The Macrobrachium rosenbergii nodavirus: a detailed review of structure, infectivity, host immunity, diagnosis and prevention

Abstract

The Macrobrachium rosenbergii nodavirus causes white tail disease, which primarily infects giant freshwater prawns, Macrobrachium rosenbergii. The infection leads to almost 100% mortality in post-larvae, causing significant economic losses in aquaculture farms. To develop effective measures against outbreaks, a good understanding of the virus is essential. In this review, we discuss key aspects of the Macrobrachium rosenbergii nodavirus including its structure, mechanisms of transmission and infection and common strategies for detection and prevention of outbreaks. Structurally, cryogenic electron microscopy revealed that the nodavirus has a T = 3 icosahedral structure with dimeric blade-like spikes on its surface. Homology modelling comparing wild-type and enzymatically cleaved Macrobrachium rosenbergii nodavirus-like particles revealed the significance of these spikes or protruding domains for binding. In vitro and in vivo studies have identified key aspects of Macrobrachium rosenbergii nodavirus infectivity, including (i) the viral binding targets such as transglutaminase and caveolin-1, (ii) utilisation of B2-like proteins in promoting infectivity and intracellular migration, (iii) replication mechanisms and (iv) co-infection with the extra small virus. Though susceptible at a post-larvae stage, adult Macrobrachium rosenbergii is immune to Macrobrachium rosenbergii nodavirus infection. During outbreaks, polymerase chain reaction and in situ hybridisation-based detection techniques are commonly used to identify infected populations. Currently, the most useful strategies for an outbreak are physical biosecurity measures and prophylaxis such as vaccination and immunostimulants. Finally, critical gaps in research include development of immortalised shrimp cell models, elucidation of time-resolved protein changes post-infection and development of therapies to treat infections to mitigate economic losses during outbreaks.

Viral Shrimp Diseases Listed by the OIE: A Review

“…WTD (white tail disease) is caused by Macrobrachium rosenbergii nodavirus ( Mr NV) and extra small virus (XSV), and it induces critical economic losses, especially at the hatchery and nursery stages [ 140 ]. WTD was first reported in Guadeloupe (French West Indies) in 1995 or 1997 (named white tail disease from Pointe Noire, Guadeloupe in 1997) and later in Martinique (French West Indies) (1999), China (2003), India (2004), Thailand (2006), Taiwan (2006), Australia (2008), Malaysia (2012) [ 141 , 142 , 143 , 144 ] ( Figure 21 ). White-tailed disease occurs in the freshwater shrimp M. rosenbergii , which is cultivated in many countries, and has an extremely high mortality rate (often reaching 100%) and causes enormous economic loss [ 145 ].…”

“…WTD is caused by Mr NV ( Macrobrachium rosenbergii nodavirus) which is accompanied by another virus, XSV (extra small virus) [ 142 ] ( Table 1 ). Mr NV is a small icosahedral with non-enveloped two single-stranded RNA virus (RNA1: size 2.9 kb, RNA2: size 1.26 kb) approximately 26–27 nm in diameter and was observed in the cytoplasm of connective cells classified into the family Nodaviridae, which consists of two genera, Alphanodavirus and Betanodavirus, Nodaviruses have T = 3 capsids of a single polypeptide that is 43 kDa [ 54 , 144 ].…”

“…Since it is difficult to classify Mr NV as an Alphanodavirus as it mainly infects insects and Betanodavirus which mainly infects fish, it has been proposed that it be classifies as a Gammanodavirus genus belonging to the Nodaviridae family [ 146 , 150 ]. Shrimp infected with Mr NV target hemocytes and myonuclei in the lower abdomen, they then spread to the rest of the abdomen, and subsequently, throughout the body via the hemolymph circulatory system, thereby observing the almost tissues of infected shrimp except for hepatopancreas and eyestalks [ 142 ]. Mr NV, a viral particle with an initial diameter of 27 nm, was observed in WTD-infected shrimp, and shortly thereafter, a second type of virus particle with an abnormally small diameter of 15 nm was observed in the WTD-infected shrimp tissue, which was named XSV [ 152 ].…”

“…Mr NV and XSV can be transmitted horizontally in the form of dead tissue, live carriers, and free virions through formulas of M. rosenbergii infected with WTD, and natural hosts of adjacent ecosystems and culture systems [ 142 , 146 ]. In the WTD horizontal transmission experiment, artemia was exposed to Mr NV and XSV by immersion and oral routes, confirming that it could act as a reservoir or carrier for the Mr NV and XSV [ 140 ].…”

“…To control the spread of WTD, it is essential to develop highly sensitive and rapid diagnostic methods that can detect pathogens early, because effective methods such as vaccines or treatment for controlling and preventing WTD have not been presented [ 142 ]. Screening using sensitive diagnostic methods such as reverse-transcription polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA) to select specific pathogen free (SPF) brood stock and post-larvae can be an effective method [ 153 ].…”