Mathematical Modeling

From the time of William Farr, who studied epidemic disease problems in the 1870s, mathematicians have been interested in 'epidemic curves' and secular trends in the incidence of infectious diseases. With the development of computer-based mathematical modeling techniques, there has been a resurgence of interest in the population dynamics of infectious diseases. There has also been a resurgence in controversies surrounding the use of models critics say 'for every model there is an equal and...

Vaccination

Vaccination is the main method of prophylaxis and Akabane vaccines have been produced in Japan and Australia. In Japan and Australia, inactivated vaccines have been developed that induce high antibody titers after two doses given with a 4 week interval. In trials, these vaccines prevented development of a viremia and fetal infection on challenge or after natural exposure and were safe when used in pregnant animals. As antibody titers decline fairly rapidly, annual revaccination is recommended....

Pathogenicity

There is considerable variation in the pathogenicity of strains of capripoxvirus. Little is known concerning the genes responsible in the capripoxvirus genome for virulence or host restriction some preliminary results have been published. Figure 1 Sheeppox showing rhinitis and conjunctivitis. a month in sheep and goats, whereas in cattle the necrotic papules that penetrate the thickness of the skin may remain as 'sitfasts' for up to a year. Severe disease is accompanied by significant loss of...

Pathogenesis

Vesicular exanthema virus gains entry via abrasions usually around the snout and mouth or on the feet. Secondary vesicles may occur as a result of direct local spread or following viremia. Abortion may occur and death of baby pigs from agalactia in their dams also occurs. Feline calicivirus produces vesicular lesions on the muzzle, and within the oral cavity and the respiratory tract. These tend to rupture quickly. During the past decade a more severe disease termed virulent-systemic (VS)...

Particle Properties and Relations of Particles with Cells

Benyvirus virions are nonenveloped rods which have a helical symmetry (Figure 1). The diameter of the particles is c. 20 nm and they usually show several length maxima ranging from c. 80 to 400 nm depending on the RNA species encapsidated. Additional length maxima may be due to end-to-end aggregation or breakage of particles. The right-handed helix of BNYVV particles has a 2.6 nm pitch with an axial repeat of four turns involving 49 sub-units of the c. 21 kDa major coat protein which consists...

Origin and Evolution

The subject of viral evolution over millions of years has received relatively little study due to the lack of a fossil record. Moreover, viruses are considered polyphyletic, and thus most of the more than 70 families of viruses are thought to have originated independently. In this regard, ascoviruses may provide a unique opportunity to obtain insights into virus evolution over long periods. Phylogenetic comparisons of ascovirus genes sequenced to date including those coding DNA polymerase and...

Notifications

Surveillance systems such as statutory notification tend to be based mainly on clinical features. These can be very useful for common diseases with distinctive clinical syndromes, such as measles and mumps. It is important however not to make a disease notifiable unless there is a good reason for it 'good' reasons include a mass vaccination program (when surveillance is virtually mandatory), any other mass control program, serious diseases for which contact tracing, mass or close contact...

Nonplant Endornaviruses

DsRNAs are found not only in plants, but also frequently in a variety of fungi in fact, they have been recorded in all major fungal taxonomic groups, including various plant pathogens. The genomes of most mycoviruses consist of dsRNAs, and these fungal dsRNA viruses have so far been classified into five families Reoviridae, Totiviridae, Partitiviridae, Chrysoviri-dae, and Hypoviridae. Members of only one of these families, the Hypoviridae, contain a single large dsRNA genome about 10-12 kbp in...

Noncoding Regions and cisSignals

The first region of BMV RNAs to attract attention as a potential regulatory element was the 3'-end. Synergistic work by multiple groups showed that the 3'-noncoding regions of BMV RNAs are highly conserved, multifonc-tional domains that direct negative-strand RNA synthesis, contribute to RNA encapsidation, translation, and stability, and possess multiple tRNA-like features and functions. Limited early sequence data showed that BMV RNAs 1-4 share a tRNA-like CCAOH 3'-end. In 1972, Hall and...

Nodaviridae

Members of the Nodaviridae that infect fish belong to the genus Betanodavirus for which the type species is Striped jack nervous necrosis virus (SJNNV). These viruses are nonenveloped with icosahedral symmetry and virion diameters of approximately 30 nm. The viral genome consists of two molecules of positive-sense ssRNA. RNA1, the largest RNA genome segment encodes the viral polymerase. RNA2 encodes the virion capsid protein. A third RNA, transcribed from the 3' terminal region of RNA1, encodes...

Multigene Families

A large proportion of the ASFV genome encodes multigene families (MGFs) consisting of related protein-coding Nucleotide metabolism, transcription, replication, and repair Ribonucleotide reductase (small subunit) Ribonucleotide reductase (large subunit) Proliferating cell nuclear antigen (PCNA) like Helicase superfamily II similar to origin binding protein FTS-J-like methyl transferase domain IkB homolog and inhibitor of calcineurin phosphatase* CD2-like. Causes hemadsorbtion to infected cells*...

