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Disease in the Developing World

Glossary

GENERAL TERMS

Abortive infection
When a virus infects a cell (or host) but cannot complete the full replication cycle, i.e. a non-productive infection.

Acute infection
Relatively brief infections, i.e. a few days to a few weeks, following which the virus is usually eliminated completely from the body by the immune system.

Aerobic
Growing or thriving only in the presence of oxygen.

Aerosol transmission
A cloud or mist of solid or liquid particles containing pathogenic microorganisms, released by sneezing or coughing.

Amino acid
Any of a group of 20 molecules that are combined to form proteins in living organisms. The sequence of amino acids in a protein, and hence protein function, is determined by the DNA sequence of genes in chromosomes.

Analgesic
A drug that relieves pain.

Antibiotic
A substance either derived from a mold or bacterium or produced synthetically that inhibits or kills certain microorganisms, specifically bacteria, to treat infections.

Antibody
Any of a large number of large proteins produced by the immune system, in response to an antigen, which the antibody then neutralizes, tags or destroys. A protein molecule in the blood serum or other body fluids that destroys or neutralizes bacteria, viruses or other harmful toxins. Antibody production occurs in response to the presence of an antagonistic, usually foreign substance (antigen) in the body. Antibodies are members of a class of proteins known as immunoglobulins that are produced and secreted by B-lymphocytes in response to stimulation by an antigen. The antigen/antibody reaction forms the basis of humoral, or non-cellular, immunity.

Antigen
A substance, usually a protein or carbohydrate, that when introduced into the body stimulates the production of an antibody. Antigens include toxins, molecules on the surface of bacteria, foreign blood cells and the cells of transplanted organs.

Arbovirus
Any of a large group of viruses transmitted by arthropods, such as mosquitoes and ticks, that includes the causative agents of encephalitis, yellow fever and dengue.

Asexual reproduction
A type of reproduction in which an organism replicates itself, by budding or dividing, without the involvement of other organisms.

Assembly
The stage of viral replication during which all the structural components come together at one site in the cell, and the basic structure of the virus particle is formed.

Asymptomatic
To be without noticeable symptoms of disease.

Attachment (viral)
The binding of a virus particle to a specific receptor on the surface of a host cell in the process of infection.

Autoimmune disease
Any of a large group of diseases characterized by abnormal functioning of the immune system that causes the production of antibodies against the body's own tissues.

Autotrophs
Microorganisms that use inorganic materials as sources of nutrients.

Bacterium
A single-celled microscopic organism.

Binary fission
A form of asexual reproduction in which a cell divides into two daughter cells after DNA replication.

Budding
A form of asexual reproduction in which a bud or outgrowth from the end or side of the parent cell emerges and develops into a new organism.

Capsid
A protein shell comprising the main structural unit of a virus particle; may stimulate the body's immune system.

Capsomeres
Repetitive protein subunits which form the viral capsid; often arranged in a symmetric pattern.

Carrier
Organism that carries a virus either in the form of an infection or while it is in incubation.

Chemolithotrophs
Organisms which obtain their energy from the oxidation of inorganic compounds.

Chemostat
An apparatus designed to grow bacteria indefinitely, while keeping the conditions and the colony size constant, by having a continuous flow of liquid nutrient wash the colony and steadily remove bacteria.

Chromosome
Linear body in the cell nucleus that carries the cell's genes.

Chronic infection
The converse of an acute infection, i.e. prolonged and stubborn. Caused by viruses which are able to persist in the body.

Complement
A group of more than 30 proteins that act together to enhance the actions of other immune defense mechanisms of the body.

Encephalitis
Inflammation of the brain.

Endemic
A disease that is constantly present to a greater or lesser degree in people of a certain class or in people living in a particular location.

Enterovirus
Any of a subgroup of viruses that infect the gastrointestinal tract and often spread to other areas of the body, especially the nervous system.

Envelope, viral
A lipid membrane enveloping a virus particle.

Epidemic
A widespread outbreak of an infectious disease in which many people are infected at the same time.

