Macronovirus

Macronovirus is the only genus of the family Sarthroviridae. It contains one species: Extra small virus (XSV, Macronovirus macrobrachii).^[2]

Macronovirus
Transmission electron micrographs of negatively-stained Extra small virus; bar = 50 nm
Virus classification
(unranked):	Virus
Realm:	Riboviria
Order:	Tombendovirales
Family:	Sarthroviridae
Genus:	Macronovirus
Species
Macronovirus macrobrachii
Synonyms[1]
Macrobrachium satellite virus 1

It is found in The French West Indies, Thailand, Taiwan, China, and India.^[3]

Etymology

The genus name, Macronovirus, is a combination of Macro, from the host Macrobrachium rosenbergii and no, from helper virus nodavirus.^[3]

The family name, Sarthroviridae, is a combination of S, from Small and arthro, from host arthropoda.^[4]

Hosts

Macronovirus's cell tropism is muscle and connective cells of diseased animals, and its natural hosts are arthropods.^[4]

Structure

The virion of XSV has a genome consisting of linear single-stranded RNA of positive polarity, 0.8kb in size, with two genes. This encodes two capsid proteins, CP-17 and CP-16. The virion is non-enveloped, spherical, with a capsid of about 15 nm with icosahedral symmetry. The virion is constructed from two capsid proteins CP-17 and CP-16. It has a Monopartite, linear, ssRNA(+) genome.^[3]

Gene expression

The virion RNA is infectious and serves as both the genome and viral messenger RNA.^[3]

Replication

Its replication is cytoplasmic, and has 8 steps.^[3]

1. Attachement to host receptors mediates entry into the host cell.
2. Uncoating, and release of the viral genomic RNA into the cytoplasm.
3. Viral RNA is translated in a polyprotein to produce replication proteins.
4. Replication by helper virus occurs in viral factories made of membrane vesicles derived from the ER. A dsRNA genome is synthesized from the genomic ssRNA(+).
5. The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
6. Expression of the capsid proteins.
7. Assembly of new virus particles.
8. Virus release.

Disease

Whitish muscle disease, which develops in post-larvae of freshwater prawn Macrobrachium rosenbergii and is caused by Macrobrachium rosenbergii nodavirus (MrNV) and its associate Extra small virus. Main symptom is a whitish appearance of the muscles, particularly noticeable in the abdomen. Mortalities can reach 100%.^[3]