Viral diseases in commercially exploited crabs: a review

Viruses and viral diseases of crabs were observed and investigated earlier than the first observation of viruses in shrimp. In fact, crabs were used as biological models to investigate crustacean virology at the beginning of shrimp aquaculture development. More than 30 viruses have been reported in crabs, including those related to the known virus families Reoviridae, Bunyaviridae, Roniviridae and a group of Bacilliform enveloped nuclear viruses. This review reports data on several important viral diseases of crabs, particularly those associated with pathology of organs and tissues of commercially and ecologically significant host species.     

Viral diseases of penaeid shrimp with particular reference to four viruses recently found in shrimp from Queensland

The culture of penaeid shrimp world-wide is primarily dependent on wild-caught broodstock which has an enormous potential to introduce new pathogens, particularly viruses, into culture systems. Of the 13 viruses described for cultured penaeid shrimp, seven have been described within the past 5 years; the most devastating viral epidemics on record for cultured penaeid shrimp have also occurred within the past 5years. During examination of local wild and cultured shrimp, four new viruses were found. Bennettae baculovirus was discovered in the digestive gland of wild Metapenaeus bennettae. It closely resembles monodon baculovirus (MBV) but has a more slender virion, does not cross-react with a DNA probe for MBV and is not infectious to Penaeus monodon. Two morphologically indistinguishable viruses, one pathogenic (gill-associated virus, GAV) and the other benign (lymphoid organ virus, LOV), were found in cultured P. monodon. LOV and GAV closely resemble yellow head virus (YHV) of Thailand. A parvo-like virus was found recently in dying post-larvae of P. japonicus. As the intensity of shrimp culture world-wide increases, researchers can expect to discover more penaeid viruses. The need to close the life cycle of P. monodon and other cultured species and develop rapid diagnostic methods for viral infections has become imperative.     

Detection and quantification of hepatopancreatic parvovirus in penaeid shrimp by real-time PCR assay

As one of the major pathogens, hepatopancreatic parvovirus (HPV) can cause severe diseases in penaeid shrimp. We developed a TaqMan-based real-time PCR assay for the HPV detection in China. A pair of primers (HPVF and HPVR) and a TaqMan probe were designed according to the HPV genomic sequence of Chinese isolate (GenBank: GU371276). Our data showed that the primers and TaqMan probe were specific for HPV, and they exhibited no cross-reaction with infectious hypodermal and hematopoietic necrosis virus (IHHNV), white spot syndrome virus (WSSV) and specific pathogen free (SPF) shrimp DNA. The assay had a detection limit of four plasmid HPV DNA copies per reaction. Furthermore, HPV was detected in 16 of 21 Fenneropenaeus Chinensis, 3 of 52 Litopenaeus vannamei and 2 of 2 Marsupenaeus japonicus penaeid shrimp samples. In addition, HPV was also detected in crabs. Therefore, this assay could be successfully used as a sensitive and rapid molecular-based diagnostic method to screen HPV-free animals and survey the prevalence of HPV in cultured populations of penaeid shrimp in China.     

Major viral diseases of the black tiger prawn (Penaeus monodon) in Thailand

There are five different viruses which are currently being studied for their impact on commercial farming of the black tiger prawn (Penaeus monodon) in Thailand. Some of these viruses cause disease in other penaeid shrimp species and even other crustacean species. Some occur not only in cultivated shrimp in other Asian countries, but also in those from Australia and the western hemisphere. In descending order from greatest to least economic impact on the Thai shrimp industry, the five viruses are: white-spot baculovirus, yellow-head virus, hepatopancreatic parvo-like virus, infectious hypodermal and hematopoeitic necrosis virus and monodon baculovirus. The purpose of this review is to summarize recent work on these viruses and to suggest future directions of research that may be useful in the effort to develop a sustainable shrimp industry.     

