First detection of yellow head virus genotype 3 (YHV-3) in cultured Penaeus monodon, mainland China

Coinfection with Yellow Head Virus Genotype 8 (YHV-8) and Oriental Wenrivirus 1 (OWV1) in Wild Penaeus chinensis from the Yellow Sea

At present, there are few studies on the epidemiology of diseases in wild Chinese white shrimp Penaeus chinensis. In order to enrich the epidemiological information of the World Organisation for Animal Health (WOAH)-listed and emerging diseases in wild P. chinensis, we collected a total of 37 wild P. chinensis from the Yellow Sea in the past three years and carried out molecular detection tests for eleven shrimp pathogens. The results showed that infectious hypodermal and hematopoietic necrosis virus (IHHNV), Decapod iridescent virus 1 (DIV1), yellow head virus genotype 8 (YHV-8), and oriental wenrivirus 1 (OWV1) could be detected in collected wild P. chinensis. Among them, the coexistence of IHHNV and DIV1 was confirmed using qPCR, PCR, and sequence analysis with pooled samples. The infection with YHV-8 and OWV1 in shrimp was studied using molecular diagnosis, phylogenetic analysis, and transmission electron microscopy. It is worth highlighting that this study revealed the high prevalence of coinfection with YHV-8 and OWV1 in wild P. chinensis populations and the transmission risk of these viruses between the wild and farmed P. chinensis populations. This study enriches the epidemiological information of WOAH-listed and emerging diseases in wild P. chinensis in the Yellow Sea and raises concerns about biosecurity issues related to wild shrimp resources.

Viral Shrimp Diseases Listed by the OIE: A Review

Shrimp is one of the most valuable aquaculture species globally, and the most internationally traded seafood product. Consequently, shrimp aquaculture practices have received increasing attention due to their high value and levels of demand, and this has contributed to economic growth in many developing countries. The global production of shrimp reached approximately 6.5 million t in 2019 and the shrimp aquaculture industry has consequently become a large-scale operation. However, the expansion of shrimp aquaculture has also been accompanied by various disease outbreaks, leading to large losses in shrimp production. Among the diseases, there are various viral diseases which can cause serious damage when compared to bacterial and fungi-based illness. In addition, new viral diseases occur rapidly, and existing diseases can evolve into new types. To address this, the review presented here will provide information on the DNA and RNA of shrimp viral diseases that have been designated by the World Organization for Animal Health and identify the latest shrimp disease trends.

A Novel Bunyavirus Discovered in Oriental Shrimp (Penaeus chinensis)

Herein, we describe a novel bunyavirus, oriental wenrivirus 1 (OWV1), discovered in moribund oriental shrimp (Penaeus chinensis) collected from a farm in China in 2016. Like most bunyaviruses, OWV1 particles were enveloped, spherical- to ovoid-shaped, and 80-115 nm in diameter. However, its genome was found to comprise four segments of (-)ssRNA. These included an L RNA segment (6,317 nt) encoding an RNA-directed RNA polymerase (RdRp) of 2,052 aa, an M RNA segment (2,978 nt) encoding a glycoprotein precursor (GPC) of 922 aa, an S1 RNA segment (1,164 nt) encoding a nucleocapsid (N) protein of 243 aa, and an S2 RNA segment (1,382 nt) encoding a putative non-structural (NSs2) protein of 401 aa. All the four OWV1 RNA segments have complementary terminal decanucleotides (5'-ACACAAAGAC and 3'-UGUGUUUCUG) identical to the genomic RNA segments of uukuviruses and similar to those of phleboviruses and tenuiviruses in the Phenuiviridae. Phylogenetic analyses revealed that the RdRp, GPC, and N proteins of OWV1 were closely related to Wēnzhōu shrimp virus 1 (WzSV-1) and Mourilyan virus (MoV) that infect black tiger shrimp (P. monodon). Phylogenetic analyses also suggested that OWV1 could be classified into a second, yet to be established, species of the Wenrivirus genus in the Phenuiviridae. These wenriviruses also clustered with Wenling crustacean virus 7 from shrimps and bunya-like brown spot virus from white-clawed crayfish. Of note there were no homologs of the NSs2 of OWV1 and MoV/WzSV-1 in GenBank, and whether other crustacean phenuiviruses also possess a similar S2 RNA segment warrants further investigation. In addition, we established a TaqMan probe-based reverse-transcription quantitative PCR method for detection of OWV1, and it was detected as 1.17 × 102-1.90 × 107 copies/ng-RNA in gills of 23 out of 32 P. chinensis samples without an obvious gross sign. However, the discovery of OWV1 highlights the expanding genomic diversity of bunyaviruses.

