Oligoadenylate synthetase 25OAS

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An enzyme involved in the early stages of interferon induction. Upon activation by double-stranded RNA, 2'5'-OAS polymerizes ATP into pppA(2'p5'A)n(2'5'A). 2'5'A then activates a cellular endonucle-ase, 2'5'-OAS-dependent RNase L, which then degrades both cellular and viral RNAs at UU or AU nucleotides.

Samuel CE (1991) Virology 183,1

oligonucleotide mapping A technique for RNA characterization based upon the use especially of T1 ribonuclease to obtain RNA fragments separable by chromatog-raphy. Now replaced by more specific sequence analysis.

oligonucleotides Short polynucleotides containing about 2-10 nucleotides joined by phosphodiester bonds.

oligopeptide A short-chain linear peptide containing from 2 to 10 amino acids joined by peptide bonds.

Oliveros virus (OLI) A serologically distinct species of the Tacaribe complex of the family Arenaviridae, isolated in 1990 in Oliveros, a village in Argentina from a trapped rodent, Bolomys obscurus. Phylogenetic analysis confirmed that the virus is a distinct member of the Tacaribe complex of New World arenaviruses, most closely related to Latino virus. Role in human disease unknown.

Bowen MD et al (1996) Virology 217, 362 Mills JN et al (1996) Am J Trop Med Hyg 54, 399

OLV virus Synonym for H-3 virus.

Omo virus (OMOV) A serotype of Qalyub virus in the genus Nairovirus. Isolated from the rodent Mastomys erythroleucus in Ethiopia.

Rodhain F et al (1985) Ann Inst Pasteur Virol 136E, 243

Omsk hemorrhagic fever virus (OHFV) A tick-borne species in the genus Flavivirus, member of the Mammalian tick-borne encephalitis serogroup. Vectors are ticks,

Dermacentor pictus and D. marginatus, in which transovarian transmission is reported. Man may also be infected by direct contact with infected muskrats. Causes a biphasic illness in humans with fever, enlargement of lymph nodes, gastrointestinal symptoms, and hemorrhages from nose, stomach and uterus, but little or no CNS involvement. Mortality 1-2%. Disease occurs in the former central USSR. Causes fever in rhesus monkeys injected i.p. On first isolation does not infect adult mice.

Netzky GI (1967) Jap J Med Sci Biol (suppl) 20, 141

Omsk virus See Omsk hemorrhagic fever virus.

Onchorhynchus masou herpesvirus Synonym for salmonid herpesvirus 2.

Oncorhynchus masou virus Synonym for salmonid herpesvirus 2.

oncogene A gene which encodes a protein whose expression leads to cell transformation. Originally discovered during studies of Rous sarcoma virus in the 1970s when the src gene was isolated and shown to have a cell homolog. Since then, more than 100 viral oncogenes and proto-oncogenes (cellular genes that may become disregulated to cause cell transformation) have been described. In general, viral oncogenes are transduced genetic sequences found in the genome of acutely transforming viruses which have cellular homologs (proto-oncogenes) from which they were derived. Evolutionary changes in the virus genome have led in some cases to considerable differences between the products of the viral oncogenes and their cellular homologs, but their relationship can be clearly seen at the genetic level. In describing oncogenes, the gene is italicized (e.g. jun) and the protein product capitalized (e.g. JUN protein). The viral oncogene is written v-jun and the cellular gene counterpart c-jun.

Cooper GM (1995) Oncogenes, Second edition.

Boston: Jones and Bartlett

Hesketh R (1994) The Oncogene Handbook.

London: Academic Press

Rasheed S (1995) In The Retroviridae, vol. 4, edited by JA Levy. New York: Plenum Press, p. 293


oncogenic Tumor-inducing.

oncogenic RNA virus Old name for group of RNA tumor viruses, now included in the family Retroviridae.

oncoproteins Proteins produced from onco-genes: tumor-inducing proteins.

oncornaviruses Old name for the RNA tumor viruses.

Oncovirinae An old name for a subfamily of oncogenic retroviruses. No longer in use.

one-hit kinetics In systems where one particle can initiate infection, the number of plaques appearing is directly proportional to the first power of the concentration of the inoculum. If this concentration is doubled, the number of plaques will be doubled.

one-step growth curve An experiment in which all the cells in a particular culture are infected simultaneously, so that events in individual cells can be inferred from events in the whole population.