Epidemiology
The branch of medical science dealing with the incidence, distribution and control of disease in a population.

Extremophiles
Organisms, typically bacteria, that are adapted to living in extreme conditions, such as in salt, ice or thermal springs.

Fusion protein
The protein(s) on the surface of a virus particle responsible for fusion of the virus envelope with cellular membranes.

Gene expression
The transcription of genetic information from the DNA gene to a messenger RNA molecule, for ultimate translation into a protein.

Genome
The genetic material of an organism.

Genome replication
The stage of cellular replication at which the genome is copied to form new progeny genomes.

Germ theory
The medical theory that infectious diseases result from the action of microorganisms.

Haemagglutination-inhibition
An assay used for certain types of viruses which are able to agglutinate red blood cells. Haemagglutination-inhibition records blocking of this process by antibodies and thus the presence of antibodies against the virus.

Heterotrophs
Microorganisms which require carbon dioxide and other organic compounds for their nutrition and energy needs.

Humoral immunity
The branch of the immune system in which antibodies are produced in response to a foreign antigen.

Immunity, adaptive
The slower-acting component of the immune system that confers specific immunity against a pathogen such as a virus. Adaptive, or acquired immunity is triggered by vaccines. Also called cell-mediated immunity.

Immunity, innate
The rapid-responding non-specific component of the immune system that responds to invading microorganisms and other pathogens. Also called humoral immunity.

Immunomodulator
Any substance that influences the immune system.

Immunosuppression
Damage to the immune system induced by drugs or resulting from certain disease processes, such as HIV infection.

Inflammatory disease
Disease with inflamed tissue, characterized by pain, swelling, redness and heat.

Inoculum
Cells added to start a culture or, in the case of viruses, viruses added to infect a culture of cells. Also, biological material injected into a human to induce immunity (a vaccine).

Latent infection
Viruses that can down-regulate their gene expression to establish a latent state, with strictly limited gene expression and without ongoing virus replication. Latent virus infections typically persist for the entire life of the host.

Lymphocyte
A white blood cell present in the blood, lymph and lymphoid tissue. The two major types are T cells and B cells.

Lymphoedema
Swelling of the subcutaneous tissues caused by obstruction of the lymphatic drainage. It results from fluid accumulation and may arise from surgery, radiation or the presence of a tumor in the lymph nodes.

Macrophage
A large scavenger immune cell that ingests degenerated cells, blood tissue and foreign particles, and secretes messenger proteins (monokines) involved in inflammatory reactions, lymphocyte activation and acute systemic immune responses.

Mastitis
Inflammation of breast tissue.

Matrix protein
A structural protein of a virus particle which underlies the envelope and links it to the core.

Maturation
The stage of viral replication at which a virus particle becomes infectious.

Miasmatist
One who has made a special study of infectious particles or germs floating in the air.

Molecular epidemiology
The use of nucleotide sequence information to study the diversity and distribution of microbial populations.

Myoclonus
A sudden twitching of muscles or parts of muscles, without any rhythm or pattern, occurring in various brain disorders.

Nematode
Roundworm that can cause a variety of diseases, including filariasis, ascariasis, and trichinosis.

Neutralization
Blocking of virus infection by antibodies; also, an assay which measures this.

Nucleocapsid
The core of a virus particle consisting of the genome plus a complex of proteins.

Opportunistic infection
An infection in an immune-compromised person caused by an organism that does not usually cause disease in healthy people. Many of these organisms are carried in a latent state by virtually everyone and only cause disease when given the opportunity of a damaged immune system.

Outbreak
The occurrence of a large number of cases of a disease in a short period of time.

Pandemic
An epidemic that affects multiple geographic areas at the same time.

Paramyxovirus
Any of a group of viruses that contain RNA and are similar to but larger and more variable in size than the related myxovirus. The paramyxoviruses include the Sendai virus, the parainfluenza viruses, and the viruses that cause measles and mumps.

Pasteurization
Partial sterilization of food at a temperature that destroys harmful microorganisms without major changes in the chemistry of the food.

