Pinocytosis See viropexis

Piratuba virus A possible species in the genus Orbivirus, isolated from mosquitoes in the Amazon region of Brazil. Antigenically related to Changuinola virus. Not associated with disease in humans.

Pirital virus (PIRV) A species in the genus Arenavirus isolated in Venezuela. Natural rodent host is the cane rat, Sigmodon alstoni. Not known to cause human disease. Genetically related to Tacaribe complex viruses.

Pirodavir An antiviral compound that inhibits picornavirus replication by binding to a hydrophobic pocket of capsid protein VP1 beneath the canyon floor and inhibiting binding or uncoating of the virion.

Andries K et al (1992) Antimicrob Agents Chemother 36, 10

Piry virus (PIRYV) A species in the genus Vesiculovirus. Antigenically related to Vesicular stomatitis virus. Isolated from an opposum in Para, Brazil. Laboratory human infections have resulted in a febrile illness with myalgia, arthralgia and abdominal tenderness.

Piscivirus A proposed name, not adopted,

Playas virus (PLAV)

for the genus of fish rhabdoviruses now known as Novirhabdovirus.

Pixuna virus (PIXV) A species in the genus Alphavirus. Closely related to and perhaps a serological type of Venezuelan equine encephalitis virus. Isolated from rodents, Proechimys guyannensis oris, and mosquitoes in Brazil. No known association with disease.

Shope RE et al (1964) Am J Trop Med Hyg 13, 723

PK (15) cells (CCL 33) A heteroploid cell line from the kidneys of a pig, Sus scrofa.

Pl 1 Ut (NBL-9) cells (CCL 74) Initiated from the trypsinized uterine tissue of an adult female raccoon, Procyon lotor.

plaque The area of lysis, or 'hole' formed in a lawn of cells due to infection with a single infectious unit of a cytopathic virus.

plaque assay An assay in which the concentration of infective particles in a virus solution is determined as the number of plaques induced on a lawn of bacteria or eukaryotic cells. It can also be used to distinguish between different strains or distinct viruses by the features of the plaque.

plaque-forming units (pfu) The number of plaques formed per unit of volume or weight of a virus suspension.

plaque mutants Mutants producing plaques different in size or appearance from those produced by the wild-type. Plaque size may be affected by speed of replication, sensitivity or resistance to inhibitors in the agar, and pH.

plaque neutralization test (plaque reduction test) A method either for identifying a virus (or serotype) or for titrating an antiserum by analyzing the inhibitory effect of antibodies on the infectivity of the virus using the plaque assay.

plaque picking The selection of individual plaques which are formed by a single infection event. Clones of a virus can thus be selected and further studied.

plasma membrane The external lipid bilayer membrane of cells. Enveloped viruses transfer their nucleocapsids across membranes by fusing with them, resulting in simultaneous envelope removal and cell entry.

plasma-derived vaccine The production of inactivated hepatitis B vaccine derived from the plasma of Hepatitis B virus carriers is an important source of hepatitis B vaccine used in millions of recipients worldwide, without any known transmission of virus. Although most developed countries have now adopted the genetically engineered recombinant hepatitis B vaccine made in yeast or mammalian cells as standard because of its proven reliability and absolute safety, the high cost means that many countries can only afford to immunize with plasma-derived vaccine.

plasmids Genetic elements composed of double-stranded circular DNA which replicate separately from the bacterial chromosome within the bacterial cell wall. Some can induce their direct transmission to other bacteria, although they differ from viruses in having no extracellular infective particle. Some plasmids are under stringent control and as little as one copy is replicated per genome. Others, under more relaxed control, replicate many copies per cell. They may carry genetic determinants which can be translocated from the plasmid to the bacterial chromosome. Some of these determinants mediate antibiotic resistance. See also episomes.

Lederberg J (1952) Physiol Rev 32, 403

plasmid vector A plasmid which is used for cloning 'foreign' DNA. The plasmid is often manipulated to contain desirable features such as resistance to two or more antibiotics, ability to produce multiple copies, single-cutting restriction enzyme sites and strong promoters.

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