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Medical Microbiology and Virology > 23 Gastrointestinal tract infections - parasites > Flashcards

23 Gastrointestinal tract infections - parasites Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

What are examples of protozoa which infect GI tract?

Small intestine

Large intestine

A 
Small intestine -
giardia
cryptosporidium
cyclospora
cystoisospora
microsporidia

large intestine -
entamoeba histolytica
balantidium coli

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2
Q

What are examples of helminths (worms) which infect GI tract?

Small intestine

A 
Small intestine -
ascaris
ancylostoma
necator americanus
strongyloides
taenia saginata - beef tapeworm
taenia solium - pork tapeworm
trichinella

diphyllobothrium latum
hymenolepsis nana

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3
Q

What are examples of helminths (worms) which infect GI tract?

Large intestine

A

Enterobius

Trichuris

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4
Q

What are the two species of entamoeba?

How are they different clinically?

A

Entameoba histolytica - causes inflammatory bloody diarrhoea as invades mucosa

Entamoeba dispar does not cause symptoms

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5
Q

What is life cycle of entamoeba histolytica?

A

Mature cysts ingested - contaminated food/ water

Excysts into tropohzoite in intestine

Trophozoites Multiples by binary fission into further trophozoites. Some become cysts.

Cysts shed in stool - survive environment 30 days
Trophozoites bind to intestine causing damage, and ingesting RBC

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6
Q

E histolytica can cause dysentery, and lead to GI perforation

What are extra-intestinal manifestations?

How to diagnose?

A

Spreads via bloodstream to liver and cause liver abscess. Fever/ hepatomegaly/ jaundice may suggest this

Can occasionally spread to lungs

Stool for OCP - see trophozoites in dysentery, cysts may be seen - need to differentiate E dispar

Serology if consider liver abscess

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7
Q

What is treatment of E. histolytica infection

If bloody diarrhoea, first treat for shigellosis (as more likely) while awaiting stool microscopy

A

Kill trophozoites -
kills amoebic trophozoites in intestinal/ extra-intestinal infection
- metronidazole 500mg TDS 5 days. 10 days if liver abscess
- tinidazole 2g OD 3 days

Eliminate amoebae from gut -

  • both not absorbed from GI tract. Start treatment after finishing metro/tinidazole. 10 day coure
  • paromomycin
  • diloxanide 500mg TDS

If collection >10cm - may require drainage as risk of rupture

If asymptomatic, but amoeba in stool - treat diloxanide/ paromomycin to prevent further transmission. If in developing country, do not treat as endemic/

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8
Q

Giardia has multiple names in use -
giardia intestinalis
giardia duodenalis
giardia lamblia

What is life cycle of giardia?

A

Cyst ingested via contaminated drinking water

Excyst in gut into trophozoite

Multiplies into trophozoites, and cysts which are excreted in faeces. Trophozoites excreted, but do not survive long

Commonly passed amongst families
Infects other mammals

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9
Q

What symptoms does giardia cause?

A

Can be asymptomatic

self-limiting course 7-10 days

Chronic diarrhoea - particularly immunocompromised

Stools are often loose, foul smelling and often fatty

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10
Q

How to diagnose giardia infection?

A

Identify trophozoites/ cysts in stool

PCR stool

Multiplex tests can detect giardia/ cryptosporidum/ E histolytica

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11
Q

What is treatment of giardiasis?

A

Metronidazole 400mg TDS 5 days

Alternatives -
Tinidazole

Nitazoxanide

Albendazole

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12
Q

Cryptosporidium is important cause of diarrhoea in immunocompromised

Two species -
Cryptosporidium hominis - most common
Cryptosporidium parvum

What are symptoms?

A

Mild diarrhoea

Severe profuse diarrhoea for 15-40 days in immunocompetent

Chronic diarrhoea if CD4 <100

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13
Q

How to diagnose cryptosporidium infection?

A

Wet prep stool does not identify it

fluorescence microscopy with auramine/ ZN stain

Ag detection via ELISA

PCR - commonly in multiplex assay which can detect giardia/ cryptosporidum/ E histolytica

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14
Q

What is treatment of cryptosporidium infection?

A

Starting ART

Nitazoxanide/ paromomycin can be used in immunocompetent, but are not fully effective

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15
Q

Cyclospora/ cystoisospora and microsporidia are similar to cryptosporidium. Life cycle takes place at epithelial cells mucosa

Usually immunocompromised affected

What is treatment?

A

Start ART

Co-trimoxazole

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16
Q

Most clinically important intestinal worms are nematodes (soil-transmitted helminths)

What are two general life cycles?

A

Infection occurs via ingestion eggs -

  • ascaris
  • enterobius - threadworm
  • trichuris - whipworm

Infection occurs via skin penetration, which then undertake migration through lungs to the intestine -

  • hookworm - ancylostoma/ necator
  • strongyloides

With exception of trichuris, all inhabit small bowel where nutrients are more abundant

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17
Q

What is general life cycle of nematode, in which eggs are ingested

ascaris
enterobius
trichuris

A

Ingestion of eggs

Eggs hatch in small intestine. Larvae enter circulation and migrate into lungs

Larvae are coughed up and swallowed, re-entering GI tract. Maturation continues in small intestine, where they feed on intestinal content. Trichuris moves to large intestine

Mature larvae produce fertilised eggs which can survive for long time in soil (up to 10 years). Require warm temperature and high humidity for infective larvae to develop in eggs.

