Echinococcus granulosus - Laboratory Diagnosis, Treatment, Prevention, Control

Laboratory diagnosis of Echinococcus granulosus

The laboratory diagnosis of Echinococcus granulosus begins with collection of samples:

Sample

• urine

• sputum

• hydatid fluid aspiration

Aspiration of Echinococcus granulosus hydatid fluid from an intact cyst in the lung has been attempted for diagnosis but this is not recommended because of the possibility of anaphylactic reactions if fluid leaks and the risk of secondary echinococcosis due to spillage of protoscolices from the viable cysts.

Microscopy

Microscopy of Echinococcus granulosus depends on the demonstration of brood capsules and protoscolices in hydatid fluid aspiration.

Direct Wet Mount Examination

• the direct wet mount is prepared by mixing saline, and sometimes iodine or lactophenol cotton blue (LPCB) can be used

• centrifuged hydatid fluid deposit may reveal protoscolices as colorless white structures

• if lactophenol cotton blue (LPCB) is used for wet mount preparation, the protoscolices and scolices appear deep blue which helps in easy detection and identification

Acid Fast staining

• smears from centrifuged Echinococcus granulosus hydatid fluid deposit after acid-fast staining reveals purple or pink colored protoscolices and scolices

Casonis’ skin test

Casonis’ skin test is an immunodiagnostic test based on an immediate hypersensitivity skin test. It is used in the diagnosis of cystic echinococcosis caused by Echinococcus granulosus.

However, due to low sensitivity (55%-75%) and low specificity, false positive reactions may occur in patients suffering from other cestode infections- limiting the value of this test

The procedure for the test:

• inject 0.2ml of sterile hydatid fluid intradermally in one arm

  * hydatid fluid is obtained from cysts in humans during surgery, from sheep during an autopsy, and sterilized by filtration

• inject 0.2ml of sterile normal saline intradermally in another arm as a control

• if a large wheal measuring 5cm or more in diameter with multiple pseudopodia is seen, it indicates a positive reaction

Serological test

Serological tests are used for the primary diagnosis of cystic echinococcosis (CE) due to Echinococcus granulosus infection. This test is based on the detection of specific hydatid antibodies present in the serum as well as hydatid antigens in the serum, urine, or other body fluids.

Detection of antibodies

Echinococcus granulosus antibodies, if developed in the host body, can be detected by the following methods:

• Indirect haemagglutination (IHA)

• immunoelectrophoresis-in-gel, counter-current immunoelectrophoresis (CIEP)

• enzyme-linked immunosorbent assay (ELISA)

• Western Blot

The antibody-based immunoassay tests have several disadvantages including

• low sensitivity results in false negative as antibodies are not produced in 10% of cases and in 40% of cases where lungs and liver are involved while cysts in the brain produce no antibodies

• low specificity as Captons’ arc 5 antigen shows cross-reactivity with sera from alveolar echinococcosis and neurocysticercosis

• these tests cannot differentiate between old or recent infections as hydatid-specific antibodies remain in circulation for a longer time

Detection of antigen

Echinococcus granulosus antigen can be detected by the following methods:

• bacterial Co-agglutination (Co-A) – in urine samples

• immunoelectrophoresis-in-gel, counter-current immunoelectrophoresis (CIEP) – in urine samples

• enzyme-linked immunosorbent assay (ELISA)

• Latex agglutination test (LAT)

A major advantage of antigen detection methods is that can differentiate between old or recent infections as hydatid antigens disappear immediately after cure by surgery or chemotherapy.

Imaging methods

Echinococcus granulosus can also be diagnosed by imaging methods such as:

• X-ray

• Ultrasound

• CT scan

• MRI

Other tests

• Other tests includes histopathological tests (Periodic acid-Schiff stain i.e. PAS stain, Fine-needle aspiration cytology i.e. FNAC)

Treatment of Echinococcus granulosus

The treatment of Echinococcus granulosus takes place by the following methods:

Surgery

• surgery remains the main course of treatment for cystic echinococcosis (CE)

• done if the site of infection is operatable – lungs, liver

• performed if enlarged cysts are likely to interfere with viral organ functions

• however, surgery is associated with morbidity, mortality (2%), and recurrence rate (2%-25%)

Chemotherapy

This chemotherapy process is followed if the Echinococcus granulosus cyst is small in size or situated in in-operable areas. Drugs of choice include albendazole and mebendazole.

Prevention, and Control of Echinococcus granulosus

To prevent and control Echinococcus granulosus infection, the following steps can be taken:

• regular treatment of reservoir i.e. dogs

• prevent dogs from eating raw offal of domestic animals- especially in slaughterhouses

• good personal hygiene – washing hands after feeding or petting/touching the dog

• proper disposal of dog feces

• eating well-cooked food, vegetables or proper washing of fruits before consumption

• drinking safe boiled water – especially in endemic areas