Epidemiology of cercarial stage of trematodes in freshwater snails from Chiang Mai province,Thailand

Objective:To investigate the epidemiological situation of cercarial trematodes infection in freshwater snails from different water resources in Chiang Mai province,Thailand.Methods:The snail specimens were collected from 13 districts of Chiang Mai province during April 2008 to February 2012.The prevalence of cercarial infection in snails was investigated using the crushing method.The drawing was done with the help of a camera lucida for the morphological study.Results:A total of 2479 snail individuals were collected and classified into 7 families,11 genera,and 14 species,Among them,8 snails species were found to be infected with an overall prevalence of 17.27%(428/2479),which infected with nine groups of cercariae;gymnocephalous cercaria,strigea cercaria,megalurous cercaria,monostome cercaria,parapleurolophocercous cercaria(Haplorchis cercaria),pleurolophocercous cercaria,furcocercous cercaria(Transversotrema cercaria),xiphidiocercaria,and virgulate cercaria.The parapleurolophocercous cercaria was found to be the dominant type among the cercarial infection in the snails(64.25%).Conclusions:The various species of snails found in the research location act as the intermediate hosts for the high prevalence of parasitic infection of many species of mammals.This work will provide new information on both the distribution and first intermediate host of trematodes.

Larval stages of digenetic trematodes in Melanopsis praemorsa snails from freshwater bodies in Palestine

Objective:To detect the species of larval trematodes(cercariae) in Melanopsis praemorsa snails from 5 different fresh water bodies in Palestine.Methods:A total of 1 880 Melanopsis praemona snails were collected from different fresh water bodies in Palestine from October,2008 to November,2010.Cercariae in Melanopsis praemona snails were obtained by lighting and crushing methods.The behavior of cercariae was observed using a dissecting microscope.Results:Three different species of larval trematodes were identified from Melanopsis praemona snails collected only from Al-Bathan fresh water body,while snails from other water bodies were not infected. These species were microcercous cercaria,xiphidiocercaria and brevifurcate lophocercous cercaria.These cercariae called Cercaria melanopsi palestinia 1,Cercaria melanopsi palestinia H and Cercaria melanopsi palestinia III have not been described before from this snail in Palestine. The infection rate of Melanopsis praemona collected from Al-Bathan fresh water body was 5.7%, while the overall infection rate of snails collected from all fresh water bodies was 4.3%.Details are presented on the morphology and behavior of the cercariae as well as their development within the snail.Conclusions:These results have been recorded for the first time and these cercariae may be of medical and veterinary importance.

Human Invasion by Lesser Known Medically Important Trematodes in the Proximity of Tshwane,Gauteng Province,South Africa

It is well-documented that digenetic trematodes exhibit complex life cycles where the definitive hosts are vertebrates—mostly birds,other mammals and reptiles.It is also known that digenetic trematodes are host specific,but changes in our feeding habits, agricultural and social practices,have led to human beings infected with parasites that were previously regarded to be of no or insignificant medical importance. The objective of this study was to identify the less known digenetic parasites in the water bodies around Tshwane that may result in possible

A relatively high zoonotic trematode prevalence in Orientogalba ollula and the developmental characteristics of isolated trematodes by experimental infection in the animal model

Background:Food-borne parasitic diseases decrease food safety and threaten public health.The snail species is an intermediate host for numerous human parasitic trematodes.Orientogalba ollula has been reported as intermediate hosts of many zoonotic trematodes.Here,we investigated the prevalence of zoonotic trematodes withinO.ollula in Guangxi,China,and assessed their zoonotic potential.Methods:Snails were collected from 54 sites in 9 cities throughout Guangxi.The snail and trematode larvae species were determined by combining morphological characteristics and molecular markers.The trematodes prevalence and constituent ratio were calculated and compared among different habitat environments.Phylogenetic trees of the trematode species were constructed using the neighbor-joining method with nuclear internal transcribed spacer 2(ITS2)sequences.The developmental cycles of the isolated trematodes were examined by experimental infection in ducks.The developmental characteristics ofEchinostoma revolutum was recorded by dissecting infected ducklings from 1-day post infection(dpi)to 10 dpi.Results:The overall prevalence of trematode larvae was 22.1%(1818/8238)inO.ollula from 11 sample sites.Morphological together with molecular identification,showed thatE.revolutum,Australapatemon sp.,Hypoderaeum conoideum,Pharyngostomum cordatum,andEchinostoma sp.parasitizedO.ollula,with the highest infection rate ofE.revolutum(13.0%).However,noFasciola larvae were detected.The trematodes prevalence and constituent ratio varied in two sub-biotypes(P<0.01).A neighbor-joining tree analysis of ITS2 sequences resulted in distinct monophyletic clades supported by sequences from isolated larvae with high bootstrap values.Ducklings exposed toO.ollula infected withEchinostoma sp.,E.revolutum,andH.conoideum larvae were successfully infected.The animal model forEchinostoma revolutum was successfully established.E.revolutum matured from larvae to adult at 10 dpi in the intestine of the duck,and the developmental characteristics ofE.revolutum were characterized by the maturation of the reproductive and digestive organs at 6-8 dpi.Conclusions:This study revealed a high prevalence of zoonotic trematodes inO.ollula from Guangxi,China.Existing trematodes infection in animals and human clinical cases,coupled with the wide geographical distribution ofO.ollula,necessitate further evaluations of the potential risk of spillover of zoonotic infection from animal to human and vice versa.