Markers of Infection

Serological diagnosis of HBV infection relies on the detection of HBsAg in serum, and its persistence for longer than 6 months indicates progression to chronic infection. Appearance of anti-HBs (antibody to HBsAg) indicates recovery from infection, or acquired immunity after preventive vaccination. Detection of HBeAg denotes active viral replication, as does the detection of serum HBV-DNA by qualitative or quantitative PCR tests. Seroconversion to anti-HBe occurs after recovery from acute...

Introduction

The intestinal tract, lined by replicating epithelial cells, bathed in nutrient fluids and maintained at optimal temperature provides an ideal milieu for growth of many viruses. 'Enteric viruses' represent a wide spectrum of viral genera that invade and replicate in the mucosa of the intestinal tract, and that can be grouped as follows viruses causing localized inflammation at any level of the intestinal tract, predominantly in small intestinal mucosa, resulting in acute gastroenteritis, for...

Infection Cycle

Baculoviruses produce two distinct virion phenotypes, occlusion-derived virus and budded virus, which are responsible for infection of insects (per os infection) and insect cells (cell-to-cell spread), respectively. Infection for both GVs and NPVs begins with the ingestion and solubilization of the occlusion bodies in the host larval midgut. The released occlusion-derived virus then fuses with the micro-villi of midgut epithelial cells, and nucleocapsids pass through the cytoplasm to the...

Implications for Vaccine Development

Our increasing knowledge of the structure of viral epi-topes has given rise in some quarters to the expectation that it should be possible to develop peptide-based viral vaccines. However, the results so far have been disappointing. In spite of the hundreds of viral epitopes that have been identified by studying the antigenicity of pep-tide fragments of viral proteins, no commercial peptide vaccine has yet reached the marketplace. Although most peptide fragments are immunogenic in the sense...

Immunosorbent Electron Microscopy

In immunosorbent electron microscopy (ISEM) (Figures 2(b), 4(a), and 4(b)), the electron microscope grids carrying a support film are coated with antibodies specific for viruses having the same morphology as the ones found in the electron microscopical adsorption test or with antibodies to viruses being suspected to be present in the plant material under investigation. Over a thousand times more virus particles can be detected on such antibody-coated grids than on uncoated grids or on grids...

Host Range and Propagation

The host range of the collective isolates of CMV is over 1300 species in more than 500 genera of over 100 families, with new hosts reported each year. Some recently described strains from new hosts have lost the ability to infect many of the typical hosts of CMV. This may be a general feature for adaptation to unusual hosts. CMV infects most of the major horticultural crops as well as many weed species the latter act as reservoirs for the virus. Infection of various indicator plants was used to...

Host Factors in RNA Replication

As for many other viruses, the small size of the 8.2 kbp BMV genome relative to the complexity of BMV replication suggests that many, if not most, steps in BMV RNA replication involve contributions from host factors. Since most of the viral genome is devoted to RNA replication functions, host factors appear particularly likely to be involved in that process as well. Biochemical and genetic results support these ideas and have begun to elucidate some of the relevant host factors and...

Other Control Methods

Although ACMV and EACMV-like CMGs interact syn-ergistically, there is evidence that EACMV-like CMGs may hinder infection by other EACMV-like viruses and interfere with their replication. Studies in Uganda showed that plants initially infected by mild strains of EACMV-UG were much less likely to become severely diseased when exposed in the field than plants initially CMG-free. This cross-protective effect seems to be an important cause of symptom amelioration in post-CMD pandemic areas of East...

Organization and Molecular Biology of the GLV dsRNA Genome

The 6277 nt GLV dsRNA genome contains only two large open reading frames (ORFs), both on the same strand of RNA (Figure 2). The first ORF (nts 368-3015) encodes the precursor polypeptide for the GLV capsid protein. Thirty-two amino acid residues from the N-terminus of this precursor protein are apparently removed by a cellular cysteine protease before the processed capsid protein is assembled into the virion. The second ORF (nts 2806-5976) is -1 relative to ORF 1, and the two ORFs overlap by...

Electron Microscopy of Viruses

G Schoehn and R W H Ruigrok, CNRS, Grenoble, France 2008 Elsevier Ltd. All rights reserved. Most viruses are too small to be observed with light microscopy and many are too large or too irregular to crystallize. Therefore, electron microscopy (EM) is the method of choice for the direct visualization of viruses and viral proteins or subviral particles. However, electrons do not travel far in air and therefore the inside of the microscope has to be under very high vacuum (10 5 to 108 torr). This...

