Epidemiological Investigation of Enterocytozoon hepatopenaei (EHP) in Shrimp Cultured Along the Coast of China from 2021 to 2022

Enterocytozoon hepatopenaei (EHP) is a specialized intracellular parasitic microsporidian species that infects the hepatopancreas of shrimp and causes hepatopancreatic microsporidiosis (HPM). It was discovered in stunted Penaeus monodon in Thailand in 2004. It is a fungal pathogen that can infect various crustacean hosts. It affects farmed shrimp in Southeast Asia and South America, including Thailand, Vietnam, China, Indonesia, India, Malaysia, South Korea and Venezuela. An E. hepatopenaei infection does not cause death in shrimp, but can lead to necrosis and rupture of the hepatopancreatic epithelial cells. This results in reduced digestive and absorptive functions of the hepatopancreatic gland and impaired nutrient storage functions. Therefore, an EHP infection usually leads to shrimp growth retardation or stagnation that greatly reduces shrimp production and seriously affects the high-quality development of shrimp farming. E. hepatopenaei infections were detected in farmed shrimp in coastal provinces of China since 2013 and their high infection rate causes serious economic losses to the cultured shrimp industry. It is difficult to confirm EHP infections solely based on the symptoms of diseased shrimp in the field owing to the extremely small size of EHP and the lack of obvious symptoms in the early stages of EHP infection. Furthermore, the early stages of infection are difficult to accurately detect by light microscopy and histopathological sections. Pathological changes of EHP infection are only observed in the middle and later stages by histopathological sections. In addition, tissue section preparation is time-consuming and complex. This makes it unsuitable as a practical technical method to detect EHP. In contrast, molecular biology methods have become a common laboratory method to detect EHP. This study collected 936 shrimp samples from coastal areas in China from 2021 to 2022, detected EHP positive samples by TaqMan quantitative polymerase chain reaction (qPCR), and analyzed the morphology by histopathology. This study aims to clarify the prevalence of EHP in major shrimp farming species in coastal provinces and cities in China from 2021 to 2022, and to clarify the hazard risk of EHP in cultured shrimp.TaqMan qPCR assays showed that the positive detection rate of EHP in shrimp samples from coastal areas was 10.67% (54/506) in 2021. There was a decreasing trend compared with the national aquatic animal disease surveillance plan from 2017 to 2020.