Nematodes (Roundworms) Flashcards
Ascaris lumbricoides - habitat, transmission, risk factors, morphology, life cycle, clinical features, diagnosis, treatment
Ascariasis
Habitat: small intestine
Transmission: SOIL contaminated with embryonated eggs
Risk factors: poor hygiene, poor sanitation, human faeces as fertiliser
Morphology: big worms up to 10cm, egg with thick outer cutis
Life cycle: ingestion of eggs –> hatched larvae enter circulation and migrate to lungs –> coughed up and swallowed again to enter GI tract –> mature in small intestines
Clinical features:
- asymptomatic, malnutrition (if severe), abdominal discomfort
- intestinal blockage, BILIARY OBSTRUCTION
Diagnosis:
- stool microscopy for eggs
Treatment: Albendazole single dose; Pyrantel in pregnancy
Enterobius vermicularis - habitat, morphology, life cycle, clinical features, diagnosis, treatment
Enterobiasis (pinworm infection)
Habitat: colon/caecum
Morphology: tapering ends, slightly smaller than ascaris; eggs are flat on one side and convex on the other
Life cycle: female migrates to lay eggs at night –> larve inside eggs mature within 4-6 hrs –> eggs ingested –> larvae hatch in small intestine –> adults in caecum
Clinical features:
- asymptomatic
- perianal itchiness (at night)
Diagnosis:
- look for adult worms in peri-anal area 2-3 hrs after sleep
- scotch tape to collect eggs in morning x3
- examine debris from nails
Treatment: Albendazole/ Pyrantel
Trichuris trichiura - habitat, transmission, morphology, clinical features, diagnosis, treatment
Trichuriasis (whipworm infection)
Habitat: colon/caecum
Transmission: SOIL contaminated with embryonated eggs
Morphology: whip, eggs with thick cutis and operculum at both ends
Clinical features:
- asymptomatic
- diarrhoea, colitis, anaemia
- dysentery and rectal prolapse if very severe
Diagnosis: stool for eggs, endoscopy
Treatment: Albendazole
Trichinella spiralis - habitat, transmission, morphology, life cycle, clinical features, diagnosis, treatment
Trichinellosis
Habitat: small intestine
Source: undercooked meat (pork)
Morphology: “tree bark” whirls
Life cycle: ingestion of undercooked meat (separate cycle in pigs) –> larva released in small intestine –> adults in small intestine –> larva deposited in mucosa –> encysted larva in striated muscle (dead end)
Clinical features:
- diarrhoea, nausea, vomit, abdominal pain
Diagnosis:
- MUSCLE BIOPSY (but sometimes difficult to tell which muscle to take from – usually incidental finding of known lesion on imaging and then proceed to investigate)
Treatment: Albendazole
Strongyloides stercoralis - habitat, transmission, life cycle, clinical features, diagnosis, treatment
Strongyloidiasis
Habitat: small intestine
Transmission: penetration of larvae through skin e.g. walking barefoot
Life cycle: larvae penetrate skin of host –> migrate to small intestine –> become adults –>deposit eggs in intestinal mucosa –> larvae hatch and excreted in stool OR migrate to large intestine and penetrate intestinal mucosa to enter circulation (hyperinfection) –> go to other organs e.g. lungs
Clinical features:
- asymptomatic
- pruritic RASH (at area of acquisition), dry COUGH (larve goes through lungs, coughed up and swallowed to GI), DIARRHOEA, HYPERINFECTION syndrome (lots of worms + eggs = lots of larvae in intestine –> re-infect host = increase infective load)
Diagnosis:
- stool for LARVAE (not eggs), occasionally seen in sputum when there is hyperinfection and high viral load
Treatment: Ivermectin
Ancylostoma duodenale; Necator americanus - habitat, transmission, life cycle, clinical features, diagnosis, treatment
Hookworm infections
Habitat: small intestine
Transmission: Larva from environment penetrates skin e.g. barefoot walking
Life cycle: also exit circulation in lungs, coughed up and re-swallowed to enter GI again
Clinical features: asymptomatic, abdominal pain, iron deficiency anaemia (hooks cause minor bleed)
Diagnosis: find eggs in stool
Treatment: Albendazole, pyrantel
Wuchereria bancrofti - habitat, transmission, life cycle, clinical features, diagnosis, treatment
Lymphatic filariasis
Habitat: lymphatics
Transmission: Mosquitoes
Life cycle: infected mosquito injects larvae –> adults in lymphatics produce microfilariae which migrate to lymph and blood vessels –> infect mosquitoes
Clinical features: asymptomatic, lymphedema
Diagnosis: MICROFILARIAE in BLOOD smear
Treatment: Diethylcarbamazine (contraindicated if there is co-existing onchocerciasis!)
- killing worms causes further inflammation as fragments and contents are released which exacerbates corneal infiltration
Onchocerca volvulus - transmission, life cycle, clinical features, diagnosis, treatment
River blindness
Transmission: Blackfly
Life cycle: blackfly injects larvae –> adults in subcutaneous nodules –> produce microfilariae that are found in skin and lymphatics
Clinical features:
- asymptomatic or local inflammatory response
- itchy skin rash/nodules, corneal infiltrates (WBC cause clouding of cornea and blindness), retinitis
Diagnosis: skin nip biopsy for larvae
Treatment: Ivermectin (no severe inflammatory response invoked so not aggravating cornea; don’t use steroids since immunosuppression will increase infection!)
- contraindicated in Loa Loa infection
Ectoparasites - examples
Mite: Sarcoptes scabiei
Louse: Pediculus humanus, Phthirus pubis
Sarcoptes scabiei - clinical features, diagnosis, treatment
Scabies
Clinical features:
- pruritus, burrows over wrist/elbow/armpit/finger web
Diagnosis: Skin scrape for mite, mite eggs
Treatment: Benzylbenzoate, lindane, permethrin (topical)
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treat household contacts, wash bedding/clothing with hot water at 60 degrees or disinfested inside closed plastic bag for a week
Pediculus humanus - clinical features, diagnosis, treatment
Pediculosis corporis/ capitis
(Head/Body louse)
Clinical features: asymptomatic, “something moving”
Diagnosis: finding adult louse
Treatment: permethrin (topical)
Phthirus pubis - transmission, clinical features, diagnosis, treatment
Pediculosis pubis
Crab louse ("claw-like" appendages to grab onto hair)
Transmission: close person to person contact/ sexual contact
Clinical features: asymptomatic, something moving on pubic hair or eye lashes
Diagnosis: finding lice/eggs
Treatment: permethrin (topical)
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bedding/clothing washed, treat sexual partners
