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

Abstract

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. However, the positive rate of EHP in shrimp samples from coastal areas reached 13.72% (59/430) in 2022. There was an increase in the EHP positive detection rate compared with the national surveillance data from 2019 to 2020. The detection results of EHP in samples collected from different regions showed that the positive rate of EHP was high in samples collected from Liaoning (10%) and Shandong (18.80%) in 2021, and in samples collected from Liaoning (14.63%), Hebei (29.17%), Tianjin (28.57%), and Shandong (16.88%) in 2022. The results of samples collected from different shrimp varieties showed that EHP was mainly detected in P. vannamei in 2021 and 2022, with positive rates of 14.10% (54/383) and 16.71% (58/347), respectively. Among them, one sample of Exopalaemon carinicauda was positive for EHP, while no EHP positive sample was detected in Macrobrachium rosenbergii, Protocrayfish cruzi, Penaeus monodon, Marsupenaeus japonicus, and Penaeus chinensis. This study collected and analyzed 506 and 430 shrimp samples from coastal provinces and cities in China in 2021 and 2022, respectively by TaqMan qPCR. These detection results are more reliable than those of previous studies owing to the large sample size and the high specificity and sensitivity of the detection method. The results provided an important reference for a comprehensive understanding of the epidemic situation of EHP in major cultured shrimp in coastal areas of China from 2021 to 2022. Histopathological examination of EHP-positive P. vannamei revealed that scattered or clustered EHP spores and EHP protoplasts were observed in hepatopancreatic epithelial cells.The epidemiological survey and molecular epidemiological analysis of shrimp farmed in coastal provinces, municipalities, and some inland provinces of China in 2021 to 2022 showed that the prevalence rate of EHP is generally decreasing compared to previous years. This indicated that remarkable achievements were made to prevent and control EHP in China's shrimp farming industry in recent years. However, EHP is widely prevalent in farmed shrimp in coastal provinces in Northern China. Therefore, measures such as strict EHP quarantine of brood stock and seedlings and the promotion of non-EHP seedlings should be taken to further reduce the epidemic range and risk of EHP and promote the green and high-quality development of the shrimp culture industry in China.

Keywords

• ehp
• epidemiological investigation
• taqman real-time fluorescence quantitative pcr (taqman qpcr)
• histopathology