白斑综合症病毒感染相关蛋白质相互作用的研究进展

白斑综合症病毒（white spot syndrome virus,WSSV）是危害对虾的主要病原,给全球水产养殖业带来了巨大经济损失,但至今仍未发现有效的防治方法。研究病毒与宿主的相互作用对于深入了解病毒的致病机理和宿主的免疫机制,从而寻找合适的抗病毒措施具有非常重要的理论意义和实际应用价值。该文主要介绍了蛋白质相互作用的研究方法,以及WSSV病毒蛋白之间、病毒—宿主蛋白之间和宿主蛋白之间相互作用的研究进展,为有效地防治WSSV及相关科研提供参考。     

A lymphoma-like neoplasm arising from hematopoietic tissue in the white shrimp, Penaeus vannamei Boone (Crustacea: Decapoda)

A pond-reared adult female Pacific white shrimp (Penaeus vannamei Boone, Crustacea: Decapoda) from an experimental shrimp culture facility in Hawaii was found to possess a lymphatic neoplasm. Present in this animal were bilateral hypertrophied hematopoietic nodules present ventral and lateral to the ventral nerve cord, and smaller multiple ectopic foci of similar appearing lymphoid cells in the gills, the subcutis, and other tissues. The lesions contained numerous anaplastic and hypertrophied lymphoid cells, many of which displayed bizarre mitotic figures, including polypolar metaphase figures. Numerous multinuclear giant cells present in the lesion were presumed to have originated from cells with polypolar mitotic figures. The characteristics of the cells composing these lesions, the expansive and invasive nature of the lesions, and the presence of ectopic foci of neoplastic cells support classification of this lesion as a hematopoietic sarcoma. Focal lesions of the type that are diagnostic of infections by the penaeid shrimp virus IHHN were present in the neoplastic hematopoietic tissue and other tissues of this shrimp, suggesting the possible role of viral infection in the development of neoplastic lesions in this animal.     

Infectious hypodermal and hematopoietic necrosis,a newly recognized virus disease of penaeid shrimp

Populations of the Pacific blue shrimp, Penaeus stylirostris, reared at the University of Arizona's experimental shrimp culture facility on Oahu in Hawaii from late 1980 through 1981, were severely affected by a highly acute and lethal disease of viral etiology. Also found to be susceptible to the disease were P. vannamei and P. monodon. The disease was named infectious hypodermal and hematopoietic necrosis (IHHN) disease to describe the principal lesions observed. The histopathology of acute and subacute IHHN disease in these species was dominated by the presence of conspicuous eosinophilic intranuclear-inclusion bodies of the Cowdry type A variety in ectodermally (especially the cuticular hypodermis) and mesodermally (especially the hematopoietic tissues) derived tissues that were undergoing necrosis. Electron microscopy of affected tissues demonstrated the presence of two or three types of virus-like particles with cubic morphology and diameters of 17 to 27 nm that suggest IHHN virus to be either a parvo- or picornavirus.     

对虾病毒病研究现状

对虾病毒病已严重危害世界对虾养殖业的发展,引起国内外学者的广泛关注。对近几年来对虾病毒病的研究现状和动态进行了概述,重点介绍了杆状病毒科(Baculoviridae)、细小病毒科(Parvoviridae)、呼肠孤病毒科(Reoviridae)、虹彩病毒科(Iridoviridae)、小RNA病毒科(Picornaviridae)、弹状病毒科(Rhabdoviridae)、被膜病毒科(Togaviridae)等几个科15种对虾病毒的特征、临床症状、病理特征、宿主范围和主要检测方法;对病毒病的传播途径、防治措施和存在的问题也进行了简要介绍。     

Parasitic crustaceans as vectors of viruses, with an emphasis on three penaeid viruses

