Urogenital schistosomiasis and soiltransmitted helminthiasis(STH)in Cameroon:An epidemiological update at Barombi Mbo and Barombi Kotto crater lakes assessing prospects for intensified control interventions

Background:The crater lakes of Barombi Mbo and Barombi Kotto are well-known transmission foci of schistosomiasis and soil-transmitted helminthiasis having had several important control initiatives previously.To collect contemporary epidemiological information,a cross-sectional survey was undertaken inclusive of:signs and symptoms of disease,individual treatment histories,local water,sanitation and hygiene(WASH)-related factors and malacological surveillance,with molecular characterisation of specimens.Methods:At each lake,a community cross-sectional survey was undertaken using a combination of stool and urine parasitological sampling,and interview with pro-forma questionnaires.A total of 338 children and adults participated.Material from snail and parasite species were characterised by DNA methods.Results:Egg-patent prevalence of urogenital schistosomiasis was 8.7%at Barombi Mbo(all light-intensity infections)and 40.1%at Barombi Kotto(21.2%heavy-intensity infections).Intestinal schistosomiasis was absent.At Barombi Kotto,significantly more women reported signs and symptoms associated with female genital schistosomiasis.While there had been extensive recent improvement in WASH-related infrastructure at Barombi Mbo,water contact risk scores were higher among schistosomiasis-infected participants(P<0.001)and at Barombi Kotto in general(P<0.001).Across both lakes,mean prevalence of STH was very low(6.3%)evidencing an impressive decrease of 79.0%over the last decade;neither Strongyloides stercoralis nor Ascaris lumbricoides were found.A total of 29 freshwater sampling sites were inspected for snails,13 in Barombi Mbo and 16 in Barombi Kotto;water chemistry differed significantly(P<0.0001)between lakes for both mean pH(7.9 v.9.6)and mean conductivity(64.3μS v.202.1μS)respectively.Only two Bulinus camerunensis found on the central island of Barombi Kotto were observed to shed schistosome cercariae,but schistosome DNA was later detected in Bulinus sampled from both lakes as well as in Indoplanorbis exustus,an invasive species from Asia.Conclusions:STH is currently at very low levels while urogenital schistosomiasis is of greatest concern at Barombi Kotto.This assessment highlights a unique opportunity for further study of the epidemiological dynamics at these crater lakes,to evaluate future intensified interventions both in terms of gaining and sustaining control at Barombi Kotto or in moving towards local interruption of transmission of both diseases at Barombi Mbo.

Intestinal schistosomiasis in Uganda at high altitude(>1400 m):malacological and epidemiological surveys on Mount Elgon and in Fort Portal crater lakes reveal extra preventive chemotherapy needs

Background:Intestinal schistosomiasis is of public health importance in Uganda but communities living above 1400 m are not targeted for control as natural transmission is thought unlikely.To assess altitudinal boundaries and at-risk populations,conjoint malacological and epidemiological surveys were undertaken on Mount Elgon(1139 m-3937 m),in Fort Portal crater lakes and in the Rwenzori Mountains(1123 m-4050 m).Methods:Seventy freshwater habitats[Mount Elgon(37),Fort Portal crater lakes(23),Rwenzori Mountains(8)and Lake Albert(2)]were inspected for Biomphalaria species.Water temperature,pH and conductivity were recorded.A parasitological examination of 756 schoolchildren[Mount Elgon(300),Fort Portal crater lakes(456)]by faecal microscopy of duplicate Kato-Katz smears from two consecutive stool samples was bolstered by antigen(urine-CCA dipstick)and antibody(SEA-ELISA)diagnostic assays.Results:Biomphalaria spp.was found up to 1951 m on Mount Elgon and 1567 m in the Fort Portal crater lakes.Although no snail from Mount Elgon shed cercariae,molecular analysis judged 7.1%of snails sampled at altitudes above 1400 m as having DNA of Schistosoma mansoni;in Fort Portal crater lakes three snails shed schistosome cercariae.Prevalence of intestinal schistosomiasis as measured in schoolchildren by Kato-Katz(Mount Elgon=5.3%v.Fort Portal crater lakes=10.7%),CCA urine-dipsticks(18.3%v.34.4%)and SEA-ELISA(42.3%v.63.7%)showed negative associations with increasing altitude with some evidence of infection up to 2000 m.Conclusions:Contrary to expectations,these surveys clearly show that natural transmission of intestinal schistosomiasis occurs above 1400 m,possibly extending up to 2000 m.Using spatial epidemiological predictions,this now places some extra six million people at-risk,denoting an expansion of preventive chemotherapy needs in Uganda.

Towards interruption of schistosomiasis transmission in sub-Saharan Africa:developing an appropriate environmental surveillance framework to guide and to support‘end game’interventions

Schistosomiasis is a waterborne parasitic disease in sub-Saharan Africa,particularly common in rural populations living in impoverished conditions.With the scale-up of preventive chemotherapy,national campaigns will transition from morbidity-to transmission-focused interventions thus formal investigation of actual or expected declines in environmental transmission is needed as‘end game’scenarios arise.Surprisingly,there are no international or national guidelines to do so in sub-Saharan Africa.Our article therefore provides an introduction to key practicalities and pitfalls in the development of an appropriate environmental surveillance framework.In this context,we discuss how strategies need to be adapted and tailored to the local level to better guide and support future interventions through this transition.As detection of egg-patent infection in people becomes rare,careful sampling of schistosome larvae in freshwater and in aquatic snails with robust species-specific DNA assays will be required.Appropriate metrics,derived from observed prevalence(s)as compared with predetermined thresholds,could each provide a clearer insight into contamination-and exposure-related dynamics.Application could be twofold,first to certify areas currently free from schistosomiasis transmission or second to red-flag recalcitrant locations where extra effort or alternative interventions are needed.