -> lay eggs. Eggs either hatch in GI and autoinfect (re-enter bloodstrem), or they hatch in soil, mature to filariform, and can infect others.
- Strongiloidosis: usually symptomless, if not then diarrhea, pneumonitis, pruritus
- Diagnosis: larva in stool, larva migration test, eosinophilia
- Therapy: tiabendazole, ivermectin
Ascaris lumbricoides: Morphology/Taxonomy Location Life cycle Disease Diagnostics Therapy
- Spindleworm, Nematode. Males 15-20cm, females 20-35cm. Egg has 3-layer capsule
- Worldwide but mostly tropical
- Ingest eggs from dirt (geohelminth) -> larvae develop in SI -> enter bloodstream -> get to lung -> back to esophagus -> mature in SI. Eggs released in stool, back to soil
- Disease: pneumonia, nutritional obstruction. May migrate to bile ducts, appendix, peritoneum and cause other problems.
- Diagnosis: eggs in feces, maybe sputum
- Therapy: Mebendazole, lebamizole (intestinal), tiabendazole (migration)
Trichuris trichuria: Morphology/Taxonomy Location Life cycle Disease Diagnostics Therapy
- “Whipworm,” nematode. 3-5cm. Anterior whip-like portion.
- Worldwide
- Geohelminth egg in ground, releases larva -> ingestion of eggs/larvae in soil-contamined food -> larva migrates to cecum/ileum, mature and produce eggs -> eggs in stool, back into soil
- Disease: GI upset, blood loss, diarrhea, rectal prolapse due to straining in defecation
- Diagnosis: eggs in stool (elongated lemon shape)
- Treatment: Mebendazole
What is filiarisis?
Which worms cause it?
Tissue infection by nematodes, spread by biting flies or mosquitoes
4 nematodes to know: Lymphatic filiarisis: Wucheria bancrofti
Subcutaneous filiarisis: Loa loa, Onchocerca volvulus, Dracunculus medinensis
Wuchereria bancrofti: Location Vector Disease Diagnosis Therapy Prevention
- Location: Asia
- Vector: Mosqutio (culex)
- Lymphedema in arms, legs, groin. Can cause elephantiasis. Commonly affects scrotum. Most common forms of acute stage: adenolymphangitis, orchitis, epididymitis with fever. May also see chyluria or hydroceles. May have cough from microfiliariae spreading to lungs.
- Diagnosis: microfilaria in blood smear, better to test at night (more prevalent at night).
- Treatment: Ivermectin, Albendazole, Diethylcarbamazine
Loa loa: Location Vector Disease Diagnosis Therapy
- Location: West/Central Africa (“African Eye Worm”)
- Vector: Fly (Chrysops)
- Larva mature over 6 months, can live 17 years in organism. Enter blood circulation during the day, often spread to conjunctiva where they can be visualized. Cause local subQ swelling/pruritius, angioedema.
- Diagnosis: Visualize in eye, serology, microfilariae in blood
- Therapy: Diethylcarbamazine
Onchocerca volvulus: Location Vector Disease Diagnosis Therapy
-Africa, Central America.
-Mosqutios (Simulium)
-Onchocerciasis, River Blindness: Microfilariae enter ocular structures. Also pruritus, hyper or hypopigmented dermatitis.
Diagnosis: Skin biopsy, microfilaria
-Therapy: Ivermectin
Dracunculus medinensis: Location Vector Disease Diagnosis Therapy
- Africa, India
- Ingest water contaminated with larvae by copepod crab (intermediate host), matures to adult in 9-12 months.
- Dracunculosis: female produces toxins that help penetrate skin so larvae can get back into the water
- Diagnosis: clear from worm eruption from skin ulcer
- Treatment: wrap worm around stick. Albendazole helps.
