Identification of schistosome-infected snails by detecting schistosomal antigens and DNA sequences

Abstract

Cercarial shedding tests do not provide species identification of the schistosomes concerned and cannot detect prepatent schistosomal infections. We have demonstrated that both immunodetection by ELISA of schistosomal antigens in snail hemolymph, and dot hybridization of snail extracts by a DNA probe representing highly repeated sequences, proved suitable for detecting infected snails during prepatency as well as patency. A group-specific monoclonal antibody was found to be suitable for detecting Schistosoma mansoni infection in Biomphalaria sp., but not for positive identification of S. haematobium in Bulinus sp. Comparative evaluation of the diagnostic qualities, and technical aspects and cost of these tests, point to the superiority of the immunodetection approach for large scale detection of snails prepatently infected with S. mansoni. This approach is potentially useful for providing extended information on schistosome-snail epidemiology that may facilitate rapid evaluation of the danger of post-control reinfection, and help make decisions on the time and place of supplementary control measures. In this context the potential usefulness of the immunodetection or DNA probing approach for facilitating catalytic model representation of schistosome-snail epidemiology warrants further evaluation. Specific identification of S. haematobium in Bulinus by either of these approaches may be possible depending on the development of suitable antibodies or DNA probes.

Assessing S. mansoni prevalence in Biomphalaria snails in the Gombe ecosystem of western Tanzania: the importance of DNA sequence data for clarifying species identification

“…While increased sensitivity and utility of PCR is consistent with many other studies [ 12 , 16 , 37 , 39 , 42 – 46 ], almost all have been based only on PCR-based identification, rather than sequencing. In our study, all three 500 bp amplicons sequenced from Kigoma showed amplification of a trematode other than S. mansoni (most similar to Macroderoides spiniferus, which has been reported to infect snails in Florida, with a fish final host [ 47 ]).…”

“…Diagnosis of schistosomes in their snail intermediate hosts has traditionally relied on exploiting the propensity of snails to shed cercaria when exposed to light, using microscopy identification of schistosome cercariae [ 11 ]. However, a limitation of this approach is that it can only identify patent infections [ 12 ]. It is also difficult to distinguish between other closely related trematodes infecting vertebrate hosts, such as the rodent-associated S. rodhaini , which is also in the S. mansoni group and can hybridise with S. mansoni [ 13 , 14 ].…”

“…It is also difficult to distinguish between other closely related trematodes infecting vertebrate hosts, such as the rodent-associated S. rodhaini , which is also in the S. mansoni group and can hybridise with S. mansoni [ 13 , 14 ]. Other approaches have thus been developed for diagnosing infections in humans and snails [ 1 ], with some exploiting antibodies produced by infected individuals [ 15 ] or molecular techniques targeting repeat regions of DNA [ 12 , 16 , 17 ]. Molecular-based identification using the polymerase chain reaction (PCR) can be more sensitive at detecting low levels of infection, but the relatively higher cost and inefficient use in the field means that microscopy has instead been promoted and is still preferable under some situations [ 18 ].…”

Distribution of Biomphalaria Snails in Associated Vegetations and Schistosome Infection Prevalence Along the Shores of Lake Victoria in Mbita, Kenya: A Cross-Sectional Study

“…9 Although classical detection is routinely used in the laboratories for identification of human schistosome-infected vector snails, few snails are always found shedding human cercariae and it is worth noting that molecular techniques could be the most accurate method in determining positive Biomphalaria host snails both in their prepatent and patent stages of infection. [22][23][24] In determining the abundance of snails based on the vegetation types, the results revealed that there were higher number of snails in the C. gracilis relative to E. crassipes and E.fluactuants. This finding implies snails' preference to C. gracilis.…”

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“…A combination of direct search in random sampling (Nekola, 2003;Gittenberger et al, 2013) and leaf litter-sieving method in non-random subplots were used. The minimum distance between the sample plots were maintained at 100 m (Hamburger et al, 1992). The quadrats (20 x 20 m) were established at every 100 m distance and 44 sample plots were selected using GIS fishnet plot generation method (Nekola, 2003).…”