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.Skin Diseases, Viral: Skin diseases caused by viruses.Cat Diseases: Diseases of the domestic cat (Felis catus or F. domesticus). This term does not include diseases of the so-called big cats such as CHEETAHS; LIONS; tigers, cougars, panthers, leopards, and other Felidae for which the heading CARNIVORA is used.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.Hemolytic Plaque Technique: A method to identify and enumerate cells that are synthesizing ANTIBODIES against ANTIGENS or HAPTENS conjugated to sheep RED BLOOD CELLS. The sheep red blood cells surrounding cells secreting antibody are lysed by added COMPLEMENT producing a clear zone of HEMOLYSIS. (From Illustrated Dictionary of Immunology, 3rd ed)Cell Line: Established cell cultures that have the potential to propagate indefinitely.Plaque, Atherosclerotic: Lesions formed within the walls of ARTERIES.Dental Plaque: A film that attaches to teeth, often causing DENTAL CARIES and GINGIVITIS. It is composed of MUCINS, secreted from salivary glands, and microorganisms.Virus Cultivation: Process of growing viruses in live animals, plants, or cultured cells.Antibody-Producing Cells: Cells of the lymphoid series that can react with antigen to produce specific cell products called antibodies. Various cell subpopulations, often B-lymphocytes, can be defined, based on the different classes of immunoglobulins that they synthesize.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.Rickettsia rickettsii: A species of gram-negative, aerobic bacteria that is the etiologic agent of ROCKY MOUNTAIN SPOTTED FEVER. Its cells are slightly smaller and more uniform in size than those of RICKETTSIA PROWAZEKII.Rickettsia prowazekii: A species of gram-negative, aerobic bacteria that is the etiologic agent of epidemic typhus fever acquired through contact with lice (TYPHUS, EPIDEMIC LOUSE-BORNE) as well as Brill's disease.Rickettsia: A genus of gram-negative, aerobic, rod-shaped bacteria often surrounded by a protein microcapsular layer and slime layer. The natural cycle of its organisms generally involves a vertebrate and an invertebrate host. Species of the genus are the etiological agents of human diseases, such as typhus.Pancreatin: A mammalian pancreatic extract composed of enzymes with protease, amylase and lipase activities. It is used as a digestant in pancreatic malfunction.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).Culture Techniques: Methods of maintaining or growing biological materials in controlled laboratory conditions. These include the cultures of CELLS; TISSUES; organs; or embryo in vitro. Both animal and plant tissues may be cultured by a variety of methods. Cultures may derive from normal or abnormal tissues, and consist of a single cell type or mixed cell types.Idoxuridine: An analog of DEOXYURIDINE that inhibits viral DNA synthesis. The drug is used as an antiviral agent.Neutral Red: A vital dye used as an indicator and biological stain. Various adverse effects have been observed in biological systems.Virology: The study of the structure, growth, function, genetics, and reproduction of viruses, and VIRUS DISEASES.Methods: A series of steps taken in order to conduct research.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.Methylcellulose: Methylester of cellulose. Methylcellulose is used as an emulsifying and suspending agent in cosmetics, pharmaceutics and the chemical industry. It is used therapeutically as a bulk laxative.Pokeweed Mitogens: Proteins isolated from the roots of the pokeweed, Phytolacca americana, that agglutinate some erythrocytes, stimulate mitosis and antibody synthesis in lymphocytes, and induce activation of plasma cells.Rickettsia typhi: The etiologic agent of murine typhus (see TYPHUS, ENDEMIC FLEA-BORNE).