The substructure of three repetitive DNA regions of Schistosoma haematobium group species as a potential marker for species recognition and interbreeding detection

Abstract

Background Schistosoma haematobium is the causative agent of human urogenital schistosomiasis affecting ~112 million people in Africa and the Middle East. The parasite is transmitted by snails of the genus Bulinus, which also transmit other closely related human and animal schistosomes. The accurate discrimination of S. haematobium from species infecting animals will aid effective control and elimination programs. Previously we have shown the utility of different repetitive nuclear DNA sequences (DraI, sh73bp, and sh77bp) for the identification of S. haematobium-group species and inter-repeat sequences for discriminating S. haematobium from S. bovis.ResultsIn this current study we clarify the structural arrangement and association between the three repetitive sequences (DraI, sh73bp, and sh77bp) in both S. haematobium and S. bovis, with a unique repeat linker being found in S. haematobium (Sh64bp repeat linker) and in S. bovis (Sb30bp repeat linker). Sequence data showed that the 3′-end of the repeat linker was connected to the DraI repetitive sequence array, and at the 5′-end of the repeat linker sh73bp and sh77bp were arranged in an alternating manner. Species-specific oligonucleotides were designed targeting the species-specific repeat linkers and used in a reverse line blot (RLB) hybridization assay enabling differentiation between S. haematobium and S. bovis. The assay was used to discriminate natural infections in wild caught Bulinus globosus.ConclusionThis research enabled the characterisation of species-specific DNA regions that enabled the design of species-specific oligonucleotides that can be used to rapidly differentiate between S. haematobium and S. bovis and also have the potential to aid the detection of natural hybridization between these two species.

Occurrence ofSchistosoma bovison Pemba Island, Zanzibar: implications for urogenital schistosomiasis transmission monitoring

“…As we move towards or reach elimination, there becomes a need for more sensitive methods to monitor the levels of transmission when egg–patent human infections become scarce ( Le and Hsieh, 2017 ; Stothard et al ., 2017 ), the risk of infection and also a way to prove transmission interruption when it is finally reached. Xenomonitoring is a nucleic acid-based molecular diagnostic used to monitor the transmission of several vector-borne diseases ( Cunningham et al ., 2016 ; Minetti et al ., 2016 ; Cook et al ., 2017 ), including to some extent schistosomiasis where tools are being developed for the xenomonitoring of snails that could support schistosomiasis transmission and elimination monitoring ( Hamburger et al ., 2004 ; Allan et al ., 2013 ; Lu et al ., 2016 ; Abbasi et al ., 2017 ). The first stage for snail xenomonitoring for schistosomiasis is the identification of patent schistosome infections within the snails and collecting cercariae shed from them.…”

Development of a Molecular Snail Xenomonitoring Assay to Detect Schistosoma haematobium and Schistosoma bovis Infections in their Bulinus Snail Hosts

“…However, several assays have been developed for detecting trematode species in freshwater snails, including Fasciola spp. [22,[37][38][39][40][41][42][43][44], other wildlife trematode species [45], and medically important schistosome species-S. japonicum [46,47], S. mansoni [24,27,28,[48][49][50][51][52][53][54], and S. haematobium [23,26,27,30,52,54,55]. The first developed assay for the molecular detection of S. haematobium DNA in Bulinus employs the highly repetitive Dra1 target, and this has been the marker of choice for studies investigating S. haematobium infections in snails due to its high sensitivity [55].…”

“…Screening snails provides evidence on the extent of environmental contamination (i.e., schistosome miracidia penetrating snails), as well as environmental infection risk (i.e., schistosome sporocysts and cercariae developing inside the (pre-patent) snails, eventually emerging from the (patent) snail. Most of the available snail-schistosome xenomonitoring assays do not include internal controls [23,28,30], an important feature in any diagnostic tool that helps prevent false-negative results [27]. Many assays will assume that a negative result means non-infection, not necessarily reaction failure.…”

Molecular Tools and Schistosomiasis Transmission Elimination

“…Differentiation between snails infected by human schistosomes and those infected by animal schistosomes is also possible by molecular tools. 33,34 PCR, the molecular tool preceding LAMP, 35,36 was usually rejected for field studies, as it depended on high and expensive technology and on molecular biology know-how.…”