L cell virus Cultures of L cells (a line of mouse cells) were reported to release virus particles. These particles resembled C-type viruses. On injection into newborn mice and hamsters no tumors were induced. Infection could not be transmitted to mouse or rat embryo cultures. A subline of L cells, A9, which is 8-azagua-nine-resistant, also releases virus particles, but they induce morphological changes (foci) in mouse embryo fibrob-last cultures. Focus formation was more efficient on N-type than B-type mouse cells.

L99 virus A strain of Seoul virus in the genus Hantavirus. Isolated from the rat Rattus losea.

L-132 cells (CCL 5) A heteroploid cell line derived from normal human embryonic lung. Reported to be a sensitive cell line for the primary isolation of entero-viruses.

laboratory acquired infections Before the development of biosafety cabinets it was not uncommon for occupational virus infections to occur in laboratory workers, especially if spread by the aerosol route. The introduction of guidelines for safe handling of infectious agents in the early 1980s has been followed in the 1990s by the introduction of mandatory safety practices that, if properly executed, reduce the hazards of working in a virus laboratory to a minimum.

Kiley MP and Lloyd G (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. 933 Richmond JY and McKinney RW (1999) Biosafety in Microbiological and Biomedical Laboratories, Fourth edition. Washington: US Government Printing Office laboratory strains Viruses which have been propagated in the laboratory in vivo or in vitro. They may be different in many properties from clinical or field isolates, known as wild strains. See vaccine virus markers.

lacertid herpesvirus 1 (LaHV-1) An unas-signed virus in the family Herpesviridae, identified in the green lizard, Lacerta viridis. Lizards captured in Italy and taken to France developed papillomatous skin lesions. A herpesvirus was identified by electron microscopy in the lesions from one animal.

Synonym: green lizard herpesvirus.

Raynaud A and Adrian M (1970) CR Acad Sci Ser D 283, 845

La Crosse virus (LACV) A strain of

California encephalitis virus in the genus Bunyavirus. Isolated from the brain tissue of a woman with fatal meningo-encephalitis in La Crosse, Wisconsin, USA in 1960. Between 1960 and 1970, 509 cases of human infection were reported, mainly in Wisconsin and Minnesota. Large serosurveys in Midwestern US states indicated that there may be 1000 infections per reported case, so very few result in overt disease. Classical encephalitis occurs, but some 10% of infected children develop epilepsy, and a few deaths have occurred. Antibodies are found in small forest mammals, and virus can be isolated from mosquitoes, especially Aedes triseriatus, a woodland insect that usually feeds on squirrels and chipmunks. In addition, discarded tyres that hold rainwater provide a breeding ground for the mosquitoes and bring the disease to urban areas. The range of Aedes trise-riatus in the USA covers the area east of the Mississippi river. There are three genetically distinct subgroups: A, B and C.

Calisher CH and Thompson WH (editors) (1983) California Serogroup Viruses. New York: Alan Liss

El Said LHE et al (1979) Am J Trop Med Hyg 28, 364

Janssen RS et al (1986) J Virol 59, 1 Klimas RA et al (1984) Am J Epidemiol 114, 112

lactate dehydrogenase virus

lactate dehydrogenase virus A synonym for Lactate dehydrogenase-elevating virus.

Lactate dehydrogenase-elevating virus

(LDV) A species in the genus Arterivirus. Infects only species of Mus. Has been isolated from wild and laboratory mice, Mus musculus, in Europe, USA and Australia. Mus caroli can be infected experimentally. The virus productively infects macrophages and causes a life-long infection with permanent viremia but no disease. Infection recognized by abnormally high levels of plasma lactate dehydrogenase, and both elevated enzyme levels and infectious LDV titers (104-106ID50 ml-1) persist for the life of the mouse. Certain other plasma enzyme levels are also raised in infected mice due to a failure to clear them from the circulation, apparently as a result of impaired function of the reticuloendothelial system. The infection is usually silent, with no obvious pathological changes. Antibodies are produced but infectious virus-antibody complexes continue to circulate. There is a minor degree of splenomegaly and certain immunopathological changes. Virus is found in all the body tissues, and is excreted in urine, saliva and feces. Transmission between mice does not occur readily and probably results mainly from blood transfer during fighting. Fetuses and young can be infected by a mother who becomes infected during pregnancy or lactation. Virions are enveloped, 55nm in diameter, containing a spherical core 25-35nm in diameter. The nucleocapsid protein (12-14kDa) is associated with positive single-stranded RNA, 14.1kb in length, encoding nine open reading frames. Genome expression involves formation of a 3' co-terminal nested set of subgenomic mRNAs, each carrying a non-coding 5' leader of 156-212 nucleotides derived from the 5' end of the genome and a 3' non-coding segment which is polyadenylated. Productive cytocidal replication of LDV only occurs in a subpopulation of macrophages which are continuously renewed in lymphoid tissues, liver and testis to support the persistent infection. It is the continuous destruction of this subpopulation that results in decreased clearance leading to elevated levels of lactate dehydrogenase and other enzymes in the blood plasma. In certain mouse strains, e.g. C58 and AKR, LDV can cytocidally infect anterior horn neurons via interaction with endogenous murine retroviruses to cause paralysis known as 'age-dependent poliomyelitis'. This disease only occurs in mice with some degree of immunodeficiency, e.g. as a result of aging. Synonyms: age-dependent polioencephalitis of mice virus; enzyme-elevating virus; lactic dehydrogenase virus; Riley virus.

Plagemann PGW et al (1999) Curr Top Virol 1, 27

Rowson KEK and Mahy BWJ (1985) J Gen Virol 66, 2297

lagenavirus A name proposed for viruses which appear bottle-shaped on electron microscopy. The only one so far reported is Lactate dehydrogenase-elevating virus, but the name was not adopted.

Almeida JD and Mims CA (1974) Microbios 10, 175

lagomorph herpesvirus 1 Synonym for lep-orid herpesvirus 1.

Lagos bat virus (LBV) A species in the genus Lyssavirus. Antigenically related to, but distinguishable from, Rabies virus. Isolated from a Nigerian fruit bat, Eidolon helvum, in 1956 on Lagos Island, Nigeria and in 1974 was also found in bats, Micropteropus pussilis, in the Central African Republic. Not known to cause disease in humans. Pathogenic for adult mice, dogs and rhesus monkeys on i.c. injection, but adult mice are not affected by i.p. injection. Guinea pigs, rabbits and monkeys, Cercocebus torquatus, are not killed by peripheral inoculation.

Bourhy H et al (1993) Virology 194, 70

Lagovirus A genus in the family Caliciviridae comprised of viruses of rabbits and hares.

Laguna Negra virus (LNV) A species in the genus Hantavirus. Isolated from the rodent Calomys laucha in the Chaco region of Paraguay. Associated with an outbreak of hantavirus pulmonary syndrome involving 17 confirmed cases, two of whom died.

Johnson AM et al (1997) Virology 238, 115

largemouth bass virus (LMBV)

La Joya virus (LJV) A tentative species in the genus Vesiculovirus. Isolated from mosquitoes, Culex dunni, in Panama. Not reported to cause human disease.

Calisher CH et al (1989) Intervirology 30, 241

Lake Clarendon virus (LCV) A tentative species in the genus Orbivirus. Isolated from ticks, Argas robertsi, in south-east Queensland, Australia. Not known to cause disease in humans.

George TD et al (1984) Aust J Biol Sci 37, 85

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