In vitro white spot syndrome virus (WSSV) replication in explants of the heart of freshwater crab, Paratelphusa hydrodomous

The shrimp microsporidian Enterocytozoon hepatopenaei (EHP): Biology, pathology, diagnostics and control

Disease is a major limiting factor in the global production of cultivated shrimp. The microsporidian parasite Enterocytozoon hepatopenaei (EHP) was formally characterized in 2009 as a rare infection of the black tiger shrimp Penaeus monodon. It remained relatively unstudied until mid-2010, after which infection with EHP became increasingly common in the Pacific whiteleg shrimp Penaeus vannamei, by then the most common shrimp species farmed in Asia. EHP infects the hepatopancreas of its host, causing hepatopancreatic microsporidiosis (HPM), a condition that has been associated with slow growth of the host in aquaculture settings. Unlike other infectious disease agents that have caused economic losses in global shrimp aquaculture, EHP has proven more challenging because too little is still known about its environmental reservoirs and modes of transmission during the industrial shrimp production process. This review summarizes our current knowledge of the EHP life cycle and the molecular strategies that it employs as an obligate intracellular parasite. It also provides an analysis of available and new methodologies for diagnosis since most of the current literature on EHP focuses on that topic. We summarize current knowledge of EHP infection and transmission dynamics and currently recommended, practical control measures that are being applied to limit its negative impact on shrimp cultivation. We also point out the major gaps in knowledge that urgently need to be bridged in order to improve control measures.

Visualizing Nudivirus Assembly and Egress

The dynamics of nuclear envelope has a critical role in multiple cellular processes. However, little is known regarding the structural changes occurring inside the nucleus or at the inner and outer nuclear membranes. For viruses assembling inside the nucleus, remodeling of the intranuclear membrane plays an important role in the process of virion assembly. Here, we monitored the changes associated with viral infection in the case of nudiviruses. Our data revealed dramatic membrane remodeling inside the nuclear compartment during infection with Oryctes rhinoceros nudivirus, an important biocontrol agent against coconut rhinoceros beetle, a devastating pest for coconut and oil palm trees. Based on these findings, we propose a model for nudivirus assembly in which nuclear packaging occurs in fully enveloped virions.

Enveloped viruses hijack cellular membranes in order to provide the necessary material for virion assembly. In particular, viruses that replicate and assemble inside the nucleus have developed special approaches to modify the nuclear landscape for their advantage. We used electron microscopy to investigate cellular changes occurring during nudivirus infection and we characterized a unique mechanism for assembly, packaging, and transport of new virions across the nuclear membrane and through the cytoplasm. Our three-dimensional reconstructions describe the complex remodeling of the nuclear membrane necessary to release vesicle-associated viruses into the cytoplasm. This is the first report of nuclear morphological reconfigurations that occur during nudiviral infection.

The Development and Characterization of a Cell Culture System from Indian Mud Crabs Scylla serrata

Commercially available culture media and supplements were tested for their potential to produce primary cell cultures from tissues of Indian mud crabs Scylla serrata. Eight commercially available culture media from Sigma-Aldrich (Leibovitz's L-15, Medium 199, Grace's Insect Medium, Minimal Essential Medium, Dulbecco's Modified Eagle Medium, TC-100 Insect Medium, IPL-41 Insect Medium, and Roswell Park Memorial Institute) were examined. Three different supplements (amino acid and sugar [AS], crab muscle extract [CME], and natural seawater [NSW]) were also examined. The hemocyte culture appeared to grow well for a maximum period of 21 d in 2 × L-15 medium supplemented with AS and 15% fetal bovine serum (FBS). Partial amplification and sequencing of the cytochrome oxidase subunit I (COI) gene confirmed that the primary hemocytes originated from Indian mud crabs. The effects of four metals on hemocyte viability were evaluated using the MTT assay. Of the four metals examined (arsenic, lead, cobalt, and nickel), cobalt and nickel were more toxic to the crab cells than the other metals. Both acridine orange/ethidium bromide and Hoechst staining showed the presence of apoptosis and necrosis in metal-treated groups, which suggests that metals in an aquatic environment induce death of the Indian mud crab's hemocytes. The hemocyte primary cell culture was also used to study the cytotoxicity effect of bacterial extracellular products from Vibrio harveyi and white spot syndrome virus. This study demonstrates that hemocyte primary cell culture can be used as a tool to study viral and bacterial pathogenesis and to assess the cytotoxicity of pollutants present in aquatic environments.

Medium optimization and characterization of cell culture system from Penaeus vannamei for adaptation of white spot syndrome virus (WSSV)

The lack of shrimp cell lines and difficulty in establishing shrimp cell culture systems, with an appropriate medium is a major concern in the aquaculture sector. The present study attempts to address this issue by developing an in vitro cell culture system from various tissues (hemocytes, heart, lymphoid tissue, hepatopancreas, gill, eye stalk, and muscle) of Penaeus vannamei (P.vannamei) using commercially available L-15 medium. The cell culture medium was formulated using five different media such as HBSCM-1, HBSCM-2, HBSCM-3, HBSCM-4, and HBSCM-5 containing L-proline and glucose with fetal bovine serum (FBS) supplements. Among the different media used, the HBSCM-5 medium with supplements showed good attachment and proliferation of cells with fibroblast-like, epithelioid, round, and adherent cell morphology in hemocyte culture. The same medium was further screened using different tissues to enhance the cell growth. The hemocytes, heart, and lymphoid tissue cells were passaged five times and maintained up to 20 days. Hepatopancreas and gill cells initially showed good morphological features and survived for more than ten days following subculture cells. Eye stalks and muscle cells perished within five days and did not show any unique morphology. The primary hemocyte cells were subjected to species identification, using cytochrome oxidase subunit I (COI) gene. To assess the primary hemocyte cell culture, cells were used for in vitro propagation of white spot syndrome virus (WSSV) and confirmed by the conventional polymerase chain reaction (PCR). Similarly, the primary cells were treated with bacterial extracellular products (ECPs) from Vibrio parahaemolyticus and Vibrio harveyi, to evaluate the cytotoxicity.

