Marburg Virus Disease: An RNA virus infection of rhesus, vervet, and squirrel monkeys transmissible to man.Virus Diseases: A general term for diseases produced by viruses.Ross River virus: A species of ALPHAVIRUS associated with epidemic EXANTHEMA and polyarthritis in Australia.Hemorrhagic Fevers, Viral: A group of viral diseases of diverse etiology but having many similar clinical characteristics; increased capillary permeability, leukopenia, and thrombocytopenia are common to all. Hemorrhagic fevers are characterized by sudden onset, fever, headache, generalized myalgia, backache, conjunctivitis, and severe prostration, followed by various hemorrhagic symptoms. Hemorrhagic fever with kidney involvement is HEMORRHAGIC FEVER WITH RENAL SYNDROME.Alphavirus Infections: Virus diseases caused by members of the ALPHAVIRUS genus of the family TOGAVIRIDAE.Respiratory Syncytial Virus Infections: Pneumovirus infections caused by the RESPIRATORY SYNCYTIAL VIRUSES. Humans and cattle are most affected but infections in goats and sheep have been reported.Queensland: A state in northeastern Australia. Its capital is Brisbane. Its coast was first visited by Captain Cook in 1770 and its first settlement (penal) was located on Moreton Bay in 1824. The name Cooksland was first proposed but honor to Queen Victoria prevailed. (From Webster's New Geographical Dictionary, 1988, p996 & Room, Brewer's Dictionary of Names, 1992, p441)RNA Viruses: Viruses whose genetic material is RNA.Marburgvirus: A genus in the family FILOVIRIDAE consisting of one species (Lake Victoria marburgvirus) with several strains. The genus shows no antigenic cross-reactivity with EBOLAVIRUS.West Nile Fever: A mosquito-borne viral illness caused by the WEST NILE VIRUS, a FLAVIVIRUS and endemic to regions of Africa, Asia, and Europe. Common clinical features include HEADACHE; FEVER; maculopapular rash; gastrointestinal symptoms; and lymphadenopathy. MENINGITIS; ENCEPHALITIS; and MYELITIS may also occur. The disease may occasionally be fatal or leave survivors with residual neurologic deficits. (From Joynt, Clinical Neurology, 1996, Ch26, p13; Lancet 1998 Sep 5;352(9130):767-71)Slow Virus Diseases: Diseases of viral origin, characterized by incubation periods of months to years, insidious onset of clinical manifestations, and protracted clinical course. Though the disease process is protracted, viral multiplication may not be unusually slow. Conventional viruses produce slow virus diseases such as SUBACUTE SCLEROSING PANENCEPHALITIS, progressive multifocal leukoencephalopathy (LEUKOENCEPHALOPATHY, PROGRESSIVE MULTIFOCAL), and AIDS. Diseases produced by unconventional agents were originally considered part of this group. They are now called PRION DISEASES.Virus Replication: The process of intracellular viral multiplication, consisting of the synthesis of PROTEINS; NUCLEIC ACIDS; and sometimes LIPIDS, and their assembly into a new infectious particle.Arbovirus Infections: Infections caused by arthropod-borne viruses, general or unspecified.Vaccinia virus: The type species of ORTHOPOXVIRUS, related to COWPOX VIRUS, but whose true origin is unknown. It has been used as a live vaccine against SMALLPOX. It is also used as a vector for inserting foreign DNA into animals. Rabbitpox virus is a subspecies of VACCINIA VIRUS.West Nile virus: A species of FLAVIVIRUS, one of the Japanese encephalitis virus group (ENCEPHALITIS VIRUSES, JAPANESE). It can infect birds and mammals. In humans, it is seen most frequently in Africa, Asia, and Europe presenting as a silent infection or undifferentiated fever (WEST NILE FEVER). The virus appeared in North America for the first time in 1999. It is transmitted mainly by CULEX spp mosquitoes which feed primarily on birds, but it can also be carried by the Asian Tiger mosquito, AEDES albopictus, which feeds mainly on mammals.Respiratory Syncytial Viruses: A group of viruses in the PNEUMOVIRUS genus causing respiratory infections in various mammals. Humans and cattle are most affected but infections in goats and sheep have also been reported.Respiratory Syncytial Virus, Human: The type species of PNEUMOVIRUS and an important cause of lower respiratory disease in infants and young children. It frequently presents with bronchitis and bronchopneumonia and is further characterized by fever, cough, dyspnea, wheezing, and pallor.Alphavirus: A genus of TOGAVIRIDAE, also known as Group A arboviruses, serologically related to each other but not to other Togaviridae. The viruses are transmitted by mosquitoes. The type species is the SINDBIS VIRUS.Receptors, Virus: Specific molecular components of the cell capable of recognizing and interacting with a virus, and which, after binding it, are capable of generating some signal that initiates the chain of events leading to the biological response.Virus Cultivation: Process of growing viruses in live animals, plants, or cultured cells.RNA, Viral: Ribonucleic acid that makes up the genetic material of viruses.Virus Shedding: The expelling of virus particles from the body. Important routes include the respiratory tract, genital tract, and intestinal tract. Virus shedding is an important means of vertical transmission (INFECTIOUS DISEASE TRANSMISSION, VERTICAL).Ebolavirus: A genus in the family FILOVIRIDAE consisting of several distinct species of Ebolavirus, each containing separate strains. These