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.

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.