Strategies of soil microbial N-cycling in different cadmium contaminated soil with wheat straw return.

Cadmium contamination inevitably affects the microbially mediated transformation of nitrogen in soils with wheat straw return. The responses of nitrogen functional microorganisms to cadmium in acidic and alkaline soils under wheat straw returned are still unclear. In this study, quantitative polymerase chain reaction (qPCR) and sequencing of nitrifying and denitrifying bacteria were performed to investigate the effects of wheat straw application on nitrogen conversion in different Cd-contaminated soils during an incubation experiment. Results showed that the presence of Cd decreased the abundance of hao gene catalyzing nitrification and norB gene catalyzing denitrification process, resulting the accumulation of NH4+-N and reduction of NO3--N in the acidic soils. Additionally, Cd-contamination stimulates the nitrification catalyzed by bacterial amoA gene and thus reduced the NH4+-N content in the alkaline soils. Meanwhile, Cd dominated the decrease of NO3--N content by promoting denitrification process catalyzed by nirS gene. Among all nitrifying and denitrifying microorganisms, Nitrosospira are tolerant to Cd stress under alkaline condition but sensitive to acidic condition, which dominantly harbored hao gene in the acidic soils and bacterial amoA gene in the alkaline soils. This study aimed to provide reasonable information for the rational adoption of wheat straw returning strategies to realize nitrogen regulation in Cd-contaminated farmland soil.

Working Regime Criteria for Microscale Electrohydrodynamic Conduction Pumps.

We investigated the microscale electrohydrodynamic (EHD) conduction pumps in a wide range of working regimes, from the saturation regime to the ohmic regime. We showed that the existing macro- and microscale theoretical models could not accurately predict the electric force of microscale EHD conduction pumps, especially for the cases of a strong diffusion effect. We clarified that the failure is caused by a rough estimate of the heterocharge layer thickness. We revised the expression of heterocharge layer thickness by considering the diffusion effect and developed a new theoretical model for the microscale EHD conduction pumps based on the revised expression of heterocharge layer thickness. The results showed that our model can accurately predict the dimensionless electric force of the microscale EHD conduction pumps even for the cases of a strong diffusion effect. Furthermore, we developed a working regime map of microscale EHD conduction pumps and found that the microscale EHD conduction pumps more easily fall into the saturation regime compared with the macroscale EHD conduction pumps due to the enhanced diffusion effect; in other words, the microscale EHD conduction pumps have a wider saturation regime. We showed that the conduction number C0 could not distinguish the working regime of the microscale EHD conduction pumps because it does not take the diffusion effect into account. By employing the revised expression of heterocharge layer thickness, we proposed a new dimensionless number, C0D to distinguish the working regimes of microscale EHD conduction pumps.

Dynamics of fungal and bacterial communities in different types of soil ageing with different dosages of cadmium.

This study investigated the structure of fungal and bacterial communities in different types of Cd-contaminated soils. The results showed that obvious variations in microbial structure between contaminated alkaline soils and acidic soils. Proteobacteria, Gemmatimonadetes, Bacteroidetes and Basidiomycota dominated the studied communities in the alkaline soils, whereas Actinobacteria, Chloroflexi, Firmicutes, Acidobacteria, Saccharibacteria and Ascomycota were more abundant in the acidic soils. Additionally, Cd tolerant (Proteobacteria, Bacteroidetes, Ascomycota) and sensitive (Actinobacteria, Acidobacteria, Basidiomycota) in alkaline soils and JL-soils, Cd tolerant (Actinobacteria, Acidobacteria, Basidiomycota) and sensitive (Saccharibacteria, Proteobacteria, Bacteroidetes, Ascomycota, Mucoromycota) in the acidic soils were identified. Redundancy analysis and correlation analysis demonstrated that it was significantly affected by different environment parameters in alkaline soils and acidic soils. Varied bacterial community structures in all soils were dominantly influenced by pH and SOM. The similarities among different groups indicated the effect of soil type on microbial community structure was greater than that of Cd level. The above conclusions may provide a new perspective for the bio-remediation of Cd in different types of soils.

