Nearestneighbor base frequency analysis

A classical method of characterizing DNA molecules, which compares the frequencies with which any pair of adjacent bases occurs. Now largely supplanted by nucleotide sequence analysis.

Nebraska calf diarrhea virus A strain of calf rotavirus. Associated with gastroenteritis in calves. Has been propagated in bovine embryonic kidney cell cultures, where it is cell-associated. Agglutinates human O erythrocytes.

Fauvel M et al (1978) Intervirology 9, 95

necrosis Death of cells in a circumscribed piece of tissue. This may be directly due to virus infection or may occur in the surrounding uninfected cells following the release of toxic materials from the infected cell. See also apoptosis.

necrotic rhinitis virus Synonym for Bovine herpesvirus 1.

Neethling virus Synonym for Lumpy skin disease virus.

Nef protein A protein (negative factor) induced in cells infected by Human and Simian immunodeficiency viruses. Its exact function during replication has not been defined, but it decreases expression of the HIV receptor CD4 on T cells, and causes removal of CD4 from the cell surface by increasing endocytosis of CD4.

Aiken C et al (1994) Cell 76, 853 Greenway AL et al (1994) Virology 198, 245

negative staining A method for visualizing virus particles by drying them in a film of electron-dense material, such as phospho-tungstic acid (PTA), which outlines the particle and reveals surface structures in the electron microscope.

Brenner S and Horne RW (1959) Biochim Biophys Acta 34, 103

negative strand The RNA strand complementary to the positive (messengersense) strand. It forms the genome of several families of plant and animal RNA viruses which form an order termed the Mononegavirales or single negative-strand viruses. Synonym: minus strand.

Pringle CR (1997) Arch Virol 142, 2321 Roberts A and Rose JK (1998) Virology 247, 1

Negishi virus (NEGV) A tick-borne virus in the genus Flavivirus. Isolated from two fatal cases of human encephalitis in Japan, but one isolate was lost. Sequence analysis of the existing isolate indicates that it is a strain of Louping ill virus.

Negri bodies Intracytoplasmic acidophilic diagnostic inclusion bodies seen in the neuronal cells of the cerebellum, hippocampus, thalamus, hypothalamus and brainstem of animals or humans who have died of rabies. Rarely found in the cortex.

Miyamoto K and Matsumoto S (1965) J Cell Biol 27, 677

Nelson Bay orthoreovirus (NBV) A species in the genus Orthoreovirus belonging to Subgroup 2, related to the avian ortho-reovirus antigenic group. Isolated from the heart blood of a flying fox in New South Wales, Australia. Passage i.c. in suckling mice causes paralysis and death. Causes cell fusion and CPE in a line of pig kidney cells.

Gard G and Compans RW (1970) J Virol 6, 100

neo-antigens Antigens that only appear in cells after transformation. They are coded for by the transforming virus. Often called 'tumor antigens' or 'T antigens'.

neonatal calf diarrhea coronavirus (NCDV) A strain of Bovine coronavirus. Causes severe diarrhea, usually in calves less than 5 days old. Replicates in bovine kidney cell cultures producing syncytia. Some strains, such as the highly pathogenic strain LY-138, have not been propagated in vitro and are replicated by passage in calves. The strains can then be purified from the contents of the small intestines. Serial passage resulted in attenuation and this virus can induce resistance to virulent virus. A similar disease is caused by calf rotavirus.

neutralization

Synonym: Bovine coronavirus.

Hajer I and Storz J (1979) Arch Virol 59, 47 Woode GN and Bridger JC (1975) Vet Rec 96, 85

neoplasm A localized population of proliferating cells not governed by the usual limitations of normal growth. May be benign or become malignant if it metastasizes.

Nephropathia epidemica virus Synonym for Hantaan virus.

Nepuyo virus (NEPV) A serotype of Marituba virus in the genus Bunyavirus, belonging to the group C viruses. Isolated from bats and mosquitoes in Trinidad, Honduras, Mexico, Panama, and Belem, Brazil. Not associated with disease in humans.

Netivot virus (NETV) A serotype of Umatilla virus in the genus Orbivirus. Recovered from a pool of Culex pipiens captured in Israel.

Neudoerfl virus (NEUV) A strain of Tickborne encephalitis virus (European subtype) in the genus Flavivirus. Isolated in Neudoerfl an der Leitha, Austria.

neural spread Dissemination of virus infection by spreading along peripheral nerves. Plays an essential role for viruses such as rabies, herpes simplex and pseudorabies viruses, which do not generally spread by viremia. Other viruses such as polio, reovirus and mouse hepatitis may utilize both viremia and neural spread to disseminate infection.

neuraminidase (NA) An enzyme which splits N-acetylneuraminic acid from glycoprotein viral receptors on the cell membrane. The crystal structure shows that NA is a tetrameric molecule with each subunit containing six sheets of four P-strands each, arranged like the blades of a propeller. The enzymatic site is a hydrophobic depression in the center of the P-sheets. Neuraminidase activity is carried by one of the two types of glyco-protein peplomer on the surface of members of the Orthomyxoviridae. The second type is a hemagglutinin or attachment site by which the virus is joined to the cell receptor site. This can be destroyed by the neuraminidase, releasing the virus. In most members of the Paramyxoviridae, both neuraminidase and hemagglutinin activity are carried on the same peplomer. However, morbilliviruses such as measles lack neu-raminidase activity. A new class of antiinfluenza virus inhibitors which target the active enzymatic site based upon the crystal atomic structure of the neu-raminidase has been developed and licensed for use (see oseltamivir, tami-flu and zanamivir).

Tisdale M (2000) Rev Med Virol 10, 45 von Itzstein M et al (1993) Nature 363, 418

neuro-2a cells (CCL 131) A cell line established from a spontaneous tumor of a strain A albino mouse.

Neurocytes hydrophobiae Name given to a supposed protozoan etiological agent of rabies. The structure is now known as the 'Negri body'.

Calkins GN (1909) Protozoology. New York: Lea and Febiger neurodegeneration Breakdown of neuronal structure and function, the end stage of prion disease.

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