Host Range and Transmission

BCMV naturally infects P. vulgaris (kidney bean), P. acutifolius (tepary bean), P. atropurpureus, P. coccineus (runner bean), P. mungo (black gram), Glycine max (soybean), Macroptilium lathyroides (horse gram), Pisum sativum (pea), Rhynchosia minima, Vicia faba (broad bean), Vigna radiata (mung bean, green gram), V. angularis (azuki bean), and V. unguiculata (cowpea). Peanut stripe isolates naturally infect Arachis hypogea (peanut), Dolichos lablab (hyacinth bean), Indigofera amoena, G. max,...

Modes of Transmission

HIV can be transmitted by sexual contact, exposure to blood, and from mother to child with variable efficiency (Table 1). Although HIV has been isolated from a variety of body fluids, only blood, semen, genital fluids, and breast milk have been proven as sources of infection. Unprotected sexual contact is the predominant mode of HIV transmission throughout the world. Despite a relatively low efficiency of transmission per sexual act, numerous factors can enhance transmission. Receptive anal...

Adenoviruses Molecular Biology

K N Leppard, University of Warwick, Coventry, UK 2008 Elsevier Ltd. All rights reserved. Adenoviruses were first discovered during the 1950s, in studies of cultures from human adenoids and virus isolation from respiratory secretions. Their study accelerated dramatically in the 1960s after it was demonstrated that a human adenovirus could cause tumors in experimental animals, leading to the hope that such work would lead to a better understanding of human cancer. What has been learned...

Virion and Genome Structure

BIV, JDV, and FIV are RNA viruses with two identical single-stranded RNA molecules of approximately 8.5, 7.7, and 9.5 kb per genome, respectively. The viral genomes, viral enzymes, and nucleoproteins (NC) involved in viral assembly are all packaged within the nucleocapsid core (Figure 2(a)). The mature core is shaped like a cone, typical of primate lentiviruses. Viral enzymes are protease (PR), reverse transcriptase (RT), and integrase (IN) encoded by the pol gene. FIV also produces a...

Enterovirus 71 HEVA

EV71 was initially isolated in 1969 from a case of fatal encephalitis in California. Since then it has caused several outbreaks in different parts of the world including Australia, Bulgaria, Hong Kong, Hungary, Japan, and Sweden. Clinical symptoms of infection have been various, sometimes associated with CNS involvement. In recent years Southeast Asia has suffered from large epidemics of EV71, manifested, for example, in Taiwan 1998 with 405 patients hospitalized and 78 fatalities. Epidemiology...

Biological Properties

The natural host range of mycoviruses is likely to be restricted to the same or closely related vegetative compatibility groups that allow lateral transmission. Until recently, there were no known experimental host ranges for fungal viruses because of lack of suitable infectivity assays. Experimental host ranges for some mycoviruses, however, were recently demonstrated and shown to extend to different vegetative compatibility groups and even to different genera. For example, the prototype...

Diagnosis and Disease Management

External signs of disease associated with infection by highly pathogenic aquareoviruses, including lethargy, inappetance, anorexia, abnormal swimming behavior, petechial hemorrhages, lateral recumbency, distended abdomen, high mortality rates, are not pathognomonic and laboratory investigation is required for definitive diagnosis. Several of the known aquareoviruses have been detected by virus isolation on any of a number of fish cell lines in common use in diagnostic laboratories. Depending on...

Organization of the Genome and Properties of the Encoded Proteins

The genome organization of BNYVV is outlined in Figure 2. BNYVV RNA1 contains one large open reading frame (ORF) for a replication-associated protein which is cleaved autocatalytically by a papain-like proteinase. In in vitro systems, its translation may start either at the first AUG at position 154 or at a downstream AUG at position 496. The resulting proteins of 237 and 220 kDa, respectively, contain in their N-terminal part methyltransferase motifs (MetT), in their central part helicase...

Properties of the Virion and Genome

The morphology and structure of the CCHFV virion was first described in the early 1970s from the brains of infected newborn mice. It is now known that CCHFV and nairoviruses in general, are typical of other members of the family Bunyaviridae in terms of their basic structure, morphogenesis, replication cycle, and physicochemical Figure 2 Dorsal view of a Hyalomma marginatum marginatum female tick. Photo courtesy of Dr. Zati Vatansever, Ankara University Faculty of Veterinary Medicine, Ankara,...

Virion Proteins and RNA Segments

The spherical bunyavirus particle is about 100 nm in diameter and electron microscopy reveals a fringe of spikes on the surface (Figure 2). The virion consists of four structural proteins two internal proteins (N and L) and two external glycoproteins, termed Gn and Gc, which are inserted in the Golgi-derived viral membrane (Figure 3). The N protein (2100 copies per particle) encapsidates the RNA genome segments to form ribonucleoprotein complexes termed RNPs or nucleocapsids, to which the L...

