A mechanism through which certain cells can increase the rate in which genetic mutations occur, often in response to stress. This mechanism may help explain how bacteria develop resistance to certain antibiotics.

A condition in which there is a deficit in the number of healthy red blood cells in the blood, resulting in fatigue and feelings of weakness.

The process through which pathogenic microorganisms, by way of genetic mutation, develop the ability to withstand exposure to the drugs that had once been successful in eradicating them.

A class of drugs used to kill or inhibit the growth of disease-causing microorganisms. Typically antibiotics are used to treat infections caused by bacteria, but in some cases they are also used against other microorganisms, such as fungi and protozoa.

A class of drugs used to kill or inhibit the growth of disease-causing microorganisms. Typically antibiotics are used to treat infections caused by bacteria, but in some cases they are also used against other microorganisms, such as fungi and protozoa.

An umbrella term for a range of conditions in which the immune system mistakenly attacks healthy tissue in the body.

A taxonomic class of bacteria.

A large group of unicellular microorganisms that lack a cell nucleus. Some bacteria are pathogenic and harmful to humans, some have no effect at all on humans, and some are beneficial.

One of several families of antibiotics, including penicillins, cephalosporins, carbapenems, and monobactams, containing a molecular ring-shaped structure made up of three carbon atoms and one nitrogen atom.

A bacterium, virus, or other biological toxin used in bioterrorism or biological warfare.

The deliberate release of a virus, bacterium, or other biological agent to cause illness and death in people, animals, or plants.

A bacterium, virus, or other biological toxin used in bioterrorism or biological warfare.

Large tubes that carry air into smaller branches of the lungs after the air has passed through the mouth, nasal passages, and windpipe.

A class of diseases in which abnormal cells divide without control and are able to invade healthy tissues in various parts of the body.

A class of biological agents that the Centers for Disease Control and Prevention views as posing the highest priority risk to U.S. national security.

The smallest unit of living matter capable of functioning independently.

A semipermeable barrier that separates the interior of a cell from the external environment.

A federal agency under the U.S. Department of Health and Human Services that works with partners across the United States to ensure public health—through health promotion; prevention of disease, injury, and disability; and preparedness for new health threats.

An organized structure of DNA and proteins within the nucleus of a cell that contains many genes.

Any disease that is long lasting (3 months or more) or recurrent—as opposed to an acute disease—and cannot be prevented by a vaccine or cured by medication.

A prolonged form of localized immune response to harmful agents and damaged tissue that is characterized by redness, swelling, heat, pain, and/or loss of function.

A condition caused by chronic liver disease characterized by the development of scar tissue leading to a loss of liver function.

The process of shifting from one prevailing state in regional or global climate to another. Climate change is typically the preferred term over “global warming” because it helps to convey that the characteristics of climate change are not limited to rising temperatures.

A general term for any disease-causing infectious agent spread by direct or indirect contact.

A type of protein secreted by cells in the immune system that carries signals  that facilitate cell-to-cell communication  and help regulate the way the immune system responds to inflammation and infection.

Any abnormal condition  that affects all or part of an organism, resulting in symptoms such as pain or loss of function.

Short for deoxyribonucleic acid, DNA is any of the nucleic acids that contain the genetic instructions necessary for the development and functioning of all living organisms as well as some viruses.

A branch of science that deals with the relation of organisms to one another and their physical environment.

A functional unit that consists of all the living organisms in a particular area, as well as the nonliving, physical components in the environment—such as air, soil, water, and sunlight—with which the organisms interact, and how natural and human-made changes affect these interactions.

The female gamete, or sex cell, which carries the hereditary material of the female parent and unites with the male sperm cell during sexual reproduction.

Inflammation of the brain, often caused by a virus.

The baseline level of disease usually present in a community.

An often sudden increase in the level of disease in a specific population over a given period of time.

The change in heritable traits in a population of organisms over successive generations.

An external skeleton that protects and supports an organism, in contrast to an internal endoskeleton.

Sometimes referred to as a zygote, this is the resulting initial cell formed when a sperm cell unites with an egg cell.

A taxonomic kingdom of spore-forming organisms distinct from plants, animals, and bacteria that includes microorganisms such as yeast and molds, as well as mushrooms.

The structure in the body, beginning with the mouth and extending to the anus, through which food is ingested, broken down, and absorbed to provide the body with nutrients, and waste products are excreted.

The physical and functional unit of heredity made up of DNA. Every individual has two copies of each gene, one inherited from the mother and the other from the father.

A branch of biology that studies heredity and variation in organisms.

In the context of microbiology, a microorganism that causes disease.

A theory in medicine stating that microorganisms are the causative agents of infectious, contagious diseases.

The process by which regional economies, societies, and cultures are becoming integrated through a global network of trade, migration, communication, and the spread of new technology.

The specific geographical area or physical environment that is inhabited by an organism or a population of organisms.

An organism that harbors a parasite or another organism where there is a symbiotic relationship between the two organisms. In some cases, the relationship is commensal, or mutually beneficial, but in the case of a parasite and host, the host may be hurt by the parasite's presence.

The system of biological structures and processes that protects the body from foreign substances, including pathogens.

The process of strengthening the body’s defense against a particular infectious agent, often accomplished by receiving a vaccine.

The period of time between exposure to an infectious agent and the appearance of symptoms of the infection or disease it causes.