Parasitic crustaceans serve as both hosts and vectors of viruses as well as of parasites and other microbial pathogenic agents. Few of the presumably numerous associations are known, but many can be anticipated. Recently, branchiurans and gnathiid isopods have been documented to host helminths and blood parasites. Because the agents can be observed readily with a microscope, these are better recognized than are the smaller viral, bacterial, and fungal agents. Some agents are harmful to the host of the crustacean parasite and others are not. Viruses probably fit both these categories, since viruses that do not appear pathogenic are often seen in ultrastructural images from a range of invertebrate hosts, including crustaceans. Some viruses have been implicated in causing disease in the host, at least under appropriate conditions. For example, lymphocystis virus may possibly be transmitted to the dermis of its fish hosts by copepods and to the visceral organs by a cymothoid isopod. Similarly, argulid branchiurans seem to transmit the viral agent of spring viremia of carp as well as carp pox, and copepods have been implicated in transmitting infectious hematopoietic necrosis, infectious salmon anemia, and infectious pancreatic necrosis to salmon. Other viruses can be vectored to their hosts through an additional animal. We exposed three viruses, Taura syndrome virus (TSV), white spot syndrome virus (WSSV), and yellowhead virus (YHV), all of which cause mortalities in wild and cultured penaeid shrimps, to crustacean parasites on fish and crabs. Using real-time polymerase chain reaction analysis, we show that TSV in the cyclopoid copepod Ergasilus manicatus on the gill filaments of the Gulf killifish, Fundulus grandis, the acorn barnacle Chelonibia patula on the carapace of the blue crab, Callinectes sapidus, and gooseneck barnacle Octolasmis muelleri on the gills of C. sapidus, can replicate for at least 2 weeks and establish what should be an infective dose. This result was additionally supported by positive in situ hybridization reactions. All three parasites are the first known non-penaeid hosts in which replication occurs. The mean log copy number of WSSV also suggested that replication occurred in E. manicatus. The mean log copy number of YHV gradually decreased in all three parasites and both hosts over the 2-week period. The vector relationships indicate an additional potential means of transmitting and disseminating the disease-causing agents to the highly susceptible and economically valuable penaeid shrimp hosts.     

Susceptibility to infection and pathogenicity of White Spot Disease (WSD) in non-model crustacean host taxa from temperate regions

Despite almost two decades since its discovery, White Spot Disease (WSD) caused by White Spot Syndrome Virus (WSSV) is still considered the most significant known pathogen impacting the sustainability and growth of the global penaeid shrimp farming industry. Although most commonly associated with penaeid shrimp farmed in tropical regions, the virus is also able to infect, cause disease and kill a wide range of other decapod crustacean hosts from temperate regions, including lobsters, crabs, crayfish and shrimp. For this reason, WSSV has recently been listed in European Community Council Directive 2006/88. Using principles laid down by the European Food Safety Authority (EFSA) we applied an array of diagnostic approaches to provide a definitive statement on the susceptibility to White Spot Syndrome Virus (WSSV) infection in seven ecologically or economically important crustacean species from Europe. We chose four marine species: Cancer pagurus, Homarus gammarus, Nephrops norvegicus and Carcinus maenas; one estuarine species, Eriocheir sinensis and two freshwater species, Austropotamobius pallipes and Pacifastacus leniusculus. Exposure trials based upon natural (feeding) and artificial (intra-muscular injection) routes of exposure to WSSV revealed universal susceptibility to WSSV infection in these hosts. However, the relative degree of susceptibility (measured by progression of infection to disease, and mortality) varied significantly between host species. In some instances (Type 1 hosts), pathogenesis mimicked that observed in penaeid shrimp hosts whereas in other examples (Types 2 and 3 hosts), infection did not readily progress to disease, even though hosts were considered as infected and susceptible according to accepted principles. Results arising from challenge studies are discussed in relation to the potential risk posed to non-target hosts by the inadvertent introduction of WSSV to European waters via trade. Furthermore, we highlight the potential for susceptible but relatively resistant hosts to serve as models to investigate natural mitigation strategies against WSSV in these hosts. We speculate that these non-model hosts may offer a unique insight into viral handling in crustaceans.     