Identification and structural characterization of febuxostat metabolites in rat serum and urine samples using UHPLC-QTOF/MS.

Febuxostat is a novel nonpurine type of highly selective xanthine oxidoreductase inhibitor. A rapid and sensitive ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry method for simultaneous separation and determination of febuxostat and its metabolites in rat serum and urine was developed at various time points after oral administration to the rats. The febuxostat metabolites were predicted by biotransformation software and transformed to a personal compound database to quickly determine the possible metabolites from the MS1 data. The possibility of the MS/MS fragmentation was calculated by the Molecular Structure Correlator software. As a result, five phase I and two phase II metabolites in rat serum, and seven phase I and three phase II metabolites in rat urine were identified, of which four metabolites (M2, M5, M6, M7) have not been reported before. The metabolite toxicities are predicted, and the results are helpful for the design of new xanthine oxidoreductase inhibitors.

[Investigation on the species distribution and infection status of host snails of Angiostrongylus cantonensis in Shanghai].

OBJECTIVE: To investigate the species distribution and infection status of host snails of Angiostongylus cantonensis in Shanghai. METHODS: From August 2012 to October 2014, 10 districts or counties were selected for this investigation in Shanghai, including Jiading, Qingpu, Putuo, Baoshan, Yangpu, Minhang, Songjiang, Jinshan, Chongming, and Pudong. All of the snails were examined by lung-microscopy and tissue homogenate methods. RESULTS: Totally 1074 snail samples were identified, belonging to 8 families, 10 species, including Pomacea canaliculata (133), Achatina fulica (25), Cipangopaludina chinensis (183), Bellamya aeruginosa (78), Physa acuta (349), Radix swinhoei (224), Bradybaena similaris (45), B. ravida sieboldiana (32), Limax flavus (2), and Philomycus bilineatus (3). A. fulica was sold in market, and was not found in the field. The natural population of P. canaliculata was found in the field in Jinze Town of Qingpu District. A. cantonensis larvae were not detected. CONCLUSION: No snails were found to be infected with A. cantonensis in Shanghai. Attention needs to be paid to the monitoring of P. canaliculata.

Recyclable water-modified deep eutectic solvents for removal of multiple heavy metals from soil.

Removing heavy metals from soil has always been a challenge in terms of safety and effectiveness. Deep eutectic solvents (DESs) are recognized as environmentally friendly reagents with great potential in the removal of heavy metals from soil. In this study, water was introduced as a third component to form new ternary deep eutectic water solvents (DEWSs) to improve their performance. The removal capacity, applicable conditions and mechanisms of sixteen DEWSs for heavy metals were systematically investigated. Experimental results showed that the presence of water significantly enhanced the removal efficiency of three DESs (Choline chloride plus Urea, DEU; Choline chloride plus l-lactic acid, DELA; and Choline chloride plus Ethylene glycol, DEEG) for heavy metals. However, as the molar ratio of water increased, the eutectic systems in the DEWSs weakened and eventually disappeared. Under optimum conditions, DEWLA7 (DELA : H2O = 2 : 8) showed the highest removal rate for cadmium, lead, copper and zinc, which were 43.42%, 94.73%, 90.72% and 96.44%, respectively. Hydrogen bonding, adsorption of oxygen functional groups, exchangeable hydrogen substitution, changes in viscosity properties and co-precipitation all contributed to the removal of heavy metals by DEWLA7. Notably, DEWLA7 had no significant effect on the content of major minerals and nutrients in the soil. Furthermore, DEWLA7 proved to be reusable for soil washing, and still retains a high removal rate of 37.32%-83.66% after multi-stage filtration treatment. Therefore, DEWLA7 was an unexplored and excellent soil washing agent with great potential in economic and social benefits.

Sports game intervention aids executive function enhancement in children with autism - An fNIRS study.

