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 and σ2 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.

[Discovery of Culex inatomii (Diptera : Culicidae) in Chongming, Shanghai].

Objective: To record the discovery of Culex inatomii in Chongming, Shanghai. Methods: Larvae and adult mosquitos of Cx. inatomii were collected in Dongtan of Chongming Island from May to November in 2015 and 2016, and their morphological characteristics were observed. The genomic DNA was extracted from adult mosquitos, PCR was performed to amplify the cytochrome c oxidaseⅠ(COⅠ) gene. Multiple alignment of COⅠ sequence was conducted with ClustalW2. Pairwise distances within and between species were calculated using MEGA v5.10 based on COⅠ sequences of Cx. inatomii, Cx. modestus, Cx. pipiens pallens, and Cx. tritaeniorhynchus. The phylogenetic tree of the above four species was constructed using neighbor joining, maximum likelihood, and Bayesian methods. Results: One hundred and fifty-six adult female mosquitos and 36 larvae of Cx. inatomii were collected. Larvae were reared to adult stage in the laboratory (17 female, 19 male). Morphologically, the subapical lobe of the sidepiece in male genitalia was divided into two parts, the anterior part having 2 bladed setae, and the posterior part having 1 bladed setae and 1 lanceolar strong setae. This strucutre can be used to distinguish Cx. inatomii from Cx. modestus. PCR of COⅠ resulted in products of approximately 650 bp. They were sequenced and the sequencing result was submitted to GenBank (accession number, KX555565-KX555570). Multiple sequence alignment revealed a 96% sequence similarity of COⅠ between Cx. inatomii and Cx. modestus. The genetic distance between Cx. inatomii and Cx. modestus was 0.047, and that within them each was 0.003 and 0.011, respectively. The phylogenetic tree showed that the four species clustered as a monophyletic clade, and each formed an individual lineage. Cx. inatomii had a closer relationship with Cx. modestus, while distant from the other two species. Conclusion: We recorded the discovery of Cx. inatomii in Chongming, Shanghai.