03670nas a2200277   4500000000100000008004100001260003200042653003300074653002900107653001100136653001500147653001300162100002000175700002200195700002200217700002400239700001700263700002400280700001400304245014200318856009800460300001100558490000600569520280300575022001403378       2026                            d  c07/2026bFrontiers Media SA10aSchistosomiasis Surveillance10aMolecular Xenomonitoring10aSnails10aTrematodes10aCameroon1 aKengne Fokam AC1 aBassock Bayiha ED1 aFeudjio Soffack S1 aWoutouoba Ntieche D1 aMouatchoua B1 aMelachio Tanekou TT1 aNjiokou F00aXenomonitoring surveillance of schistosome transmission: implications for schistosomiasis elimination and zoonotic transmission awareness  uhttps://www.frontiersin.org/journals/tropical-diseases/articles/10.3389/fitd.2026.1855013/pdf  a1 - 110 v73 a<p><strong>Background</strong></p>

<p>In Cameroon, despite numerous mass screening and treatment campaigns against schistosomiasis, reinfection persists, mainly due to continued contact with infested water bodies. Consequently, the disease remains a significant threat to population health and socioeconomic development. In this study, we assessed the environmental risk of schistosomiasis transmission by screening intermediate hosts. This complementary approach helps identify active transmission sites at human–water contact points and may help interrupt parasite transmission through targeted control interventions.</p>

<p><strong>Methods</strong></p>

<p>We conducted a longitudinal study in Nkolbisson, a semi-rural area near Yaoundé, where mass drug administration campaigns have been implemented for more than a decade. Four human-water contact points were surveyed, and snails were collected and categorized by species. Infestation rates were determined using both parasitological techniques and molecular xenomonitoring with two primers. ETTS2/ETTS17 primers detected ribosomal DNA of Biomphalaria snails, Schistosoma species, and other trematodes, while SMF/R-F/SMF/R-R primers were specific to the Schistosoma mansoni 28S ribosomal region. Daily cercarial production was monitored in 34 infected Biomphalaria pfeifferi over eight days, and positive amplicons were sequenced and subjected to a nucleotide BLAST search for comparison with existing sequences.</p>

<p><strong>Results</strong></p>

<p>A total of 1,482 freshwater snails from four species were collected: Biomphalaria pfeifferi (361) , Lymnaea natalensis (465) , Physa acuta (348) , and Melanoides tuberculata (134). Five morphologically distinct cercarial types were identified. Parasitological infestation rates were 19.59% for B. pfeifferi and 7.94% for L. natalensis . Molecular xenomonitoring revealed significantly higher infestation rates for B. pfeifferi : 45.14% with ETTS primers and 23.07% with S. mansoni -specific SMF primers. Infected snails produced a mean of 3151.25± 2165 cercariae per snail over eight days, with some individuals releasing over 2500 cercariae daily. Sequencing analysis confirmed the identity of S. mansoni , showing 100% sequence similarity with reference strains.</p>

<p><strong>Conclusions</strong></p>

<p>The study identified active transmission foci where humans remain at high risk of S. mansoni infection and exposure to zoonotic trematodes despite years of mass chemotherapy. Molecular xenomonitoring proved to be more sensitive than traditional parasitological methods for detecting infected snails. It may consequently support targeted snail control strategies to complement mass drug administration for the sustainable elimination of schistosomiasis.</p>
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