Epidemiological parameters of White Spot Syndrome Virus infections in Litopenaeus vannamei and L. setiferus

An experimental protocol based on a mathematical epidemiology model was developed to study the transmission, virulence, and recovery rates of White Spot Syndrome Virus (WSSV). Two modes of transmission were compared for WSSV in Litopenaeus vannamei. We compared transmission by ingestion of infected cadavers to transmission by cohabitation with infected animals. In addition, we compared the ingestion transmission of WSSV in L. vannamei and in L. setiferus. Finally, we compared the virulence and recovery rates of WSSV in L. vannamei and L. setiferus. The transmission rate of WSSV to L. vannamei by cohabitation was 0.01. The transmission rate by ingestion of infected cadavers was over an order of magnitude larger at 0.46, suggesting that cohabitation is a much less important mode of transmission for WSSV. A statistically significant difference was detected between the estimates of ingestion transmission of L. vannamei (0.46) and those of L. setiferus (0.84), yet no differences in the virulence or recovery rates were detected between hosts. The overall estimated virulence rate was 0.34, and the overall estimated recovery rate from a WSSV infection was 0.007 for both species. According to epidemiological theory the threshold density of hosts necessary for an epidemic to occur is directly related to the virulence and recovery rates and inversely related to the transmission rate. Therefore, the epidemic threshold density may be lower for ingestion transmission than cohabitation transmission and lower for L. setiferus than for L. vannamei.

A cross-sectional study of SEN virus in liver transplant recipients

A new DNA virus, referred to as SEN virus (SEN V), has been isolated and is associated with blood-product transfusion and possibly Non A to Non E hepatitis. We performed a cross-sectional analysis of SEN V in liver transplant recipients at our center. Polymerase chain reaction was used to test for 2 genotypes of SEN V (SEN V:C/H and SEN V:D) in 58 unselected patients. Comparisons were made between SEN V--positive and SEN V--negative groups in terms of age, time posttransplantation, indications for transplantation, serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, and cytomegalovirus and Epstein-Barr virus status. Thirty of 58 transplant recipients (51.7%) were SEN V positive; 15.5% were positive for SEN V:C/H, 24.1% for SEN:D, and 12.1% for both strains. No significant differences were found based on primary indication for transplantation, including hepatitis C virus (HCV). Of the 14 of 21 patients with HCV seropositivity and HCV reinfection, 79% were positive for SEN V (P =.02). There was no difference in the proportion of patients with abnormal serum ALT and/or AST levels. A trend for the SEN V--positive group to have a greater mean ALT level (82 v 41 U/L; P =.067) was attributable to the subgroup with HCV recurrence because there was no difference in mean ALT levels (34.9 v 34.5 U/L; P =.968) in non--HCV-infected transplant recipients. Even in the subgroup (n = 14) with recurrent HCV, there was no statistically significant difference in mean ALT levels (140 v 105 U/L; P =.665). Age and cytomegalovirus or Epstein-Barr virus status were not significantly different between the 2 groups, but a significant difference in posttransplantation time was noted (16.8 v 32 months; P =.021). We conclude that SEN V is common among liver transplant recipients but does not appear to cause graft dysfunction as an isolated agent. There is a suggestion that SEN V may be associated with HCV recurrence, but we did not detect biochemical differences attributable to SEN V.

Viral impacts on total abundance and clonal composition of the harmful bloom-forming phytoplankton Heterosigma akashiwo