Executive dysfunction is a prevalent issue in children diagnosed with autism spectrum disorder (ASD). While the efficacy of physical exercise in enhancing cognitive abilities in these children is well-documented, research exploring the relationship between physical exercise and brain function remains limited. This study aimed to investigate the impact of cognitively stimulating exercise on executive functions (EF) in children with ASD. The study enrolled thirty children with ASD who were randomly allocated into two groups: a sports game learning group (n = 15) and a control group (n = 15). Functional near-infrared spectroscopy was utilized to monitor cerebral function alterations pre- and post- an eight-week intervention program. The study focused on three core components of executive function: working memory, inhibitory control (IC), and cognitive flexibility (CF). Results revealed a significant improvement in the EF in the intervention group. After eight weeks of intervention, neural activity, along with improved EF performance, was enhanced significantly in the prefrontal cortex (PFC). During post-intervention, EF tasks were also significantly activated in the dorsolateral PFC, orbitofrontal cortex, and frontal pole area. Furthermore, an increase in short-distance functional connectivity within the PFC was observed during resting states. These results imply that engagement in sports game training can significantly improve EF information processing, augmenting task-related cortical activations and the efficiency of brain function networks in children with ASD.

Soil nitrogen cycling gene abundances in response to organic amendments: A meta-analysis.

Quantification of nitrogen (N) cycling genes contributes to our best understanding of N transformation processes. The application of organic amendment (OA) is widely recognized as an effective measure to improve N management and soil fertility in various ecosystems. However, our understanding of N-cycling gene abundances in response to OA application remains deficient. We performed a meta-analysis embracing 124 sets of observation data to study the impact of OA application on the main N-cycling gene abundances, including nifH, amoA, nirS, nirK and nosZ. We found that the significantly positive response of N-cycling gene abundances to OA application was attributed to the rotation cropping system (by 6.45 %-104.20 %) in the field experiment (by 19.43 %-52.56 %), OA application alone (by 8.29 %-111.70 %) especially manure addition (by 33.43 %-98.70 %), application dose of OAs within 10-20 t ha-1 (by 45.33 %-381.90 %), fertilization duration <5 years (by 43.69 %-112.63 %), C/N of OA <25 (by 37.87 %-160.90 %), SOC lower than 1.2 % (by 41.44 %-157.89 %) and application to alkaline soil (by 32.24 %-134.40 %). Moreover, soil organic carbon (SOC) and pH were the most essential regulators associated with N-cycling gene abundances with OA application. Identification of key driving factors of the abundance of N-cycling functional genes will help remedy strategies for managing OAs in ecosystems.

Inhibition of microbially mediated total organic carbon decomposition in different types of cadmium contaminated soils with wheat straw addition.

Wheat straw returning is a common agronomic measure in the farmland. Understanding organic carbon transformation is of great significance for carbon budget under the premise of widespread distribution of cadmium (Cd) contaminated soils. An incubation experiment was conducted to assess the influence of Cd contamination on the decomposition and accumulation of total organic carbon (TOC) as well as the composition and abundance of bacterial communities in eight soil types with wheat straw addition. The results showed that inhibition of Cd contamination on microbially mediated organic carbon decomposition was affected by soil types. The lower cumulative C mineralization and higher TOC content could be observed in the acidic soils relative to that in the alkaline soils. The content of Cd in soil exhibits different effects on the inhibition in decomposition of TOC. The high dosage level of Cd had stronger inhibitory impact due to its high toxicity. The decomposition of TOC was restricted by a reduction in soil bacterial abundance and weakening of bacterial activities. Redundancy analysis (RDA) indicated that Proteobacteria and Gemmatimonadetes were abundant in alkaline Cd-contaminated soils with wheat straw addition, while Bacteroidetes dominated cumulative C mineralization in acidic Cd-contamination soils. Moreover, the abundance of predicted functional bacteria indicated that high-dose Cd-contamination and acid environment all inhibited the decomposition of TOC. The present study suggested that pH played an important role on carbon dynamics in the Cd-contaminated soils with wheat straw addition.

Identification of the soil physicochemical and bacterial indicators for soil organic carbon and nitrogen transformation under the wheat straw returning.