Pathogen
Any disease-producing agent; i.e. virus, bacteria or other microorganism.

Penetration
The stage of viral replication at which the virus genome enters the cell.

Persistent infection
Infections in which ongoing virus replication occurs, but the virus adjusts its replication and pathogenicity so as to avoid killing the host. Persistent infections differ from chronic infections in that in chronic infections, the virus is usually eventually cleared by the host (unless the infection proves fatal); but in persistent infections, the virus may continue to be present and to replicate in the host for its entire lifetime.

Phage
A virus for which the natural host is a bacterial cell.

Phototrophs
Bacteria capable of using light energy for metabolism.

Plasmid
Autonomously replicating extra-chromosomal circular DNA molecules, distinct from the normal bacterial genome and nonessential for cell survival under nonselective conditions. Some plasmids are capable of integrating into the host genome. A number of artificially constructed plasmids are used by researchers to carry foreign genes into cells.

Polypeptide
A short chain of amino acids, in contrast to a protein, which is a much longer amino acid chain.

Prions
An infective group of complex proteins suggested as the causative agents of infectious human diseases such as Creutzfeldt-Jakob disease and kuru, and the animal diseases, scrapie and bovine spongiform encephalopathy, or "mad cow disease."

Prophylactic
Preventive measure or medication.

Provirus
Viral genetic material, in the form of DNA, that has been integrated into the host genome. HIV, when it is dormant in human cells, is in a proviral form.

Receptor
A specific protein on the surface of a cell used by external signaling molecules such as hormones to elicit a cellular response. Also used by viruses as an attachment point for infecting cells.

Release, viral
The stage of viral replication at which virus particles escape the infected cell.

Reservoir host
A host that carries a pathogen without injury to itself and serves as a source of infection for other host organisms.

Retrovirus
Any of a group of viruses that carries its genetic information in the form of RNA, rather than DNA. These viruses use their RNA to synthesize DNA, the reverse of the usual flow of genetic information.

Serotype
A group of closely related microorganisms distinguished by a characteristic set of antigens.

Serum
The clear, thin fluid portion of the blood which remains after coagulation; antibodies and other proteins are found in the serum.

Subcutaneous tissues
Tissues that are just beneath the skin.

Symbiotic
The relationship between two interacting organisms or populations.

T cells
Thymus-derived white blood cells (lymphocytes) that participate in a variety of cell-mediated immune responses.

T-cytotoxic cells
A subset of T lymphocytes that directly kills foreign cells, especially virally infected host cells.

T-helper cells
A subset of T lymphocytes that normally orchestrates the immune response by signaling other cells in the immune system to perform their special functions.

Trematode
Any of numerous flatworms of the class Trematoda, including both external and internal parasites of animal hosts, that have a thick outer cuticle and one or more suckers or hooks for attaching to host tissue. Also called a fluke.

Tropism
The ability of a virus to infect specific cell or tissue types.

Uncoating
The stage of viral replication at which structural proteins are lost and the virus genome is exposed to the replication machinery.

Vaccine
A substance that contains antigenic components, either weakened, dead or synthetic, from an infectious organism that produces active, or acquired, immunity against that organism.

Vector
An organism, such as a mosquito or tick, that carries disease-causing microorganisms from one host to another.

Viremia
The presence of viruses in the bloodstream.

Virions
Structurally mature, extracellular virus particles.

Virus attachment protein
The protein on the surface of a virus particle responsible for binding to the receptor.

Virus
A noncellular biological entity that can reproduce only within a host cell. Viruses consist of nucleic acid covered by protein; some animal viruses are also surrounded by membrane. Inside the infected cell, the virus commandeers the genetic machinery of the host to produce progeny virus.

Zoonotic disease
A disease of animals, such as rabies or psittacosis, that can be transmitted to humans.


DISEASES

African Trypanosomiasis
Also known as sleeping sickness, a vector-borne parasitic disease, transmitted by the tsetse fly, which occurs only in sub-Saharan Africa.

