Modified Tuberculosis Stain Reveals Worm Eggs

Eggs of the parasitic lung fluke, that causes paragonimiasis, can be found in sputum and can be stained with the classical reagents for acid – fast bacilli, and with some alterations, ZNS is very effective for diagnostic purposes.

An international team working with a nongovernmental organization in Laos, (Service Fraternel d'Entraide; Vientiane, Lao People's Democratic Republic), examined a paragonimiasis index case's sputum with wet film direct examination (WF) and ZNS. They also reexamined stored ZNS slides from two provinces and compared prospectively WF, ZNS, and formalin-ether concentration technique (FECT) for sputum examination of patients with chronic cough, from September 2009 until April 2010. Finally, they compared the three techniques and assessed excess direct costs associated with the use of different diagnostic methods.

Paragonimus eggs were clearly visible in WF and ZNS sputum samples of the index case. They appeared brownish-reddish in ZNS and were detected in six of 263 archived ZNS slides corresponding to five patients. One hundred sputum samples from 43 patients were examined with three techniques, which revealed that six patients had paragonimiasis, from 13 positive samples. Sensitivity per slide of the FECT was 84.6%; for ZNS it was 76.9%; and for the WF technique, it was 61.5%. Briefly heated ZNS slides contained more eggs than slides heated for five minutes, 42 eggs per slide (eps) versus 29 eps. Bloodstained sputum portions contained more eggs than unstained parts.

The authors concluded that Paragonimus eggs could easily be detected in today's widely used ZNS of sputum slides. The ZNS technique appears superior to the standard WF sputum examination for paragonimiasis and eliminates the risk of tuberculosis transmission. Additional operational costs per slide were zero for ZNS, US$0.10 for WF, and $0.79 for FECT. The authors recommend that in addition to ZNS use for the diagnosis of TB, routine examination for Paragonimus eggs of each slide with the ×10 lens, total magnification ×100, in geographic areas where paragonimiasis may be endemic.

Paragonimiasis is a food-borne parasitic infection caused by the lung fluke, most commonly Paragonimus westermani. It infects an estimated 22 million people worldwide and Paragonimus species are distributed throughout the Americas, Africa, and Southeast Asia. P. westermani is distributed in Southeast Asia and Japan and P. kellicotti is endemic to North America. The study was published online on May 17, 2011, in the journal Public Library of Science Neglected Tropical Diseases.

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