Studies on the Ultrastructure of Infected Host Cells by Means of Conventional Electron Microscopy

Alterations of the fine structure in infected host cells are studied by means of conventional electron microscopy in ultrathin sections that are obtained from plant tissues after chemical fixation, dehydration, and embedding in resinlike polymers such as epoxides or methacrylates (Epon, Araldite, Spurr's resin, LR White, or LR Gold). Cryosec-tioning after rapid freezing procedures is used less frequently. Cytological alterations are easily detected in ultrathin sections from well-selected...

The DNA p Satellites of Begomoviruses

Begomovirus Structure

Identification of the Begomovirus Satellites The first begomovirus satellite discovered, referred to as tomato leaf curl virus-sat (ToLCV-sat), was identified in tomato plants infected with the monopartite begomo-virus tomato leaf curl virus (ToLCV) originating from Australia. The component is a small (682 nt) circular ssDNA with no extensive open reading frames (ORFs) and sequence similarity to its helper virus limited to sequences within the apex of two stem loop structures. The first...

Vegetable Viruses

Pepino Mosaic Virus Geographical distribution Pepino mosaic virus (PepMV) was originally described in Peru on pepino (Solatium muricatum) and found to infect tomato and related wild species symptomlessly, in experimental trials. Since 1999, PepMV outbreaks have been reported almost simultaneously in many European countries (Austria, Bulgaria, Finland, France, Germany, Hungary, Italy, Netherlands, Norway, Poland, Slovakia, Spain, Sweden, Switzerland, Ukraine, and UK) where it is considered an...

Host Responses

The low sporadic disease incidence and remote locations of most outbreaks have led to limited careful study of the host responses to virus infection. Perturbations of the innate and acquired immune responses are consistent with fatal disease outcome. In a few studies patients that survived Ebola infections were reported to have generated a virus-specific immunoglobulin M (IgM) response and to have transient expression of pro-inflammatory cytokines. In sharp contrast, fatal EBOV cases have...

Herpesviridae

Herpesviruses have been isolated from channel catfish (Ictalurus punctatus), common and koi carp (C. carpio), common goldfish ( Carassius auratus), eel (Anguilla spp.), rainbow trout, masou salmon, lake trout (S. namaycush), sturgeon, walleye, and Japanese flounder. Channel catfish virus is the only fish herpesvirus assigned to the genus, Ictalurivirus, and this genus is not assigned to any of the three subfamilies (Alphaherpesvirinae, Betaherpesvirinae, and Gammaherpesviri-nae) of the family...

History

The genus Cardiovirus contains two species, Encephalomyo-carditis virus and Theilovirus (Table 1). The first report of a cardiovirus was by Theiler in 1934. He reported that a neurological disease of mouse could be transmitted by intracerebral or intranasal inoculation, and was caused by a virus, which persisted in the central nervous system (CNS). This virus is known as Theiler's murine encephalomyelitis virus (TMEV). The disease was described as a polio-like infection with destruction of...

Treatment of Chronic Hepatitis B

Prior to the introduction of specific antiviral therapeutics, persistent HBV infection was treated with interferon, with mixed success. In some studies, up to one-third of treated individuals cleared the virus, but the treatment was rather less successful in certain populations, particularly individuals from the Far East. Interferon seems to work by modulating the immune response of the host, rather than a direct antiviral effect, and was found to be most successful in individuals who had...

History of Herpesvirus Discovery

Diseases caused by herpesviruses have been known since ancient times, but it was not until the beginning of the twentieth century that the viruses causing these diseases were detected. Human alphaherpesviruses (members of subfamily Alphaherpesvirinae) such as herpes simplex virus (HSV) and varicella-zoster virus (VZV) were the first to be propagated in cell culture and visualized by electron microscopy. Later, betaherpesviruses (members of subfamily Betaherpesvirinae) such as human...

Further Reading

Afonso CL, Piccone ME, Zaffuto KM, et al. (2004) African swine fever virus multigene family 360 and 530 genes affect host interferon response. Journal of Virology 78 1858-1864. Andres G, Alejo A, Salas J, and Salas ML (2002) African swine fever virus polyproteins pp220and pp62 assemble into the core shell. Journal of Virology 76 12473-12482. Borca MV, Carrillo C, Zsak L, et al. (1998) Deletion of a CD2-like gene, 8-DR, from African swine fever virus affects viral infection in domestic swine....

Le Dantec Group

At the L gene amino acid level, Fukuoka virus (FUKAV) and Le Dantec virus (LDV) appear to be related, although FUKAV was previously classified in the Kern Canyon group on the basis of its antigenic properties (see below). LDV was originally recovered in 1965 from a patient with a febrile illness, headaches, and spleen and liver hypertrophy in Senegal. In CF tests with other known rhabdoviruses, Le Dantec virus was found to be antigenically related to Keuraliba virus, a previously ungrouped...

