Schistosoma mansoni, S. japonicum: Characterization of Host Attraction and Attachment, With Evaluation of a Novel Environmental Surveillance Device

Abstract

The goal of this study was to develop a passive, low-cost, low-technological, rapid surveillance method for detecting schistosome cercariae in schistosomiasis endemic regions, compared to other available methods. Schistosomiasis is a parasitic disease that is linked to abdominal pain, enlarged liver, and multiple organ failure, yet it is highly preventable as individuals are infected through dermal contact with contaminated waters. In areas where transmission mitigation efforts have been successful, a combination of control initiatives were employed, such as mass drug treatment, hygiene improvement, and monitoring of transmission foci. The environmental detection methods currently in use are labor- and time- intensive or cost-prohibitive in rural developing areas with high transmission rates and very limited resources. Three aims were formulated in order to develop and evaluate the device. The first aim was to examine the chemotactic response of Schistosoma mansoni and S. japonicum cercariae to media containing oleic acid (OA) and explore how cercarial age plays a role in that response. The second aim was to apply the findings from the first aim to the development of an environmental surveillance device for schistosome cercariae (ESDSC) and to laboratory optimize the device to maximize cercarial capture. After examining the performance of the device, the third aim was to compare the ESDSC to other environmental surveillance methods that are currently available for the detection of schistosome cercariae through a review of the literature. While both S. mansoni and S. japonicum cercariae exhibited highest attachment to media when freshly shed, they preferentially attached to different media types: S. mansoni to beeswax with 0.3 g/mL OA and S. japonicum to plain beeswax. An ESDSC was designed from inexpensive, easily sourced materials (acrylic and aluminum sheets) and a S. mansoni-specific ESDSC was laboratory tested by utilizing beeswax with 0.3 g/mL of OA to attract cercariae. The cercarial capture capability of the ESDSC was tested in different orientations, depths, distances (from origin of cercariae), and with or without the application of a heat source. The highest median cercarial capture rate of 3.3% was observed with the device in a horizontal orientation, submerged, and within 25 cm of the cercarial point of origin. There were no instances in which the ESDSC failed to capture any cercariae, even at a distance of 70 cm. Through a review of the literature, the ESDSC was compared to other environmental surveillance methods based on five attributes: time and labor, technical training, cost, infrastructure and capital investment, and sensitivity. Compared to the other surveillance methods, the ESDSC requires minimal time and labor, technical training, cost and resources; however, it exhibits only a moderate level of sensitivity. The value of the device will have greatest realization in endemic regions where health and economic resources are limited. What may work in one endemic region may not work best in another when factors such as availability of infrastructure, resources, and skilled technicians are considered. The ESDSC has the potential to function as a preliminary screening to detect contaminated sites so that complex and costly surveillance methods can be targeted more efficiently.