The tidepool shrimp, Palaemon ritteri Holmes, constitutes a novel host to the white spot syndrome virus

The white spot syndrome virus (WSSV) is a lethal and contagious pathogen for penaeid shrimp and a growing number of other crustacean species. To date, there are no effective prophylactic or therapeutic treatments commercially available to interfere with the occurrence and spread of the disease. In addition, the significance of alternative vectors on the dispersal of this disease has been largely ignored and therefore the ecological dynamics of the WSSV is still poorly understood and difficult to ascertain. Thus, an important issue that should be considered in sanitary programmes and management strategies is the identification of species susceptible to infection by WSSV. The results obtained provide the first direct evidence of ongoing WSSV replication in experimentally infected specimens of the tidepool shrimp Palaemon ritteri. Viral replication was detected using a validated set of primers for the amplification by RT-PCR of a 141 bp fragment of the transcript encoding the viral protein VP28. It is therefore conceivable that this shrimp may play a significant role in the dispersal of WSSV.

Characterization of two novel ADP ribosylation factors from giant freshwater prawn Macrobrachium rosenbergii and their responses to WSSV challenge

ADP-ribosylation factors (Arfs) are small GTP-binding proteins that have an essential function in intracellular trafficking and organelle structure. To date, little information is available on the Arfs in the economically important giant freshwater prawn Macrobrachium rosenbergii and their relationship to viral infection. Here we identified two Arf genes from M. rosenbergii (MrArf1 and MrArf2) for the first time. Phylogenetic analysis showed that MrArf1, together with MjArf1 from shrimp Marsupenaeus japonicus belonged to Class I Arfs. By contrast, MrArf2 didn't not match any of the Arfs classes of I/II/III, although it could be clustered with an Arf protein from M. japonicas called MjArfn, which may represent an analog of the Arf. MrArf1 was ubiquitously expressed in all the examined tissues, with the highest transcription level in the hepatopancreas, whereas MrArf2 was only highly expressed in the hepatopancreas and exhibited very low levels in the heart, stomach, gills and intestine. The expression level of MrArf1 in the gills was down-regulated post 24 h WSSV challenge, and reached the maximal level at 48 h. MrArf1 in the hepatopancreas went up from 24 to 48 h WSSV challenge. MrArf2 transcript in the gill also went down at 24 h and then was upregulated at 48 h WSSV challenge. MrArf2 increased significantly in the hepatopancreas 24 h after infection and then went down at 48 h WSSV challenge. RNAi results showed that knockdown of MrArf1 or MrArf2 could inhibit the expression of the envelope protein gene vp28 of the WSSV. So, it could be speculated that MrArf1 and MrArf2 might play important roles in the innate immune system against WSSV infection.

Tissue distribution of hepatopancreatic parvo-like virus of shrimp in freshwater rice-field crab, Paratelphusa hydrodomous (Herbst)

An attempt was made to determine the replication efficiency of hepatopancreatic parvo-like virus (HPV) of shrimp in different organs of freshwater rice-field crab Paratelphusa hydrodomous (Herbst) using bioassay, PCR, RT-PCR, ELISA, Western blot and q-PCR analyses. Another attempt was made to use this crab as an alternative to penaeid shrimp for the large-scale production of HPV. This crab was found to be highly susceptible to HPV by intramuscular injection. The systemic HPV infection was confirmed by PCR and Western blot analyses in freshwater crab. The expression of capsid protein gene in different organs of infected crab was revealed by RT-PCR analysis. Indirect ELISA was used to quantify the capsid protein in different organs of the crab. The copy number of HPV in different organs of the infected crab was quantified by q-PCR. The results revealed a steady decrease in CT values in different organs of the infected crab during the course of infection. The viral inoculum that was prepared from different organs of the infected crab caused significant mortality in post-larvae of tiger prawn, Penaeus monodon (Fabricius). The results revealed that this rice-field crab could be used as an alternative host for HPV replication and also for large-scale production of HPV.

In vitro propagation of hepatopancreatic parvo-like virus (HPV) of shrimp in C6/36 (Aedes albopictus) cell line

Hepatopancreatic parvovirus (HPV) which causes infection in many species of penaeid shrimp is a serious viral pathogen in the young life stages of shrimp. An attempt was made to develop an in vitro system using C6/36 subclone of Aedes albopictus cell line for propagation of HPV. The results revealed that C6/36 cells were susceptible to this virus and the infected cells showed CPE in the form of vacuole formation. The results of PCR, immunocytochemistry and Western blot revealed the HPV-infection in C6/36 cell line. The RT-PCR analysis confirmed the replication of HPV in C6/36 cell line. The HPV load was quantified at different time intervals by ELISA and real time PCR, and the results showed the increase of viral load in C6/36 cell line in time course of infection. HPV propagated in C6/36 cell line was used to infect post-larvae of shrimp and the results showed that the twentieth passage of HPV propagated in C6/36 cell line caused 100% mortality in post-larvae after 6 weeks post infection (d.p.i.). The infected post-larvae showed clinical signs of reduced growth, reduced preening, muscle opacity and atrophy of hepatopancreas. The HPV-infection was confirmed by PCR. The results of the present study showed that C6/36 cell line can be used as an in vitro model for HPV replication instead of whole animal.