Panherpes PCR with Degenerate Primers

The method is based on the fact that herpesvirus genomes contain highly conserved genes, which are present in all because they code for proteins essential for viral growth. One of the most conserved is the herpesvirus DNA polymerase (DPOL) gene. Investigators aligned the DPOL genes of all herpesviruses for which sequence data were available, in order to identify short blocks of greatest amino acid identity that encode domains essential for DPOL function. This procedure allowed the design of...

Modes of Virus Transmission

Virus transmission may be 'horizontal' or 'vertical'. The vast majority of transmission is horizontal, that is, between individuals within the population at risk. Modes of horizontal transmission of viruses can be characterized as direct contact, indirect contact, common vehicle, airborne, vector-borne, iatrogenic, and nosocomial. Vertical or transplacental transmission occurs between the mother and her fetus or newborn. Some viruses are transmitted in nature via several modes, others...

Properties of the Virion

Arterivirus particles are spherical, enveloped, and 40-60 nm in diameter (Figures 1(a) and 1(b)). Unfixed Figure 1 (a) An electron micrograph of extracellular PRRSV particles. (b) Schematic representation of an arterivirus particle and its seven structural proteins. (c) An electron micrograph of EAV particles budding from smooth membranes in (or close to) the Golgi region of infected baby hamster kidney cells (BHK-21) cells. (d) An electron micrograph of typical double-membrane vesicles found...

Clinical Features Presentation

The clinical manifestations of EBOV and MARV are often compared to that of severe sepsis or septic shock. Following a 2-21 day incubation period, cases often present with a variety of nonspecific symptoms including high fever, chills, malaise, and myalgia. As the disease progresses, there is evidence of multisystemic involvement, and manifestations include prostration, anorexia, vomiting, nausea, abdominal pain, diarrhea, shortness of breath, hypotension, edema, confusion, maculopapular rash,...

Distribution Host Range Transmission and Economic Significance

Carmoviruses occur worldwide and are generally reported to cause mild or asymptomatic infections on relatively restricted natural host ranges. Most accumulate to high concentrations in infected tissues and are mechanically transmitted. Beetle transmission has been reported for some carmoviruses as has transmission in association with soil and or irrigation water, and in some cases in association with fungal zoospores. A number of carmoviruses have been identified in association with ornamental...

Adenoviruses Malignant Transformation and Oncology

A S Turnell, The University of Birmingham, Birmingham, UK 2008 Elsevier Ltd. All rights reserved. Transforming and Oncogenic Properties of Human Adenoviruses Human adenoviruses (Ads) are small, nonenveloped DNA viruses with linear, double-stranded genomes of about 35 kbp that are associated with a broad range of infections, but are most commonly linked with acute infections of the upper respiratory and gastrointestinal tracts. The clinical manifestations of an adenovirus infection are dependent...

Virion Structure and Composition

The viruses in the genera Caulimovirus, Cavemovirus, Soymovirus, and Petuvirus form nonenveloped, isometric particles that vary in size from 43 to 50 nm. The virion is Virus members in the family Caulimoviridae Caulimovirus Carnation etched ring virus CERV Strawberry vein banding SVBV virus Aquilegia necrotic mosaic ANMV virusb Petuvirus Petunia vein clearing PVCV Soymovirus Blueberry red ringspot BRRSV Peanut chlorotic streak PCSV virus Soybean chlorotic mottle SbCMV virus Cestrum yellow leaf...

Defining the Correlates of Protection

A major difficulty in HIV-1 vaccine research has been in determining which host immunological factors, if any, correlate with protection from infection or protection from disease progression. The influence of human leukocyte antigen (HLA) genotype on HIV progression is a clear indicator that the adaptive immune response is implicated in the control of infection. However, only rare cohorts of individuals seem to resist HIV-1 infection despite frequent exposure to the virus, or control an...

Epidemiology Geographic Distribution Host Range and Transmission

Cardioviruses have a worldwide distribution and are associated with a wide variety of species. Rodents, especially rats, are considered to be the natural host and reservoir of EMCV. In wild rodents, the virus usually persists without causing disease, whereas infection in laboratory rodents, especially baby mice, commonly produces fatal encephalitis and or myocarditis. In pigs, natural infections with EMCV have different clinical characteristics, probably depending on different EMCV strains,...

The Surface Protein HBsAg

The 226-amino-acid (aa) residue S protein is quite hydrophobic and structural models suggest that it contains four membrane-spanning regions (Figure 4(a)). The major hydrophilic loop is exposed on the surface of viral particles and is the main target of the immune response to HBsAg. This domain is rich in cysteine residues, which are believed to be linked by disulfide bridges, forming a complex structure that includes the a determinant and d y and w r subdeterminants. Antibody (anti-HBs)...