AIDS (acquired immunodeficiency syndrome)
The disease caused by HIV, or human immunodeficiency virus, which is passed from one person to another through blood-to-blood and sexual contact.

Chagas disease
A vector-borne parasitic disease, transmitted by triatomine insects, which exists only on the American continent, in an area ranging from Mexico to the south of Argentina.

Chickenpox
Also known as varicella disease, a highly contagious infectious disease caused by the varicella-zoster virus, which is relatively benign in children but may be complicated by pneumonia and encephalitis in adults.

Cholera
An acute intestinal infection caused by the bacterium Vibrio cholerae, which is usually spread through contaminated food and water supplies. Symptoms include watery diarrhea, vomiting and leg cramps. Cholera may lead to dehydration, shock and ultimately death.

Creutzfeldt-Jakob Syndrome
A rare and fatal human neurodegenerative condition that occurs worldwide. It may be inherited or associated with the use of contaminated corneal transplants, electrode implants, dura mater grafts or receipt of human growth hormone.

Dengue
A mosquito-borne infection caused by one of four closely related virus serotypes of the genus Flavivirus, which is endemic in urban and semi-urban areas of the tropics and sub-tropics.

Diphtheria
A globally occuring infectious disease, which is spread from person to person by respiratory droplets from the throat through coughing and sneezing. It can lead to breathing problems, heart failure, paralysis and sometimes death.

Dracunculiasis
More commonly known as Guinea worm disease, a preventable infection caused by the parasite Dracunculus medinensis. It affects poor rural communities lacking safe water supplies in sub-Saharan Africa.

Dysentery
An infection of the gut caused by Shigella bacteria, which causes stomach pains and diarrhea. It is spread through contaminated food and water, as well as person-to-person contact.

Ebola
A severe, often-fatal disease caused by the Ebola virus that has appeared sporadically in the Democratic Republic of the Congo, Gabon, Sudan, the Ivory Coast, Uganda and the Republic of the Congo since its initial recognition in 1976.

Filarial Elephantiasis
Also known as elephantiasis, a disease caused by parasitic worms, including Wuchereria bancrofti, Brugia malayi, and B. timori, all transmitted by mosquitoes. Symptoms include excessively enlarged arms, legs, genitalia and breasts.

Helminthiasis
An infection by a parasitic worm (a helminth), which can be in the intestines, under the skin or in the general area of the gut.

Hepatitis
Meaning "inflammation of the liver," it is generally caused by infection with one of five viruses, called hepatitis A,B,C,D and E.

Iodine deficiency
This condition, caused by insufficient iodine intake, mainly affects poor, preschool children and pregnant women living in iodine-deficient areas of Africa and Asia. In children, it decreases survival rates, causes goiters and impairs growth and development; in pregnant women it causes miscarriages, stillbirths and other complications.

Lassa fever
An acute viral illness occurring only in West Africa, which is mild or has no observable symptoms in some people, but causes a severe multi-system disease in others.

Leishmaniasis
A parasitic disease transmitted by the bite of some species of sand flies, which occurs in the tropical and subtropical world as well as southern Europe. It most commonly manifests either in a cutaneous (skin) or visceral (internal organ) form.

Leprosy
A chronic bacterial disease of the skin and nerves in the hands and feet and, in some cases, the lining of the nose. Relatively rare, it is found mainly in Brazil, India, Madagascar, Mozambique, Nepal and the United Republic of Tanzania.

Lymphatic filariasis
A parasitic disease, caused by microscopic, thread-like worms that take up residence in the human lymph system, which affects people in countries in the tropics and sub-tropics of Asia, Africa, the Western Pacific, the Caribbean and South America.

Malaria
A life-threatening parasitic disease transmitted by mosquitoes, which affects millions of people throughout the world.

Measles
Also called rubeola, an acute, highly communicable viral disease that is widespread in many developing countries. It is characterized by a skin rash, as well as a range of respiratory and other symptoms.