Recent observations that viruses are very abundant and biologically active components in marine ecosystems suggest that they probably influence various biogeochemical and ecological processes. In this study, the population dynamics of the harmful bloom-forming phytoplankton Heterosigma akashiwo (Raphidophyceae) and the infectious H. akashiwo viruses (HaV) were monitored in Hiroshima Bay, Japan, from May to July 1998. Concurrently, a number of H. akashiwo and HaV clones were isolated, and their virus susceptibilities and host ranges were determined through laboratory cross-reactivity tests. A sudden decrease in cell density of H. akashiwo was accompanied by a drastic increase in the abundance of HaV, suggesting that viruses contributed greatly to the disintegration of the H. akashiwo bloom as mortality agents. Despite the large quantity of infectious HaV, however, a significant proportion of H. akashiwo cells survived after the bloom disintegration. The viral susceptibility of H. akashiwo isolates demonstrated that the majority of these surviving cells were resistant to most of the HaV clones, whereas resistant cells were a minor component during the bloom period. Moreover, these resistant cells were displaced by susceptible cells, presumably due to viral infection. These results demonstrated that the properties of dominant cells within the H. akashiwo population change during the period when a bloom is terminated by viral infection, suggesting that viruses also play an important role in determining the clonal composition and maintaining the clonal diversity of H. akashiwo populations. Therefore, our data indicate that viral infection influences the total abundance and the clonal composition of one host algal species, suggesting that viruses are an important component in quantitatively and qualitatively controlling phytoplankton populations in natural marine environments.

Spectrum of virus inhibition by consensus interferon YM643

The spectrum of viruses inhibited by a genetically engineered consensus interferon (IFN) YM643 (interferon alfacon-1) was evaluated using a cytopathic effect inhibition assay or plaque inhibition assay for five DNA viruses and 12 RNA viruses. This activity was compared to that of natural IFN-alpha derived from Namalwa lymphoblastoid cell line [IFN-alpha (Namalwa)]. The viruses inhibited by both IFNs were herpesvirus types 1 and 2, human cytomegalovirus, varicella-zoster virus, vesicular stomatitis virus, yellow fever virus, bovine viral diarrhoea virus, Semliki Forest virus, western equine encephalitis virus, encephalomyocarditis virus, rhinovirus type A, respiratory syncytial virus, Newcastle disease virus and influenza virus type A (H1N1). Neither IFN inhibited coxsackie virus B1, reovirus type 3 or vaccinia virus in the experimental conditions used. The specific activity of YM643 in human cells generally ranged from 3.6x10(7) to 2.1x10(9) IU/mg, which was greater than that of IFN-alpha (Namalwa), which ranged from 3.1x10(6) to 4.6x10(8) IU/mg against all sensitive viruses, except human cytomegalovirus and rhinovirus type 1A, which displayed approximately equal sensitivity to both IFNs. Significantly, the potency of YM643 against bovine viral diarrhoea virus and yellow fever virus, which were selected to serve as surrogates of hepatitis C virus, equalled or exceeded that of IFN-alpha (Namalwa). These results suggest that the genetically engineered YM643 is more potent than natural IFN-alpha.

Modulation of host immune responses by clinically relevant human DNA and RNA viruses

Numerous mechanisms allow viruses to evade host immune surveillance, and new evasion strategies continue to be identified. In addition to interference with antigen processing and presentation, direct viral modulation of host immune responses can also be achieved by altering the host cytokine milieu and the development of immunoregulatory cells. A better understanding of these viral evasion strategies will help to define critical host defense mechanisms and will lead to novel immune-based therapeutic strategies in the future.

Tumor necrosis factor (TNF)-alpha and TNF receptors in viral pathogenesis

Tumor necrosis factor-alpha (TNF-alpha) and TNF receptors (TNFR) are members of the growing TNF ligand and receptor families that are involved in immune regulation. The present report will focus on the role of the prototypic ligand TNF and its two receptors, TNFR1 and TNFR2, in viral pathogenesis. Although TNF was reported years ago to modulate viral infections, recent findings on the molecular pathways involved in TNFR signaling have allowed a better understanding of the molecular interactions between cellular and viral factors within the infected cell. The interactions of viral proteins with intracellular components downstream of the TNFR have highlighted at the molecular level how viruses can manipulate the cellular machinery to escape the immune response and to favor the spread of the infection. We will review here the role of TNF and TNFR in immune response and the role of TNF and TNFR signaling in viral pathogenesis.