viruses cause outbreaks of a contagious, hemorrhagic disease (HEMORRHAGIC FEVER, EBOLA) in humans, usually with high mortality.Simian virus 40: A species of POLYOMAVIRUS originally isolated from Rhesus monkey kidney tissue. It produces malignancy in human and newborn hamster kidney cell cultures.Antiviral Agents: Agents used in the prophylaxis or therapy of VIRUS DISEASES. Some of the ways they may act include preventing viral replication by inhibiting viral DNA polymerase; binding to specific cell-surface receptors and inhibiting viral penetration or uncoating; inhibiting viral protein synthesis; or blocking late stages of virus assembly.HIV Infections: Includes the spectrum of human immunodeficiency virus infections that range from asymptomatic seropositivity, thru AIDS-related complex (ARC), to acquired immunodeficiency syndrome (AIDS).Virus Assembly: The assembly of VIRAL STRUCTURAL PROTEINS and nucleic acid (VIRAL DNA or VIRAL RNA) to form a VIRUS PARTICLE.Plant Viruses: Viruses parasitic on plants higher than bacteria.DNA Viruses: Viruses whose nucleic acid is DNA.Disease Outbreaks: Sudden increase in the incidence of a disease. The concept includes EPIDEMICS and PANDEMICS.Acyclovir: A GUANOSINE analog that acts as an antimetabolite. Viruses are especially susceptible. Used especially against herpes.Defective Viruses: Viruses which lack a complete genome so that they cannot completely replicate or cannot form a protein coat. Some are host-dependent defectives, meaning they can replicate only in cell systems which provide the particular genetic function which they lack. Others, called SATELLITE VIRUSES, are able to replicate only when their genetic defect is complemented by a helper virus.Sindbis Virus: The type species of ALPHAVIRUS normally transmitted to birds by CULEX mosquitoes in Egypt, South Africa, India, Malaya, the Philippines, and Australia. It may be associated with fever in humans. Serotypes (differing by less than 17% in nucleotide sequence) include Babanki, Kyzylagach, and Ockelbo viruses.Measles virus: The type species of MORBILLIVIRUS and the cause of the highly infectious human disease MEASLES, which affects mostly children.Influenza A Virus, H1N1 Subtype: A subtype of INFLUENZA A VIRUS with the surface proteins hemagglutinin 1 and neuraminidase 1. The H1N1 subtype was responsible for the Spanish flu pandemic of 1918.ColoradoRabies virus: The type species of LYSSAVIRUS causing rabies in humans and other animals. Transmission is mostly by animal bites through saliva. The virus is neurotropic multiplying in neurons and myotubes of vertebrates.Influenza A Virus, H5N1 Subtype: A subtype of INFLUENZA A VIRUS comprised of the surface proteins hemagglutinin 5 and neuraminidase 1. The H5N1 subtype, frequently referred to as the bird flu virus, is endemic in wild birds and very contagious among both domestic (POULTRY) and wild birds. It does not usually infect humans, but some cases have been reported.Antibodies, Viral: Immunoglobulins produced in response to VIRAL ANTIGENS.CD4 Lymphocyte Count: The number of CD4-POSITIVE T-LYMPHOCYTES per unit volume of BLOOD. Determination requires the use of a fluorescence-activated flow cytometer.Viral Load: The quantity of measurable virus in a body fluid. Change in viral load, measured in plasma, is sometimes used as a SURROGATE MARKER in disease progression.Influenza A Virus, H3N2 Subtype: A subtype of INFLUENZA A VIRUS comprised of the surface proteins hemagglutinin 3 and neuraminidase 2. The H3N2 subtype was responsible for the Hong Kong flu pandemic of 1968.Hepatitis B virus: The type species of the genus ORTHOHEPADNAVIRUS which causes human HEPATITIS B and is also apparently a causal agent in human HEPATOCELLULAR CARCINOMA. The Dane particle is an intact hepatitis virion, named after its discoverer. Non-infectious spherical and tubular particles are also seen in the serum.Culicidae: A family of the order DIPTERA that comprises the mosquitoes. The larval stages are aquatic, and the adults can be recognized by the characteristic WINGS, ANIMAL venation, the scales along the wing veins, and the long proboscis. Many species are of particular medical importance.Acquired Immunodeficiency Syndrome: An acquired defect of cellular immunity associated with infection by the human immunodeficiency virus (HIV), a CD4-positive T-lymphocyte count under 200 cells/microliter or less than 14% of total lymphocytes, and increased susceptibility to opportunistic infections and malignant neoplasms. Clinical manifestations also include emaciation (wasting) and dementia. These elements reflect criteria for AIDS as defined by the CDC in 1993.Plant Diseases: Diseases of plants.Virus Activation: The mechanism by which latent viruses, such as genetically transmitted tumor viruses (PROVIRUSES) or PROPHAGES of lysogenic bacteria, are induced to replicate and then released as infectious viruses. It may be effected by various endogenous and exogenous stimuli, including B-cell LIPOPOLYSACCHARIDES, glucocorticoid hormones, halogenated pyrimidines, IONIZING RADIATION, ultraviolet light, and superinfecting viruses.Genes, Viral: The functional hereditary units of VIRUSES.Herpes Simplex: A group of acute infections caused by herpes simplex virus type 1 or type 2 that is characterized by the development of one or more small fluid-filled vesicles with a raised erythematous base