18
Q

What is general life cycle of nematode, in which skin penetration occurs

  • hookworm - ancylostoma/ necator
    (excluding strongyloides)
A

Egg in soil - larvae hatches

Filariform larva penetrate skin

Move to bloodtsream, and end up in lungs

Larvae coughed up and swallowed, re-entering GI tract. Use suckers to attach to intestinal mucosa, and rupture capillaries and suck blood

Eggs passed in faeces

19
Q

What is general life cycle of nematode, in which skin penetration occurs.

  • strongyloides
A

Overall similar to hookworm

Strongyloides females produce larvae which pass out in faeces

Two paths for larvae to take -

  • free living - adult worms in soil, produce eggs. New larvae hatch from these eggs. These can then penetrate host skin, and move via bloodstream/ lungs to small intestine
  • parasitic - adult worms reside in small intestine, producing eggs which hatch in intestine. Larvae released in stool

If host is immunocompromised, then larvae produced can auto-infect before being released in faeces. This can cause disseminated strongyloides. Chronic auto-infection can persist for more than 30 years

20
Q

What are clinical features of ascaris infection?

A

Intestinal obstruction

Abdominal pain/ GI dsitrubance

Cholangitis

Liver abscess

Pneumonitis as migrates through lungs - Loefflers syndrome

21
Q

What are clinical features of trichuris infection?

A

Chronic diarrhoea

Impaired nutrition/ growth retardation - because trichuris normally affects children

Rectal prolapse

22
Q

What are clinical features of hookworm infection?

A

Dermatitis - migrate through skin. Cutaneous larva migrans is hookworm which remains in skin - usually dog/ cat hookworms, which humans are dead end host

Pneumonitis

IDA - blood feeding

Impaired nutrition/ growth retardation

23
Q

What are clinical features of strongyloides infection?

A

Usually immunocompromised/ HTLV infection

Diarrhoea

Malabsorption

Gram negative infection associated

Overwhelming larvae infection can be fatal

24
Q

How to diagnose parasitic worm (soil transmitted helminth) infection?

A

Stool OCP

Stronglyoides serology 90% sensitive

Bloods - eosinophilia

25
Q

What is treatment for following soil transmitted helminths?

Ascaris

Enterobius

Trichuris

Strongyloides

A

Ascaris - albendazole/ mebendazole

Enterobius - mebendazole

Trichuris - albendazole/ mebendazole

Strongyloides - ivermectin

26
Q

How to prevent soil transmitted helminth infection?

A

Improve hygiene/ sanitation

Chemotherapy erradication programme

27
Q

Cestodes (Tapeworms) are uncommon in resource rich countries

What is source of these infections?

Taenia solium

Taenia saginata

Diphyllobothrium latum

Hymenolepsis nana

A

Taenia solium - pork tapeworm

Taenia saginata - beef tapeworm

Diphyllobothrium latum - fish tapeworm

Hymenolepsis nana - rodents/ insects are host

28
Q

What is treatment of tapeworm infection?

A

Praziquantel or niclosamide

29
Q

Trichinella is nematode which is not soil-transmitted helminth

What is its life cycle?

A

Pork roundworm, has cysts in pork tissue - then ingested by human in undercooked meat

Excyst in small intestine, and mature to adults

Adults produce larvae, which move via circulation to tissue, where they form cysts

30
Q

What are symptoms of trichinella infection?

A

Diarrhoea/ fatigue

In severe infection - meningitis/ pneumonitis/ periorbital oedema

31
Q

How to diagnose trichinella infection?

What is treatment?

A

Stool OCP
Muscle biopsy
Serology

Albendazole/ mebendazole
Steroids if severe disease

32
Q

Cestode taenia solium causes cysticerocisis

What is its life cycle?

A

Eggs or gravid proglottids ingested by pig

Form cysticerci in pork tissue

Undercooked pork ingested by human

Embryonated eggs hatch, move through circulation to tissue such as brain/ muscle forming cysticerci there

Humans are dead end hosts

33
Q

What are symptoms of cysticerci infection?

A

Seizure

Stroke

Headache

Lumps under skin if invade muscle

34
Q

How do diagnosis cysticercoccis?

A

X-ray - calcified cysts

CT brain

Biopsy muscle

Serology

Eosinophilia

35
Q

What is treatment of cysticercosis?

A

Albendazole and praziquantel in combination

Steroids

May need anti-epileptic drugs

If all cysts are calcified, and asymptomatic - no treatment required

36
Q

What are species of schistosomiasis?

A

S. mansoni
S. japonicum
S. mekongi

S. haematobium

37
Q

What is life cycle of schistosomiasis?

A

Eggs shed in faeces/ urine

Eggs hatch and release miracidia which penetrate snail tissue

Cercariae released from snail, then penetrate human skin

Enter circulation, and migrate to portal blood in liver

Then move to venous plexus of bladder (eggs in urine), or mesenteric venules of bowel (eggs in stool)

38
Q

What are symptoms of schistosomiasis infection?

A

Swimmers itch

Fever

Chills

Rigors

Muscle ache

Haematuria - can lead to bladder cancer with chronic infection

blood in stool

39
Q

How to diagnose schistosomiasis infection?

A

Stool/ urine for eggs - Kato-katz technique

Eosinophilia

Serology can be used

40
Q

What is treatment of schistosomiasis?

A

Praziquantel

41
Q

What are strategies to control schistosomiasis?

A

Mass chemotherapy

Avoid fresh water

Snail population control

Boil water before using if for bathing

Medical Microbiology and Virology (60 decks)

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