Wheat straw returning is widely practiced in agriculture; therefore, it is critical to determine the physicochemical and bacterial indicators in soil for the organic carbon storage, accumulative C mineralization, total nitrogen improvement, and nitrogen mineralization in various soil types after wheat straw returning. This study evaluated the influenced indicators of wheat straw addition on soil organic carbon and nitrogen transformation in diverse soil types. For this purpose, an incubation experiment was conducted to analyze the carbon and nitrogen transformation in soil from eight Chinese provinces treated with the same dry weight of wheat straw. The results indicated that the primary physicochemical and bacterial indicators that predict the carbon and nitrogen transformations in the acidic and alkaline soils were different. Of all the natural physicochemical properties of soil, cation exchange capacity and clay content were significantly correlated with organic carbon, mineralized carbon, total nitrogen, and mineralized nitrogen in the alkaline soil. In the acidic soil, the initial C/N ratio of soil was the most significant indicator of carbon and nitrogen transformation. From the perspective of the carbon- and nitrogen-relating bacterial communities, Proteobacteria were largely responsible for the accumulative C mineralization in both types of soil. Furthermore, Proteobacteria strongly regulated the organic carbon storage in the acidic soil after wheat straw addition, whereas Gemmatimonadetes was the main predicted indicator in the alkaline soil. Additionally, total nitrogen and mineralized nitrogen levels were largely explained by Bifidobacterium and Luteimonas in the alkaline soil and by Nitrospira and Bdellovibrio in the acidic soil. Soil physicochemical and biological properties significantly influence soil carbon and nitrogen transformation, which should be considered crucial indicators to guide the rational regulation of straw return in several areas.

Spatiotemporal adaptive attention graph convolution network for city-level air quality prediction.

Air pollution is a leading cause of human diseases. Accurate air quality predictions are critical to human health. However, it is difficult to extract spatiotemporal features among complex spatiotemporal dependencies effectively. Most existing methods focus on constructing multiple spatial dependencies and ignore the systematic analysis of spatial dependencies. We found that besides spatial proximity stations, functional similarity stations, and temporal pattern similarity stations, the shared spatial dependencies also exist in the complete spatial dependencies. In this paper, we propose a novel deep learning model, the spatiotemporal adaptive attention graph convolution model, for city-level air quality prediction, in which the prediction of future short-term series of PM2.5 readings is preferred. Specifically, we encode multiple spatiotemporal dependencies and construct complete spatiotemporal interactions between stations using station-level attention. Among them, we design a Bi-level sharing strategy to extract shared inter-station relationship features between certain stations efficiently. Then we extract multiple spatiotemporal features with multiple decoders, which it is extracted from the complete spatial dependencies between stations. Finally, we fuse multiple spatiotemporal features with a gating mechanism for multi-step predictions. Our model achieves state-of-the-art experimental results in several real-world datasets.

Contribution of ammonia-oxidizing archaea and bacteria to nitrogen transformation in a soil fertilized with urea and organic amendments.

The contribution of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) is crucial for nitrogen transformation. The effects of four organic amendments (OAs) plus urea on soil nitrogen transformation and the contribution of the ammonia-oxidizing microbial community were investigated using an incubation experiment. The OAs plus urea treatments included pig manure plus urea (PM + U), wheat straw plus urea (WS + U), compost plus urea (CP + U) and improved-compost plus urea (IC + U), while no OAs and urea amended control was noted as CK. The abundance and composition of AOA and AOB were determined using high through-put sequencing. Compared with CK, the OA plus urea treatments significantly enhanced the amount of total mineralized nitrogen released during the incubation process. After incubation, the highest mineralized nitrogen and net nitrogen mineralization was under the PM + U treatment and the lowest was in the WS + U treatment. In conclusion, among all OA plus urea treatments, the microbial biomass nitrogen content was the highest in WS + U treatment and dissolved organic nitrogen content was the highest with the PM + U treatment. Additionally, the abundance of AOB was inhibited in comparison to that of AOA; however, AOB contributed more to nitrification than AOA. Soil NO3--N and dissolved organic nitrogen were the principal components influencing the distribution of AOA and AOB. The result illustrated that the OAs plus urea, especially PM plus urea promoted mineralization to produce more dissolved organic nitrogen and NH4+-N, thus accelerating the growth of AOB to strengthen nitrification in soil.