Genotypes of TT virus (TTV) compared between liver disease patients and healthy individuals using a new PCR system capable of differentiating 1a and 1b types from others*

TT virus (TTV) lacks obvious pathogenicity; almost all of the infected hosts are symptom-free. A possibility remains, however, that certain strains can cause liver disease while most others are non-pathogenic. Genotypes 1 a and 1 b have been proposed to contain such pathogenic strains. To test this possibility, we constructed a PCR system capable of detecting TTV of the 1 a and 1 b genotypes differentially from the other genotypes, and compared the frequencies of these genotypes between patients with liver disease of unknown etiology (n=42) and healthy individuals (n=50). The assay comprised 3 steps: i) PCR to amplify a 3.2-kb fragment using universal primers; ii) 2nd-round PCR, starting from the 3.2-kb amplicon, for a approximately 280-nt fragment by use of genotype 1-specific primers; and iii) digestion of the approximately 280-nt amplicon with MboI and BanI to discriminate between 1 a and 1 b. Eventually, 40 (95%) of the patients and 47 (94%) of the controls were positive for the 3.2-kb amplicon, and the 1 a, 1 b, 1 a+1 b, and non-1 genotypes of TTV were found in 2 (5%) vs 4 (9 percent), 5 (13%) vs 4 (9%), 1 (3%) vs 1 (2%) and 32 (80%) vs 38 (81%) of the 40 patients and 47 controls, respectively: the distribution was almost identical between the two groups. The hypothesis that the genotype 1 of TTV may be more closely associated with liver disease than other genotypes was not supported by this study.

Histopathology and cytopathology of white spot syndrome virus (WSSV) in cultured Penaeus monodon from peninsular Malaysia with emphasis on pathogenesis and the mechanism of white spot formation

Since 1994, white spot syndrome virus (WSSV) has been detected in cultured shrimp Penaeus monodon in Peninsular Malaysia. The gross signs, target organs and histo-cytopathology for the viral infection were studied and it was found to infect most organs and tissues including oocytes, but not hepatopancreatocytes and epithelial cells of the midgut, which were regarded as refractory tissues. Based on a time-sequence of ultrastructural cytopathology, 4 cytopathic profiles and 6 phases of viral morphogenesis were described. The virions were elliptical to short rods with trilamilar envelopes that measured 305 +/- 30 x 127 +/- 11 nm. Viral nucleosomes were often present singly in infected nuclei and were associated with the early stages of viral replication. The structure of WSSV pathognomonic white, cuticular lesions was examined at the microscopic and ultrastructural levels and the mechanism of their formation appeared to be related to the disruption of exudate transfer from epithelial cells to the cuticle via cuticular pore canals.

The prevalence of TT virus (TTV) infection and its relationship to hepatitis in children

TT virus (TTV) is a newly discovered virus from a patient with post-transfusion hepatitis. We investigated the frequency and pathogenesis of TTV infection in children. A semi-nested PCR assay was used to amplify TTV-DNA in serum samples from 254 ambulatory children without liver disease, 20 with hepatitis of unknown etiology, and 18 transfusion recipients or hemophiliacs. In positive samples, TTV-DNA was quantified by real-time quantitative PCR using a fluorescent probe. We detected TTV-DNA in 20% of children with hepatitis of unknown etiology, which was not statistically different from the 23% prevalence in ambulatory children. In transfusion recipients or hemophiliacs, the frequency was higher (50%) than that in ambulatory children (P = 0.01). Among ambulatory children, TTV-DNA was frequently detected in children with acute gastroenteritis (36%). TTV-DNA was detected in 10% of the infants under 6 months old, and 20% of the children from 7 to 12 months old. The prevalence was constant after the age of 1 year; however, the copy number of TTV-DNA was significantly higher in children under 1 year of age (mean: 10(5.4) versus 10(3.8) copies/ml, P= 0.008). Finally, TTV-DNA was quantified serially in three children with chronic hepatitis who were positive for TTV-DNA. The presence or amount of TTV-DNA was unrelated to the serum alanine aminotransferase level. These results indicate that TTV infection is common in children. The larger quantity of TTV-DNA in infants and the high prevalence of TTV in children of all ages suggest that TTV may be transmitted in early childhood. Its relationship to hepatitis is doubtful in children.

