Hepatopancreatic Microsporidiosis / Enterocytozon hepatopenaei (EHP)

Name

Hepatopancreatic microsporidiosis

Clinical signs

Shrimp infected with microsporidiosis due to EHP exhibit slowed growth, indicated by a significant size difference among shrimp within the same pond, with size variations of more than five times in an infected population.

In some cases, the back of the shrimp shows a white color, particularly in the digestive tract similar to white feces. Shrimp infected with EHP also have lesions within the cytoplasm of the hepatopancreas cells.

Method of diagnosis

The spread of EHP infection that is detected early can still be prevented to maximize yields. Diagnosis can be done in the laboratory with real-time PCR test (targeting the small subunit ribosomal RNA), in situ hybridization, loop-mediated isothermal amplification (LAMP), and preparation of a histology sample from the shrimp hepatopancreas.

Source: Parasitology Research

Name

Enterocytozoon hepatopenaei

Pathogen type

Fungi (part of microsporidian parasites)

Synonyms

None.

Characteristics

EHP is an endemic parasite in Australasia (a region in Oceania) that can infect cultivated vannamei shrimp in Asia. EHP spores measure 1.1 ± 0.2 to 0.6-0.7 ± 0.1 µm and can persist for a long time in water. As a microsporidian, EHP does not require another host for transmission besides shrimp. EHP infection usually makes shrimp more susceptible to AHPND, WSSV, or Vibrio bacterial infections.

Toxicity

When this parasite attacks shrimp, the danger posed is the difference in shrimp growth rate, causing slowed growth in shrimp. Although there has not been any documented mortalities as a direct result of EHP, infected shrimp is more susceptible to other diseases, causing a loss for farmers.

Predispositional factors

EHP infection is more likely to occur in ponds with weak biosecurity measures. Concurrent infection with EHP and vibriosis has been linked to the occurrence of White Feces Disease (WFD). However, not all ponds positive for EHP always experience WFD, and vice versa.

Transmission

EHP infection is directly spread horizontally through cannibalism. Additionally, since the parasite's spores are released with the shrimp's feces, pond water and bottom surfaces are suspected to be potential media for infection.

Epidemiology

The EHP parasite was first found infecting tiger shrimp in Thailand, before it spread to other Asian regions such as China, Indonesia, Malaysia, Vietnam, and India.

Host or vector

Although it needs no vector to spread, research has found that EHP can infect Polychaete.

Infectious dose

Uncertain, but PCR diagnosis detects EHP positivity in low and high doses.

Incubation period

3-4 weeks.

Susceptibility to drugs

There is no current drug for this disease.

Susceptibility to disinfectants/probiotics

There is no current probiotic for this disease.

Physical inactivation

Spores cannot be inactivated by desiccation.

Early warning

The presence of parasite spores can be checked through laboratory testing using real-time PCR on shrimp infected with WFD, as well as on juvenile and post-larval shrimp.

Prevention

EHP can be prevented by improving biosecurity management in cultivation ponds, keeping water constantly clean. Reducing the stocking density also helps.

Treatment

There is no current treatment for this disease.

Eradication

If a pond is affected by EHP, measures that can be taken include inactivating or cleaning the spores from the pond by applying lime or CaO at a dose of 6 tons/ha, then plowing it into the soil 10-12 cm deep and adding water until it is absorbed. Allow it to sit for 1 week before drying. The soil pH will rise to 12 and then drop after a few days as it absorbs carbon dioxide and becomes CaCO₃.

Additionally, increase the frequency of water exchanges, remove infected or dead shrimp to prevent transmission through cannibalism, and perform siphoning or add probiotics to maintain water quality in the pond.

The appropriate steps to prevent or manage ponds infected with EHP include implementing strict biosecurity measures, such as separating nets and equipment, installing physical barriers, informing neighboring farms if an infection occurs, and conducting partial harvests if possible.

Long-term solutions for EHP infection include regular screening of shrimp fry using PCR testing, using SPF or SPR fry, and reducing organic material inputs in the cultivation pond.

Annisa Fitriah Faisa dan Adi Pancoro. 2018. Deteksi Dini Enterocytozoon hepatopenaei (EHP) pada Udang Vaname (Litopenaeus vannamei) Menggunakan Metode PCR (Polymerase Chain Reaction). Jurnal Riset Akuakultur. 13 (3), 267-275.

Chiarahkhongman, P. 2013. Tambak Bersih Kurangi Berak Putih. Symposium Udang 2013 dalam TROBOS Aqua Edisi 86 (VII) tahun 2019.

Diseases of Crustaceans ─ Hepatopancreatic microsporidiosis caused by Enterocytozoon hepatopenaei (EHP). Australian Government.

Genics Pty Ltd. 2023. Genics Education Series: Enterocytozoon hepatopenaei (EHP) or “hepatopancreatic microsporidosis”.

Rajendran, R.V., Shivam, S., Praveena, P.E., Rajan, J.J.S., Kumar, T.S., Avunje, S., Jagadeesan, V., Babu, S.V.A.N.V.P., Pande, A., Krishnan, A.N., Alavandi, S.V., Vijayan, K.K. 2015. Emergence of Enterocytozoon hepatopanaei (EHP) in farmed Penaeus (Litopenaeus) vannamei in India. Aquaculture. doi: 10.1016/j.aquaculture.2015.12.034

The Fish Site. Enterocytozoon Hepatopenaei (EHP) Diseases guide.