Environmental determinants of distribution of freshwater snails and trematode infection in the Omo Gibe River Basin,southwest Ethiopia

Background:Determination of infection rates of snail populations is one of the basic tools for epidemiological studies of snail borne diseases.In this study,we opted to determine the trematode infection of freshwater snails in the Omo-Gibe River Basin,southwest Ethiopia.Methods:We collected snail samples from 130 observation sites in lakes,wetlands,rivers,reservoirs and irrigation canals surveyed during the dry season(March to May)in 2016.The snail samples were examined for trematode infections by cercarial shedding immediately after collection.Habitat conditions,water quality,human water contact practices and other human activities were assessed at each survey site.A redundancy analysis(RDA)was used to examine the relationship between cercarial infection and environmental variables.The statistical significance of eigenvalues and cercariae-environment correlations generated by the RDA were tested using Monte Carlo permutations at 499 permutations.Results:A total of 3107 snails belonging to five species were collected.The most abundant species was Biomphalario pfeifferi,representing 66%of the total collection.Overall,109(3.6%)of the snails were found infected with trematodes(cercariae).Biompholario pfeifferi was found to be the most highly infected,accounting 85%of all infected snails.A total of eight morphologically different types of cercariae were recorded,which included:Echinostoma cercariae,brevifurcate apharyngeate distome cercariae,amphistome cercariae,brevifurcate apharyngeate monostome cercariae,xiphidiocercariae,longifurcate pharyngeate distome cercariae,strigea cercariae and unidentified cercariae.Brevifurcate apharyngeate distome cercariae,and Echinostoma cercariae were the most abundant cercariae,accounting for 36 and 34%of all infection,respectively.The mean concentration of water conductivity and 5 days biological oxygen demand were higher in irrigation canals and lake sampling points.Human activities such as open field defecation,urination,livestock grazing,farming,and swimming were highly correlated with trematode infection.Conclusions:The abundance,occurrence and infection rates of snail species were largely influenced by water physicochemical quality,sanitation and water contact behaviour of the inhabitants.Human activities,such as open field defecation and urination,livestock grazing,farming,and swimming were important predictors of the abundance of cercariae.Therefore,awareness creation should be implemented for proper containment of excreta(urine and faeces)and reducing human and animal contacts with surface waters to reduce snail-borne disease transmission.

Molluscicidal effect of Achyranthes aspera L.(Amaranthaceae)aqueous extract on adult snails of Biomphalaria pfeifferi and Lymnaea natalensis

Background:Intestinal schistosomiasis caused by Schistosoma mansoni is a wide spread disease in most parts of Ethiopian highlands.Snail control is one major strategy in schistosomiasis control.The use of molluscicidal plant products is becoming interesting due to their environmental friendliness,accessibility and easy application.This research is aimed to evaluate the molluscicidal effect of Achyranthes aspera on Biomphalaria pfeifferi and Lymnaea natalensis snails,which are of great medical and veterinary importance in Ethiopia.Methods:Adult B.pfeifferi snails were exposed to the various concentrations of A.aspera aqueous leaf extract for 24,48 and 72 h.Similarly,adult L.natalensis snails were exposed to the extract for 24 h.Mortality data were analyzed using probit regression model.Phytochemical content of the plant was analyzed using standard screening methods.Results:The plant’s molluscicidal effect on the two snail species was demonstrated.The 24 h LC50 and LC90 values against L.natalensis were 69.5 and 93.9 ppm respectively.In the 24,48 and 72 h exposure of B.pfeifferi,the LC50 values were 72.4,69.9,64.7 ppm and the LC90 were 96.5,93.8,92.8 ppm,respectively.The phytochemical screening tests indicated presence of saponins.Conclusion:From the findings of this study,A.aspera has a molluscicidal potential.The result provides a useful foundation for further in-depth studies to ensure its wider applicability in different water bodies and evaluate its toxic effects on non-target species.

Molecular epidemiology of Giardia duodenalis infection in humans in Southern Ethiopia:a triosephosphate isomerase gene-targeted analysis

Background:Giardia duodenalis is a species complex consisting of multiple genetically distinct assemblages.The species imposes a major public health crisis on developing countries.However,the molecular diversity,transmission dynamics and risk factors of the species in these countries are indeterminate.This study was conducted to determine the molecular epidemiology of G.duodenalis infection in asymptomatic individuals in Southern Ethiopia.Methods:From March to June 2014,fresh stool samples were collected from 590 randomly selected individuals.Socio-demographic data were gathered using a pre-tested structured questionnaire.The genotyping was done using triosephosphate isomerase gene-based nested polymerase chain reaction and DNA sequencing.The genetic identity and relatedness of isolates were determined using the basic local alignment search tool and phylogenetic analysis.Risk factors associated with G.duodenalis infection were analysed using binary and multinomial logistic regression models.Results:The results showed that 18.1%(92/509)of the study subjects were infected by G.duodenalis.Among the isolates,35.9%(33/92)and 21.7%(20/92)were sub-typed into assemblages A and B,respectively,whereas 42.4%(39/92)showed mixed infections of A and B.Most of the assemblage A isolates(94%,31/33)were 100%identical to sequences registered in GenBank,of which the majority belonged to sub-assemblage AII.However,the high genetic variability and frequency of double peaks made sub-genotyping of assemblage B more problematic and only 20%(4/20)of the isolates matched 100%with the sequences.The risk factors of age(P=0.032)and type of drinking water source(P=0.003)both showed a significant association with the occurrence G.duodenalis infection.Conclusions:This study established the endemicity of G.duodenalis in Southern Ethiopia.Infection with assemblage A was more frequent than with assemblage B,and the rate of infection was higher in children and in municipal/tap and open spring water consumers than the other groups.Sub-typing of assemblage B and determining the origin of double peaks were challenging.The present study confirms the need for further inclusive studies to be conducted focusing on sub-types of assemblage B and the origin of heterogeneity.