Larva Migrans, Trichinellosis and Tissue Nematodes
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Direct answer
Larva migrans and trichinellosis are tissue nematode infections in which larvae cause damage while migrating or encysting in human tissues. Visceral and ocular larva migrans are caused by Toxocara species from dogs and cats, while trichinellosis follows eating undercooked meat containing Trichinella larvae. Marked eosinophilia is a common feature, and serology or muscle biopsy supports the diagnosis.
What you must remember
- Visceral larva migrans: Toxocara canis or Toxocara cati larvae migrate without maturing, causing fever, hepatomegaly, pneumonitis and eosinophilia.
- Ocular larva migrans: a solitary posterior pole retinal granuloma, typically unilateral, in young children with pica or geophagia.
- Cutaneous larva migrans: Ancylostoma braziliense produces a serpiginous, creeping eruption after barefoot contact with contaminated sand.
- Trichinella spiralis: acquired from undercooked pork or game meat; larvae encyst as nurse cells within striated muscle fibres.
- Phases of trichinellosis: enteric symptoms first, then myalgia, periorbital oedema and fever in the muscle phase.
- Laboratory clues: marked eosinophilia is typical, and creatine kinase is often raised in trichinellosis.
- Löffler syndrome: transient pulmonary eosinophilia from Ascaris larvae passing through the lungs.
- Strongyloides stercoralis: autoinfection can lead to hyperinfection with corticosteroids, and ivermectin is the drug of choice.
Matching syndrome, parasite and treatment
A 6-year-old child with pica has a unilateral white posterior pole lesion and a raised eosinophil count, while a traveller returns with a serpiginous rash after walking on a beach. The table pairs each syndrome with its parasite, key clue and standard treatment.
| Syndrome | Parasite | Key clue | Treatment |
|---|---|---|---|
| Visceral larva migrans | Toxocara canis, T. cati | Eosinophilia, hepatomegaly, serology | Albendazole |
| Ocular larva migrans | Toxocara species | Posterior pole granuloma, unilateral | Laser or steroids for the lesion |
| Cutaneous larva migrans | Ancylostoma braziliense | Creeping track on the skin | Ivermectin or albendazole |
| Trichinellosis | Trichinella spiralis | Myalgia, periorbital oedema, eosinophilia | Albendazole or mebendazole with steroids |
Eosinophilia unites most tissue nematode infections and should prompt a focused exposure history. Clinicians should ask about pets, pork intake and beach or soil contact, because the history often points to the diagnosis before serology returns. Stool examination is often negative in trichinellosis because the larvae are in muscle, so the diagnosis rests on serology or biopsy.
Where the exam tries to catch you
Questions on this topic usually test whether the candidate can link the route of infection, the organ involved and the correct test.
- Trap: trichinellosis is diagnosed by stool examination. Correct: the larvae lie in muscle, so stool is usually negative and the diagnosis rests on eosinophilia, creatine kinase, serology or muscle biopsy.
- Trap: cutaneous larva migrans involves the internal organs. Correct: it stays in the skin and produces a serpiginous track after contact with contaminated sand.
- Trap: ocular larva migrans is bilateral. Correct: it is typically unilateral and presents as a posterior pole granuloma in a child with pica.
- Trap: Löffler syndrome is caused by Strongyloides. Correct: pulmonary eosinophilia classically results from Ascaris larvae passing through the lungs.
Frequently asked questions
What is the usual cause of ocular larva migrans?
Ocular larva migrans is usually caused by Toxocara larvae, which produce a granuloma at the posterior pole of the retina. It typically affects one eye in young children with pica or geophagia. Toxocara serology supports the diagnosis when no other cause is found.
What is the characteristic muscle involvement in trichinellosis?
Trichinellosis causes myositis, with pain and tenderness in muscles such as the gastrocnemius and masseter. Larvae encyst within striated muscle fibres, forming nurse cells. Raised creatine kinase and marked eosinophilia accompany the muscle phase of the disease.
Which tissue nematode causes Löffler syndrome?
Ascaris lumbricoides causes Löffler syndrome during larval migration through the lungs. It produces transient pulmonary infiltrates with eosinophilia and cough. The condition is self-limiting and is treated with an anthelmintic such as albendazole.
Why is Strongyloides stercoralis dangerous in patients on corticosteroids?
Strongyloides stercoralis can cause hyperinfection in patients on corticosteroids, because steroids suppress the immune control that normally limits its autoinfection cycle. Larvae then disseminate to the gut, lungs and other organs. Ivermectin is the drug of choice, and patients planned for steroid therapy should be screened first.