23 Gastrointestinal tract infections - parasites Flashcards
What are examples of protozoa which infect GI tract?
Small intestine
Large intestine
Small intestine - giardia cryptosporidium cyclospora cystoisospora microsporidia
large intestine -
entamoeba histolytica
balantidium coli
What are examples of helminths (worms) which infect GI tract?
Small intestine
Small intestine - ascaris ancylostoma necator americanus strongyloides taenia saginata - beef tapeworm taenia solium - pork tapeworm trichinella
diphyllobothrium latum
hymenolepsis nana
What are examples of helminths (worms) which infect GI tract?
Large intestine
Enterobius
Trichuris
What are the two species of entamoeba?
How are they different clinically?
Entameoba histolytica - causes inflammatory bloody diarrhoea as invades mucosa
Entamoeba dispar does not cause symptoms
What is life cycle of entamoeba histolytica?
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
E histolytica can cause dysentery, and lead to GI perforation
What are extra-intestinal manifestations?
How to diagnose?
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
What is treatment of E. histolytica infection
If bloody diarrhoea, first treat for shigellosis (as more likely) while awaiting stool microscopy
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/
Giardia has multiple names in use -
giardia intestinalis
giardia duodenalis
giardia lamblia
What is life cycle of giardia?
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
What symptoms does giardia cause?
Can be asymptomatic
self-limiting course 7-10 days
Chronic diarrhoea - particularly immunocompromised
Stools are often loose, foul smelling and often fatty
How to diagnose giardia infection?
Identify trophozoites/ cysts in stool
PCR stool
Multiplex tests can detect giardia/ cryptosporidum/ E histolytica
What is treatment of giardiasis?
Metronidazole 400mg TDS 5 days
Alternatives -
Tinidazole
Nitazoxanide
Albendazole
Cryptosporidium is important cause of diarrhoea in immunocompromised
Two species -
Cryptosporidium hominis - most common
Cryptosporidium parvum
What are symptoms?
Mild diarrhoea
Severe profuse diarrhoea for 15-40 days in immunocompetent
Chronic diarrhoea if CD4 <100
How to diagnose cryptosporidium infection?
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
What is treatment of cryptosporidium infection?
Starting ART
Nitazoxanide/ paromomycin can be used in immunocompetent, but are not fully effective
Cyclospora/ cystoisospora and microsporidia are similar to cryptosporidium. Life cycle takes place at epithelial cells mucosa
Usually immunocompromised affected
What is treatment?
Start ART
Co-trimoxazole
Most clinically important intestinal worms are nematodes (soil-transmitted helminths)
What are two general life cycles?
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
What is general life cycle of nematode, in which eggs are ingested
ascaris
enterobius
trichuris
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.
What is general life cycle of nematode, in which skin penetration occurs
- hookworm - ancylostoma/ necator
(excluding strongyloides)
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
What is general life cycle of nematode, in which skin penetration occurs.
- strongyloides
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
What are clinical features of ascaris infection?
Intestinal obstruction
Abdominal pain/ GI dsitrubance
Cholangitis
Liver abscess
Pneumonitis as migrates through lungs - Loefflers syndrome
What are clinical features of trichuris infection?
Chronic diarrhoea
Impaired nutrition/ growth retardation - because trichuris normally affects children
Rectal prolapse
What are clinical features of hookworm infection?
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
What are clinical features of strongyloides infection?
Usually immunocompromised/ HTLV infection
Diarrhoea
Malabsorption
Gram negative infection associated
Overwhelming larvae infection can be fatal
How to diagnose parasitic worm (soil transmitted helminth) infection?
Stool OCP
Stronglyoides serology 90% sensitive
Bloods - eosinophilia
What is treatment for following soil transmitted helminths?
Ascaris
Enterobius
Trichuris
Strongyloides
Ascaris - albendazole/ mebendazole
Enterobius - mebendazole
Trichuris - albendazole/ mebendazole
Strongyloides - ivermectin
How to prevent soil transmitted helminth infection?
Improve hygiene/ sanitation
Chemotherapy erradication programme
Cestodes (Tapeworms) are uncommon in resource rich countries
What is source of these infections?
Taenia solium
Taenia saginata
Diphyllobothrium latum
Hymenolepsis nana
Taenia solium - pork tapeworm
Taenia saginata - beef tapeworm
Diphyllobothrium latum - fish tapeworm
Hymenolepsis nana - rodents/ insects are host
What is treatment of tapeworm infection?
Praziquantel or niclosamide
Trichinella is nematode which is not soil-transmitted helminth
What is its life cycle?
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
What are symptoms of trichinella infection?
Diarrhoea/ fatigue
In severe infection - meningitis/ pneumonitis/ periorbital oedema
How to diagnose trichinella infection?
What is treatment?
Stool OCP
Muscle biopsy
Serology
Albendazole/ mebendazole
Steroids if severe disease
Cestode taenia solium causes cysticerocisis
What is its life cycle?
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
What are symptoms of cysticerci infection?
Seizure
Stroke
Headache
Lumps under skin if invade muscle
How do diagnosis cysticercoccis?
X-ray - calcified cysts
CT brain
Biopsy muscle
Serology
Eosinophilia
What is treatment of cysticercosis?
Albendazole and praziquantel in combination
Steroids
May need anti-epileptic drugs
If all cysts are calcified, and asymptomatic - no treatment required
What are species of schistosomiasis?
S. mansoni
S. japonicum
S. mekongi
S. haematobium
What is life cycle of schistosomiasis?
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)
What are symptoms of schistosomiasis infection?
Swimmers itch
Fever
Chills
Rigors
Muscle ache
Haematuria - can lead to bladder cancer with chronic infection
blood in stool
How to diagnose schistosomiasis infection?
Stool/ urine for eggs - Kato-katz technique
Eosinophilia
Serology can be used
What is treatment of schistosomiasis?
Praziquantel
What are strategies to control schistosomiasis?
Mass chemotherapy
Avoid fresh water
Snail population control
Boil water before using if for bathing