The entry, establishment, and replication of pathogens inside a host organism.

A type of illness caused by a pathogenic agent, including viruses, bacteria, fungi, protozoa, parasites, or abnormal proteins known as prions.

A type of protein produced by cells of the immune system that help keep viruses, bacteria, and cancer cells from growing.

The use of veins through which medications and solutions are administered.

An infection that is currently not producing or showing any symptoms but has the potential of being reactivated and then manifesting symptoms.

A broad group of molecules including fats and waxes that are insoluble in water and are an important part of living cells.

An infection of the protective membranes that cover the brain and spinal cord, known collectively as the meninges.

Sometimes referred to as a microorganism, a microbe is an organism that is microscopic and thus invisible to the naked eye. 

The relative occurrence of a disease or a condition that causes illness.

The number of deaths in a given time or place.

The moist linings of body passages and internal cavities involved with absorption and secretion of substances.

A change in the sequence of DNA in a cell’s genome that can be caused by radiation, viruses, certain types of chemicals, errors, or environmental factors that occur during cell division and DNA replication.

A unit of length equal to one one-billionth (1 x 10^-9) of a meter.

Part of the U.S. Department of Health and Human Services and the National Institutes of Health, NIAID conducts and supports basic and applied research to better understand, treat, and ultimately prevent infectious, immunologic, and allergic diseases.

The process by which certain heritable traits that contribute to the survival and reproductive success of an organism become more widespread within a population over successive generations.

Also called neurotoxins, these refer to poisonous substances that cause damage to cells in the nervous system.

A living being that can reproduce, grow, react to external stimuli, and maintain its internal equilibrium.

An unexpected increase in the incidence of a particular disease over a given time period and geographic range. A general term that may refer either to an epidemic or a pandemic.

An increase in the occurrence of a particular disease over a very large region, such as a continent or the entire globe, that is greater than what is expected over a given period of time.

A close relationship between two organisms in which one organism, the parasite, benefits at the expense of the host organism.

A biological agent that causes disease.

A ring of DNA usually found in bacteria that is separate from and can replicate independently from DNA in a chromosome and can provide bacteria with some advantages, such as antibiotic resistance.

Large molecules composed of one or more chains of amino acids in a specific order determined by the base sequence of nucleotides in the DNA coding.

A taxonomic group of single-celled microorganisms that live in almost every kind of habitat and include some pathogenic parasites of humans and other animals. 

The process that allows technicians to create artificial pieces of DNA in which two or more DNA sequences, often from separate organisms, are combined in ways that would not normally occur naturally.

The process of producing a copy of a strand of DNA.

An organism in which a parasite that is pathogenic for some other organism lives and reproduces without harming its host.

The part of the anatomy that has to do with the passage of air and includes the nose, larynx, trachea, and lungs.

An inflammatory disease that may be caused by an untreated or improperly treated case of strep throat.

A type of virus that is responsible for causing upper respiratory tract infections in humans, otherwise known as the common cold.

Short for ribonucleic acid, RNA is a molecule with long strands of nucleic acids containing a nitrogenous base, a ribose sugar, and a phosphate. RNA is responsible for controlling a number of chemical activities, including protein synthesis, within cells.

A serious mental illness characterized by the presence of hallucinations, delusions, disorganized speech or thinking, a loss of contact with reality, and a noticeable deterioration of functioning in everyday life.

Any abnormal tissue on the skin caused by injury or disease.

One of the most basic units of biological classification, ranking just below the genus and comprising individuals or populations capable of interbreeding.

The male gamete, or sex cell, which carries the hereditary material of the male parent and unites with the female egg cell during sexual reproduction.

An infection caused by any one of several harmful species or subspecies of bacteria of the genus Staphylococcus.

The process of destroying all forms of life, including infectious agents, from a surface, fluid, or biological medium with the use of heat, chemicals, irradiation, high pressure, filtration, or some combination of these methods.

A genetic variant or specific subtype of a microorganism, such as a virus or bacteria.

The process of land conversion and development around the periphery of major cities.

A subjective indication of the presence of disease or a departure from the body’s normal state of functioning. 

The process by which tissues are intentionally grown under controlled conditions.

A poisonous substance, often a protein, produced by the metabolic processes of living cells or organisms that can cause disease if introduced into the body.

The main trunk of the network of tubes that carries air to and from the lungs, sometimes referred to as the “windpipe.”

The area, sometimes referred to as an ecotone, encompassing the edges of two distinct ecosystems, such as the area where a forest intersects with grassland.

A vaccine that is effective against all forms of the influenza virus.

Disease of the organs involved in the excretion of fluids and reproduction.

A biological preparation that improves the immune system’s ability to recognize and destroy harmful infectious agents.

An organism (usually an arthropod such as a flea, mosquito, or tick) that carries an infectious agent from one host to another.

An infectious agent that is only capable of replicating itself inside the living cells of other organisms.

A special type of cell that works as part of the immune system to defend the body against disease and infection.

The directing and coordinating authority for health within the United Nations system, responsible for providing leadership on global health matters, shaping the health research agenda, setting norms and standards, articulating evidence-based policy options, providing technical support to countries and monitoring and assessing health trends.

A broad group of microscopic fungi that includes harmless forms of yeast used in baking and alcoholic fermentation as well as pathogenic species that can cause disease. 

Any disease that can be transmitted from vertebrate animals to humans.