Ontario encephalomyelitis virus Synonym for Porcine hemagglutinating encephalo-myelitis virus.

O'Nyong-Nyong virus (ONNV) A species in the genus Alphavirus. The complete nucleotide sequence shows a close genetic relationship to Semliki Forest virus. In humans it causes a febrile illness with lymphadenitis, severe joint pains and rash. Epidemic spread occurs with anopheline mosquitoes as vector. Occurs in Uganda, Kenya, Tanzania, Malawi and Senegal. Pathogenic for suckling mice given i.c.; older mice are resistant. Infant mice which survive the infection are stunted and show patchy alopecia. Virus is propagated in chick embryo fibroblast cell cultures.

Chanas AC et al (1979) Arch Virol 59, 231 Levinson R et al (1990) Virology 175, 110

opal codon UGA One of the three termination codons. See nonsense codons.

opal mutant Virus with mutation resulting in a chain termination codon UGA.

open circular DNA Circular DNA in which one or both strands are not covalently closed.

open reading frame (ORF) A set of codons for amino acids uninterrupted by stop codons. Usually encodes one or more proteins.

opossum adenovirus A possible species in the genus Mastadenovirus. Isolated from an opossum, Didelphis marsupialis, primary kidney cell culture showing spontaneous CPE. Did not replicate in rabbit, hamster, human or rhesus monkey kidney cell cultures, or in HeLa or HEP-2 cells.

Morales-Ayala F et al (1964) Bacterial Proc, p. 117

opossum viruses A and B Not viruses. Chlamydiae.

opportunistic infections Infections which become established due to immuno-suppression of the patient, e.g. as a result of chemotherapy or AIDS.

Glaser CA et al (1994) Clin Infect Dis 18, 14

opportunistic pathogens A variety of infectious pathogens, including many viruses, cause opportunistic infections in immunosuppressed persons. Amongst the viruses, those that are normally latent, such as cytomegalovirus, herpes simplex virus, JC polyoma virus and varicella-zoster virus, cause most common problems, especially in AIDS patients.

OPV Oral poliovirus vaccine, originally developed by Albert Sabin.

Oran virus A strain of Andes virus in the genus Hantavirus isolated from Oligoryzomys longicaudatus in Argentina. Caused fatal hantavirus pulmonary syndrome in humans.

Calderon G et al (1999) Emerg Inf Dis 5, 792

orangutan herpesvirus Synonym for

Pongine herpesvirus 2.

Orbivirus (Latin: orbis = a ring) A genus of the family Reoviridae containing 19 recognized species and 13 tentative species. All multiply in insects and several also in vertebrates. Virion 80nm in diameter, with a double protein shell: the outer one without readily definable capsomeres, the inner with 32 seemingly ring-shaped cap-someres arranged with icosahedral symmetry and visible in the presence of the outer shell. Only slightly sensitive to lipid solvents, inactivated at pH 3. The double-stranded RNA genome consists of 10 segments between 822 and 3954 bp, total 19.2kb. There are seven virion and three non-structural proteins. The single-shelled nucleocapsid having lost the outer shell has transcriptase activity with an optimum temperature of 28°C. Replicate with CPE in BHK21 cells. Kill newborn mice but not adults on i.c. injection. Do not kill mice of any age on i.p. injection. The type species is Bluetongue virus. They have no common antigen but the 153 known viruses are divided into 19 species on the basis of antigenic cross-reactions. The species and their principal vectors are:

(1) African horse sickness virus (9 serotypes) (Culicoides)

(2) Bluetongue virus (24 serotypes) (Culicoides)

(3) Changuinola virus (12 serotypes) (phlebotomines or culicine mosquitoes)

(4) Chenuda virus (7 serotypes) (ticks)

(5) Chobar Gorge virus (2 serotypes) (ticks)

(6) Corriparta virus (5 serotypes) (culicine mosquitoes)

(7) Epizootic hemorrhagic disease virus (8 serotypes) (Culicoides)

(8) Equine encephalosis virus (7 serotypes) (Culicoides)

(9) Eubenangee virus (4 serotypes) (Culicoides, anopheline and culicine mosquitoes)

(10) Great Island virus (36 serotypes) (ticks)

