Paragonimus westermani - Laboratory Diagnosis, Treatment, Prevention, Control

Laboratory diagnosis of Paragonimus westermani

The laboratory diagnosis of Paragonimus westermani includes:

Specimen

• Sputum

• Feces

* eggs are detected in samples 2 to 3 months after infection.

Microscopy

Diagnosis of pulmonary paragonimiasis is based on a demonstration of operculated Paragonimus westermani eggs in the sputum of feces.

Sputum Microscopy

• sputum (not saliva) should be collected in the morning and immediately examined

• if sputum is highly muscoid or viscous, it is treated with an equal volume of 3% sodium hydroxide (NaOH)

• saline or iodine wet-mount microscopy is usually done – first under low power and then under high power

• the concentration of sputum can be done by the formalin-ether sedimentation method

• demonstration of golden-brown operculated eggs confirms pulmonary infection by Paragonimus westermani

• since sensitivity is 25% to 30%, repeated samples should be examined – upto 7 samples must be collected at different intervals during 15 day period

Stool Microscopy

• usually important in children as they have the habitat of swallowing the sputum

• at least 3 stool samples must be examined for Paragonimus westermani eggs during 7 days period

Immunodiagnosis

Detection of antibodies

Since Paragonimus westermani induces immune response i.e. presence of circulating antibodies, serological methods can be used for laboratory diagnosis. Crude extract of adult Paragonimus westermani retrieved from laboratory cats is used as antigen in these assays.

Serological tests used to detect serum antibodies include

• Complement fixation test

  * has prognostic value as this test does not detect antibodies after specific therapy

• Indirect haemagglutination

• Counter-current immunoelectrophoresis

• Latex agglutination

• Western Blot (sensitivity- 96%, specificity- 99%)

These tests may show false positive/ cross-reactivity with Fasciola hepatica but do not detect antibodies to other Paragonimus species.

Disadvantages of serological tests

A major disadvantage of serological methods is that antibody levels against Paragonimus westermani remain high even up to 2 or more years after successful treatment.

Advantages of serological tests

The advantages of Serodiagnostic methods:

• diagnosis during the pre-patent period during which eggs have not yet been released in stool or sputum

• in cases of extra-pulmonary paragonimiasis as eggs are not found in the stool or sputum

Skin Test

The intradermal skin test for Paragonimus westermani infection is a simple and reliable test:

Procedure

• saline extract of the parasite i.e. antigen diluted at 1:2000 is intradermally injected (0.1ml) in one arm

• an equal volume of normal saline is injected intradermally on the other arm as a control

• development of a large wheel, pseudopodium, or erythema after 15 minutes to 30 minutes indicates infection

Even after successful treatment, this test may be positive from 1 year to 20 years. Thus, it is used for epidemiological studies rather than diagnostic methods.

Imaging Methods

The imaging methods are most useful to differentiate between paragonimiasis and tuberculosis. Some tests used for Paragonimus westermani diagnosis include:

X-ray: for pulmonary paragonimiasis

CT- scan: for cerebral paragonimiasis

MRI: for cerebral paragonimiasis

Treatment of Paragonimus westermani

Drugs of choice for the treatment of Paragonimus westermani infection are Praziquantel, Bithionol, and Niclofolan.

Prevention, Control of Paragonimus westermani

The control and prevention of Paragonimus westermani can be obtained by following steps:

• avoid consumption of raw/undercooked meat, crayfish, crabs

• proper filtration and/or boiling of drinking water

• immediate treatment of infections in pigs, cattle, and people

• use of molluscicides to control snails

• reduce contamination of water sources by infected animals, and human feces as well as sputum