on the skin or mucous membrane. It occurs as a primary infection or recurs due to a reactivation of a latent infection. (Dorland, 27th ed.)Antigens, Viral: Substances elaborated by viruses that have antigenic activity.Vesicular stomatitis Indiana virus: The type species of VESICULOVIRUS causing a disease symptomatically similar to FOOT-AND-MOUTH DISEASE in cattle, horses, and pigs. It may be transmitted to other species including humans, where it causes influenza-like symptoms.Virus Latency: The ability of a pathogenic virus to lie dormant within a cell (latent infection). In eukaryotes, subsequent activation and viral replication is thought to be caused by extracellular stimulation of cellular transcription factors. Latency in bacteriophage is maintained by the expression of virally encoded repressors.Viral Proteins: Proteins found in any species of virus.Hemagglutinin Glycoproteins, Influenza Virus: Membrane glycoproteins from influenza viruses which are involved in hemagglutination, virus attachment, and envelope fusion. Fourteen distinct subtypes of HA glycoproteins and nine of NA glycoproteins have been identified from INFLUENZA A VIRUS; no subtypes have been identified for Influenza B or Influenza C viruses.Polymerase Chain Reaction: In vitro method for producing large amounts of specific DNA or RNA fragments of defined length and sequence from small amounts of short oligonucleotide flanking sequences (primers). The essential steps include thermal denaturation of the double-stranded target molecules, annealing of the primers to their complementary sequences, and extension of the annealed primers by enzymatic synthesis with DNA polymerase. The reaction is efficient, specific, and extremely sensitive. Uses for the reaction include disease diagnosis, detection of difficult-to-isolate pathogens, mutation analysis, genetic testing, DNA sequencing, and analyzing evolutionary relationships.Oncogenic Viruses: Viruses that produce tumors.Vero Cells: A CELL LINE derived from the kidney of the African green (vervet) monkey, (CERCOPITHECUS AETHIOPS) used primarily in virus replication studies and plaque assays.Simian immunodeficiency virus: Species of the genus LENTIVIRUS, subgenus primate immunodeficiency viruses (IMMUNODEFICIENCY VIRUSES, PRIMATE), that induces acquired immunodeficiency syndrome in monkeys and apes (SAIDS). The genetic organization of SIV is virtually identical to HIV.Cytomegalovirus Infections: Infection with CYTOMEGALOVIRUS, characterized by enlarged cells bearing intranuclear inclusions. Infection may be in almost any organ, but the salivary glands are the most common site in children, as are the lungs in adults.Seasons: Divisions of the year according to some regularly recurrent phenomena usually astronomical or climatic. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Cercopithecus aethiops: A species of CERCOPITHECUS containing three subspecies: C. tantalus, C. pygerythrus, and C. sabeus. They are found in the forests and savannah of Africa. The African green monkey (C. pygerythrus) is the natural host of SIMIAN IMMUNODEFICIENCY VIRUS and is used in AIDS research.AIDS-Related Opportunistic Infections: Opportunistic infections found in patients who test positive for human immunodeficiency virus (HIV). The most common include PNEUMOCYSTIS PNEUMONIA, Kaposi's sarcoma, cryptosporidiosis, herpes simplex, toxoplasmosis, cryptococcosis, and infections with Mycobacterium avium complex, Microsporidium, and Cytomegalovirus.Mumps virus: The type species of RUBULAVIRUS that causes an acute infectious disease in humans, affecting mainly children. Transmission occurs by droplet infection.Parainfluenza Virus 1, Human: A species of RESPIROVIRUS also called hemadsorption virus 2 (HA2), which causes laryngotracheitis in humans, especially children.Viral Vaccines: Suspensions of attenuated or killed viruses administered for the prevention or treatment of infectious viral disease.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Mosaic Viruses: Viruses which produce a mottled appearance of the leaves of plants.Virion: The infective system of a virus, composed of the viral genome, a protein core, and a protein coat called a capsid, which may be naked or enclosed in a lipoprotein envelope called the peplos.Hepatitis A virus: A species in the genus HEPATOVIRUS containing one serotype and two strains: HUMAN HEPATITIS A VIRUS and Simian hepatitis A virus causing hepatitis in humans (HEPATITIS A) and primates, respectively.Disease Progression: The worsening of a disease over time. This concept is most often used for chronic and incurable diseases where the stage of the disease is an important determinant of therapy and prognosis.Cytomegalovirus: A genus of the family HERPESVIRIDAE, subfamily BETAHERPESVIRINAE, infecting the salivary glands, liver, spleen, lungs, eyes, and other organs, in which they produce characteristically enlarged cells with intranuclear inclusions. Infection with Cytomegalovirus is also seen as an opportunistic infection in AIDS.Semliki forest virus: A species of ALPHAVIRUS isolated in central, eastern, and southern Africa.Avian Sarcoma Viruses: Group of alpharetroviruses (ALPHARETROVIRUS) producing sarcomata and other tumors in chickens and other fowl and also in pigeons, ducks, and RATS.Neutralization Tests: The measurement of infection-blocking titer of ANTISERA by testing