Barley Yellow Mosaic Virus Barley Mild Mosaic Virus

Bymoviruses have bipartite ssRNA genomes and each segment (RNA1 and RNA2) carries a single open reading frame (ORF) which encodes a polyprotein. The coat protein (CP) gene is located at the C-terminus of the RNA1. Barley yellow mosaic virus (BaYMV) and barley mild mosaic virus (BaMMV) are major pathogens of winter barley in Europe and East Asia. Yellow discolored patches of different sizes are often the first sign of field infection in early spring. First symptoms are chlorotic or pale green...

Chloris Striate Mosaic Virus

This virus found in 1963 in Australia causes striate mosaic in Chloris gayana Kunth and other grass species and in cereals including barley, maize, and oats. It is transmitted by the leafhopper Nesoclutha pallida (Evans). Natural hosts are Table 1 Taxonomic position of maize viruses Table 1 Taxonomic position of maize viruses bNot described, virus with low or no agronomical importance. several grasses, and barley, oats, maize, and wheat. Infected plants develop chlorotic grayish white striation...

Phylogenetic Information

Assigned species within the genus Avihepadnavirus include DHBV isolated from Pekin ducks (Anas domesticus) and HHBV from grey herons (Ardea cinerea). Many DHBV isolates have been found in domesticated ducks and, in the wild, in the mallard, the species from which most domesticated ducks are derived. Viruses less closely related to DHBV have been isolated from geese and other duck species and include the Ross's goose hepatitis B virus (RGHBV) from Ross's geese (Anser rossii), Mandarin duck...

Antigenic Variation in Influenza Viruses

Influenza viruses are classified as types A, B, or C based on cross-reactivity of internal antigens. Type A influenza viruses, those most commonly associated with human infection, show two distinct mechanisms of antigenic variation antigenic shift and antigenic drift. Antigenic shift is a replacement of one subtype of surface antigen with another. There are two surface glycoprotein antigens, hemagglutinin (HA) and neuraminidase (NA) that exist in multiple serotypes. To date there are 16...

Proteins Encoded by Endornaviruses

All five endornaviruses that have been completely sequenced encode a single unusually long ORF, from 4500 to 5500 aa residues in length, which is one of the unique molecular features of endornaviruses Figure 1 . Conserved motifs encoding RdRp and Hel are found in the same regions of these long ORFs. The genes encoding RdRp and Hel are structurally similar to those encoded by the ssRNA genome of members of the alpha-like supergroup of RNA viruses. Thus, the endornavirus RdRp and Hel probably...

BEFV Genome Organization and the Encoded Proteins

The 14 900 nt BEFV genome is the largest known for any rhabdovirus and one of the largest and most complex genomes for any nonsegmented, negative-sense RNA virus. The genome comprises 12 genes, flanked by terminal, partially complementary leader and trailer t sequences, and arranged in the order 3'- -N-P C-M-G-GNS-a1 a2 a3-P-y-L-t-5'. By analogy with other rhab-doviruses, the 3' leader 50 nt and 5' trailer 70 nt sequences are likely to have important roles in the initiation and control of...

Functions of the Viral Proteins

Functions have been ascribed to most of the regions of the polyproteins encoded by both RNA-1 and RNA-2 of CPMV. In most cases, however, it is not certain at what stage s in the cleavage pathway they manifest their activity. Figure 3 Expression of CPMV RNA-1 and RNA-2. Both RNAs contain a single long open reading frame, which is processed to yield a series of proteins. The positions of the initiation and termination codons and the dipeptides at the proteolytic processing sites are shown. In the...

Virion Particle Structure and Phylogenetic Considerations

Figure Drawing Model

Human rhinoviruses HRVs represent the serologically most diverse group of picornaviruses over 100 serotypes have already been identified . The reason for this diversity is not known. Ultrastructural analysis of rhinoviruses by X-ray crystallography resulted in a structural model of rhinoviruses Figure 3 . Along the fivefold icosahedral axis of the virion a 2.5 nm depression, the so-called 'canyon', was detected. The genomic region encoding the peptide residues that form this structure is more...

Taxonomic Identification Genome Organization and Replication Cycle of Rhinoviruses

The Host Fight Rhinovirus

The establishment of cell and tissue culture techniques as well as nucleotide sequencing methods allowed for taxonomic classification of rhinoviruses. An overall RNA sequence compilation revealed a close genetic similarity to polio- and coxsackiviruses hence, rhinoviruses were identified as members of the family Picornaviridae. The genomic organization is similar in all genera of Picornaviridae Figure 1 . The 5' end of the RNA is joined to a small viral protein called VPg, which is a...

Classification and Evolution

CMVs are members of the family Herpesviridae and belong to subfamily Betaherpesvirinae Table 1 . Formally, this subfamily is divided into three genera, namely Cytomegalovirus HCMV-like viruses from primates , Muromegalovirus MCMV-like viruses from rodents , and Roseolovirus HHV-6-like viruses, so far only from great apes . There is Table 1 Primate and other viruses classified in or potentially belonging to the subfamily Betaherpesvirinae Genus Host group Host species abbreviation Formal name...