Meningitis
An infection of the meninges, the thin lining that surrounds the brain and the spinal cord. Several forms of this disease, which is transmitted from person to person, are common among children in Sub-Saharan Africa.

Mumps
An acute viral disease characterized by fever, swelling and tenderness of one or more of the salivary glands.

Onchocerciasis
A disease caused by nematode Onchocerca volvulus, which is transmitted by the bite of certain species of female Simulium, or black, flies. It occurs most frequently in central Africa but is also present in Yemen, Brazil, Colombia, Ecuador, Guatemala, southern Mexico and Venezuela.

Pertussis
Also known as whooping cough, a highly contagious acute bacterial disease caused by Bordetella pertussis, which affects the respiratory tract, sometimes causing the infected person to gasp for air between coughing spells with a characteristic "whooping" sound.

Plague
Mainly a rodent disease, it is transmitted from rodents to humans by rodent flea bites. Endemic in many countries in Africa, the Americas and Asia, it may be fatal if left untreated.

Poliomyelitis
More commonly known as polio, a highly infectious viral disease which may affect the central nervous system, causing paralysis and even death. Due to a global effort to eradicate the disease though vaccination, polio is now relatively rare and found only in parts of Africa and south Asia.

Rabies
A zoonotic viral disease, transmitted to humans though close contacts with saliva from infected domestic and wild animals, which causes respiratory, gastrointestinal and/or central nervous system symptoms. Once symptoms of the disease develop, it is fatal in both animals and humans.

Rift Valley fever
An acute, fever-causing viral disease that affects domestic animals and humans and occurs in eastern and southern Africa, Madagascar, Saudi Arabia and Yemen.

Rotavirus
A virus that infects the lining of the intestine and is the leading cause of diarrheal disease and dehydration among infants in both developed and developing countries.

Rubella
Also called German measles, an infection caused by the rubella virus which affects the skin and lymph nodes. It is generally mild in children, but when transmitted to an unborn child through its pregnant mother, it may cause serious birth defects or death.

Schistosomiasis
Also known as bilharziasis, a parasitic disease caused by five species of water-borne flatworm, or blood flukes, called schistosomes.

Severe acute respiratory syndrome (SARS)
A viral respiratory illness that was first reported in Asia in February 2003.

Shigellosis
An infectious disease, endemic throughout the world, which is caused by a group of bacteria called Shigella, and which causes diarrhea, fever and stomach cramps.

Smallpox
A serious, contagious and sometimes fatal infectious disease, which is characterized by raised bumps appearing on the face and body of an infected person. Eradicated through a global vaccine program, the last naturally occurring case occurred in Somalia in 1977.

Tetanus
A globally occurring disease, commonly called lockjaw, which is contracted through a cut or wound that becomes contaminated with tetanus bacteria and subsequently affects the nervous system.

Trachoma
An infection of the eye, caused by the bacterium Chlamydia trachomatis, which can lead to blindness. It affects poor communities in Africa, Asia, and the Middle East and in some parts of Latin America and Australia.

Tuberculosis
A disease caused by the bacterium Mycobacterium tuberculosis, which usually attack the lungs.

Typhoid fever
A life-threatening illness caused by the bacterium Salmonella Typhi. Common in parts of the developing world, it is usually spread through contaminated food and water.

Varicella Disease
Also known as chickenpox, a highly contagious infectious disease caused by the varicella-zoster virus, which is relatively benign in children but may be complicated by pneumonia and encephalitis in adults.

Vitamin A deficiency
A public health problem in many areas of Africa and South-East Asia, this condition, caused by an insufficient supply of Vitamin A, is associated with blindness in children, increased risk of mortality and night blindness among pregnant women, and increased risk of disease and death from severe infections among the general population.

Whooping cough
Also known as Pertussis, a highly contagious acute bacterial disease caused by Bordetella pertussis, which affects the respiratory tract, sometimes causing the infected person to gasp for air between coughing spells with a characteristic "whooping" sound.

Yellow fever
A disease, caused by the yellow fever virus, which occurs in East and West Africa and South America. Symptoms range from mild illness to death.


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