Larva Migrans
Dr Y. J. Peter
Department of Medical Microbiology and Parasitology, Faculty of Basic Clinical Sciences, College of Health Sciences, University of Abuja
Learning Objectives
To understanding basic concepts of parasitology and be able to illustrate these with some important examples.
Discuss the epidemiology, life cycle, clinical presentation, management and control of some important parasitic infections.
Describe how parasitic infections affect communities and how knowledge of their life cycle is necessary for effective prevention and control.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Classification of Parasites
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Helminths
Nematodes (roundworms)
Intestinal
Blood and tissue
Cestodes (tapeworms)
Intestinal
Tissue (larval stage)
Trematodes (flukes/flatworms)
Intestinal
Liver/lung
blood
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Helminths
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Tissue Helminths
Nematodes
Trematodes
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Introduction
"Zoonotic pathogens are agents which do not confine to one host only but may cause infections in several hosts including man (with or without clinical manifestation)."(Teufel et al., 1999)
Infections of humans caused by the transmission of disease agents that naturally live in animals
WHO defines zoonoses as diseases and infections that are naturally transmitted between vertebrate animals and humans
Zoonoses, or zoonotic diseases, are caused by infectious agents that are transmissible under natural circumstances from vertebrate animals to humans.
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Tissue Nematodes
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Larva migrans
Larva migrans occurs when humans are infected with nematodes that normally parasitize animal hosts. Humans are dead-end hosts; the larvae degenerate, inducing an immune response to the dead or dying worms, and they do not become reproductively mature in humans.
Eosinophilia is a common feature, and stool exams for ova and parasites are not helpful in the diagnosis.
There are several forms of larva migrans.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Larva migrans 2
Larva migrans - is a disease caused by larva of various nematode parasites that normally live in cats and dogs.
Cutaneous larva migrans is a skin disease caused by larva of animal hookworm species, Ancylostoma braziliense.
Visceral larva migrans is cause by animal nematodes that infect man but are not capable of maturing in the host, example Toxocara canis, Toxocara cati. They may travel through the intestinal blood stream into circulation reaching the heart, liver or brain.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Cutaneous larva migrans
Cutaneous larva migrans (CLM) is characterized by an erythematous, pruritic, serpiginous skin lesion. Also called creeping eruption, CLM is acquired when bare skin (often the hands and feet) contacts the soilborne larvae of the parasite.
It is usually caused by the dog or cat hookworm Ancylostoma braziliense or Ancylostoma caninum. The larvae migrates in the epithelial layers of the skin and leave red, itchy tracts on the skin.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Cutaneous larva migrans – sole of foot
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Cutaneous larva migrans - hand
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Cutaneous Larva migrans
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Epidemiology
The larvae infect dogs or cats by burrowing through the skin. The adults live in the host’s intestine and shed eggs in the faeces, which develop into larvae in the sandy soil.
Infections are commonest in warmer climates, especially in holidaymakers who visit tropical sandy beaches. Infection is commoner in children than adults.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Life cycle
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Clinical features
Cutaneous disease—the larvae penetrate the skin of humans (an accidental host), causing tingling, itching, and vesicle formation. They then migrate through the skin, causing a characteristic raised, erythematous, pruritic, serpiginous track. In severe infections, many tracks may be seen.
Pulmonary disease—haematogenous dissemination to the lungs is rare and may present with chronic cough.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Diagnosis
The diagnosis is usually made based on clinical history (walking or lying on sand) and characteristic serpiginous rash. The main differential diagnosis is larva currens (strongyloidiasis) which migrates more quickly (1cm in 5min, compared with 1cm per hour).
Skin biopsy may show an eosinophilic inflammatory infiltrate, but the migrating parasite is rarely found.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Visceral larva migrans
Toxocariasis is caused by the dog roundworm Toxocara canis or, less commonly, the cat roundworm Toxocara cati. Clinical presentations include visceral larva migrans (VLM) and ocular toxocariasis. The lifecycle of T. canis and T. cati occur in dogs and cats, respectively.
Eggs are shed in the stool of the definitive host, and humans are infected accidentally by ingestion of eggs in faecally contaminated soil or encysted larvae in the tissues of infected hosts.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Visceral larva migrans 2
Ingestion of eggs from the dog roundworm (Toxocara canis) and raccoon roundworm (Baylisascaris procyonis) can lead to Ocular Larva Migrans (OLM) and Neural Larva Migrans (NLM).
The larvae hatch out of the eggs in the intestine and migrate throughout the circulation. Larvae lodge in various tissues, which results in the formation of granulomas around the larvae. Eosinophilic granulomas form around the larva in stomach, intestinal tissues and the other tissues that the larvae has migrated to invade.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Visceral larva migrans 3
Marine mammals (e.g, seals, dolphins, and whales) are the normal hosts of whale-worm (Anisakis).
These larvae (about 15 mm in length) are found in intermediate hosts such as cod, herring, salmon, and rockfish, which, if accidentally eaten in raw or undercooked fish dishes, can invade the gastric mucosa and intestinal muscle.
Following ingestion, the eggs hatch and penetrate the intestinal wall, larvae can also migrate to tissues outside the gastrointestinal tract e.g, liver, heart, lungs, brain, eyes, and muscles.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Epidemiology
Toxocariasis has a worldwide distribution and is commonest in tropical rural populations. The prevalence of infection is unknown, but sero-epidemiological surveys show prevalence rates ranging from 3% to 54%. Most seropositive people are asymptomatic.
Visceral larva migrans (VLM) is commoner in children, whereas Ocular larva migrans (OLM) occurs in both children and adults.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Clinical features
Most infections are asymptomatic.
VLM—presents with hepatitis and pneumonitis, as the larvae migrate through the organs. May also result in fever, anorexia, malaise, irritability, and pruritic urticarial rash. CNS manifestations include eosinophilic meningoencephalitis, space-occupying lesion, myelitis, and cerebral vasculitis.
OLM—presents with visual impairment and a whitish, elevated granuloma on eye examination. May present with uveitis, papillitis, or endophthalmitis.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Pathogenesis
Toxocara canis and Toxocari cati, which exist as roundworm infections in dogs and cats, require an external environment to become infective for people.
Children pick these larvae up in contaminated playgrounds and develop Cutaneous larva migrans (CLM), Visceral larva migrans (VLM) or Ocular larva migrans (OLM) when the larval forms move through the human body.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Symptoms
Symptoms of VLM include fever, hepatomegaly, and eosinophilia; OLM can lead to impaired vision and blindness in the affected eye. It causes extreme abdominal pain that mimics appendicitis or small bowel obstruction.
A single larva in the brain (NLM) can lead to serious motor dysfunction and blindness, and infections by the raccoon roundworm can be fatal
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Thank you for paying attention
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Any Questions
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