New insights into the sustainable use of soluble straw humic substances for the remediation of multiple heavy metals in contaminated soil.

This study addresses the research gap in understanding the differences in straw decomposition and variations in humic substances (HS) extracted from various treatment conditions. The aim is to explore the potential of soluble straw HS in remediating heavy metal pollution in soils. The study characterizes straw decomposition structures using scanning electron microscopy (SEM) and X-ray diffraction (XRD), while employing gel permeation chromatography (GPC) and fluorescence spectroscopy (EEM) to analyze the molecular weight and degree of humification of extracted straw HS. The removal efficiency of HS for heavy metals is assessed, with a focus on aerobic humic substances (AE-HS) showing the highest potential for heavy metal removal. Spectral analysis and mass spectrometry analysis reveal the role of phenolic compounds, carboxylic acids, and aromatic compounds in AE-HS, forming humates or complexes to remove heavy metals from contaminated soil. Notably, the optimized AE-HS achieved the highest removal efficiency of 96.18 %, 82.75 %, 60.43 %, and 41.66 % for cadmium, copper, zinc, and lead, respectively. This study provides new insights into the preparation of straw for use as a heavy metal remover and has implications for the use of straw humic substances in soil remediation.

The complete mitochondrial genome of the rodent intra-arterial nematodes Angiostrongylus cantonensis and Angiostrongylus costaricensis.

The two rodent intra-arterial nematodes, Angiostrongylus cantonensis and Angiostrongylus costaricensis, can cause human ill-health. The present study aimed to characterize and compare the mitochondrial (mt) genomes of these two species, and clarify their phylogenetic relationship and the position in the phylum Nematoda. The complete mt genomes of A. cantonensis and A. costaricensis are 13,497 and 13,585 bp in length, respectively. Hence, they are the smallest in the class of Chromadorea characterized thus far. Like many nematode species in the class of Chromadorea, they encode 12 proteins, 22 transfer RNAs, and two ribosomal RNAs. All genes are located on the same strand. Nucleotide identity of the two mt genomes is 81.6%, ranging from 77.7% to 87.1% in individual gene pairs. Our mt genome-wide analysis identified three major gene arrangement patterns (II-1, II-2, and II-3) from 48 nematode mt genomes. Both patterns II-1 and II-2 are distinct from pattern II-3, which covers the Spirurida, supporting a closer relationship between Ascaridida and Strongylida rather than Spirurida. Thymine (T) was highly concentrated on coding strands in Chromadorea, but balanced between the two strands in Enoplea, probably due to the gene arrangement pattern. Interestingly, the gene arrangement pattern of mt genomes and phylogenetic analysis based on concatenated amino acids indicated a closer relationship between the order Ascaridida and Rhabditida rather than Spirurida as indicated in previous studies. These discrepancies call for new research, reassessing the position of the order of Ascaridida in the phylogenetic tree. Once consolidated, the findings are important for population genetic studies and target identification.

Response of N2O emission and denitrification genes to different inorganic and organic amendments.

Denitrification is a key biochemical process in nitrogen cycling and nitrous oxide (N2O) production. In this study, the impacts of different inorganic and organic amendments (OAs) on the abundance of denitrifying genes (nirS, nirK and nosZ) and the level of N2O emission were examined with incubation experiments. Six treatments included the indicated applications: (i) no fertilization (CK); (ii) urea application alone (U); (iii) wheat straw plus urea (U + WS); (iv) pig manure plus urea (U + PM); (v) compost product plus urea (U + CP); and (vi) improved compost product plus urea (U + IC). The results indicated that all fertilization treatments increased accumulative N2O emissions compared with the CK treatment. The U + WS, U + PM and U + CP treatments increased N2O emissions by 2.12-141.3%, and the U + IC treatment decreased N2O emissions by 23.24% relative to the U treatment. nirK was the dominant denitrification gene rather than nirS and nosZ found in soil. Additionally, the highest abundance of nirK gene was that with the U + PM treatment, and the lowest was that with the U + IC treatment. Additionally, changes in the nirK gene were highly correlated with levels of dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and nitrate nitrogen (NO3-N). Automatic linear modeling revealed that N2O emission was closely related to the nirK gene, DOC and NO3-N. Overall, the use of urea and improved compost as co-amendments retarded N2O emission to a considerable degree compared with other OA additions.