(11) Ieri virus (3 serotypes) (mosquitoes)

(12) Lebombo virus (1 serotype) (culicine mosquitoes)

(13) Orungo virus (4 serotypes) (culicine mosquitoes)

(14) Palyam virus (11 serotypes) (Culicoides, culicine mosquitoes)

(15) Umatilla virus (4 serotypes) (culicine mosquitoes)

(16) Wad Medani virus (2 serotypes) (ticks)

(17) Wallal virus (3 serotypes) (Culicoides)

(18) Warrego virus (3 serotypes)

(Culicoides, anopheline and culicine mosquitoes) (19) Wongorr virus (8 serotypes) (Culicoides, mosquitoes)

In addition there are 13 tentative species in the genus awaiting further characterization.

Mertens PPC (1999) In Encyclopedia of Virology, Second edition, edited by A Granoff and RG Webster. London: Academic Press, p. 1043 Roy P and Gorman B (editors) (1990) Curr Top Microbiol Immun 162, 200 pp orcinol reaction A colorimetric assay for the presence of carbohydrates, especially pentose sugars. Used to determine RNA concentrations, e.g. the amount of RNA in a virus preparation. See dipheny-lamine reaction.

Lin RIS and Schjeide OA (1969) Anal Biochem 27, 473

Oregon sockeye disease virus Synonym for Infectious hematopoietic necrosis virus in the genus Rhabdovirus.

ORF Abbreviation for open reading frame.

orf subgroup viruses Synonym for para-poxvirus.

Orf virus (ORFV) The type species of the genus Parapoxvirus. Virions are ovoid, 252 x 158nm, with a characteristic surface structure that appears in the electron microscope as a spiral coil or 'ball of yarn'. DNA genome 130-150kb, G+C is 64%. Virus is inactivated by chloroform, but ether may not inactivate. Causes disease predominantly in lambs and kids. There are vesicles on the lips and nose, progressing to pustules, ulcers and warty scabs. Malignant aphtha is a severe form of the disease which may be fatal. Papilloma of chamois is caused by Orf virus, and there is evidence of natural infection in dogs, goats, Himalayan tahr, musk-ox, reindeer, steenbok and alpaca. Man may be infected from animals but human-to-human infection is very rare. Does not naturally infect cattle but they can be infected experimentally as can rabbits, horses, dogs and monkeys. Dried scabs retain infectivity at room temperature for years. Virus does not replicate on the CAM but multiplies in ovine and bovine cell cultures. An active vaccine applied by scarification has been used. Synonyms: contagious pustular dermatitis of sheep virus; contagious pustular stomatitis of sheep virus; ecthyma conta-giosum of sheep virus; infectious labial dermatitis virus; scabby mouth virus; sore mouth virus.

Robinson AJ and Balassa TC (1981) Vet Bull 51, 771

organ culture A form of primary tissue culture in which the cells are not trypsinized in order to maintain their interactions as close as possible to the situation in vivo.

Oriboca virus (ORIV) A species in the genus Bunyavirus, belonging to the group C serogroup. Isolated from the opossum, Didelphis marsupialis, and from rodents, Proechimys sp and Oryzomys capito. Mosquito-borne. Found in Brazil, Surinam, French Guiana and Trinidad. Can cause a febrile illness in humans.

Causey OR et al (1961) Am J Trop Med Hyg 10, 227

Karabatsos N and Shope RE (1979) J Med Virol 3, 167

origin of viruses The question of where viruses arose has been the subject of much speculation. Most popular theories claim that viruses arose from cellular RNA or DNA, but some think viruses evolved with primordial life forms during the earliest origins of life on earth. There are also claims by some well-respected scientists that viruses were seeded on earth from outer space. It may never be possible to prove or disprove any of these theories.

Holland JJ (1998) In Virology, vol. 1 of Topley and Wilson's Microbiology & Microbial Infections, Ninth edition, edited by BWJ Mahy and L Collier. London: Arnold, p. 11

Oriximina virus (ORXV) A serotype of Candiru virus in the genus Phlebovirus, belonging to the Candiru complex in the sandfly fever serogroup. Isolated from Lutzomyia sp in Para, Brazil.