Types of trematodes infecting freshwater snails found in irrigation canals in the East Nile locality,Khartoum,Sudan

Background:The planorbid freshwater snails of the two genera,Biomphalaria and Bulinus-have been vigorously studied due to the role they play as intermediate hosts of schistosomiasis.In Sudan specifically,most studies have focused on the chemical and ecological control of the two genera,but few studies have looked at their biological control.This study explored the coexistence of other species of freshwater snails and the two genera along with their trematode infections in relation to a number of environmental factors in the East Nile locality,Khartoum state,Sudan.Methods:Freshwater snails from irrigation canals(abueshreens)were sampled monthly from January 2004 to December 2005.The snails were examined for trematode infections by cercarial emergence immediately after collection and then weekly for an additional four weeks to allow for the maturation of prepatent infections.Vegetation cover in the study sites as well as the physicochemical characteristics of the water,including temperature,were also recorded.Results:A total of 10,493 snails,representing seven species,were collected.The most abundant species was Biomphalaria pfeifferi,representing 48.6%of the sample.Overall,14.1%of the snails were found to be shedding some type of cercariae.Five species were found to have infections;among these the Bulinus truncatus species was found to be the most heavily infected,with an overall prevalence of 46.2%.Double infections were recorded in only two B.truncatus snails and one Cleopatra bulimoides snail.Twenty different morphotypes of cercariae were recorded,seven of which appeared not to conform to previously described cercariae from Africa.Xiphidiocercariae type 1 was the most common type of cercariae recovered,accounting for 44.3% of all infections.The density of snails tended to be lower during the summer months than the winter months,except for M.tuberculata snails,which were not affected by seasonal changes.Conclusion:The findings of this study indicate that besides schistosomes,other larval trematodes are found,and some use the same intermediate hosts as the schistosomes.Further studies should be conducted to determine whether some of these trematodes could be manipulated for the biological control of schistosomiasis.

Surgical outcomes of complicated cataract with pediatric trematode granulomatous uveitis

AIM:To describe the clinical characteristics and surgical outcomes of complicated cataract with pediatric trematodal granulomatous uveitis(TGU).METHODS:Patients of cataract with TGU in the membranous(inactive) stage underwent cataract surgery with intraocular lens(IOL) implantation.Preoperative history and ophthalmic examination were conducted for all cases,whereas Schimphlug imaging and corneal topography were done for some patients.Postoperative follow up was done on the 1st,2nd,and 5th postoperative days after surgery.Then,it was done at least at one,three,and six months postoperatively.Intraoperative and postoperative complications and the methods of their management were reported.RESULTS:Twelve eyes of 12 male children were included in this study ranging from 8 to 16y.The mean best corrected Snellen visual acuity(BCVA) was significantly improved from 0.09±0.06 preoperatively to 0.37±0.11 at the final visit 6mo postoperatively(P<0.001).Schimphlug imaging and corneal topography showed flattening of the anterior surface of the inferior cornea.Intraoperative difficulties and complications included the poor dilatability of the drown down pupil,strong posterior synechia between the anterior lens capsule and the iris at the site of the inferior retrocorneal vascularized membrane and hyphema.All cases underwent primary hydrophobic IOL implantation.CONCLUSION:Surgery for this type of cataract is relatively safe and effective.It is associated with some specific difficulties and complications that should be considered during surgery and follow up.

Phylogenetic analysis reveals cryptic species diversity within minute intestinal fluke,Stellantchasmus falcatus Onji and Nishio,1916(Trematoda,Heterophyidae)

Objective:To examine the taxonomic boundaries in the Stellantchasmus populations in different hosts and reveal the cryptic speciation of the Stellantchasmus in Thailand based on both morphological and molecular approaches.Methods:Stellantchasmus falcatus(S.falcatus) s.l.was collected from different hosts throughout Thailand.The worms were examined and measured.The nuclear ITS2 gene and the mitochondrial COI gene were used to investigate the S.falcatus s.l.from Dermogenus pusillus and Liza subviridis.Results:Stellantchasmus was one of food-borne trematode that widely distribute throughout Thailand.The comparison of S.falcatus s.l.from Dermogenus pusillus and Liza subviridis indicated a genetic divergence of nuD NA with 3.6% and mtD NA with 19.3%,respectively.Morphological characteristics were fairly different in the ratio of body size,length of prepharynx,and ratio of organ size.Conclusions:Our results provide initial evidence that S.falcatus s.l.from different hosts tend to be a different species based on both molecular and morphological characters.Cryptic species complexes are generally found among parasites that tend to have large populations and/or rapid evolution.The degree of genetic diversity existing would suggest the practice of targeted regimes to design and minimize these lections of anthelmintic resistance in the future.

