Global Alert and Response (GAR)

Hepatitis D


Glossary


Glossary

albumin a water soluble protein. Serum albumin is found in blood plasma and is important for maintaining plasma volume and osmotic pressure of circulating blood. Albumin is synthesized in the liver. The inability to synthesize albumin is a predominant feature of chronic liver disease.

ALT alanine aminotransferase an enzyme that interconverts L-alanine and D-alanine. It is a highly sensitive indicator of hepatocellular damage. When such damage occurs, ALT is released from the liver cells into the bloodstream, resulting in abnormally high serum levels. Normal ALT levels range from 10 to 32 U/l; in women, from 9 to 24 U/l. The normal range for infants is twice that of adults.

amino acids the basic units of proteins, each amino acid has a NH-C(R)-COOH structure, with a variable R group. There are altogether 20 types of naturally occurring amino acids.

antibody a protein molecule formed by the immune system which reacts specifically with the antigen that induced its synthesis. All antibodies are immunoglobulins.1

antigen any substance which can elicit in a vertebrate host the formation of specific antibodies or the generation of a specific population of lymphocytes reactive with the substance. Antigens may be protein or carbohydrate, lipid or nucleic acid, or contain elements of all or any of these as well as organic or inorganic chemical groups attached to protein or other macromolecule. Whether a material is an antigen in a particular host depends on whether the material is foreign to the host and also on the genetic makeup of the host, as well as on the dose and physical state of the antigen.1

antigenome RNA molecule complementary to the viral single stranded RNA genome.

AST aspartate aminotransferase the enzyme that catalyzes the reaction of aspartate with 2-oxoglutarate to give glutamate and oxaloacetate. Its concentration in blood may be raised in liver and heart diseases that are associated with damage to those tissues. Normal AST levels range from 8 to 20 U/l. AST levels fluctuate in response to the extent of cellular necrosis.1

bilirubin is the chief pigment of bile, formed mainly from the breakdown of hemoglobin. After formation it is transported in the plasma to the liver to be then excreted in the bile. Elevation of bile in the blood causes jaundice.26

capsid the protein coat of a virion, composed of large multimeric proteins, which closely surrounds the nucleic acid.1

carcinoma a malignant epithelial tumour. This is the most frequent form of cancer.

cDNA complementary DNA. DNA synthesized by RNA-directed DNA polymerase as a copy of RNA, usually isolated mRNA or viral genomic RNA. It differs in sequence from eukaryotic chromosomal DNA by the absence of introns.

cirrhosis a chronic disease of the liver characterized by nodular regeneration of hepatocytes and diffuse fibrosis. It is caused by parenchymal necrosis followed by nodular proliferation of the surviving hepatocytes. The regenerating nodules and accompanying fibrosis interfere with blood flow through the liver and result in portal hypertension, hepatic insufficiency, jaundice and ascites.

codon the smallest unit of genetic material that can specify an amino acid residue in the synthesis of a polypeptide chain. The codon consists of three adjacent nucleotides.

cytopathic effects include morphological changes in the cell appearance (rounding up of cells), agglutination of red blood cells (haemagglutination assay with influenza virus), zones of cell lysis on monolayers of tissue culture or finally immortalization of animal cell lines (foci formation).

cytoplasm the protoplasm of the cell which is outside of the nucleus. It consists of a continuous acqueous solution and the organelles and inclusions suspended in it. It is the site of most of the chemical activities of the cell.

encephalopathy an acute reaction of the brain to a variety of toxic or infective agents, without any actual inflammation such as occurs in encephalitis.1

endemic continuously prevalent in some degree in a community or region.26


endoplasmic reticulum a network or system of folded membranes and interconnecting tubules distributed within the cytoplasm of eukaryotic cells. The membranes form enclosed or semienclosed spaces. The endoplasmic reticulum functions in storage and transport, and as a point of attachment of ribosomes during protein synthesis.

