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Experimental transmission and tissue tropism of Macrobrachium rosenbergii nodavirus (MrNV) and its associated extra small virus (XSV).

Department of Zoology, C. Abdul Hakeem College, Melvisharam 632 509, Vellore District, Tamil Nadu, India.
Diseases of Aquatic Organisms (Impact Factor: 1.73). 01/2005; 62(3):191-6. DOI: 10.3354/dao062191
Source: PubMed

ABSTRACT White tail disease (WTD) was found to be a serious problem in hatcheries and nursery ponds of Macrobrachium rosenbergii in India. The causative organisms have been identified as M. rosenbergii nodavirus (MrNV) and its associated extra small virus (XSV). Experimentally transmitted to healthy animals, they caused 100% mortality in post-larvae but failed to cause mortality in adult prawns. The RT-PCR assay revealed the presence of both viruses in moribund post-larvae and in gill tissue, head muscle, stomach, intestine, heart, hemolymph, pleopods, ovaries and tail muscle, but not in eyestalks or the hepatopancreas of experimentally infected adult prawns. The presence of these viruses in ovarian tissue indicates the possibility of vertical transmission. Pleopods have been found to be a suitable organ for detecting these viruses in brooders using the RT-PCR technique.

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    ABSTRACT: White tail disease (WTD) caused by Macrobrachium rosenbergii nodavirus (MrNV) has been found in the giant freshwater prawn (Macrobrachium rosenbergii) and has recently been the cause of high mortalities in many countries such as India, China, Taiwan and Thailand. In mid 2004, the index case of WTD in Australia presented in adult broodstock M. rosenbergii from Flinders River in western Queensland. In order to understand the phylogenetic relationship of the Australian recognizate of MrNV to other MrNV recognizates, the complete sequences of the Australian MrNV (RNA1 and RNA2) were determined. Nucleotide and phylogenetic analysis revealed that the Australian strain of MrNV (RNA1) was between 94% and 97% identical to Malaysian, the French West Indies, Chinese and the Thai recognizates. Also, the nucleotide sequence of the Australian MrNV (RNA2) was 92% identical to the French West Indies, Chinese and the Thai recognizates. The nucleotide comparison of protein B2 showed a different relationship between MrNV and fish nodaviruses. However, the phylogenetic tree of protein B2 determined that some fish nodaviruses are closely related to insect nodavirus. These results can be used to develop effective diagnostic tests and design specific RNA interference (RNAi) against protein B2 to control other nodaviruses in the future.
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    ABSTRACT: Macrobrachium rosenbergii is the most important cultured freshwater prawn in the world and it is now farmed on a large scale in many countries. Generally, freshwater prawn is considered to be tolerant to diseases but a disease of viral origin is responsible for severe mortalities in larval, post-larval and juvenile stages of prawn. This viral infection namely white tail disease (WTD) was reported in the island of Guadeloupe in 1995 and later in Martinique (FrenchWest Indies) in Taiwan, the People's Republic of China, India, Thailand, Australia and Malaysia. Two viruses, Macrobrachium rosenbergii nodavirus (MrNV) and extra small virus-like particle (XSV) have been identified as causative agents of WTD. MrNV is a small icosahedral non-enveloped particle, 26-27 nm in diameter, identified in the cytoplasm of connective cells. XSV is also an icosahedral virus and 15 nm in diameter. Clinical signs observed in the infected animals include lethargy, opaqueness of the abdominal muscle, degeneration of the telson and uropods, and up to 100 % within 4 days. The available diagnostic methods to detect WTD include RT-PCR, dot-blot hybridization, in situ hybridization and ELISA. In experimental infection, these viruses caused 100 % mortality in post-larvae but failed to cause mortality in adult prawns. The reported hosts for these viruses include marine shrimp, Artemia and aquatic insects. Experiments were carried out to determine the possibility of vertical transmission of MrNV and XSV in M. rosenbergii. The results indicate that WTD may be transferred from infected brooders to their offspring during spawning. Replication of MrNV and XSV was investigated in apparently healthy C6/36 Aedes albopictus and SSN-1 cell lines. The results revealed that C6/36 and SSN-1cells were susceptible to these viruses. No work has been carried out on control and prevention of WTD and dsRNA against protein B2 produced RNAi that was able to functionally prevent and reduce mortality in WTD-infected redclaw crayfish.
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