Evaluation of the applicability of organic amendments from microbially driven carbon and nitrogen transformations.

Pig manure (PM), wheat straw (WS), compost product (CP) and improved compost product (IC) are very important agricultural organic resources. In this study, their applicability as soil organic fertilizations (OFs) in terms of their properties and influence on soil properties through an incubation experiment and a field verification were evaluated. The property differences indicated that wheat straw has the highest C/N ratio, and compost products contain more aromatic compounds compared with pig manure and wheat straw. The results of incubation experiment showed that OFs promoted the carbon and nitrogen transformation driven by related microorganisms and their functional metabolisms. The PM treatment had the highest proportion of Labile organic carbon to soil organic carbon (LOC/SOC) and ratio of dissolved organic carbon to soil organic carbon (DOC/SOC), while WS treatment had the lowest values. The highest net N mineralization rate and nitrification rate was observed in the WS treatment, but the lowest amounts were under the PM treatment. Additionally, the similar findings were also obtained from the field examination. Therefore, compost products were more applicable in agricultural soil as OF insight from changes in carbon, nitrogen and microbial community. Furthermore, the result of UV-vision showed that the largest amount of aromatic structure was observed in IC relative to CP. It can be concluded that CP was more conducive to fix carbon and provide available nitrogen for crops among four OFs.

Soil organic carbon transformation and dynamics of microorganisms under different organic amendments.

Organic amendments (OAs) application is a practical strategy to improve soil organic carbon (SOC) in agriculture. The present study evaluated the impact of different OAs on the transformation of carbon and the dynamics of microorganisms in a 77-day incubation experiment. The OA treatments applied included wheat straw (U + WS), pig manure (U + PM), compost (U + CP), and improved compost (U + IC), and the no amendment group was the CK. After incubation, the SOC increased significantly in the U + WS group, but the other OA treatments had no significant effect relative to the CK. Among the OA treatments, U + CP and U + IC had lower CO2-C cumulative mineralization and the highest humification of dissolved organic carbon (DOC). U + PM had the lowest SOC content and the lowest aromatization of DOC. Redundancy analyses (RDA) showed that the CO2-C cumulative mineralization directly influenced the DOC, extracted organic carbon (EOC) and microbial biomass carbon (MBC) in all treatments. Proteobacteria positively correlated with SOC and MBC, Bacteroidetes were significantly related to DOC, and Gemmatimonadetes had a significant negative relationship with CO2-C cumulative mineralization. These results showed that U + CP and U + IC were more conducive to carbon sequestration, and U + PM was the most unfavourable during the incubation. Wheat straw played an important role in the steady improvement of the SOC.

[Multiplex PCR assay for the detection of Angiostrongylus cantonensis larvae in Pomacea canaliculata].

OBJECTIVE: To establish a multiplex PCR assay for detecting Angiostrongylus cantonensis larvae in Pomacea canaliculata. METHODS: A pair of specific primers was designed based on the sequences of the small subunit rDNA of A. cantonensis (GenBank jAY295804), in combination with 16s rDNA specific primers of P. canaliculata, a multiplex PCR was developed. The PCR was performed on positive and negative snails, and the amplified products were analyzed by agarose gel electrophoresis and DNA sequencing. DNA template of 200 III stage larvae of A. cantonensis was diluted by negative snail DNA (1200 ng/microl, 120 ng/microl, 12 ng/microl, 1200 pg/microl, 120 pg/microl and 12 pg/microl), to find the minimum detectable level. Single blind method was used to evaluate the accuracy. After being detected by lung microscopy, 172 snails from field were tested by the multiplex PCR to assess the sensitivity and specificity. RESULTS: Agarose gel electrophoresis and DNA sequencing analysis indicated that the target sequences were efficiently amplified by the PCR assay (550 bp for P. canaliculata, 405 bp for A. cantonensis). The minimum detectable level was 120 pg/microl. The coincidence between the two methods stood for 84.3% (145/172), including 45 positives and 100 negatives. 24 snails were PCR positive and microscopy negative, 3 snails were PCR negative and microscopy positive. The sensitivity and specificity of multiplex PCR was 93.8% and 80.6%, respectively. Its positive rate (40.1%, 69/172) was significant higher than that of lung-microscopy (27.9%, 48/172)(chi2 = 14.8, P < 0.01). CONCLUSION: A multiplex PCR method has been developed for the detection of A. cantonensis larvae in P. canaliculata.