enzyme any protein catalyst, i.e. substance which accelerates chemical reactions without itself being used up in the process. Many enzymes are specific to the substance on which they can act, called substrate. Enzymes are present in all living matters and are involved in all the metabolic processes upon which life depends.1, 26

epidemic an outbreak of disease such that for a limited period a significantly greater number of persons in a community or region suffer from it than is normally the case. Thus an epidemic is a temporary increase in incidence. Its extent and duration are determined by the interaction of such variables as the nature and infectivity of the casual agent, its mode of transmission and the degree of preexisting and newly acquired immunity.26

epitope or antigenic determinant. The small portion of an antigen that combines with a specific antibody. A single antigen molecule may carry several different epitopes.1

fulminant describes pathological conditions that develop suddenly and are of great severity.1

genome the total genetic information present in a cell. In diploid cells, the genetic information contained in one chromosome set.1

Golgi apparatus a cytoplasmic organelle which is composed of flattened sacs resembling smooth endoplasmic reticulum. The sacs are often cup-shaped and located near the nucleus, the open side of the cup generally facing toward the cell surface. The function of the Golgi apparatus is to accept vesicles from the endoplasmic reticulum, to modify the contents, and to distribute the products to other parts of the cell or to the cellular environment.

hepadnavirus family of single stranded DNA viruses of which hepatitis B virus (HBV) and woodchuck hepatitis virus (WHV) are members.

hepatocytes liver cells.1

humoral pertaining to the humors, or certain fluids, of the body.1

icterus jaundice.

IgA antibodies IgA has antiviral properties. Its production is stimulated by aerosol immunizations and oral vaccines.

IgG antibodies IgG is the most abundant of the circulating antibodies. It readily crosses the walls of blood vessels and enters tissue fluids. IgG also crosses the placenta and confers passive immunity from the mother to the fetus. IgG protects against bacteria, viruses, and toxins circulating in the blood and lymph.

IgM antibodies IgMs are the first circulating antibodies to appear in response to an antigen. However, their concentration in the blood declines rapidly. This is diagnostically useful, because the presence of IgM usually indicates a current infection by the pathogen causing its formation. IgM consists of five Y-shaped monomers arranged in a pentamer structure. The numerous antigen-binding sites make it very effective in agglutinating antigens. IgM is too large to cross the placenta and hence does not confer maternal immunity.

immunoglobulin (Ig): is a sterile preparation of concentrated antibodies (immunoglobulins) recovered from pooled human plasma processed by cold ethanol fractionation. Only plasma that has tested negative for a) hepatitis B surface antigen (HBsAg), b) antibody to human immunodeficiency virus (HIV), and c) antibody to hepatitis C virus (HCV) is used to manufacture IG. IG is administered to protect against certain diseases through passive transfer of antibody. The IGs are broadly classified into five types on the basis of physical, antigenic and functional variations, and labelled respectively IgM, IgG, IgA, IgE and IgD.

incidence the number of cases of a disease, abnormality, accident, etc., arising in a defined population during a stated period, expressed as a proportion, such as x cases per 1000 persons per year.1

interferon a class of proteins processing antiviral and antitumour activity produced by lymphocytes, fibroblasts and other tissues. They are released by cells invaded by virus and are able to inhibit virus multiplication in noninfected cells. Interferon preparations have been shown to have some clinical effect as antiviral agents. The preparations so far available have produced side effects, such as fever, lassitude, and prostration, not dissimilar from those accompanying acute virus infection itself.1

jaundice is a yellow discoloration of the skin and mucous membranes due to excess of bilirubin in the blood, also known as icterus.26


lymphocyte a leukocyte of blood, bone marrow and lymphatic tissue. Lymphocytes play a major role in both cellular and humoral immunity. Several different functional and morphologic types must be recognized, i.e. the small, large, B-, and T-lymphocytes, with further morphologic distinction being made among the B-lymphocytes and functional distinction among T-lymphocytes.1

necrosis death of tissue.1

nucleotide a molecule formed from the combination of one nitrogenous base (purine or pyrimidine), a sugar (ribose or deoxyribose) and a phosphate group. It is a hydrolysis product of nucleic acid.1

nucleus a membrane-bounded compartment in an eukaryotic cell which contains the genetic material and the nucleoli. The nucleus represents the control center of the cell. Nuclei divide by mitosis or meiosis.

