Abstract
Schistosomiasis is a parasitic disease affecting over 250 million people in the tropics. In non-endemic regions, imported Schistosoma infections are commonly diagnosed by serology, but based on antibody detection an active infection cannot be distinguished from a cured infection and it may take more than 8 weeks after exposure before seroconversion occurs. In endemic populations, excellent results have been described in diagnosing low-grade active Schistosoma infections by the detection of the adult worm-derived circulating anodic antigen (CAA) utilising robust lateral flow (LF) assays combined with up-converting phosphor (UCP) reporter technology. The purpose of this study is to explore the diagnostic value of the UCP-LF CAA assay in a non-endemic setting. CAA concentrations were determined in 111 serum samples originating from 81 serology-positive individuals. In nine individuals, serum could be collected before travel and an additional five provided samples before and after seroconversion occurred. Based on detectable CAA levels, an active infection was seen in 56/81 (69%) of the exposed individuals, while the 10 controls and the 9 sera collected before travel were tested negative for CAA. Positive CAA levels were observed starting 4 weeks after exposure and in four cases CAA was detected even before Schistosoma-specific antibodies became positive. Higher serum CAA levels were seen in migrants than in travellers and CAA concentrations dropped sharply when testing follow-up samples after treatment. This explorative study indicates the UCP-LF CAA serum assay to be a highly accurate test for detecting active low-grade Schistosoma infections in a non-endemic routine diagnostic setting.
Highlights
Schistosomiasis is an infectious tropical disease caused by trematode blood flukes of the genus Schistosoma, affecting around 258 million people worldwide [1]
Schistosoma-specific IgM antibodies directed against adult worm gut antigens were detected in an immunofluorescence assay (IFA) using sections of Rossmann’s fixed adult male S. mansoni worms, while IgG antibodies to Schistosoma-soluble egg antigens were detected in an enzyme-linked immunosorbent assay (ELISA) [5, 12]
We further explored the ultra-sensitive up-converting phosphor (UCP)-lateral flow (LF) assay for the detection of Schistosoma circulating antigen circulating anodic antigen (CAA) in serum of travellers and migrants, a patient group known to harbour mostly low worm burdens
Summary
Schistosomiasis is an infectious tropical disease caused by trematode blood flukes of the genus Schistosoma, affecting around 258 million people worldwide [1]. The classic method of detecting an infection with Schistosoma is microscopic examination of urine or faeces in the search for parasite eggs [3, 4]. When the worm burden is low, as mostly seen in imported infections, this procedure generally lacks sensitivity [3,4,5,6]. The detection of specific antibodies against Schistosoma antigens is the most commonly applied alternative diagnostic approach in non-endemic routine diagnostic laboratories, especially for travellers who have been exposed for the first time [3, 5]. Antibody tests have good sensitivity with seroconversion mostly occurring 4 to 8 weeks after exposure, some cases of late antibody detection have been described [5, 7, 8]. The major disadvantage of serology is that it does not
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