[Survey on the focus of Angiostrongylus cantonensis in Guangdong Province].

OBJECTIVE: To understand the distribution of Angiostrongylus cantonensis foci in Guangdong Province for making surveillance program. METHODS: Survey sites were chosen by strata sampling according to different geographic locations. Totally 22 survey sites were selected in four regions: East Guangdong, West Guangdong, North Guangdong and the Pearl River Delta. One or two administrative villages in each site were randomly selected for the investigation. Pomacea canaliculata and Achatina fulica collected from fields and other species of freshwater or terrestrial snails obtained in the restaurants and wet markets were examined for the third stage larvae by tissue grinding or lung examination. Rats were captured in the fields, and their hearts and lungs were dissected for adult worms. Rat feces were also collected for the detection of first stage larvae by water precipitation. RESULTS: Large number of P. canaliculata was found in all sites. A. fulica was found in most surveyed sites. Totally 2929 P. canaliculata and 1354 A. fulica were collected with a larva infection rate of 5.9% (172/2929) and 16.5% (223/1354), respectively (P<0.01). The average prevalence among the regions was different (P<0.01) with the highest prevalence in Pearl River Delta (15.6%, 152/975), especially in Dongguan City of the Delta (34.7%, 78/225). 114 Cipangopaludina sp. and 252 Bellamya sp. were bought from wet markets of 9. sites. Larvae were found only in Bellamya snails from Luoding and Kaiping cities with an infection rate of 1.4% (1/70) and 3.3% (3/91), respectively. Totally 491 rats were captured in 9 sites including Rattus norvegicus, R. flavipectus, Suncus murinus, Mus musculus, Bandicota indica, R. losea and R. rattus, with an average infection rate of 11.4% (56/491). Adult worms were found in R. norvegicus, R. flavipectus and B. indica with a prevalence of 19.8% (52/263), 2.5% (3/118) and 10.0% (1/10), respectively. Thirty-four rodent fecal samples were collected in 7 sites and examined with a larva positive rate of 44.1% (15/34). CONCLUSION: Foci of Angiostrongylus cantonensis are widely distributed in Guangdong Province as natural infection has been found in its intermediate and definitive hosts.

Angiostrongylus cantonensis: morphological and behavioral investigation within the freshwater snail Pomacea canaliculata.

An infection with Angiostrongylus cantonensis, the main causative agent for human eosinophilic encephalitis, can be acquired through the consumption of the freshwater snail Pomacea canaliculata. This snail also provides a suitable model to study the developmental morphology and behavior of A. cantonensis larvae, facilitated by the snail's distinct lung structure. We used microanatomy for studying the natural appearance and behavior of A. cantonensis larvae while developing within P. canaliculata. The distribution of refractile granules in the larval body and characteristic head structures changed during the developmental cycle. Two well-developed, rod-like structures with expanded knob-like tips at the anterior part were observed under the buccal cavity as early as the late second developmental stage. A "T"-shaped structure at the anterior end and its tenacity distinguished the outer sheath from that shed during the second molting. Early first-stage larvae obtained from fresh rat feces are free moving and characterized by a coiled tail, whereas a mellifluous "Q"-movement was the behavioral trait of third-stage A. cantonensis larvae outside the host tissue. In combination, the distribution of refractive granules, distinct head features, variations in sheaths, and behavioral characteristics can be utilized for differentiation of larval stages, and for distinguishing A. cantonensis larvae from those of other free-living nematodes.