Toxocariasis

Toxocariasis occurs following the ingestion of embryonated eggs in infected dog (Toxocara canis) or cat (Toxocara cati) faeces. Occasionally infection may occur from ingestion of encysted larvae in paratenic hosts.

Infections are often asymptomatic except for eosinophilia but occassionaly result in Visceral Larva Migrans with concurrent symptoms (fever, anorexia, weight loss, cough, wheezing, rashes, hepatosplenomegaly) and Ocular Larva Migrans to produce various ophthalmologic lesions.

Diagnosis of Toxocariasis by microscopy

• Sample type: Standard stool samples.

Stool samples may be examined for putative intestinal infections.

Diagnosis of Toxocariasis by serology

• Sample type: A minimum of 0.5ml of serum is required.

Serology is the method of choice for the diagnosis of toxocariasis. The ELISA is usually performed on serum, but can be undertaken on aqueous humour, vitreous humour or CSF under the guidance of the Consultant Parasitologist.

Please contact the serology section if you intend to send any non-serum samples.

The Toxocara IgG antibody ELISA test against larval excretory/secretory antigen is the most appropriate method for diagnosis. Sensitivity is 91% and specificity is 86% (with cross reactivity possible with strongyloidiasis, trichinosis, amoebiasis and fascioliasis). Results are expressed as an optical density value.

Positive ELISA tests will be confirmed using a Western blot. Sera that are high negative by ELISA will also have a Western blot performed. All CSFs requiring analysis for Toxocara antibody will have a Western blot performed, as the ELISA is not validated for this sample type.

Negative Toxocara serology on serum does NOT exclude ocular toxocariasis. Vitreous sampling may be necessary to confirm or exclude ocular toxocariasis. Please contact the Consultant Parasitologist for queries about ocular toxocariasis.