Magnetic resonance imaging of eosinophilic meningoencephalitis caused by Angiostrongylus cantonensis following eating freshwater snails

Background Angiostrongyliasis cantonensis is a worldwide-existing parasitic disease. However, the relevant reports on its radiological appearances are limited. In this study, we investigated magnetic resonance imaging （MRI） features of eosinophilic meningoencephalitis in a group of consecutive patients caused by human infection with Angiostrongylus cantonensis after eating freshwater snails. Methods We performed brain MR imaging on 74 patients with angiostrongyliasis cantonensis. The scanner was a 0.5T unit. For each patient MR pulse sequences of $E Tl-weighted image （TlWl） and FSE T2-weighted image （T2Wl） were used. After intravenous administration of gadolinium chelate （Gd-DTPA） repeated Tl-weighted images were obtained. MRI features of the lesions in the brain and meninges were analyzed and recorded after observing initial and follow-up MR images. The classification of the types of angiostrongyliasis cantonensis infection was done on the basis of locations of the disorders. Results Forty-one （55%） normal and 33 （45%） abnormal MRI appearances in the brain were found. According to locations of the disorders, the types of angiostrongyliasis cantonensis infection were determined as follows： seventeen cases of type meningitis, three of type myeloencephalitis, one of type neuritis and twelve of mixed type （eight of type ventriculitis and five of type pneumonitis were among them）. In type meningitis, abnormal leptomeningeal enhancement was visualized. In type myeloencephalitis, lesions in the brain parenchyma may have iso- or slightly low signal intensity on TlWl and high signal intensity on T2Wl. Enhanced nodules in various shapes were shown on gadolinium-enhanced TlWl, a few lesions appeared as crescent enhancements and some lesions did not reveal abnormal enhancement. Other than brain lesions, an enhanced nodule was seen in the cervical spinal cord in one patient. In type ventriculitis, brain ventricular enlargement was demonstrated. In type neuritis, a nodule and abnormal enhancement in the right optic nerve was revealed. In type pneumonitis, patchy ground-glass opacity and consolidative lesions at the periphery of the lungs were seen. Follow-up results indicated that most lesions in the brain could resolve in 2 to 8 weeks. Conclusions Angiostrongyliasis cantonensis presented as both single type and mixed type. Nodular enhancing lesions in the brain and/or linear enhancement in the leptomeninges were the main findings, while crescent enhancement would be the characteristic sign of the disease on gadolinium-enhanced TlWI. Focal edematous changes without contrast enhancement in the brain could be seen on MRI in some cases.

Small-scale spatial analysis of intermediate and definitive hosts of Angiostrongylus cantonensis

Background:Angiostrongyliasis is a food-borne parasitic zoonosis.Human infection is caused by infection with the third-stage larvae of Angiostrongylus cantonensis.The life cycle of A.cantonensis involves rodents as definitive hosts and molluscs as intermediate hosts.This study aims to investigate on the infection status and characteristics of spatial distribution of these hosts,which are key components in the strategy for the prevention and control of angiostrongyliasis.Methods:Three villages from Nanao Island,Guangdong Province,China,were chosen as study area by stratified random sampling.The density and natural infection of Pomacea canaliculata and various rat species were surveyed every three months from December 2015 to September 2016,with spatial correlations of the positive P.canaliculata and the infection rates analysed by ArcGIS,scan statistics,ordinary least squares(OLS)and geographically weighted regression(GWR)models.Results:A total of 2192 P.canaliculata specimens were collected from the field,of which 1190 were randomly chosen to be examined for third-stage larvae of A.cantonensis.Seventy-two Angiostrongylus-infected snails were found,which represents a larval infection rate of 6.1%(72/1190).In total,110 rats including 85 Rattus norvegicus,10 R.flavipectus,one R.losea and 14 Suncus murinus were captured,and 32 individuals were positive(for adult worms),representing an infection rate of 29.1%of the definitive hosts(32/110).Worms were only found in R.norvegicus and R.flavipectus,representing a prevalence of 36.5%(31/85)and 10%(1/10),respectively in these species,but none in R.losea and S.murinus,despite testing as many as 32 of the latter species.Statistically,spatial correlation and spatial clusters in the spatial distribution of positive P.canaliculata and positive rats existed.Most of the spatial variability of the host infection rates came from spatial autocorrelation.Nine spatial clusters with respect to positive P.canaliculata were identified,but only two correlated to infection rates.The results show that corrected Akaike information criterion,R2,R2 adjusted andσ2 in the GWR model were superior to those in the OLS model.Conclusions:P.canaliculata and rats were widely distributed in Nanao Island and positive infection has also been found in the hosts,demonstrating that there was a risk of angiostrongyliasis in this region of China.The distribution of positive P.canaliculata and rats exhibited spatial correlation,and the GWR model had advantage over the OLS model in the spatial analysis of hosts of A.cantonensis.