a series of dilutions for a given virus-antiserum interaction end-point, which is generally the dilution at which tissue cultures inoculated with the serum-virus mixtures demonstrate cytopathology (CPE) or the dilution at which 50% of test animals injected with serum-virus mixtures show infectivity (ID50) or die (LD50).Viral Plaque Assay: Method for measuring viral infectivity and multiplication in CULTURED CELLS. Clear lysed areas or plaques develop as the VIRAL PARTICLES are released from the infected cells during incubation. With some VIRUSES, the cells are killed by a cytopathic effect; with others, the infected cells are not killed but can be detected by their hemadsorptive ability. Sometimes the plaque cells contain VIRAL ANTIGENS which can be measured by IMMUNOFLUORESCENCE.Virus Attachment: The binding of virus particles to receptors on the host cell surface. For enveloped viruses, the virion ligand is usually a surface glycoprotein as is the cellular receptor. For non-enveloped viruses, the virus CAPSID serves as the ligand.BK Virus: A species of POLYOMAVIRUS apparently infecting over 90% of children but not clearly associated with any clinical illness in childhood. The virus remains latent in the body throughout life and can be reactivated under certain circumstances.Tumor Virus Infections: Infections produced by oncogenic viruses. The infections caused by DNA viruses are less numerous but more diverse than those caused by the RNA oncogenic viruses.Viruses, Unclassified: Viruses whose taxonomic relationships have not been established.JC Virus: A species of POLYOMAVIRUS, originally isolated from the brain of a patient with progressive multifocal leukoencephalopathy. The patient's initials J.C. gave the virus its name. Infection is not accompanied by any apparent illness but serious demyelinating disease can appear later, probably following reactivation of latent virus.Avian leukosis virus: The type species of ALPHARETROVIRUS producing latent or manifest lymphoid leukosis in fowl.Phylogeny: The relationships of groups of organisms as reflected by their genetic makeup.DNA, Viral: Deoxyribonucleic acid that makes up the genetic material of viruses.Orthomyxoviridae: A family of RNA viruses causing INFLUENZA and other diseases. There are five recognized genera: INFLUENZAVIRUS A; INFLUENZAVIRUS B; INFLUENZAVIRUS C; ISAVIRUS; and THOGOTOVIRUS.Bluetongue virus: The type species of ORBIVIRUS causing a serious disease in sheep, especially lambs. It may also infect wild ruminants and other domestic animals.Disease Models, Animal: Naturally occurring or experimentally induced animal diseases with pathological processes sufficiently similar to those of human diseases. They are used as study models for human diseases.Orthomyxoviridae Infections: Virus diseases caused by the ORTHOMYXOVIRIDAE.Cell Line: Established cell cultures that have the potential to propagate indefinitely.Gene Expression Regulation, Viral: Any of the processes by which cytoplasmic factors influence the differential control of gene action in viruses.Sendai virus: The type species of RESPIROVIRUS in the subfamily PARAMYXOVIRINAE. It is the murine version of HUMAN PARAINFLUENZA VIRUS 1, distinguished by host range.Moloney murine leukemia virus: A strain of Murine leukemia virus (LEUKEMIA VIRUS, MURINE) arising during the propagation of S37 mouse sarcoma, and causing lymphoid leukemia in mice. It also infects rats and newborn hamsters. It is apparently transmitted to embryos in utero and to newborns through mother's milk.Virus Integration: Insertion of viral DNA into host-cell DNA. This includes integration of phage DNA into bacterial DNA; (LYSOGENY); to form a PROPHAGE or integration of retroviral DNA into cellular DNA to form a PROVIRUS.Incidence: The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from PREVALENCE, which refers to all cases, new or old, in the population at a given time.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Capsid: The outer protein protective shell of a virus, which protects the viral nucleic acid.Yellow fever virus: The type species of the FLAVIVIRUS genus. Principal vector transmission to humans is by AEDES spp. mosquitoes.Simplexvirus: A genus of the family HERPESVIRIDAE, subfamily ALPHAHERPESVIRINAE, consisting of herpes simplex-like viruses. The type species is HERPESVIRUS 1, HUMAN.Tobacco Mosaic Virus: The type species of TOBAMOVIRUS which causes mosaic disease of tobacco. Transmission occurs by mechanical inoculation.Myxoma virus: The type species of LEPORIPOXVIRUS causing infectious myxomatosis, a severe generalized disease, in rabbits. Tumors are not always present.Virus Inactivation: Inactivation of viruses by non-immune related techniques. They include extremes of pH, HEAT treatment, ultraviolet radiation, IONIZING RADIATION; DESICCATION; ANTISEPTICS; DISINFECTANTS; organic solvents, and DETERGENTS.Cowpox virus: A species of ORTHOPOXVIRUS that is the etiologic agent of COWPOX. It is closely related to but antigenically different from VACCINIA VIRUS.Cytopathogenic Effect, Viral: Visible morphologic changes in cells infected with viruses. It includes shutdown of cellular RNA and protein synthesis, cell fusion, release of lysosomal enzymes, changes in cell membrane permeability, diffuse changes in intracellular structures, presence of viral inclusion bodies, and chromosomal aberrations. It