Helminths Flashcards
What are the worms?
- Nematodes (roundworms - filaria)
- Trematodes (flukes or flatworms)
- Cestodes (tapeworms)
What are the diagnostic methods?
- See adult worm, larvae or eggs (worms may produce huge numbers of eggs daily, examination of faeces/blood/skin)
- Antigen detection
- Serology
- PCR
What are invasive helminth infections often associated with?
Eosinophilia
What are the 4 different types of hosts?
- Definitive host (parasite reaches maturity or reproduces sexually)
- Intermediate hosts (harbour parasites during development stage)
- Paratenic hosts (intermediate host but parasite doesn’t develop further)
- Accidental/dead hosts (gets infected but don’t contribute to parasite’s ongoing life cycle as not a suitable predator)
What does Nematodes infect?
- Intestinal
- Blood and tissue
Describe intestinal nematodes
what worms? where? where egg hatch? how many stages?
Adult worms in human/animal intestine
- Two sexes
- Eggs hatch in environment or in host
- Several larval stages
How to diagnose intestinal nematodes?
- Characteristic eggs, larvae (concentration techniques on stool)
- Serology (some)
What are the intestinal nematodes species?
- Enterobius vermicularis
- Trichuris trichiura
- Ascaris lumbricoides
- Stronglyoides sterocoralis
- Trichinella spiralis
- Toxocara canis, T.cati
- Hook worms
Pathogenesis of Enterobius vermicularis
issa pinworm, threadworm
- Humans swallow eggs
- Hatch and worms mature
- Female lay eggs on perianal/perineal skin
Reinfection of original host is common
What does Enterobius vermicularis cause?
issa pinworm, threadworm
Pruritus ani
don’t scratch bum or suck your thumb!
How to diagnose Enterobius vermicularis?
issa pinworm, threadworm
Sellotape slide, characteristic eggs
Pathogenesis of Trichuris trichiura
issa whipworm
- Eggs passed in faeces
- Humans swallow eggs
- Larvae develop into adult in GIT
What are the clinical presentation of Trichuris trichiura?
issa whipworm
- Bloody stools
- Rectal prolapse
- Abdominal pain
- Trichuris Dysentery Syndrome (chronic diarrhoea, growth/intellectual retardation)
How to diagnose Trichuris trichiura?
issa whipworm
- Eggs in faeces
- Worms in rectal mucosa
Pathogenesis of Ascaris lumbricoides
issa large intestinal roundworm
- Eggs passed in faeces
- Swalloed, hatch in duodenum as larvae
- Larvae migrate through mucosa into blood
- Larvae migrate into lung airspaces
- Coughed up and swallowed
- Adult worms develop in small intestine
What are the clinical presentations of Ascaris lumbricoides?
issa large intestinal roundworm
- Allergic reactions (asthma, rashes, eosinophilia)
- Cough
- Fever
- Severe pneumonitis
- Abdominal pain
- Peritonitis
- Appendicitis
- Mechanical blockage of intestine, pancreatic or bile ducts
How to diagnose Ascaris lumbricoides?
issa large intestinal roundworm
Usually by visualising worms or eggs in faeces
Pathogenesis of hookworms
- Eggs in soil hatch and mature as larvae
- Larvae penetrates skin
- Migrate via bloodstream to lungs
- Coughed up and swallowed
- Adult worms develop in small intestine, blood sucking and lay eggs
What are the clinical presentations of hookworms?
- Hookworm anaemia
- Severe anaemia: tiredness, pallor, oedema, heart failure
- Note pale conjunctivae
- Cutaenous larva migrans (most often caused by dog/cat hookworm): itchy rash lasts many weeks (treatable)
How to diagnose hookworm?
- Eggs in faeces
- Worm
Pathogenesis of Strongyloides stercoralis
- Adult female in GIT produces eggs, develop into larvae in GIT and exit in faeces (mature into adults in soil, eggs, infectious larvae penetrate skin and migrate to GIT/some via lungs, coughed up and swallowed)
- Autoinfection cycle
- Some larvae produced from eggs in GIT become infectious (penetrate GIT mucosa/perianal skin, migrate to GIT)
- Infection persists for decades (chronic gastrointestinal symptoms)
What do immunocompromised patients suffer from Strongyloides stercoralis?
Immunocompromised patients may suffer overwhelming hyperinfection syndrome
What does Strongyloides stercoralis hyperinfection syndrome cause?
- Many systems may be involved as larvae migrate
- Gastrointestinal: severe diarrhoea +/- blood, intestinal perforation, peritonitis, septicaemia
- Pulmonary
- Skin: Larva currens (very itchym lesions come and go over a few hours)
- CNS: encephalitis, meningitis
How to diagnose Strongyloides stercoralis?
- Microscopy: larvae in stool, duodenal fluid, biopsy, sputum (not very sensitive, entero-test, USE PPE!!!)
- PCR
- Serology (does not distinguish current from old infection)
- Screen patients from tropical countries before giving immune suppression (chemotherapy/transplants)
Pathogenesis of Trichinella spiralis
- Consumption of cysts in poorly cooked meat
- Larvae released, penetrate intestinal mucosa, mature to adults
- Adult worms copulate, female produces larvae which enter bloodstream
- Larvae encyst in many tissues including striated muscle
Humans are dead-end host, no eggs
What are the clinical presentations of Trichinella spiralis?
- Most infections asymptomatic
- Early: GIT symptoms, nausea, vomiting, diarrhoea
- Many systems may be affected (muscular pain, facial swelling, heart damage, CNS symptoms: encephalitis, meningitis)
Pathogenesis of Toxocara
- Adult worm in dog/cat
- Eggs in faeces
- Human ingest eggs
- Larvae hatch and invade through intestine wall
Humans are dead-end host
What are the clinical presentations of Toxocara?
- Retinal disease may cause blindness (ocular larva migrans)
- Heavier infections: many organs involved (brain, lungs, liver: visceral larva migrans) -> fever, eosinophilia, hepatosplenomegaly, pneumonitis, convulsions
How to diagnose Toxocara?
Serology - ELISA