Oropouche virus (OROV) A species in the genus Bunyavirus. First isolated from a febrile patient in Trinidad in 1955. In 1960 it caused an outbreak of fever affecting

7000 people near Belem in Brazil, and has become a continuing problem in that region, associated with deforestation and increased contact with the principal vector, Culicoides paraensis. The disease is an acute febrile illness with headache, myalgia, arthralgia, photophobia, retro-bulbar pain, nausea and dizziness. The virus has been isolated from the three-toed sloth, Bradypus tridactylus, which appears to be involved in the sylvan cycle of transmission.

Anderson CR et al (1961) Am J Trop Med Hyg 10, 574

Pinheiro FP et al (1981) Am J Trop Med Hyg 30, 149

Wang H et al (2001) Virus Res 73, 153

orphan virus Any virus which has not been identified as the cause of a disease. See echovirus and Reoviridae.

Orphanovirus A provisional name, that was not adopted, for the genus in the family Picornaviridae now called Parechovirus.

Orthohepadnavirus A genus in the family Hepadnaviridae comprised of viruses which infect mammals. The type species, Hepatitis B virus, only infects humans naturally, although it can be transmitted experimentally to some non-human primates. There are also hepatitis B viruses of non-human primates. Other species in the genus are Ground squirrel hepatitis virus, Woodchuck hepatitis B virus, and, tentatively, Arctic squirrel hepatitis virus. Virions are spherical, 40-42nm diameter, containing relaxed circular, partially double-stranded DNA, 3.2kb in length, with 5' cohesive ends. The genome contains a gene termed 'X' (involved in transcriptional regulation) that is not found in members of the genus Avihepadnavirus. All the viruses in the genus cause acute and chronic hepatitis which can lead to hepatocellular carcinoma. In the case of human hepatitis B, transmission occurs mainly by percutaneous contact with infected blood or body fluids, sexual contact, and perinatal transmission from an infected mother, though this can be prevented by appropriate use of vaccination if the infectious status of the mother is known before birth.


Ganem D (1996) In Fields Virology, Third edition, edited by BN Fields et al. Philadelphia: Lippincott-Raven, p. 2703 Kann M and Gerlich WH (1998) In Virology, vol. 1 of Topley & Wilson's Microbiology and Microbial Infections. Ninth edition, edited by BWJ Mahy and L Collier. London: Arnold, p. 745

Orthomyxoviridae A family of negativestrand RNA viruses comprised of four genera: Influenza virus A; Influenza virus B; Influenza virus C; and 'Thogoto-like viruses'. Virions are pleomorphic, 80-120nm in diameter, usually roughly spherical but filamentous forms up to several microns in length occur. The virion envelope H is derived from cell membrane lipids into which virus-specific glycoproteins and non-glycosylated proteins are inserted during virus assembly and budding. They form projections 10-14nm in length on the virion surface. In Influenza A and B viruses the surface glycoproteins are of two types: a hemag-glutinin (HA) that is involved in virus attachment and cell fusion; and a neu-raminidase (NA) (receptor-destroying enzyme) that participates in virus release from the cell. The other envelope proteins are an abundant membrane (M) protein and a small protein (M2 in Influenza A, NB in Influenza B) that functions as an ion channel and is involved in cell fusion. In Influenza C the single surface glycopro-tein is a hemagglutinin-esterase-fusion (HEF) protein that has both cell attachment and receptor-destroying enzyme activity. The nucleocapsid has helical symmetry 9nm in diameter, and is segmented into different-sized pieces, 150-130 nm in length, each with a loop at one end. The nucleocapsid contains the genome RNA (eight segments in Influenza A and B; seven segments in Influenza C and Dhori virus; six segments in Thogoto virus) as well as three polymerase proteins, PA, PB1 and PB2, which are involved in genome transcription and replication, together with at least two non-structural proteins (NS1 and nuclear export protein or NS2). Transcription occurs in the host cell nucleus and requires capped oligonucleotide primer RNAs (10-13nt long) that are derived from newly synthesized host cell mRNAs by viral endonuclease activity of the PB2

