关键词: 卫氏并殖吸虫, 宿主, 自然感染

Abstract: Objective   To investigate the natural hosts infected with Paragonimus sp. and identify the species of the parasite in selected counties/districts of Jinhua prefecture in Zhejiang Province.  Methods   Three townships/towns were randomly sampled from each of the 9 counties/districts in Jinhua as pilot spots for the survey. Fresh-water snails were collected from the fields for examining cercariae. Crabs were collected and detected for metacercariae by routine technique and the metacercariae were fed to dogs purchased in areas free from paragonimiasis. Fecal materials of dogs and cats around the villages and streams where crabs were found infected were collected for examining eggs. The artificially infected dogs were sacrificed 55 d after infection to receive adult worms. The size of cercariae, metacercariae, eggs and adult worms was measured. After the DNA of the adult worm was extracted，PCR was used to amplify the COI gene and ITS2 gene of the mitochondria from the worms. Homology with relative strains/isolates was analyzed and phylo-genetic tree constructed.  Results   The survey demonstrated that the snail Semisulcospira libertina and the crab Sinopotamon chekiangense served as the first and second intermediate hosts respectively. Natural infection was found in Wucheng District with an infection rate of 0.2% (2/1 088)in snails and 76.7%(46/60)in crabs in Shafan township, and an infection index(II)of 2.0 in crabs, 0.1% (1/1 683)in snails and 53.0%(46/60)in crabs with an II of 0.9 in Langya town. The infection rate was 0(0/575)in snails and 30.0%(18/60)in crabs with an II of 0.1 in Baimu township of Wuyi County. Paragonimus eggs were detected in feces of stray cats with a positive rate of 8.3%(1/12)in Shafan and 0.6%(1/17)in Langya. The size and morphology of the cercariae, metacercariae, eggs and adult worms were similar to those of Paragonimus westermani. The sequences of the COI and ITS2 genes were with 390 bp and 363 bp respectively, indicating a homology of 88.2%-98.2% and 86.5%-88.1% to the 11 strains/isolates of P. westermani recorded in the GenBank. The phylogenetic trees revealed that the parasite in Jinhua was in between the Minchin(Minqing, Fujian)strain and the Japanese Mie and Chiba strains.  Conclusion  Natural paragonimus infection has been detected in snails, crabs and cats in Jinhua. The parasite has been identified as P. westermani which is phylogenetically close to those reported from Fujian Province and from Mie and Chiba of Japan.

Key words: Paragonimus westermani, Host, Natural infection