Viral infections in free-living populations of the European wildcat

While the importance of viral infections is well studied in domestic cats, only limited information is available on their occurence and prevalence in the European wildcat (Felis silvestris silvestris). The aim of this study was to determine the prevalence of antibodies to feline coronavirus (FCoV), calicivirus (FCV), herpesvirus (FHV), parvovirus (FPV), immunodeficiency virus (FIV), leukemia virus (FeLV), and FeLV antigenemia in 51 European wildcat sera. Samples were collected between 1996 and 1997 from wildcat populations in France, Switzerland, and Germany. Antibodies to FCoV were detected in two cats (4%) and FCoV RNA was detected in feces of one of these two cats. Antibodies to FCV, FHV and FPV were found at relatively low frequencies of 16%, 4%, and 2%, respectively. Antibodies to FIV were not detected. Although antigen and antibodies to FeLV were detected in 49%, and 75%, respectively, no evidence of FeLV-associated pathology was found. From the low prevalence of FCoV, FCV, FHV and FPV infections and from the fact that the European wildcats live solitarily, it was concluded that these viral infections do not spread readily within a population. Therefore, it may be assumed that release into the wild of European wildcats bred in captivity would not bring about a high risk of introducing of these viral infections to the free-ranging wildcats. As an exception, wildcats should be tested for absence of FIV infection before release if they were at risk to acquire this infection from domestic cats.

Faba bean necrotic yellows virus (genus Nanovirus) requires a helper factor for its aphid transmission

Purified faba bean necrotic yellows virus (FBNYV; genus Nanovirus) alone is not transmissible by its aphid vector, Acyrthosiphon pisum, regardless of whether it is acquired from artificial diets or directly microinjected into the aphid's hemocoel. The purified virus contains all of the genetic information required for its infection cycle as it readily replicated in cowpea protoplasts and systemically infected Vicia faba seedlings that were biolistically inoculated using gold particles coated with intact virions or viral DNA. The bombarded plants not only developed the typical disease syndrome, thus indicating that FBNYV is the sole causal agent of the disease, but also served as a source from which the virus was readily acquired and transmitted by A. pisum. The defect of the purified virus in aphid transmissibility suggests that FBNYV requires a helper factor (HF) for its vector transmission that is either nonfunctional or absent in purified virus suspensions. The requirement for an HF was confirmed in complementation experiments using two distinct isolates of the virus. These experiments revealed that aphids transmitted the purified virus isolate from artificial diets only when they had fed previously on plants infected with the other FBNYV isolate. Also, microinjected FBNYV, which persisted to the same extent in A. pisum as naturally acquired virus, was transmissible when aphids had acquired the HF from infected plants. This suggests that one of the functions of the HF in the transmission process is to facilitate virus transport across the hemocoel-salivary gland interface.

[TTV: a new hepatitis virus? Transfusion-transmitted virus]

Following the discovery of hepatitis C virus (HCV), it was clear that a proportion of cases with acute and chronic hepatitis are still negative for all known viral markers, which prompted investigations to search for new hepatitis agents. In 1997 investigators in Japan isolated a DNA clone of a novel human virus using a representation difference analysis from serum samples from a patient (TT) with post-transfusion hepatitis of unknown etiology and designated TTV for transfusion-transmitted virus. TTV DNA is common in populations at increased risk for infection with hemophilia or maintenance hemodialysis and abusers of intravenous drugs. As a nonenveloped virus with a linear, single stranded genomic DNA, TTV resembles the Parvoviridae among known animal viruses. TTV has been reported in association with post-transfusion and acute and chronic hepatitis of unknown etiology. Phylogenetic analysis indicated six different genotypes of TTV with distinct subtypes [correction of sottotypes]. Viral DNA can be detected in plasma but also in liver tissue of infected subjects, suggesting that it is hepatotropic. TTV can be transmitted parenterally by blood and blood products and probably also non-parenterally by a fecal-oral route. TTV DNA is present in a large proportion of patients with different forms of non-A-G hepatitis. A new simple genotyping assay based on a restriction fragment length polymorphism of TTV was developed. This system will provide the framework for future detailed epidemiological and clinical investigations.

DNA viruses and oncogenesis

This review addresses the biology and role of DNA viruses in oncogenesis.

High prevalance of TT virus infection in Japanese patients with liver diseases and in blood donors

BACKGROUND/AIMS

Although a novel DNA virus, TT virus (TTV), has been isolated from a patient with cryptogenic post-transfusion hepatitis, its pathogenic role remains unclear. To elucidate its prevalence and clinical impact in patients with liver diseases, the presence of TTV DNA was assessed in patients with liver diseases and blood donors (BDs) in Japan using two primer sets, one conventional and the other new and highly sensitive.