protein. Some of the mRNAs have overlapping sequences and are spliced to provide alternative products M2 and NS2 (nuclear export proteins), or are bicistronic (NA and NB of Influenza B virus). Because of the intimate involvement of influenza replication with host cell transcription and splicing mechanisms, it is blocked by substances which inhibit these processes (actinomycin D, a-amanitin). Protein synthesis occurs in the cytoplasm, and integral membrane proteins migrate through the Golgi apparatus to the plasma membrane where virions are assembled and new virions are formed by budding. In mixed infections of Influenza A viruses gene reassortment may occur during replication or assembly but this does not occur between viruses of different genera. Influenza viruses agglutinate erythro-cytes from many species, and antibody to the HA or HEF proteins neutralizes infec-tivity. Hemagglutination is the basis for serotyping because of the wide variation in HA structure that can be detected by this technique. On this basis, 15 subtypes of HA are recognized (H1 to H15); the NA protein also undergoes variation and nine subtypes are recognized (N1 to N9). Within each subtype, multiple antigenic variations can be detected and used to differentiate strains of influenza virus. All 15 H subtypes and all 9 N subtypes have been found in viruses from aquatic birds, which provide the genetic reservoir for generation of viruses infecting humans, horses, swine, domestic poultry and sea-mammals. Much less variation is seen in Influenza B and C viruses, which do not appear to have a reservoir in avian species. Thogoto virus and Dhori virus are transmitted between vertebrates by ticks and are not known to cause disease in humans. See Influenzavirus A, B and C.

Cox NJ and Kawaoka Y (1998) In Virology, vol. 1 of Topley & Wilson's Microbiology and Microbial Infections. Ninth edition, edited by BWJ Mahy and L Collier. London: Arnold, p. 385 Webster RG (1999) In Encyclopedia of Virology, Second edition, edited by A Granoff and RG Webster. London: Academic Press, p. 824

Orthopoxvirus A genus of the subfamily Chordopoxvirinae. Consists of viruses of mammals, most of which cause generalized infections with a rash. Virions are


brick-shaped, 220-450nm long and 140-260nm wide, and ether-resistant. Different species undergo genetic recombination and exhibit serological cross-reactivity and nucleic acid homol-ogy. The DNA genome is a single molecule of covalently closed double-stranded DNA, 170-250kb in length, with G+C about 36%. A hemagglutinin (HA) is produced by infected cells; it is serologically specific and is a lipid-rich pleomorphic particle 50-65nm in diameter, separate from the virion. They all produce pocks on the CAM but some strains may be more easily isolated in animals or cell cultures. They replicate in chick embryo fibroblasts, Vero cells and HeLa cell cultures. Because of the close serological relationship within the genus, species are identified by biological characters. However, they can be accurately distinguished by polymerase chain reaction-based methods. Type species is Vaccinia virus. Other species are Variola, Camelpox, Cowpox, Ectromelia, Monkeypox, Raccoonpox, Taterapox and Volepox viruses. Tentative species in the genus are skunkpox and Uasin Gishu disease viruses.

Synonym: vaccinia subgroup viruses.

Dumbell K and Smith GL (1999) In Encyclopedia of Virology, Second edition, edited by A Granoff and RG Webster. London: Academic Press, p. 1668 Fenner F et al (editors) (1989) The Orthopoxviruses. New York: Academic Press Ropp SL et al (1995) J Clin Microbiol 33, 2069

Orthopoxvirus bovis Name proposed for Cowpox virus, but not adopted.

Orthopoxvirus commune Name proposed for Vaccinia virus, but not adopted.

Orthopoxvirus officinale Name proposed for Vaccinia virus, but not adopted.

Orthopoxvirus simiae Name proposed for Monkeypox virus, but not adopted.

Orthoreovirus A genus of the family Reoviridae containing viruses which infect only vertebrates and are spread by the respiratory or fecal-oral routes. The type species is Mammalian orthoreovirus. Strains have been isolated from humans and many other mammals and birds.