Comparison of novel and standard diagnostic tools for the detection of Schistosoma mekongi infection in Lao People’s Democratic Republic and Cambodia

Background:Given the restricted distribution of Schistosoma mekongi in one province in Lao People’s Democratic Republic(Lao PDR)and two provinces in Cambodia,together with progress of the national control programmes aimed at reducing morbidity and infection prevalence,the elimination of schistosomiasis mekongi seems feasible.However,sensitive diagnostic tools will be required to determine whether elimination has been achieved.We compared several standard and novel diagnostic tools in S.mekongi-endemic areas.Methods:The prevalence and infection intensity of S.mekongi were evaluated in 377 study participants from four villages in the endemic areas in Lao PDR and Cambodia using Kato-Katz stool examination,antibody detection based on an enzyme-linked immunosorbent assay(ELISA)and schistosome circulating antigen detection by lateral-flow tests.Two highly sensitive test systems for the detection of cathodic and anodic circulating antigens(CCA,CAA)in urine and serum were utilized.Results:Stool microscopy revealed an overall prevalence of S.mekongi of 6.4%(one case in Cambodia and 23 cases in Lao PDR),while that of Opisthorchis viverrini,hookworm,Trichuris trichiura,Ascaris lumbricoides and Taenia spp.were 50.4%,28.1%,3.5%,0.3%and 1.9%,respectively.In the urine samples,the tests for CCA and CAA detected S.mekongi infections in 21.0%and 38.7%of the study participants,respectively.In the serum samples,the CAA assay revealed a prevalence of 32.4%,while a combination of the CAA assay in serum and in urine revealed a prevalence of 43.2%.There was a difference between the two study locations with a higher prevalence reached in the samples from Lao PDR.Conclusions:The CCA,CAA and ELISA results showed substantially higher prevalence estimates for S.mekongi compared to Kato-Katz thick smears.Active schistosomiasis mekongi in Lao PDR and Cambodia might thus have been considerably underestimated previously.Hence,sustained control efforts are still needed to break transmission of S.mekongi.The pivotal role of highly sensitive diagnostic assays in areas targeting elimination cannot be overemphasised.

Fish sharing as a risk factor for Opisthorchis viverrini infection:evidence from two villages in north-eastern Thailand

Background:Foodborne trematodiasis(FBT)is a significant global health problem,with the liver flukes Opisthorchis viverrini,O.felineus,and Clonorchis sinensis contributing to half of the global burden of FBT.North-eastern Thailand where O.viverrini is endemic and un-cooked fish dishes remain an integral part of the food culture has the highest reported incidence of opisthorchiasis,including associated cholangiocarcinoma.Both food sharing and eating practices are potentially important factors in FTB,suggesting an important role for the social ecology of disease transmission in these rural communities.Methods:Two rural Thai-Lao villages that were part of a 12-village project in Northeastern Thailand were selected for detailed investigation of O.viverrini infection risk associated with sharing of raw fish dishes among households.The project included screening individuals for infection and cholangiocarcinoma,a household questionnaire,and offering treatment options for positive individuals.Social network mapping was used to construct raw fish dish-sharing networks and create a proxy variable capturing variability in the degree of food sharing(DFS),measured as the number of different households with which each household shared fish dishes.Measures of associations between DFS,O.viverrini infection,the frequency of raw fish consumption,and the number of raw fish dishes consumed were generated using binary logistic regression,proportional odds ordinal logistic regression,and Poisson regression.Results:The results showed that the probability that a household has members infected with O.viverrini increased by~7%(P<0.01)for each additional household included in its network.Moreover,the frequency and number of types of raw fish dishes consumed increased significantly as the DFS increased.Of the two villages,that with the highest infection prevalence(48%versus 34.6%)had significantly higher social connectivity overall(P<0.001).Conclusions:Our findings suggest that the social ecology of human settlements may be key to understanding the transmission dynamics of some FBT.In the case of O.viverrini in Thai-Lao communities,for which food sharing is a traditional practice supporting social cohesion,food sharing network mapping should be incorporated into community-based interventions.These should encourage fish dish preparation methods that minimize infection risk by targeting households with high DFS values.