excludes malignant transformation, which is CELL TRANSFORMATION, VIRAL. Viral cytopathogenic effects provide a valuable method for identifying and classifying the infecting viruses.Variola virus: A species of ORTHOPOXVIRUS causing infections in humans. No infections have been reported since 1977 and the virus is now believed to be virtually extinct.Lassa virus: A species of ARENAVIRUS, part of the Old World Arenaviruses (ARENAVIRUSES, OLD WORLD), and the etiologic agent of LASSA FEVER. LASSA VIRUS is a common infective agent in humans in West Africa. Its natural host is the multimammate mouse Mastomys natalensis.Chikungunya virus: A species of ALPHAVIRUS causing an acute dengue-like fever.Norwalk virus: The type species in the genus NOROVIRUS, first isolated in 1968 from the stools of school children in Norwalk, Ohio, who were suffering from GASTROENTERITIS. The virions are non-enveloped spherical particles containing a single protein. Multiple strains are named after the places where outbreaks have occurred.Influenza, Human: An acute viral infection in humans involving the respiratory tract. It is marked by inflammation of the NASAL MUCOSA; the PHARYNX; and conjunctiva, and by headache and severe, often generalized, myalgia.Encephalitis Viruses: A collection of single-stranded RNA viruses scattered across the Bunyaviridae, Flaviviridae, and Togaviridae families whose common property is the ability to induce encephalitic conditions in infected hosts.DNA Virus InfectionsRisk Factors: An aspect of personal behavior or lifestyle, environmental exposure, or inborn or inherited characteristic, which, on the basis of epidemiologic evidence, is known to be associated with a health-related condition considered important to prevent.Virus Physiological Phenomena: Biological properties, processes, and activities of VIRUSES.Herpesvirus 1, Human: The type species of SIMPLEXVIRUS causing most forms of non-genital herpes simplex in humans. Primary infection occurs mainly in infants and young children and then the virus becomes latent in the dorsal root ganglion. It then is periodically reactivated throughout life causing mostly benign conditions.Epstein-Barr Virus Infections: Infection with human herpesvirus 4 (HERPESVIRUS 4, HUMAN); which may facilitate the development of various lymphoproliferative disorders. These include BURKITT LYMPHOMA (African type), INFECTIOUS MONONUCLEOSIS, and oral hairy leukoplakia (LEUKOPLAKIA, HAIRY).Infant, Newborn: An infant during the first month after birth.Hepacivirus: A genus of FLAVIVIRIDAE causing parenterally-transmitted HEPATITIS C which is associated with transfusions and drug abuse. Hepatitis C virus is the type species.Genetic Vectors: DNA molecules capable of autonomous replication within a host cell and into which other DNA sequences can be inserted and thus amplified. Many are derived from PLASMIDS; BACTERIOPHAGES; or VIRUSES. They are used for transporting foreign genes into recipient cells. Genetic vectors possess a functional replicator site and contain GENETIC MARKERS to facilitate their selective recognition.Herpesvirus 4, Human: The type species of LYMPHOCRYPTOVIRUS, subfamily GAMMAHERPESVIRINAE, infecting B-cells in humans. It is thought to be the causative agent of INFECTIOUS MONONUCLEOSIS and is strongly associated with oral hairy leukoplakia (LEUKOPLAKIA, HAIRY;), BURKITT LYMPHOMA; and other malignancies.Encephalitis Viruses, Tick-Borne: A subgroup of the genus FLAVIVIRUS that causes encephalitis and hemorrhagic fevers and is found in eastern and western Europe and the former Soviet Union. It is transmitted by TICKS and there is an associated milk-borne transmission from viremic cattle, goats, and sheep.Parainfluenza Virus 3, Human: A species of RESPIROVIRUS frequently isolated from small children with pharyngitis, bronchitis, and pneumonia.Leukemia Virus, Feline: A species of GAMMARETROVIRUS causing leukemia, lymphosarcoma, immune deficiency, or other degenerative diseases in cats. Several cellular oncogenes confer on FeLV the ability to induce sarcomas (see also SARCOMA VIRUSES, FELINE).Viral Structural Proteins: Viral proteins that are components of the mature assembled VIRUS PARTICLES. They may include nucleocapsid core proteins (gag proteins), enzymes packaged within the virus particle (pol proteins), and membrane components (env proteins). These do not include the proteins encoded in the VIRAL GENOME that are produced in infected cells but which are not packaged in the mature virus particle,i.e. the so called non-structural proteins (VIRAL NONSTRUCTURAL PROTEINS).Cricetinae: A subfamily in the family MURIDAE, comprising the hamsters. Four of the more common genera are Cricetus, CRICETULUS; MESOCRICETUS; and PHODOPUS.Foot-and-Mouth Disease Virus: The type species of APHTHOVIRUS, causing FOOT-AND-MOUTH DISEASE in cloven-hoofed animals. Several different serotypes exist.Capsid Proteins: Proteins that form the CAPSID of VIRUSES.Hemagglutinins, Viral: Specific hemagglutinin subtypes encoded by VIRUSES.Porcine respiratory and reproductive syndrome virus: A species of ARTERIVIRUS causing reproductive and respiratory disease in pigs. The European strain is called Lelystad virus. Airborne transmission is common.Hepatitis Viruses: Any of the viruses that cause inflammation of the liver. They include both DNA and RNA viruses as well viruses from humans and animals.Virulence: The degree of pathogenicity within a group or species of microorganisms or viruses as indicated by case fatality rates and/or the ability of the organism to invade the tissues of the host. The pathogenic capacity of an organism is determined by its VIRULENCE FACTORS.Recombination, Genetic: Production of new arrangements of DNA by various mechanisms such as assortment and segregation, CROSSING OVER; GENE CONVERSION; GENETIC TRANSFORMATION; GENETIC CONJUGATION; GENETIC TRANSDUCTION; or mixed infection of viruses.RNA Virus InfectionsSequence Analysis, DNA: A multistage process that includes cloning, physical mapping, subcloning, determination of the DNA SEQUENCE, and information analysis.