Four species are currently recognized which are in three subgroups: Subgroup 1 includes Mammalian orthoreovirus; subgroup two contains Avian orthore-ovirus and Nelson Bay orthoreovirus; and subgroup 3 contains Baboon orthoreovirus. There are also three tentative species in the genus, Ndelle virus of rodents, python orthoreovirus and rattlesnake orthoreovirus. Subgroup 1 viruses are of three serological types. Human isolates of each of the three types are indistinguishable from those isolated from other mammals. The avian viruses are of three serological types. There are a number of group- and type-specific antigens. Reoviruses have been isolated from humans and other animals with a variety of febrile, enteric and respiratory diseases, but the evidence that they cause disease is not strong. They can often be isolated from the respiratory tract or feces of normal humans and other animals. Injection of newborn mice with type 3 causes oily hair, jaundice and stunted growth, although often with recovery. Types 1 and 2 more often cause cardiac and pulmonary lesions. Virus has been isolated from mosquitoes but replication probably does not occur in insects. Virus particle diameter: 60-75nm; buoyant density: 1.38g/ml, contains 14.6% RNA and 86% protein. RNA is double-stranded in 10 segments, categorized in three size classes: large (L1-L3), about 3.8kb; medium, (M1-M3), about 2.3kb; and small (S1-S4), about 1.3kb in length. The positive strands of each duplex have a 5' terminal cap structure (type 1), and the negative strands have 5'-phosphory-lated termini. There are no 3' poly A tracts. The virions also contain numerous oligonucleotides and single-stranded adenine-rich RNA making up 25% of the total encapsulated nucleic acid. Single-stranded RNA is not required for infectivity and its function is unknown. Surrounding the nucleic acid core are two protein shells with icosahedral symmetry, but the detailed structure remains to be elucidated. The outer shell can be removed with trypsin leaving a subviral particle of diameter 40-45nm. Mammalian strains, but not avian, agglutinate human group O erythrocytes. Infectivity is stable between pH 2.2-8.0, resists ether, 1% phenol, 3% formalin and

20% lysol but is inactivated by 70% ethanol. Mammalian strains replicate with CPE in primary and continuous cell lines derived from a wide range of animal species. Avian strains replicate with CPE in chick embryo cell cultures. Synonym: reovirus.

Tyler KI (1999) In Encyclopedia of Virology, Second edition, edited by A Granoff and RG Webster. London: Academic Press, p. 1454

Orungo virus (ORUV) A species in the genus Orbivirus that has four serotypes (Orungo viruses 1-4). Isolated from culicine mosquitoes, humans, camels, cattle, goats, monkeys and sheep.

Orungo virus 1-4 (ORUV 1-4) Species in the genus Orbivirus, belonging to the Orungo serogroup. First isolated from the mosquito, Anopheles funestus, in Uganda, and the mosquito, Aedes dentatus, and humans in Nigeria. Can be passed in newborn mice by i.c. injection. Replicates with CPE in BHK21 cells. Develops in the cytoplasm associated with a specific viral granular matrix and accompanying filaments. Virion diameter: 63nm; core diameter: 34nm. Released from the cells by lysis or budding through membranes. Found in Uganda, Nigeria, Central African Republic and Senegal. Has been isolated from human blood and causes a febrile illness in humans, with headache, conjunctivitis, myalgia, vomiting and rash. Antibodies are found in humans, other primates, sheep and cows in Nigeria.

Tomori O (1977) Microbios 19, 157 Tomori O et al (1977) Arch Virol 55, 181

Oryctes rhinoceros virus (OrV) An unas-signed insect virus that infects scarab beetles, not rhinoceroses.

Oseltamivir A carbocyclic analog of sialic acid with potent anti-influenza neu-raminidase activity. An orally administered neuraminidase inhibitor, effective in prevention of influenza when given daily for 6 weeks during the influenza season. Also active against human experimental infection with Influenza B virus. Synonym: Tamiflu.

Hayden FG et al (2000) Antiviral Ther 5, 205

Hayden FG et al (1999) New Engl J Med 341, 1387

Nicholson KG et al (2000) Lancet 355,1845

Ossa virus (OSSAV) A strain of Caraparu virus in the genus Bunyavirus, belonging to the group C viruses. Isolated from humans, the spiny rat, Proechimys semi-spinosus, and Culex sp in Panama. Associated with a febrile illness in humans.

de Rodaniche E et al (1964) Am J Trop Med Hyg 13, 839

osteolytic syndrome A developmental abnormality syndrome in rodents caused by parvovirus infection of the fetus late in pregnancy or soon after birth. Cytolytic replication in osteogenic tissues results in animals with mongoloid features, small flat faces, microcephalic heads, protruding eyes and tongue, missing or abnormal teeth and fragile bones. May also result in persistent dwarfism.

