Abstract: Giardia duodenalis, a parasitic intestinal parasite that is zoonotic, was spread all over the world. Moreover, its infection rate had a great relationship with the region and the environment. To understand the infection situation of canine duodenal Giardia duodenalis in the neighboring countries and regions of the South China Sea, and determine whether marine isolation is an important factor affecting Giardia duodenalis transmission.From June 2018 to July 2019, 616 canine fecal samples were collected from Guangzhou, China, Ho Chi Minh City, Vietnam, Kuala Lumpur, Malaysia, Singapore, and Manila, Philippines. DNA of canine fecal samples from each region were extracted, and a nested PCR was prepared by using the TPI gene and BG gene of Giardia duodenalis. The extracted canine fecal genomic DNA was used as a template for nested PCR amplification to determine its positive infection rate. PCR-positive products were sequenced and the results were compared with Giardia duodenalis sequences in GenBank to determine their typing.Among the 616 samples, tested results of 48 samples were positive for Giardia duodenalis infection, with a positive rate of 7.79% (48/616). The infection rates in different regions were 4.81% in Guangzhou, China, 6.90% in Ho Chi Minh City, Vietnam, 9.09% in Kuala Lumpur, Malaysia, 2.86% in Singapore, and 11.52% in Manila, Philippines. Among them, 48 samples were detected at TPI and BG sites, and the positive rates were 7.63% and 5.19%, respectively. The positive samples were then sequenced and compared for the BG and TPI gene sites, and it was learned that the BG site had conglomerate B type (3.33%), conglomerate C type (86.67%), and conglomerate D type (10%). TPI site had conglomerate B type (2.12%), conglomerate C type (85.1%), and conglomerate D type (12.76%). After statistical analysis and comparison, the difference between Giardia duodenalis genotypes in various regions was not significant. Giardia duodenalis infection existed in the surrounding areas of the South China Sea, and the infection rate was relatively low in areas with relatively good public health. The genotyping distribution of canine Giardia duodenaliswas not significantly affected by the isolation of marine areas.

Key words: Giardia duodenalis, genotype, infection rate