METHODS

We studied 261 samples, 72 with chronic hepatitis associated hepatitis C virus (HCV-CH), 57 with hepatocellular carcinoma associated HCV (HCV-HCC), 12 with HCC without either HCV or hepatitis B virus (NBNC-HCC), and 120 of BDs.

RESULTS

Using two primer sets, TTV DNA was detected in 68 (94.4%), 53 (93.0%), 12 (100%), and 98 (81.7%) HCV-CH, HCV-HCC, NBNC-HCC, and BDs, respectively. The prevalence was not significantly different between HCV-CH and HCV-HCC, or between HCV-HCC and NBNC-HCC. Comparison between patients with and without TTV revealed no significant differences in backgrounds or biochemical findings. Histopathological findings in patients with HCV-CH, and number, maximum diameter, and histological differentiation of HCC also did not demonstrate any relation to TTV infection. TTV strains can be divided into five groups using phylogenetic analysis, but no disease-specific group appears to exist.

CONCLUSIONS

Our data suggest that: 1) TTV is very prevalent among patients with liver diseases and even among BDs in Japan, 2) TTV infection does not impact on liver damage with HCV infection, and 3) TTV infection also does not affect the development or progression of HCC.

TT virus sequence heterogeneity in vivo: evidence for co-infection with multiple genetic types

TT virus (TTV) is a newly described DNA virus of humans that exhibits an unusually high degree of genetic heterogeneity. We have performed extensive analysis of the TTV populations present in samples, taken over a period of 2 to 6 years, from three individuals with persistent TTV infection. TTV DNA titres estimated for sequential samples were found to be quite stable over the entire study period in two patients, but fluctuated considerably in the third. DNA sequence analysis revealed different genetic diversity among TTV populations from samples from the three patients. In one case, absolute sequence homogeneity was observed among samples over a 3 year period. In a second, a limited amount of heterogeneity was found, including one sequence exhibiting G-->A hypermutation. TTV DNA sequences from the third patient exhibited quite remarkable genetic heterogeneity: evidence was found of seven distinct infecting viruses, representing four of the six TTV genotypes that have been described. In addition, minor variants of three of these seven sequences were observed. The heterogeneity of the viral population in this individual declined steadily over a 6 year period. This patient infected with a genetically diverse TTV population had the highest viral DNA titre.

[Involvement of TTV, a new infectious factor in post-transfusion hepatitis, non A-non G]

Post-transfusion hepatitis developed in 6 of 447(1.3%) patients who received transfusion even after 1992 when HCV screening by PHA method was started. The six patients were suggested as hepatitis, non-B, non-C, non-G type. Of the six patients, 4 were found to be infected with TTV, which was identified in one of the patients. The patients became positive for TTV DNA before or almost the same time as the development of hepatitis and their amounts of TTV DNA were varied depending on the ALT level, suggesting that their hepatitis might be caused by TTV. The patients who presented hepatitis became positive for TTV DNA in the 6-10th week after transfusion, whereas more than half of the patients with a slight hepatic disorder became positive in the 2-4th week after transfusion. In addition, prolonged infection with TTV was only observed in nearly half of 23 patients.

Infection with a novel human DNA virus (TTV) has no pathogenic significance in patients with liver diseases

BACKGROUND/AIMS

A recently identified DNA virus, termed TT virus (TTV), has been associated with post-transfusional hepatitis, and a high prevalence of TTV infection in patients with acute or chronic liver disease of unknown etiology has been reported from Japan, but few data are available about TTV infection in other countries.

METHODS

Using hemi-nested-PCR amplification to detect TTV-DNA sequences in serum, we investigated TTV infection in blood donors and in patients with liver diseases of varied etiology.

