Hydatid disease (Echinococcosis)

Hydatid disease or echinococcosis is caused by infection with the cestodes (tapeworms) Echinococcus granulosus (cystic enchinococcosis) and less commonly Echinococcus multilocularis (alveolar enchinococcosis).

Humans are infected via ingestion of embryonated eggs passed by the definitive host (dog or related carnivores). Oncospheres (invasive form) hatch in the gastrointestinal tract and migrate to tissue where large cysts form (most commonly affected organs are the liver or lungs).

Infection is often asymptomatic and may be unrecognised for many years. Symptoms relate to direct mechanical pressure from the cysts or if the cyst leaks or ruptures, causing an anaphylactic reaction.

Echinococcosis should be considered in patients with a compatible exposure history and evidence of one or more cystic lesions with an organ (particularly the liver). Suspected cases should be discussed with the Parasitology consultant or registrar. Diagnosis requires a combination of serology, radiology and sampling
of lesions.

Detection of hydatid disease by microscopy (Echinococcus granulosus)

• Sample type: Aspriated cyst fluid, whole liver section, excised cyst or other fluids following putative cyst rupture (eg pleural fluid).

Aspiration of a cyst should be considered only after taking expert advice and, if felt to be indicated, should be conducted in a centre experienced in the management of hydatid disease. If viability testing is required the aspirate should be kept at room temperature and reach us with 24 hours.

Echinococcus multilocularis usually presents as suspected malignancy is diagnosed by a combination of imaging, serology and biopsy.

Detection of hydatid disease by serology (Echinococcus granulosus and multilocularis)

• Sample type: A minimum of 0.5ml of serum is required (CSF testing is available, please provide as much CSF as possible, along with a paired serum sample).

Serology is performed in two steps. An initial ELISA for Echinococcus spp. is performed. Serological cross- reactions, giving rise to false positives, can occur with sera from patients with other parasitic infections, notably larval cestodes and filarial worms, and with some neoplasms. False negatives may occur and are more common in the case of non-hepatic hydatid cysts.

A Western blot may also be performed to confirm the ELISA and to differentiate cystic from alveolar hydatid (if not possible based on radiological findings).

For watchful waiting of confirmed cases of Echinococcus granulosus or to determine patient response to surgical intervention and/or drug treatment an IgG2 subclass ELISA is available. Please contact medical staff for advice on this service.