A Novel Virus of Flaviviridae Associated with Sexual Precocity in Macrobrachium rosenbergii

Since 2010, sexual precocity, a typical sign of the iron prawn syndrome (IPS), resulting in the reduced size of farmed giant freshwater prawns Macrobrachium rosenbergii, has caused substantial production losses. However, the cause of IPS was not clear. We ran tests for eight major shrimp pathogens, but none were detected from IPS-affected prawns. We performed the histopathological examination of tissues and identified an eosinophilic inclusion in the perinuclear cytoplasm of cells in various tissues associated with nervous and endocrinal functions in the compound eyes. A subsequent bioassay with viral extracts of IPS-affected samples reproduced the gross signs of IPS. Metatranscriptomic sequencing identified a novel virus of Flaviviridae in all IPS-affected M. rosenbergii prawns, which was not found in samples without IPS. This virus contains a positive-sense, single-stranded RNA genome of 12,630 nucleotides (nt). Phylogenetic analysis of the conserved RdRp and NS3 domains showed that it may belong to a new genus between Jingmenvirus and Flavivirus. Under transmission electron microscopy (TEM), putative virus particles showed as spherical with a diameter of 40 to 60 nm. In situ hybridization found hybridization signals consistent with the histopathology in the compound eyes from IPS-affected M. rosenbergii. We provisionally name this virus infectious precocity virus (IPV) and propose the binominal Latin name Crustaflavivirus infeprecoquis gen. nov., sp. nov. We developed a nested reverse transcription-PCR diagnostic assay and confirmed that all IPS-affected prawns tested IPV positive but normal prawns tested negative. Collectively, our study revealed a novel virus of Flaviviridae associated with sexual precocity in M. rosenbergii. IMPORTANCE The iron prawn syndrome (IPS), also described as sexual precocity, results in the reduced size of farmed prawns at harvest and significant economic losses. IPS has been frequently reported in populations of farmed Macrobrachium rosenbergii since 2010, but the cause was heretofore unknown. Here, we reported a novel virus identified from prawns with IPS using infection experiments, metatranscriptomic sequencing, and transmission electron microscopy and provisionally named it infectious precocity virus (IPV). Phylogenetic analysis showed that IPV represents a new genus, proposed as Crustaflavivirus gen. nov., in the family Flaviviridae. This study provides novel insight that a viral infection may cause pathological change and sexual maturation and subsequently affect crustacean growth. Therefore, we call for quarantine inspection of IPV in transboundary trade of live M. rosenbergii and enhanced surveillance of IPV in aquaculture in the region and globally.

The role of UhpA in regulating the virulence gene expression in Edwardsiella piscicida

Edwardsiella piscicida (E. piscicida) is an important fish pathogen. However, the mechanism of Glu6P transport regulatory protein UhpA how to affect the virulence gene expression in E. piscicida is still unclear. The results in this study showed that the metabolism-related gene expression of cysteine synthase (orf 1134) and sulphate transporter (ychM) in the uhpA mutant strain ΔuhpA was 0.76-fold and 0.68-fold lower than the ones in the wild strains (p < .05). The gene expression of ethA and ethB in the ΔuhpA strain was 0.80-fold and 0.72-fold lower than the ones in the wild strains (p < .05). However, the gene expression of fliC and flgN in the ΔuhpA was 1.51-fold and 1.21-fold higher than the ones in the wild strains (p < .05). The gene expression of T3SS (esrB and esrC) and T6SS (evpB and evpC) in the ΔuhpA was 1.27-fold, 1.13-fold, 1.28-fold and 1.23-fold higher than the ones in the wild strains (p < .05). This suggested that the uhpA gene could regulate the key virulence gene expression, and the uhpA gene was associated with the pathogenicity of E. piscicida in fish.