peptide a compound of two or more amino acids linked together by peptide bonds.26

pleomorphic distinguished by having more than one form during a life cycle.1

prenylation the enzymic addition of prenyl moieties to proteins as a post-translational modification.

prevalence is the number of instances of infections or of persons ill, or of any other event such as accidents, in a specified population, without any distinction between new and old cases.26

prophylaxis is the prevention of disease, or the preventive treatment of a recurrent disorder.26

protein large molecule made up of many amino acids chemically linked together by amide linkages. Biologically important as enzymes, structural protein and connective tissue.

prothrombin time a test used to measure the activity of clotting factors I, II, V, VII, and X. Deficiency of any of these factors leads to a prolongation of the prothrombin time. The test is basic to any study of the coagulation process, and it helps in establishing and maintaining anticoagulant therapy.

reverse transcriptase RNA-directed DNA polymerase. Enzyme that synthesizes DNA according to instructions given by an RNA template.

ribozyme an RNA molecule with catalytic activity.

RT-PCR reverse transcriptase - polymerase chain reaction. A technique commonly employed in molecular genetics through which it is possible to produce copies of DNA sequences rapidly.

self-limited denoting a disease that tends to cease after a definite period; e.g., pneumonia.3

sense and antisense strands of the two strands that comprise the double helix of a DNA molecule, only sense strand contains a sequence of nucleotides that can be read out to form a protein. The complementary strand, termed the antisense strand, has a sequence of nucleotides that, if read out, would give either a garbled or a totally lacking messenger RNA.2 An artificial, antisense, single stranded RNA molecule of messenger RNA or of some other specific RNA transcript of a gene can hybridize with the specific RNA and thus interfere with the latter's actions or reactions.

serum is the clear, slightly yellow fluid which separates from blood when it clots. In composition it resembles blood plasma, but with fibrinogen removed. Sera containing antibodies and antitoxins against infections and toxins of various kinds (antisera) have been used extensively in prevention or treatment of various diseases.26

titre a measure of the concentration or activity of an active substance.

translation the process of forming a specific protein having its amino acid sequence determined by the codons of messenger RNA. Ribosomes and transfer RNA are necessary for translation.1

vaccine an antigenic preparation used to produce active immunity to a disease to prevent or ameliorate the effects of infection with the natural or "wild" organism. Vaccines may be living, attenuated strains of viruses or bacteria which give rise to inapparent to trivial infections. Vaccines may also be killed or inactivated organisms or purified products derived from them. Formalin-inactivated toxins are used as vaccines against diphtheria and tetanus. Synthetically or genetically engineered antigens are currently being developed for use as vaccines. Some vaccines are effective by mouth, but most have to be given parenterally.1, 26

viremia the presence of viruses in the blood, usually characterized by malaise, fever, and aching of the back and extremities.4

virion a structurally complete virus, a viral particle.1

viroid any of a class of infectious agents consisting of a single-stranded closed circular RNA lacking a capsid. The RNA does not code for proteins and is not translated; it is replicated by host cell enzymes. Viroids are known to cause several plant diseases.

virus any of a number of small, obligatory intracellular parasites with a single type of nucleic acid, either DNA or RNA and no cell wall. The nucleic acid is enclosed in a structure called a capsid, which is composed of repeating protein subunits called capsomeres, with or without a lipid envelope. The complete infectious virus particle, called a virion, must rely on the metabolism of the cell it infects. Viruses are morphologically heterogeneous, occurring as spherical, filamentous, polyhedral, or pleomorphic particles. They are classified by the host infected, the type of nucleic acid, the symmetry of the capsid, and the presence or absence of an envelope.1

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