Helminths of veterinary and zoonotic importance in Nigerian ruminants:a 46-year meta-analysis(1970-2016)of their prevalence and distribution

Background:The livestock industry plays a vital role in the economy of Nigeria.It serves as a major source of income and livelihood for majority of Nigerians who are rural settlers and contributes about 5.2%to the National Gross Domestic Product(GDP).Helminths however,cause economic losses due to reductions in milk production,weight gain,fertility and carcass quality.Zoonotic helminths of livestock origin cause health problems in humans.Methods:Using the Preferred Reporting Items for Systematic Review and Meta-Analysis(PRISMA)guidelines,the prevalence and distribution of helminths of veterinary and zoonotic importance in Nigerian ruminants were determined in a meta-analysis of data published between 1970 and 2016.Data were stratified based on regions,hosts,study periods,sample sizes and study types while helminths were phylogenetically grouped into cestodes,nematodes and trematodes.Results:Data from 44 studies reported across 19 Nigerian states revealed an overall pooled prevalence estimate(PPE)of 7.48%(95%CI:7.38-7.57)for helminths of veterinary and zoonotic importance from a total of 320208 ruminants.We observed a significant variation(P<0.001)between the PPEs range of 1.90%(95%CI:1.78-2.02)and 60.98%(95%CI:58.37-63.55)reported across different strata.High heterogeneity(99.78,95%CI:7.38-7.57)was observed.Strongyloides papillosus was the most prevalent(Prev:32.02%,95%CI:31.01-33.11),while,Fasciola gigantica had the widest geographical distribution.Conclusions:Helminths of veterinary and zoonotic importance are prevalent in ruminants and well distributed across Nigeria.Our findings show that helminths of ruminants may also be possible causes of morbidity in humans and economic losses in the livestock industry in Nigeria.High heterogeneity was observed within studies and the different strata.Good agricultural practices on farms,standard veterinary meat inspection and adequate hygiene and sanitation in abattoirs,farms and livestock markets need to be implemented in Nigeria in order to reduce the economic,public health and veterinary threats due to these helminths.

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.

Marked elevation of serum alpha-fetoprotein following Clonorchis sinensis infection: A rare case report

Clonorchiasis,also known as the liver fluke disease,is caused by eating raw freshwater fish or shrimps that contain Clonorchis sinensis cyst larvae,which mainly involves the hepatobiliary system.Chronic abdominal pain and distention,loss of appetite,and hepatomegaly are the most common clinical manifestation.Persistent infection with Clonorchis sinensis would result in chronic inflammation,epithelial hyperplasia,and periductal fibrosis and even progress to cholangiocarcinoma.Nevertheless,the majority of the infected people are asymptomatic or mildly symptomatic,contributing to its high misdiagnosis rate.Alpha-fetoprotein(AFP)is a well-known biomarker for hepatocellular carcinoma(HCC).A high level of AFP can also be caused by several benign diseases,causing confusion and influ-encing treatment decisions.So far,clonorchiasis with a markedly elevated level of AFP has been rarely reported.We present a case of clonorchiasis with a high level of AFP in a 52-year-old man.We hope to raise clinical awareness of this food-borne disease.Clonorchiasis should be considered in patients with extremely high levels of AFP,excluding HCC and germ cell tumors,especially if the patient has a history of ingesting raw freshwater fish or shrimps.

An overview of cercariae from the Egyptian inland water snails

The study on trematode larvae found in Egyptian molluscs was initiated by the pioneering work of Sonsino in 1892 and Looss in 1896. Since then tens of cercariae and some digenean life cycles have been reported in the country. Unfortunately, only fragmentary publications are available for identification of cercariae present in the country. In addition, some of such publications may not be accessible to some researchers, as they are either theses or published in old volumes of non-international journals. The present work was carried out with the aim of preserving our heritage through reviewing the different types of cercariae known from the Egyptian inland water snails. We provide a survey based on literature. Major types of cercariae known to exist in the country are covered. They are presented as regards description, development, taxa, importance and snail hosts. This review can be used as a field guide for identification of cercariae colonising the Egyptian inland water snails.

Hepatoma and trematode infestation: a short review

Hepatoma is a common cancer that can be seen around the world and clinical correlation between infection and hepatoma is evident. Hepatitis virus infection is proved for its relationship with hepatoma. However, the knowledge of other infections is still limited. In this short review, the relationship between hepatoma and some trematode infestation including echinococcosis fascioliasis, opisthorchiasis, clonorchiasis and schistosomiasis are described and discussed. Opisthorchiasis and clonorchiasis are confi rmed for cholangiocarcinoma carcinogenesis but still lack evidence for hepatoma carcinogenesis. Schistosomiasis can increase the severity of hepatoma.