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.Cells, Cultured: Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.Satellite Viruses: Defective viruses which can multiply only by association with a helper virus which complements the defective gene. Satellite viruses may be associated with certain plant viruses, animal viruses, or bacteriophages. They differ from satellite RNA; (RNA, SATELLITE) in that satellite viruses encode their own coat protein.Oncolytic Viruses: Tumor-selective, replication competent VIRUSES that have antineoplastic effects. This is achieved by producing cytotoxicity-enhancing proteins and/or eliciting an antitumor immune response. They are genetically engineered so that they can replicate in CANCER cells but not in normal cells, and are used in ONCOLYTIC VIROTHERAPY.Orf virus: The type species of PARAPOXVIRUS which causes a skin infection in natural hosts, usually young sheep. Humans may contract local skin lesions by contact. The virus apparently persists in soil.Human T-lymphotropic virus 1: A strain of PRIMATE T-LYMPHOTROPIC VIRUS 1 isolated from mature T4 cells in patients with T-lymphoproliferation malignancies. It causes adult T-cell leukemia (LEUKEMIA-LYMPHOMA, T-CELL, ACUTE, HTLV-I-ASSOCIATED), T-cell lymphoma (LYMPHOMA, T-CELL), and is involved in mycosis fungoides, SEZARY SYNDROME and tropical spastic paraparesis (PARAPARESIS, TROPICAL SPASTIC).Diarrhea Viruses, Bovine Viral: A group of viruses in the genus PESTIVIRUS, causing diarrhea, fever, oral ulcerations, hemorrhagic syndrome, and various necrotic lesions among cattle and other domestic animals. The two species (genotypes), BVDV-1 and BVDV-2 , exhibit antigenic and pathological differences. The historical designation, BVDV, consisted of both (then unrecognized) genotypes.Hepatitis E virus: A positive-stranded RNA virus species in the genus HEPEVIRUS, causing enterically-transmitted non-A, non-B hepatitis (HEPATITIS E).Friend murine leukemia virus: A strain of Murine leukemia virus (LEUKEMIA VIRUS, MURINE) producing leukemia of the reticulum-cell type with massive infiltration of liver, spleen, and bone marrow. It infects DBA/2 and Swiss mice.Mammary Tumor Virus, Mouse: The type species of BETARETROVIRUS commonly latent in mice. It causes mammary adenocarcinoma in a genetically susceptible strain of mice when the appropriate hormonal influences operate.Neuraminidase: An enzyme that catalyzes the hydrolysis of alpha-2,3, alpha-2,6-, and alpha-2,8-glycosidic linkages (at a decreasing rate, respectively) of terminal sialic residues in oligosaccharides, glycoproteins, glycolipids, colominic acid, and synthetic substrate. (From Enzyme Nomenclature, 1992)Cell Transformation, Viral: An inheritable change in cells manifested by changes in cell division and growth and alterations in cell surface properties. It is induced by infection with a transforming virus.Viral Core Proteins: Proteins found mainly in icosahedral DNA and RNA viruses. They consist of proteins directly associated with the nucleic acid inside the NUCLEOCAPSID.Sarcoma Viruses, Murine: A group of replication-defective viruses, in the genus GAMMARETROVIRUS, which are capable of transforming cells, but which replicate and produce tumors only in the presence of Murine leukemia viruses (LEUKEMIA VIRUS, MURINE).Archaeal Viruses: Viruses whose hosts are in the domain ARCHAEA.Hepatitis C: INFLAMMATION of the LIVER in humans caused by HEPATITIS C VIRUS, a single-stranded RNA virus. Its incubation period is 30-90 days. Hepatitis C is transmitted primarily by contaminated blood parenterally, and is often associated with transfusion and intravenous drug abuse. However, in a significant number of cases, the source of hepatitis C infection is unknown.Influenza A Virus, H7N7 Subtype: A subtype of INFLUENZA A VIRUS comprised of the surface proteins hemagglutinin 7 and neuraminidase 7. The H7N7 subtype produced an epidemic in 2003 which was highly pathogenic among domestic birds (POULTRY). Some infections in humans were reported.HeLa Cells: The first continuously cultured human malignant CELL LINE, derived from the cervical carcinoma of Henrietta Lacks. These cells are used for VIRUS CULTIVATION and antitumor drug screening assays.Fowlpox virus: The type species of the genus AVIPOXVIRUS. It is the etiologic agent of FOWLPOX.Haplorhini: A suborder of PRIMATES consisting of six families: CEBIDAE (some New World monkeys), ATELIDAE (some New World monkeys), CERCOPITHECIDAE (Old World monkeys), HYLOBATIDAE (gibbons and siamangs), CALLITRICHINAE (marmosets and tamarins), and HOMINIDAE (humans and great apes).Leukemia Virus, Bovine: The type species of DELTARETROVIRUS that