Global Alert and Response (GAR)

Hepatitis A


Glossary

adjuvant any substance which, when mixed with an antigen, increases the immune response to that antigen.1

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.

alkaline phosphatase any of group of phosphatases showing activity at alkaline pH, which are normally measured collectively in blood serum. Serum levels are elevated in various conditions, among which hepatobiliary disorders.

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.

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

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 haemoglobin. 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.46

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

cholestasis impairment of bile flow at any level from the canaliculus to the duodenum. The clinical condition resulting therefrom, characterised by icterus and pruritus, is due to the accumulation in blood and tissues of substances normally secreted in bile, particularly bilirubin, bile salts, and cholesterol.1

complete blood count chemical analysis of various substances in the blood performed with the aim of a) assessing the patient's status by establishing normal levels for each individual patient, b) preventing disease by alerting to potentially dangerous levels of blood constituents that could lead to more serious conditions, c) establishing a diagnosis for already present pathologic conditions, and d) assessing a patient's progress when a disturbance in blood chemistry already exists.

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).

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.46

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 matter and are involved in all the metabolic processes upon which life depends.46

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 prevalence. 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.46

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.46

genotype the genetic constitution of an individual.

hepatocytes are liver cells.1

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

icterus jaundice.1

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.

immunocompetent capable of responding immunologically to an antigen, as by producing antibodies or by developing cell-mediated immunity.1

immunodominant describing those epitopes in a molecule, or those components in an antigenic mixture, to which an immune response is produced preferentially.1

immunogenic capable of eliciting an immune response.

immune globulin (IG): is a sterile preparation of concentrated antibodies (immune globulins) 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.46

jaundice a yellow discoloration of the skin and mucous membranes due to excess of bilirubin in the blood, also known as icterus.46

lymphocyte a leukocyte of blood, bone marrow and lymphatic tissue. Lymphocytes play a major role in both cellular and humoral immunity, and thus 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

monoclonal antibodies preparations containing only one kind of antibody molecules, with specificity for a single antigen.Monoclonal antibodies are of great therapeutic and diagnostic potential.46

necrosis death of tissue.46

peptide a compound of two or more amino acids linked together by peptide bonds.46

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

prevalence 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.46

prodrome an early symptom suggestive of the onset of an attack or disease; a premonitory event.1

prophylaxis the prevention of disease, or the preventive treatment of a recurrent disorder.46

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.

pruritus itching

self-limited denoting a disease that tends to cease after a definite period; e.g., pneumonia.2

seroconversion the production in a host of specific antibodies as a result of infection or immunization. The antibodies can be detected in the host's blood serum following, but not preceding, infection or immunization.1

serotype a subdivision of a species or subspecies distinguishable from other strains therein on the basis of antigenic character.2

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.46

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

urobilinogen also called stercobilinogen. A colourless, reduced form of stercobilin, in which the pyrrole rings are joined by -CH2- groups. It is oxidized by air to the coloured stercobilin.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, 46

vaccinee person receiving a vaccine.

viremia the presence of viruses in the blood.

virion a structurally complete virus, a viral particle.1

virosomes immunopotentiating reconstituted influenza virosomes (IRIVs) are safe, efficacious and easily prepared carrier systems for small virion particles, such as HAV. IRIVs are spherical, unilamellar vescicles, with a diameter of about 150 nm, that combine components like haemagglutinin, neuraminidase and phospholipids of influenza virus and adsorbed HAV particles. The essential feature of IRIVs is that as well as the HAV antigen, their surface contains the fusion-inducing component haemagglutinin, which facilitates antigen delivery to immunocompetent cells. Most adults have been exposed to influenza haemagglutinin, and so IRIVs recruit primed cells leading to a rapid immune response.26

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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