The genetic variation of Angiostrongylus cantonensis in the People’s Republic of China

Background:The People’s Republic of China(P.R.China)is the presumptive home range of the rat lungworm Angiostrongylus cantonensis,a major aetiological agent of human eosinophilic meningitis.We present a study of the genetic variation of A.cantonensis in P.R.China.Our aim was to deepen the current knowledge pertaining to its origin and global spread from a molecular perspective.Methods:Adult A.cantonensis were collected in the frame of a national survey and identified based on morphological criteria.Polymerase chain reaction(PCR)was employed to amplify the target DNA sequences(cytochrome c oxidase subunit I(cox1),nicotinamide adenine dinucleotide dehydrogenase subunit 1(nad1)and internal transcribed spacer(ITS)).The PCR product of cox1 was directly submitted to sequencing,while clone sequencing was used for nad1 and ITS.The identity of the samples was verified by comparing the sequences to those of accepted A.cantonensis specimens.The specific composition of substitutions in each gene was analysed,and the genotypes were compared based on the complete cox1,nad1 and ITS genes.Results:We characterised the complete mitochondrial genes cox1 and nad1 of 130 specimens and obtained 357 nuclear sequences containing two complete ITS(ITS1 and ITS2)and 5.8S rRNA of the same samples.All specimens were genetically confirmed as A.cantonensis.Two major groups(i.e.I and II)were identified according to the phylogeny of cox1 sequences.Group I could be further categorised into six distinct clades.Almost half of the specimens(47.7%)belong to the clade Ia and 22.3%to the group II.The former was widely distributed across the study region.A variable number of repeat units in three microsatellites was observed,resulting in considerable length variation in ITS.Intragenomic variation of ITS sequences was found in a large proportion of the samples.Genotyping showed a striking difference between mitochondrial DNA and ITS.Conclusions:Our results demonstrate that A.cantonensis is the only rat lungworm species in P.R.China and shows high genetic diversity.Results of diversity and genotyping of A.cantonensis can be impacted by the sequencing strategy and biomarker.Although ITS may be a valuable marker for interspecific identification,it is not suitable for studying the intraspecific variation of A.cantonensis due to its high intragenomic variation and current challenges for direct sequencing.

A pooling strategy of a PCR-based assay to detectAngiostrongylus cantonensis in snail intermediate host,Pomacea canaliculata

Poolingfield specimens could reduce the number of assay and thus increase the efficiency in detecting and screening pathogen infections by polymerase chain reaction(PCR)-based assay.We investigated a pooling strategy in diagnosis of Angiostrongylus canto-nensis in Pomacea canaliculata.Two settings of speci-mens were prepared,divided into portions and detected by multiplex PCR.Specimens A was 0.4490 g positive lung tissue of 28 larval nodes from four snails mixed with 1.310 g negative lung tissue from six snails and divided into 32 portions.Specimens B was 0.5448 g positive lung tissue with 26 larval nodes from two snails mixed with 1.092 g negative lung tissue from seven snails and divided into 48 portions.Repeated sampling was performed and sample size-accumulated positive rate curves were drawn.According to the sample size-accumulated positive rate curves,the appropriate sample size of the two specimens were 18 and 15,respectively,which is 0.36–0.58 to the total sample size.These test characteristics and the relevant factors to the sample size would need to be determined in much larger studies and more appropriately infield populations.The result indicates that the number of larval node is not the most important,nor the only factor to the sample size.It also implies the feasibility to detect A.cantonensis in P.canaliculata by pooling strategies.

Gut microbiota in parasite-transmitting gastropods

Background Gastropoda,the largest class within the phylum Mollusca,houses diverse gut microbiota,and some gastropods serve as intermediate hosts for parasites.Studies have revealed that gut bacteria in gastropods are associated with various biological aspects,such as growth,immunity and host-parasite interactions.Here,we summarize our current knowledge of gastropod gut microbiomes and highlight future research priorities and perspectives.Methods A literature search was undertaken using PubMed,Web of Science and CNKI for the articles on the gut microbiota of gastropods until December 31,2022.We retrieved a total of 166 articles and identified 73 eligible articles for inclusion in this review based on the inclusion and exclusion criteria.Results Our analysis encompassed freshwater,seawater and land snails,with a specific focus on parasite-transmitting gastropods.We found that most studies on gastropod gut microbiota have primarily utilized 16S rRNA gene sequencing to analyze microbial composition,rather than employing metagenomic,metatranscriptomic,or metabolomic approaches.This comprehensive review provided an overview of the parasites carried by snail species in the context of gut microbiota studies.We presented the gut microbial trends,a comprehensive summary of the diversity and composition,influencing factors,and potential functions of gastropod gut microbiota.Additionally,we discussed the potential applications,research gaps and future perspectives of gut microbiomes in parasite-transmitting gastropods.Furthermore,several strategies for enhancing our comprehension of gut microbiomes in snails were also discussed.Conclusions This review comprehensively summarizes the current knowledge on the composition,potential function,influencing factors,potential applications,limitations,and challenges of gut microbiomes in gastropods,with a specific emphasis on parasite-transmitting gastropods.These findings provide important insights for future studies aiming to understand the potential role of gastropod gut microbiota in controlling snail populations and snail-borne diseases.