A parvo-like virus disease of penaeid shrimp

Cultured populations of four penaeid shrimp species (Crustacea, Decapoda) from four separate culture facilities in Asia were found to be adversely affected by a disease of presumed viral etiology. Individual shrimp with the disease displayed nonspecific signs, including poor growth rate, anorexia, reduced preening activity, increased surface fouling, and occasional opacity of tail musculature. These signs were accompanied by mortalities during the juvenile stages, after apparently normal development through the larval and postlarval stages. Accumulative mortality rates in epizootics in Penaeus merguiensis and P. semisulcatus reached as high as 50 to 100%, respectively, of the affected populations within 4 to 8 weeks of disease onset. The principal lesion, common to all four species, was necrosis and atrophy of the hepatopancreas, accompanied by the presence of large prominent basophilic, PAS-negative, Fuelgen-positive intranuclear inclusion bodies in affected hepatopancreatic tubule epithelial cells (hepatopancreatocytes). These inclusion bodies presumably developed from small, eosinophilic, intranuclear bodies that were also present in the affected tissues. Electron microscopy of affected hepatopancreatocytes revealed aggregations of 22- to 24-nm-diameter virus particles within the electron-dense granular inclusion body ground substance. The virus particle size and morphology, the close association of the nucleolus with the developing inclusion body, and the presence of intranuclear bodies within developing inclusion bodies are similar to cytopathological features reported for parvovirus infections in insects and vertebrates. It is suggested that this presumed virus disease of cultured penaeid shrimp be called HPV for Hepatopancreatic Parvo-like Virus disease.     

Viral interference between infectious hypodermal and hematopoietic necrosis virus and white spot syndrome virus in Litopenaeus vannamei

White spot syndrome virus (WSSV) is highly virulent and has caused significant production losses to the shrimp culture industry over the last decade. Infectious hypodermal and hematopoietic necrosis virus (IHHNV) also infects penaeid shrimp and, while being less important than WSSV, remains a major cause of significant production losses in Litopenaeus vannamei (also called Penaeus vannamei) and L. stylirostris (also called Penaeus stylirostris). These 2 viruses and their interactions were previously investigated in L. stylirostris. We report here laboratory challenge studies carried out to determine if viral interference between IHHNV and WSSV also occurs in L. vannamei, and it was found that experimental infection with IHHNV induced a significant delay in mortality following WSSV challenge. L. vannamei infected per os with IHHNV were challenged with WSSV at 0, 10, 20, 30, 40 and 50 d post-infection. Groups of na?ve shrimp infected with WSSV alone died in 3 d whereas shrimp pre-infected with IHHNV for 30, 40 or 50 d died in 5 d. Real-time PCR analysis showed that the delay correlated to the IHHNV load and that WSSV challenge induced a decrease in IHHNV load, indicating some form of competition between the 2 viruses.     

Infection ofArabidopsis thaliana ecotype columbia by tomato spotted wilt virus

Mechanical inoculation ofArabidopsis thaliana ecotype Columbia with tomato spotted wilt virus led to viral replication and spread as determined by dot blot and ELISA analysis. Severe symptoms were observed three to four weeks post-inoculation. Early symptoms were manifested as chlorotic spots on uninoculated leaves. Later in the infection process, some plants showed complete chlorosis and wilting prior to bolting. Bolts that were developed by infected plants were chlorotic and deformed. These preliminary results suggest thatA. thaliana could become a model system for the genetic analysis of host factors required for the replication of viruses in the family Bunyaviridae, which includes viruses that cause important diseases of both plants and animals.     

Gene expression and protein levels of thioredoxin in the gills from the whiteleg shrimp (Litopenaeus vannamei) infected with two different viruses: the WSSV or IHHNV

The thioredoxin (TRX) system in crustaceans has demonstrated to act as a cell antioxidant being part of the immune response by dealing with the increased production of reactive oxygen species during bacterial or viral infection. Since the number of marine viruses has increased in the last years significantly affecting aquaculture practices of penaeids, and due to the adverse impact on wild and cultured shrimp populations, it is important to elucidate the dynamics of the shrimp response to viral infections. The role of Litopenaeus vannamei thioredoxin (LvTRX) was compared at both, mRNA and protein levels, in response to two viruses, the white spot syndrome virus (WSSV) and the infectious hypodermal and hematopoietic necrosis virus (IHHNV). The results confirmed changes in the TRX gene expression levels of WSSV-infected shrimp, but also demonstrated a more conspicuous response of TRX to WSSV than to IHHNV. While both the dimeric and monomeric forms of LvTRX were detected by Western blot analysis during the WSSV infection, the dimer on its reduced form was only detected through the IHHNV infectious process. These findings indicate that WSSV or IHHNV infected shrimp may induce a differential response of the LvTRX protein.     

