NEMATODE (“roundwords”) INFECTIONS (Micro made easy 248)

Trichinella spiralis:

• This organisms is ingested in uncooked pork, and it travels to small intestine. There it matures and the males are passed in faeces, while females penetrate the mucosa to enter bloodstream to settle in other organs + skeletal muscle.
• Clinical features: diarrhoea, toxaemia, myositis, eosinophilia.
• Diagnosis: muscle biopsy + serology.

Ascaris lumbricoides:

• This organism is ingested as eggs, travels to SI, and enters mucosal bloodstream to migrate to lungs. Here it is coughed up and re-renters the SI to mature and produce eggs ≫ which are excreted in faeces.
• Clinical features: abdominal pain + obstruction of bile duct, appendix, or SI by worms. Pulmonary symptoms: cough, sputum etc.
• Diagnosis: stool sample containing eggs.

Strongyloides stercoralis:

• This organism penetrates the skin as larvae form from infected soil and proceeds to the lung ≫ matures and is coughed up ≫enters the SI. Three pathways from here: 1) autoinfection ≫ penetrates SI and proceeds to lung, 2) direct cycle: passes in faeces to infect others, 3) indirect cycle: passes in faeces to sexually reproduce, offspring infect others.
• Clinical features: diarrhoea, vomiting, anaemia.
  
• Diagnosis: 1) stool sample containing larvae.

Hookworm:

• Exactly the same life cycle as the Strongyloids except there is no three pathways.
• Clinical features: diarrhoea, abdominal pain, anaemia (as hookworm sucks blood by attaching to intestine).
• Diagnosis: stool sample contains eggs.

Trichuris:

• Eggs found in contaminated food, it travels to intestines where they hatch and produce eggs. These are passed in faeces, and the cycle starts again.
• Clinical features: abdominal pain + bloody diarrhoea, anaemia.
• Diagnosis: stool sample contains eggs.

Enterobius vermicularis:

• Eggs are ingested and travel to large intestine where they hatch. They then travel to perianal area to lay eggs. This causes severe itching.
• Clinical features: abdominal pain, perianal itch.
• Diagnosis: Anal tapes which get sample of eggs, viewed under microscope.

Treatment for nematodes: A simple way of remembering treatment for nematodes is to say to yourself, worms BEND. Therefore treatment should be: alBENDazole, thiabendazole, MeBENDazole.

Category: Microbiology Notes