Mud Crab Reovirus (MCRV)

Context:

Mud Crab Reovirus (MCRV) has been found to be the reason for the mass mortality of wild crab (Scylla serrate) in Andhra Pradesh State.

About Reovirus-

• Reoviridae is a family of double-stranded RNA viruses.
• Member viruses have a wide host range, including vertebrates, invertebrates, plants, protists and fungi.
• They lack lipid envelopes and package their segmented genome within multi-layered capsids. Lack of a lipid envelope has allowed three-dimensional structures of these large complex viruses (diameter ∼60–100 nm) to be obtained, revealing a structural and likely evolutionary relationship to the cystovirus family of bacteriophage.
• There are currently 97 species in this family, divided among 15 genera in two subfamilies.
• Reoviruses can affect the gastrointestinal system (such as rotaviruses) and respiratory tract.
• The name “reo-” is an acronym for “respiratory enteric orphan” viruses.The term “orphan virus” refers to the fact that some of these viruses have been observed not associated with any known disease.
• Even though viruses in the family Reoviridae have more recently been identified with various diseases, the original name is still used.
• Reovirus infections occur often in humans, but most cases are mild or subclinical. 
• Rotaviruses, however, can cause severe diarrhea and intestinal distress in children, and lab studies in mice have implicated orthoreoviruses in the expression of coeliac disease in pre-disposed individuals.
• The virus can be readily detected in feces, and may also be recovered from pharyngeal or nasal secretions, urine, cerebrospinal fluid, and blood. Despite the ease of finding reoviruses in clinical specimens, their role in human disease or treatment is still uncertain.
• Some viruses of this family, such as phytoreoviruses and oryzaviruses, infect plants. Most of the plant-infecting reoviruses are transmitted between plants by insect vectors. The viruses replicate in both the plant and the insect, generally causing disease in the plant, but little or no harm to the infected insect

About Mud Crab Reovirus (MCRV)

• Mud Crab Reovirus (MCRV) has been found to be the reason for the mass mortality of crabs (Scylla serrate) in Andhra Pradesh.
• MCRV, also known as the “sleeping disease”, has taken a toll on crabs in every farming method; crab fattening and crab polyculture, in which shrimp and crab are cultured in the same pond, and exclusive mud crab ponds.
• The viral pathogen belongs to the family of ‘Reoviridae’. It mainly affects the connective tissue of hepatopancreas, gills, and intestine.
• In 2007, the MCRV paralysed the crab species cultivation in China.

What is Mud Crab?

Scylla serrata commonly known as the Mud crab, Green crab or Mangrove Crab is an economically important species of crab found in the estuaries and mangroves of India.

There has been a huge interest in the aquaculture of this species due to their high demand/ price, high flesh content and rapid growth rates in captivity.

They are ecologically important species, The shell colour varies from deep, mottled green to dark brown, In their most common form.

In India, crab culture is developing very fast in the states of AP, Kerala, West Bengal and Odisha.

Why recently in news

• Presence of MCRV in samples collected from Nagayalanka fields was confirmed by Joint research by Centre for Advanced Study in Marine Biology (Annamalai University, Tamil Nadu) and M.S. Swaminathan Research Foundation (MSSRF).
• MSSRF has been noticing mortality in areas like Machilipatnam and Nagayalanka in Krishna district, since 2019.
• MCRV has taken a toll on wild crab in every farming method, crab polyculture and crab fattening in which shrimp and wild crab are cultured in exclusive mud crab ponds and in same pond.
• Crab fattening technology was introduced in Andhra Pradesh by Central Institute of Brackishwater Aquaculture (CIBA-Chennai), in 2014.

International Case

In China, the MCRV had paralysed the wild crab species cultivation in 2007.

Case of Andhra Pradesh

In Andhra Pradesh, total area under wild crab cultivation is around 25,000 acres. Around 4,500 acres are there in Krishna district. The wild crab is cultivated in the districts of Nellore, Guntur, Prakasam, Krishna, and Godavari districts. Wild crab is exported to South-east Asia region directly from Andhra Pradesh and it has a large market in Europe. But starting from 2019, around 60% of cultivation has been affected because of mass mortality in the State.

Source: The Hindu

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