causes a form of bovine lymphosarcoma (ENZOOTIC BOVINE LEUKOSIS) or persistent lymphocytosis.United StatesHemagglutination Inhibition Tests: Serologic tests in which a known quantity of antigen is added to the serum prior to the addition of a red cell suspension. Reaction result is expressed as the smallest amount of antigen which causes complete inhibition of hemagglutination.DucksHendra Virus: A species of HENIPAVIRUS first identified in Australia in 1994 in HORSES and transmitted to humans. The natural host appears to be fruit bats (PTEROPUS).Open Reading Frames: A sequence of successive nucleotide triplets that are read as CODONS specifying AMINO ACIDS and begin with an INITIATOR CODON and end with a stop codon (CODON, TERMINATOR).Host-Pathogen Interactions: The interactions between a host and a pathogen, usually resulting in disease.Transcription, Genetic: The biosynthesis of RNA carried out on a template of DNA. The biosynthesis of DNA from an RNA template is called REVERSE TRANSCRIPTION.Virology: The study of the structure, growth, function, genetics, and reproduction of viruses, and VIRUS DISEASES.Lymphocytic choriomeningitis virus: The type species of ARENAVIRUS, part of the Old World Arenaviruses (ARENAVIRUSES, OLD WORLD), producing a silent infection in house and laboratory mice. In humans, infection with LCMV can be inapparent, or can present with an influenza-like illness, a benign aseptic meningitis, or a severe meningoencephalomyelitis. The virus can also infect monkeys, dogs, field mice, guinea pigs, and hamsters, the latter an epidemiologically important host.DNA Primers: Short sequences (generally about 10 base pairs) of DNA that are complementary to sequences of messenger RNA and allow reverse transcriptases to start copying the adjacent sequences of mRNA. Primers are used extensively in genetic and molecular biology techniques.HIV-1: The type species of LENTIVIRUS and the etiologic agent of AIDS. It is characterized by its cytopathic effect and affinity for the T4-lymphocyte.Borna disease virus: A species in the genus Bornavirus, family BORNAVIRIDAE, causing a rare and usually fatal encephalitic disease in horses and other domestic animals and possibly deer. Its name derives from the city in Saxony where the condition was first described in 1894, but the disease occurs in Europe, N. Africa, and the Near East.Bunyamwera virus: A species in the ORTHOBUNYAVIRUS genus of the family BUNYAVIRIDAE. A large number of serotypes or strains exist in many parts of the world. They are transmitted by mosquitoes and infect humans in some areas.Viral Interference: A phenomenon in which infection by a first virus results in resistance of cells or tissues to infection by a second, unrelated virus.Retroviridae: Family of RNA viruses that infects birds and mammals and encodes the enzyme reverse transcriptase. The family contains seven genera: DELTARETROVIRUS; LENTIVIRUS; RETROVIRUSES TYPE B, MAMMALIAN; ALPHARETROVIRUS; GAMMARETROVIRUS; RETROVIRUSES TYPE D; and SPUMAVIRUS. A key feature of retrovirus biology is the synthesis of a DNA copy of the genome which is integrated into cellular DNA. After integration it is sometimes not expressed but maintained in a latent state (PROVIRUSES).Species Specificity: The restriction of a characteristic behavior, anatomical structure or physical system, such as immune response; metabolic response, or gene or gene variant to the members of one species. It refers to that property which differentiates one species from another but it is also used for phylogenetic levels higher or lower than the species.HIV: Human immunodeficiency virus. A non-taxonomic and historical term referring to any of two species, specifically HIV-1 and/or HIV-2. Prior to 1986, this was called human T-lymphotropic virus type III/lymphadenopathy-associated virus (HTLV-III/LAV). From 1986-1990, it was an official species called HIV. Since 1991, HIV was no longer considered an official species name; the two species were designated HIV-1 and HIV-2.Distemper Virus, Canine: A species of MORBILLIVIRUS causing distemper in dogs, wolves, foxes, raccoons, and ferrets. Pinnipeds have also been known to contract Canine distemper virus from contact with domestic dogs.Transfection: The uptake of naked or purified DNA by CELLS, usually meaning the process as it occurs in eukaryotic cells. It is analogous to bacterial transformation (TRANSFORMATION, BACTERIAL) and both are routinely employed in GENE TRANSFER TECHNIQUES.Gene Products, gag: Proteins coded by the retroviral gag gene. The products are usually synthesized as protein precursors or POLYPROTEINS, which are then cleaved by viral proteases to yield the final products. Many of the final products are associated with the nucleoprotein core of the virion. gag is short for group-specific antigen.Viral Fusion Proteins: Proteins, usually glycoproteins, found in the viral envelopes of a variety of viruses. They promote cell membrane fusion and thereby may function in the uptake of the virus by cells.Rinderpest virus: A species of MORBILLIVIRUS causing cattle plague, a disease with high mortality. Sheep, goats, pigs, and other animals of the order Artiodactyla can also be infected.Influenza A Virus, H7N9 Subtype: A subtype of INFLUENZA A VIRUS with the surface proteins hemagglutinin 7 and neuraminidase 9. This avian origin virus was first identified in humans in 