Natural host-range and experimental transmission of Laem-Singh virus (LSNV)

Slow growth caused by viral diseases has become a major constraint in shrimp aquaculture. Laem-Singh virus (LSNV), a positive-sense single-stranded RNA (ssRNA) virus, has been identified in Penaeus monodon showing slow growth syndrome. To examine the host-range and transmission modes of the virus, 6 species of penaeid shrimp of varying life stages, sourced from the wild and from farms, as well as juvenile mud crabs Scylla serrata, were screened using RT-nested PCR. LSNV was detected in P. monodon, Fenneropenaeus merguiensis, Metapenaeus dobsoni, and Litopenaeus vannamei, but not in E indicus, Marsupenaeus japonicus or S. serrata. LSNV was most prevalent in P. monodon followed by M. dobsoni, F. merguiensis, and L. vannamei, and real-time quantitative RT-PCR (qRT-PCR) showed that LSNV infection loads were highest in P. monodon, followed by L. vannamei, M. dobsoni, and E merguiensis. The nucleotide sequence of the LSNV RdRP gene fragment amplified by RT-nested PCR was highly conserved (99% identity) across these 4 penaeid species. LSNV was detected in both small and normal-sized P. monodon collected from the same pond. In experimental infections of both P. monodon and S. serrata, LSNV infection loads increased over time. The present study extends the known natural penaeid host-range and geographical distribution of LSNV and shows for the first time the potential susceptibility of S. serrata.     

Branchinecta belki n. sp. (Branchiopoda: Anostraca), a new fairy shrimp from Mexico,hybridizing withB. packardi Pearse under laboratory conditions

A new fairy shrimp,Branchinecta belki n.sp., endemic to the south of Coahuila state is described and figured. A total of nine species of phyllopods, including the new species, occur in ponds in the type area.The laboratory hybridization ofB. belki andB. packardi through no-choice mating tests in reciprocal crosses is discussed. A mixture of characteristics of parental species is present in male F1 and F2 hybrids. This may provide a biological tool, or search image (sensu Wiman, 1979a), for detecting male hybrids, should such exist, between theBranchinecta species of this study in nature. In addition to the reported interspecific hybridizations inStreptocephalus (Wiman, 1979a & 1979b) and inArtemia (Bowenet al., 1985) under laboratory conditions, the new evidence inBranchinecta suggests that absence of efficient premating mechanisms may be common in Anostraca.     

Ability of Monaco shrimp Lysmata seticaudata (Decapoda: Hippolytidae) to control the pest glass anemone Aiptasia pallida (Actiniaria: Aiptasidae)

The present work highlights the ability of wild and cultured Monaco shrimp Lysmata seticaudata to control the glass anemone Aiptasia pallida. Starved shrimp ingested the highest percentages of glass anemones [85.7% and 89.3% for wild (W) and cultured (C) shrimp, respectively]. The absence of symbiotic zooxanthellae in glass anemones did not influence the shrimps feeding rate, with shrimp offered aposymbiotic anemones displaying the same feeding percentages (67.3% and 70.7% for W and C shrimp, respectively) as those offered sea anemones with symbiotic zooxanthellae (70.0% and 74.4% for W and C shrimp, respectively). Shrimp offered larger sea anemones had the lowest feeding percentages (33.0% and 36.3% for W and C shrimp, respectively), along with shrimp offered an alternative food (27.3% and 36.0% for W and C shrimp, respectively). There were no significant differences in the percentage of glass anemones ingested by cultured and wild Monaco shrimp in the same feeding trial.