Research
Shrimp microsporidian Enterocytoozoon hepatopenaei (EHP)
Hepatopancreatic microsporidiosis (HPM), a disease caused by a fungi-related microsporidian parasite called EHP, has recently become a serious threat to shrimp industries worldwide. HPM is reported to be associated with slow growth and severe size variation which results in economic losses. EHP infection is primarily found in hepatopancreas of both Pacific white shrimp Penaeus vannamei and black tiger shrimp Penaeus monodon.
EHP is an obligate, intracellular parasite that forms spores. Inside the EHP spores, they contain a unique harpoon-like invasion apparatus called the polar tube. This polar tube is conserved among all microsporidian species. The polar tube typically coils inside the spore, resembling a spring. Under suitable conditions, the spores extrude the polar tube. The polar tube is proposed to penetrate the host cell membrane and provide a conduit for infectious material of the parasite to be transferred into the host cell cytoplasm. The polar tube firing process occurs on a rapid timescale (in less than 2 sec), making it challenging to image in real time.
Pathology of shrimp infected with EHP. (A) Infected shrimp show a sign of size variation and slow growth syndrome. (B) Hematoxylin and eosin (H&E) staining of hepatopancreatic tissues reveals various stages of EHP including plasmodia and mature spores. (C) Purified mature EHP spores stained with hematoxylin staining. Note that (A) is adapted from Rajendran et. al 2016, while (B) is modified from Chaijarasphong et. al 2021.
Recently, high-speed live-cell imaging has been utilized to study the polar tube firing kinetics in human infectecting microsporidia. It has been shown that the whole firing process takes less than 500 ms in Encephalitozoon spp. and the velocity of the polar tube firing approaches 300 μm/s. The kinetics vary between closely related species. However, the knowledge on the polar tube firing kinetics which is an important process for the infection is largely unknown in EHP. In addition, the physiological conditions to trigger the polar tube firing in the shrimp host remain unclear.
Outstanding questions we are trying to answer in our lab include
1) What are the kinetics of polar tube firing in EHP?
2) What are the physiological conditions for polar firing in shrimp?
3) How shrimp cells respond to EHP infection?
Structure of the polar tube in its pre-germination and post-germination stages. (A) Three-dimensional reconstruction of mosquitoes-infecting microsporidian Anncaliia algerae spore represents how the polar tube (blue color) is configured in the spore. (B) Micrograph of spore germination shows the polar tube when it is protruded. Sporoplasm or infectious material is still attached at the end of the polar tube. This figure is adapted from Jaroenlak et. al 2020