2013.Hepatitis Delta Virus: A defective virus, containing particles of RNA nucleoprotein in virion-like form, present in patients with acute hepatitis B and chronic hepatitis. It requires the presence of a hepadnavirus for full replication. This is the lone species in the genus Deltavirus.Herpesvirus 3, Human: The type species of VARICELLOVIRUS causing CHICKENPOX (varicella) and HERPES ZOSTER (shingles) in humans.RNA Replicase: An enzyme that catalyses RNA-template-directed extension of the 3'- end of an RNA strand by one nucleotide at a time, and can initiate a chain de novo. (Enzyme Nomenclature, 1992, p293)Monkeypox virus: A species of ORTHOPOXVIRUS causing an epidemic disease among captive primates.Epitopes: Sites on an antigen that interact with specific antibodies.RNA-Directed DNA Polymerase: An enzyme that synthesizes DNA on an RNA template. It is encoded by the pol gene of retroviruses and by certain retrovirus-like elements. EC 188.8.131.52.Birds: Warm-blooded VERTEBRATES possessing FEATHERS and belonging to the class Aves.Chick Embryo: The developmental entity of a fertilized chicken egg (ZYGOTE). The developmental process begins about 24 h before the egg is laid at the BLASTODISC, a small whitish spot on the surface of the EGG YOLK. After 21 days of incubation, the embryo is fully developed before hatching.African Swine Fever Virus: The lone species of the genus Asfivirus. It infects domestic and wild pigs, warthogs, and bushpigs. Disease is endemic in domestic swine in many African countries and Sardinia. Soft ticks of the genus Ornithodoros are also infected and act as vectors.Prospective Studies: Observation of a population for a sufficient number of persons over a sufficient number of years to generate incidence or mortality rates subsequent to the selection of the study group.Plasmids: Extrachromosomal, usually CIRCULAR DNA molecules that are self-replicating and transferable from one organism to another. They are found in a variety of bacterial, archaeal, fungal, algal, and plant species. They are used in GENETIC ENGINEERING as CLONING VECTORS.Vaccines, Attenuated: Live vaccines prepared from microorganisms which have undergone physical adaptation (e.g., by radiation or temperature conditioning) or serial passage in laboratory animal hosts or infected tissue/cell cultures, in order to produce avirulent mutant strains capable of inducing protective immunity.Respirovirus: A genus of the family PARAMYXOVIRIDAE (subfamily PARAMYXOVIRINAE) where all the virions have both HEMAGGLUTININ and NEURAMINIDASE activities and encode a non-structural C protein. SENDAI VIRUS is the type species.Reticuloendotheliosis virus: A species in the group RETICULOENDOTHELIOSIS VIRUSES, AVIAN of the genus GAMMARETROVIRUS that causes a chronic neoplastic and a more acute immunosuppressive disease in fowl.Viremia: The presence of viruses in the blood.Rift Valley fever virus: A mosquito-borne species of the PHLEBOVIRUS genus found in eastern, central, and southern Africa, producing massive hepatitis, abortion, and death in sheep, goats, cattle, and other animals. It also has caused disease in humans.Infectious Anemia Virus, Equine: A species of LENTIVIRUS, subgenus equine lentiviruses (LENTIVIRUSES, EQUINE), causing acute and chronic infection in horses. It is transmitted mechanically by biting flies, mosquitoes, and midges, and iatrogenically through unsterilized equipment. Chronic infection often consists of acute episodes with remissions.Chickens: Common name for the species Gallus gallus, the domestic fowl, in the family Phasianidae, order GALLIFORMES. It is descended from the red jungle fowl of SOUTHEAST ASIA.Infectious bronchitis virus: A species of CORONAVIRUS causing infections in chickens and possibly pheasants. Chicks up to four weeks old are the most severely affected.Herpesvirus 1, Suid: A species of VARICELLOVIRUS producing a respiratory infection (PSEUDORABIES) in swine, its natural host. It also produces an usually fatal ENCEPHALOMYELITIS in cattle, sheep, dogs, cats, foxes, and mink.Cross Reactions: Serological reactions in which an antiserum against one antigen reacts with a non-identical but closely related antigen.Torque teno virus: A species of non-enveloped DNA virus in the genus ANELLOVIRUS, associated with BLOOD TRANSFUSIONS; and HEPATITIS. However, no etiological role has been found for TTV in hepatitis.Enzyme-Linked Immunosorbent Assay: An immunoassay utilizing an antibody labeled with an enzyme marker such as horseradish peroxidase. While either the enzyme or the antibody is bound to an immunosorbent substrate, they both retain their biologic activity; the change in enzyme activity as a result of the enzyme-antibody-antigen reaction is proportional to the concentration of the antigen and can be measured spectrophotometrically or with the naked eye. Many variations of the method have been developed.Influenza A Virus, H5N2 Subtype: A subtype of INFLUENZA A VIRUS comprised of the surface proteins hemagglutinin 5 and neuraminidase 2. The H5N2 subtype has been found to be highly pathogenic in chickens.AKR murine leukemia virus: A strain of Murine leukemia virus (LEUKEMIA VIRUS, MURINE) isolated from spontaneous leukemia in AKR strain mice.Ectromelia virus: A species of ORTHOPOXVIRUS infecting mice and causing a disease that involves internal organs and produces characteristic skin lesions.