RESULTS

The prevalence of TTV infection was 13.7% in blood donors (23/168), 18.6% in chronic hepatitis C (19/102), 28.6% in chronic hepatitis B (16/56), 29.9% in hepatocellular carcinoma (20/67), 9.1% in cryptogenic chronic liver disease (2/22) and 39.6% in fulminant hepatitis (19/48). The prevalence of TTV infection in patients with virus-induced or idiopathic fulminant hepatitis was similar. Comparison of TTV-infected and non-infected patients did not reveal significant differences concerning demographic, epidemiological or histopathological features. In patients with hepatitis C, response to interferon therapy was not related to TTV infection. Phylogenetic analysis of TTV isolates showed that at least three different types of TTV are present in Spain.

CONCLUSIONS

Our data suggest that TTV infection is frequent among blood donors and patients with acute liver disease. However, pathogenic effects associated with TTV infection were not observed.

Human DNA oncogenic viruses and their transforming protein interactions with cell cycle control proteins

PURPOSE

Both oncogenic viruses and cell cycle control proteins are fast-growth research areas. More and more evidence indicates that virus infection and replication are often associated with apoptosis and interfere with cell cycle pathways. To understand the mechanisms by which viral proteins regulate apoptosis and target the cellular pathways may lead to the development of new remedies for some cancers.

DATA SOURCES

English literature searched by MEDLINE from January 1995 to August 1998.

STUDY SELECTION AND DATA EXTRACTION

More than one hundred research papers published in these areas over the past three years. Only new and important breakthroughs in these papers are selected. The review focuses on DNA viruses associated with the development of human cancers.

RESULTS AND CONCLUSIONS

Some DNA viruses contain oncogenic proteins which transform normal cells in vitro and induce tumors in animals. These viral proteins target the cellular pathways and block apoptosis induced by receptors or in response to signal transduction. Viral interference with host cell apoptosis leads to enhanced viral replication and may promote carcinogenesis. Oncogenes and tumor suppressor genes, such as Retinoblastoma (RB) and p53, play important roles in regulation of these interactions.

Comparison of field-collected ascovirus isolates by DNA hybridization, host range, and histopathology

Six field-collected ascovirus isolates obtained from five noctuid species in the continental United States were compared with respect to the general relatedness of their DNA, host range, and histopathology. Two isolates were from Spodoptera frugiperda, and the other four were from Autographa precationis, Heliothis virescens, Helicoverpa zea, and Trichoplusia ni. DNA-DNA hybridization studies showed that the six isolates belonged to three distinct viral species, with the isolates from S. frugiperda composing one species, those from A. precationis and H. virescens a second species, and those from H. zea and T. ni a third species. The host range and histopathology of each isolate was studied in eight noctuid species, S. frugiperda, Spodoptera ornithogalli, Spodoptera exigua, Spodoptera eridania, H. virescens, H. zea, A. precationis, and Feltia subterranea. Though some variation existed between the different isolates of each viral species, distinct patterns were apparent for each. The viral species from S. frugiperda had a host range that was limited primarily to Spodoptera species and both isolates of this virus only replicated and caused significant pathology in the fat body, whereas the viral species from A. precationis and H. virescens had a much broader host range that included most of the species tested, but also had a tissue tropism primarily restricted to the fat body. The viral species from T. ni and H. zea readily infected all the hosts tested, where the principal site of replication and significant pathology was the epidermis. In many test hosts, however, this viral species also replicated and caused significant pathology in the tracheal epithelium and to a lesser extent in the fat body. Aside from contributing to knowledge of ascovirus biology, these studies indicate that DNA hybridization profiles combined with studies of host range and tissue tropism can be used as characters for defining ascovirus species.

Transfusion-transmitted virus (TTV) in Brazil. Preliminary report

TTV is a recently discovered DNA virus, isolated from a patient with post-transfusion hepatitis of unknown etiology by Japanese researchers. In the present study, we evaluated the presence of TTV among chronic liver diseases patients in São Paulo and Pará states, representing two geographically distinct Brazilian regions. TTV DNA was found in 21/105 (20%) and 9/20 (45%) cases from São Paulo and Pará States, respectively. DNA sequence data confirmed the presence of TTV genotypes 1a and 2a, as well as other genotypes not yet described. In conclusion, TTV is present in chronic liver diseases cases from Southeast and North Brazil. However, further studies involving healthy populations are necessary before establishing any causal relationship among TTV and human hepatitis.