Virion Physical Properties Composition and Genome Organization

African swine fever virus has a sedimentation coefficient S20,wof about 3500 S and a buoyant density of 1.095 gcm 3 in Percoll and 1.19 1.24 g cm- in CsCl. Virions are susceptible to irradiation, ether, deoxycholate, and chloroform, and they are inactivated at 60 C for 30 min. Virions can survive for years at 4 C and they are stable over a wide range of pH. The asfivirus particle consists of a nucleopro-tein core that is 70 100 nm in diameter, surrounded by two internal lipid layers, and a 170...

Fungal Virus Taxonomy

A list of the virus families and genera into which mycov-iruses are classified is included in Table 1. Members of some fungal virus families, for example, the families Narnaviridae, Chrysoviridae, and Hypoviridae, infect only fungi, while members in other families, for example, the families Metaviridae, Pseudoviridae, Reoviridae, Totiviridae, and Partitiviridae, infect fungi, protozoa, plants, or animals. Except for the rhizidiomyces virus with dsDNA genome the only member in the genus...

Geographical Distribution

Image Indian Cassava Mosaic Virus

The cassava geminivirus pandemic in Africa started in the early 1990s and is still going on today. It started in Uganda in 1994, invaded several countries in East Africa around Lake Victoria, before crossing the mountains in Rwanda-Burundi, to infect the entire Congo Basin and invade up to Gabon and the south of Cameroon Figure 3 . Cassava plants were already infected with African cassava mosaic Figure 3 Distribution of cassava mosaic geminiviruses in Africa obtained from CMD surveys in Africa,...

The Cotton Leaf Curl Disease in the Indian Subcontinent

Leaf Curl Disease Cotton

The leaf curl disease of cotton Gossypium hirsutum L. was first observed in Multan, Pakistan, in 1967. The disease reappeared in 1987 in its epidemic form in most of the cotton-growing areas of Pakistan. In 1992, the disease was observed throughout the central and southern parts of Punjab in Pakistan. During 1997-98, the disease was established in the border areas of India Rajasthan, Haryana, and Punjab , joining the southern Punjab of Pakistan. The most devastating virus known as cotton leaf...

Epidemiology and Transmission

Culicoides Imicola

Most of Africa, the Middle East, southern Asia, Japan, Korea, and Australia may be regarded as being endemic for Akabane virus. Papua New Guinea and the island countries of the Pacific, however, are free from infection. The geographical distribution of this virus is controlled completely by the distribution, seasonal activity, and abundance of its insect vectors. Akabane virus was first isolated in Japan in 1959 from mosquitoes of the species Ae. vexans and Cx. tritaenio-rhynchus. Then, in...

Viral Transcripts and Proteins

Hsv Replication

Each viral protein is expressed from its own independently regulated transcript. The viral transcription map is included in Figure 1. Independent starts of overlapping transcripts, rare splicing, and temporally differentiated polyadenylation site utilization result in the number of independent transcripts expressed exceeding 100. General Properties of Transcripts and Promoters Generally, the ORFs of HSV-1 are expressed as unique, intronless mRNA molecules that are controlled by temporal...

Genome Structure

The genomes of all known CMV DNA molecules are c. 210 240 kbp in size, and most have a G C content of around 58 , in contrast to the 145 166 kbp and 46 G C content of HHV-6 and HHV-7. Structurally, two distinct CMV genome types can be discerned. The genomes of New World primate CMVs HVAotus types 1 and 3 , HCMV, and CzCMV represent one type, having internal inverted repeats flanking two unique regions the L segment consisting of unique region UL flanked by inverted repeats TRL IRL, and the S...

Evolutionary Relationships Among Arboviruses

The biological characteristic ofviral replication in arthropods followed by transmission to vertebrates in the course of blood feeding has arisen independently in seven families of viruses. Taxonomic relationships within the arboviruses were originally based on analyses of antigenic cross-reactivity data obtained from neutralization, complement fixation, and hemagglutination tests. Virion morphology, determined by electron microscopy, was also important in taxonomic classification. The...

Genome Organization and Expression

Barley Yellow Dwarf Virus

Genomic RNAs of BYDVs and CYDVs for which complete nucleotide sequences are available contain five to six ORFs Figure 3 . ORFs 1, 2, 3, and 5 are shared among all BYDVs and CYDVs. BYDVs lack ORF0. Genomic sequences of CYDV-RPV -CYDV-RPS PLRV CoMV Figure 1 Phylogenetic relationships of the predicted amino acid sequences of RNA-dependent RNA polymerases RdRps ORFs 1 and 2 of barley yellow dwarf viruses BYDVs and cereal yellow dwarf viruses CYDVs and members of the genus Sobemovirus and family...

