Helmintex test highly sensitive to intestinal schistosomiasis eggs

Last Updated: 2018-03-12

By Will Boggs MD

NEW YORK (Reuters Health) - The Helmintex test can detect egg burdens below one per gram in patients with intestinal schistosomiasis, according to new study from Brazil.

"Helmintex is now the best method for cure control, at the individual clinical level, especially in non-endemic countries," Dr. Carlos Graeff-Teixeira from Pontificia Universidade Catolica do Rio Grande do Sul, in Porto Alegre, told Reuters Health by email.

"But its main current role is as a reference method in comparative evaluation of point-of-care antigen detection tests and serology," said Dr. Graeff-Teixeira, who holds a patent for the test.

The World Health Organization recommends the Kato-Katz (KK) fecal smear method for identifying schistosomiasis eggs in feces, but it lacks accuracy where part of a population has been previously treated and low egg burden is present in stool.

The Helmintex method is based on interactions between Schistosoma mansoni eggs and superparamagnetic particles in a magnetic field. This method has demonstrated 100% sensitivity for egg burdens higher than 1.3 per gram in seeding experiments.

Dr. Graeff-Teixeira and colleagues compared the performances of KK, Helmintex and the point-of-care immunodiagnostic for detecting schistosome cathodic antigen in urine (POC-CCA), which has been proposed as a substitute for the KK method, in 580 individuals living in an area of low-intensity transmission in northeastern Brazil.

More stool samples were positive for S. mansoni eggs according to the Helmintex method (40.6%) than according to the KK method (11.9%), the researchers report in PLoS Neglected Tropical Diseases, online March 8.

The POC-CCA method yielded positive results in 71.6% of samples when trace results were considered positive and in 40.6% of samples when trace results were considered negative.

Most of the egg burdens of the individuals tested (70%) were less than one egg per gram.

The KK and Helmintex methods agreed in 11.7% of positive samples and 59.2% of negative samples, whereas only the Helmintex method was positive in 28.9% of samples.

Sensitivity, specificity and overall accuracy for detecting S. mansoni were highest for the Helmintex method (all 100%). For KK, they were 29.3%, 100.0% and 71.1%, respectively; for POC-CCA, when trace results were considered negative, they were 57.4%, 71.1% and 65.5%; and for POC-CCA, when trace results were considered positive, they were 81.9%, 35.5%, and 54.4%.

Compared with the other approaches, the Helmintex method is more labor-intensive and expensive and, therefore, not feasible as a routine field diagnostic, the researchers note.

"Our findings demonstrate that no single diagnostic method meets the 'ideal' set of properties for universal application," Dr. Graeff-Teixeira said. "Other very interesting improvements are underway with Helmintex that may simplify its current labor-intensive procedure and increase its sensitivity even further."

Dr. Nilanjan Lodh from Marquette University, in Milwaukee, Wisconsin, who has researched different methods of diagnosing schistosomiasis, told Reuters Health by email, "The new approach for detecting S. mansoni egg is sensitive and innovative and might work well in high-endemic areas, if the cost goes down and it becomes easy to operate."

"KK is less sensitive, particularly for low endemic regions, and people from these areas can serve as potential reservoirs, as most of them will be declared as not infected and they might be asymptomatic," said Dr. Lodh, who was not involved in the new study. "Also, if you do not see eggs, it does not mean the person is not infected; this has been proved many times."

"The most interesting finding is that CCA is producing false positives and has less sensitivity in low endemic settings," Dr. Lodh added. "We actually showed that for the first time comparing against molecular techniques in our paper in 2013."

SOURCE: http://bit.ly/2DkL0EL

PLoS Negl Trop Dis 2018.