The UhpA mutant of Edwardsiella piscicida enhanced its motility and the colonization in the intestine of tilapia

Edwardsiella piscicida (E. piscicida) is a significant bacterial pathogen of cultured fish, which infected fish meanly through the intestine. Glucose 6-phosphate (Glu6P) in the intestine is nutritious to the pathogen, Meanwhile, Glu6P was found using as a virulent regulating signal for bacteria. The UhpA, one of the Glu6P transport system regulatory proteins could down-regulate the uhpC/uhpB/uhpA system and decrease its pathogenicity. However, the motility and the colonization of E. piscicida affected by UhpA were still unclear. In this study, the motility and the colonization of E. piscicida were monitored. The result demonstrated that the motility of EIB202 was significantly stronger than that of in ΔuhpA according to fractions 4, 8 and 9. However, the motility of ΔuhpA was significantly stronger than that of EIB202 according to the total number at the whole experiment. Although, there was no difference in the number of bacteria in the posterior intestine of tilapia after infected with E. piscicida EIB202 and ΔuhpA. The number of bacteria in the anterior and the middle intestine of fish infected with ΔuhpA were significantly higher than that of in fish infected with EIB202 at the whole experiment (P < 0.05). Interestingly, both E. piscicida strains colonized in the anterior intestine than that of in the middle and posterior intestines of tilapia. Besides, the gene expression of IL-1β and TNF-α in the head-kidney of fish infected with ΔuhpA showed significantly higher (p < 0.05) than fish infected with EIB202 during the whole experimental period. Most importantly, the survival rate of E. piscicida EIB202 and ΔuhpA were 57% and 37% respectively. All results indicate that the uhpA gene mutant in E. piscicida could enhance its motility and the colonization in the intestine of tilapia, this illustrates the mechanism of UhpA decreases the pathogenesis of E. piscicida in fish.

A Novel Hepe-Like Virus from Farmed Giant Freshwater Prawn Macrobrachium rosenbergii

The family Hepeviridae includes several positive-stranded RNA viruses, which infect a wide range of mammalian species, chicken, and trout. However, few hepatitis E viruses (HEVs) have been characterized from invertebrates. In this study, a hepevirus, tentatively named Crustacea hepe-like virus 1 (CHEV1), from the economically important crustacean, the giant freshwater prawn Macrobrachium rosenbergii, was characterized. The complete genome consisted of 7750 nucleotides and had a similar structure to known hepatitis E virus genomes. Phylogenetic analyses suggested it might be a novel hepe-like virus within the family Hepeviridae. To our knowledge, this is the first hepe-like virus characterized from crustaceans.

TaqMan real-time and conventional nested PCR tests specific to yellow head virus genotype 7 (YHV7) identified in giant tiger shrimp in Australia

In 2013, a unique seventh yellow head virus genotype (YHV7) was detected in Black Tiger shrimp (Penaeus monodon) broodstock that suffered high mortality following their capture from Joseph Bonaparte Gulf (JBG) in northern Australia. To assist with its diagnosis and assessment of its distribution, prevalence and pathogenicity, YHV7-specific TaqMan real-time qPCR and conventional nested PCR primer sets were designed to ORF1b gene sequences divergent from the other YHV genotypes. Using high (≥10⁸) copies of plasmid (p)DNA controls containing ORF1b gene inserts of representative strains of YHV genotypes 1-7, both PCR tests displayed specificity for YHV7. Amplifications of serial 10-fold dilutions of quantified YHV7 pDNA and synthetic ssRNA showed that both tests could reliably detect 10 genome copies. Pleopods/gills from wild P. monodon sourced from locations in geographically disparate regions across northern Australia as well as 96 juveniles (48 either appearing normal or displaying signs of morbidity) from a commercial pond experiencing mortalities were screened to partially validate the diagnostic capacity of the qPCR test. Based on these data and PCR primer/probe sequence mismatches with other newly identified YHV genotypes, both YHV7-specific PCR tests should prove useful in the sensitive detection and discrimination of this genotype from YHV 2 (gill-associated virus) and YHV6 that can occur in Australian P. monodon, as well as from YHV genotypes currently listed as exotic to Australia.