Toxocara canis and human health

Soil sampling shows widespread contamination of the environment, particularly parks and playgrounds, with the eggs of Toxocara canis, the dog roundworm.1,2 Human toxocariasis occurs after ingestion of infective eggs of T canis and migration of larvas, particularly to liver, lungs, muscle, and brain, It accounts for considerable preventable childhood illness and blindness and is often associated with pica and poor hygiene. Although the clinical features vary, three syndromes are recognised: toxocaral visceral larva migrans, ocular larva migrans, and covert toxocariasis. Toxocaral visceral larva migrans is characterised by fever, malaise, cough and bronchospasm, abdominal pain, and occasionally failure to thrive. Hepatosplenomegaly, lymphadenitis, and bronchopulmonary signs predominate. Severe infection may cause myocarditis or respiratory failure. Focal or generalised seizures may occur. Epilepsy is associated with positive findings on serological testing for toxocara, but pica is also commoner inpatients with epilepsy. Contradictory reports relate toxocara to long term defects in cognitive function. Visceral larva migrans is usually, but not invariably, associated with pronounced IgE hypergammaglobulinaemia, eosinophilia, and increased concentrations of blood group A and B isohaemagglutinins. The findings of antibodies to toxocaral excretory and secretory products on enzyme linked immunosorbent assay has aided diagnosis and given greater credence to studies of seroprevalence. Ocular larva migrans was described over 40 years ago after examination of 47 eyes enucleated for retinoblastoma: 23 had larval or hyaline remnants in eosinophilic …