Adenoviruses General Features

B Harrach, Veterinary Medical Research Institute, Budapest, Hungary 2008 Elsevier Ltd. All rights reserved. Adenoviruses are middle-sized, nonenveloped, icosahe-dral, double-stranded DNA viruses of animals. The prefix adeno comes from the Greek word dSfv gland , reflecting the first isolation of a virus of this type from human adenoid tissue half a century ago. Adenoviruses have since been isolated from a large variety of hosts, including representatives of every major vertebrate class from...

Taxonomy Properties of the Virion and Genome

Endozomes And Btv

African horsesickness virus is a species of the genus Orbivirus within the family Reoviridae. The virus is nonenveloped, approximately 90 nm in diameter and has an icosahedral capsid that is made up of three distinct concentric protein layers Figure 1 , and which is very similar to the structure of bluetongue virus the prototype orbivirus . Nine distinct serotypes of AHSV have been identified by the specificity of interactions between the more variable viral proteins that make up the outermost...

Murine Cytomegalovirus

Images Cmv Virus Strand

Murid herpesvirus 1 is the type species of the genus Muromegalovirus. The term murine cytomegalovirus MCMV is more commonly used for the virus than murid herpesvirus 1. The natural host for MCMV is the house mouse, Mus musculus domesticus. Because of the strict species specificity of CMVs, MCMV is widely used as an animal model of HCMV infection. Consequently, more is known about MCMV than any other nonprimate CMV. CMV virions are spherical, c. 230 nm in diameter, and comprise four...

Other Nonassigned Rhabdoviruses

'Sigma virus' SIGMAV is the agent responsible for CO2 sensitivity in Drosophila melanogaster. It is a noncontagious rhabdovirus which is transmitted through gametes. Rochambeau virus RBUV was first isolated from mosquitoes Coquillettidia albicosta in French Guiana in 1973. It is classified as a tentative species of the genus Lyssavirus in the Eighth ICTV Report and is not related to any other dimarhadovirus, according to the phylogenetic analysis of the central region of the nucleoprotein....

Classification and History

Most currently recognized fish herpesviruses infect species that are farmed or harvested from the wild for human consumption. The conditions used in aquaculture may enhance the disease potential of these pathogens and increase their likelihood of detection. It is probable, therefore, that many more fish herpesviruses await discovery. A similar prospect applies to amphibian herpesviruses, since the two known examples originated from a single host species. Herpesviruses of fish and amphibians,...

Continuous and Discontinuous Epitopes

Protein epitopes are usually classified as either continuous or discontinuous depending on whether the amino acids included in the epitope are contiguous in the poly-peptide chain or not Figure 1 . This terminology may give the impression that the elements ofrecognition operative in epitope paratope interactions are individual amino acids, whereas it is in fact at the level of individual atoms that the recognition occurs. The distinction between continuous and discontinuous epitopes is not...

Maize Chlorotic Dwarf Virus

Corn Plant Aspect

Confirmed reports of maize chlorotic dwarf virus MCDV infection are limited to the US, where the virus was discovered in 1969. The extent of distribution of MCDV in the US is second to that of MDMV. The virus is associated with the occurrence of indigenous Johnson grass S. halepense L. Pers. , its overwintering host, and the black-faced leafhopper, Graminella nigrifrons DeLong and Mohr , its principal vector. Symptoms on susceptible maize are shortening of the upper internodes or proportionate...

Novirhabdoviruses of Fish

Novirhabdovirus Taxonomy

The genus Novirhabdovirus was established in 1998, and includes four official species as shown in Table 1 . Infectious hematopoietic necrosis virus IHNV and viral hemorrhagic septicemia virus VHSV are economically significant viruses that cause epidemics in salmonid fish. IHNV is endemic in salmonids of northwestern North America and has become established in Europe and Asia through historical aquaculture-related activities. VHSV Table 1 Fish rhabdoviruses from the published literature and...

Epidemiology

Dengue viruses occur in nature in three basic maintenance cycles Figure 2 . The primitive forest cycle involves canopy-dwelling mosquitoes and lower primates. A rural cycle, primarily in Asia and the Pacific, involves peridomestic mosquitoes Ae. albopictus and Ae. scutellaris Spp. and humans. The urban cycle, which is the most important epidemiologically and in regard to public health and economic impact, involves the highly domesticated Ae. aegypti mosquito and humans. The viruses are...

Natural History of the Disease

Natural History Disease Diagram

Exposure to HBV may result in asymptomatic, acute icteric, or, in some instances, fulminant hepatitis 0.1-0.5 . Approximately 5 of adults and 95 of peri-natally infected young children become persistently infected. The outcome depends on the age of the patient and genetic factors determining the efficiency of the host immune response. Genetic factors influencing outcome in more than one study include polymorphisms of the MHC class II glycoproteins, which influence presentation of viral peptides...