osteopetrosis virus A strain of avian leuko-sis sarcoma virus in the genus Alphavirus which can cause osteopetrosis, a disease which occurs naturally in fowls, and is characterized by enlargement of the bones, especially the leg bones. There is an increase of hard bone due to hyper-trophic activity of the periosteum. It can be transmitted by inoculation of day-old chicks or the amnion of chick embryos with blood from birds with osteopetrosis or from some cases of lymphomatosis. Osteopetrosis is often accompanied by soft tissue tumors. Infected tissue contains large amounts of virus-specific DNA, much of which is unintegrated. Turkeys do not naturally develop the disease but it can be transmitted to them. See Avian myeloblastosis virus. Synonyms: big bone disease virus; marble bone disease virus; thick leg disease virus.

Foster RG et al (1994) Virology 205,179 Robinson HL et al (1986) J Virol 59, 45 Smith RE (1982) Curr Top Microbiol Immunol 101, 75

ostreid herpesvirus 1 (OsHV-1) An unas-signed member of the family Herpesviridae which infects oysters. Experimental transmission to the Pacific oyster, Crassostrea gigas, has been reported.

Le Deuff RM et al (1994) Bull Eur Assoc Fish Pathol 14, 69

ostrich adenovirus A virus isolated from ostriches with respiratory disease.

Gough RE et al (1997) Vet Rec 140, 402

otofuke agent A small round-structured virus detected by electron microscopy in the feces of Japanese patients with gastroenteritis.

ouabain A cardiac glycoside obtained from the seeds of Strophanthus gratus or the wood of Acokanthera schimperi or A. ouabio. An inhibitor of Na+- and K+-dependent adenosine triphosphatase. Inhibits the growth of mouse cell lines K3b and JLS-V9, and the production in them of mouse type C retroviruses. Low concentrations of ouabain inhibit the growth of some enveloped viruses such as influenza and parainfluenza viruses in chick embryo cells.

Tomita Y and Kuwata T (1978) J Gen Virol 38, 223

Ouango virus (OUAV) An unassigned vertebrate rhabdovirus. Isolated in 1970 from a bird, Sitagra melanocephala, in Central African Republic. Not reported to cause disease in humans.

Oubangui virus An unclassified arbovirus. Isolated in suckling mice from a pool of female mosquitoes, Culex guiarti, collected in Bangui, Central African Republic from human bait. Infectivity resistant to chloroform. Hemagglutinates goose erythrocytes. Not reported to cause disease in humans.

Oubi virus (OUBIV) A strain of Olifantsvlei virus in the genus Bunyavirus. Isolated from Culex (Eumelanomyia) rima sp in the Ivory Coast. Not reported to cause disease in humans.

Institut Pasteur, Dakar (1982) Annual Report p. 84

Ourem virus (OURV) A serotype of Changuinola virus in the genus Orbivirus. Isolated from Lutzomyia sp in Para, Brazil. Not reported to cause disease in humans.

ovine AAV See Ovine adeno-associated virus.

Ovine adeno-associated virus (OAAV) A

species in the genus Dependovirus. Isolated from ovine feces, in association with an adenovirus in lamb kidney cell cultures. Agglutinates guinea pig and human erythrocytes. Replicates in association with the cell nucleus and requires the presence of an adenovirus.

Clarke JK et al (1979) Arch Virol 60, 171

Ovine adenoviruses A to C (OadV A-C)

Species in the genus Mastadenovirus which cause mild upper respiratory tract or enteric infections in sheep. Six serotypes are identified: ovine adenovirus 1 (Ovine adenovirus B); ovine adenoviruses 2-5 (Ovine adenovirus A); and ovine adenovirus 6 (ovine adeno-virus C), a tentative species. Because few sheep give a positive reaction in the gel diffusion test for precipitating antibodies it was suggested that the infection was not common, but the majority of sheep in Scotland have neutralizing antibodies to four serotypes of this virus. The infection must therefore be common and, as the virus can be recovered from the feces of normal sheep, its isolation from disease outbreaks must be viewed with caution. Multiplies in sheep kidney cell cultures. Agglutinates rat erythro-cytes.

Belak S (1990) In Virus infections of Ruminants, edited by Z Dinter and B Morein. Amsterdam: Elsevier Science, p. 171 Sharp JM (1977) Vet Rec 101, 524

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