Antibiotic Resistance: The process through which pathogenic microorganisms, by way of genetic mutation, develop the ability to withstand exposure to the drugs used to eradicate them.

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

Antibodies: A special type of protein found in the blood and bodily fluid that is used by the immune system to identify and neutralize foreign and harmful substances in the body, such as bacteria and viruses.

Autoimmune Disease: A condition in which the immune system mistakenly attacks healthy tissue in the body.

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.

Biological Agent: A bacterium, virus, prion, fungus, or other biological toxin that is used in bioterrorism or biological warfare.

Bioterrorism: The deliberate release of viruses, bacteria, or other biological agents to cause illness and death in people, animals, or plants.

Cell: The smallest unit of living matter capable of functioning independently.

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

Centers for Disease Control and Prevention (CDC): A federal agency under the 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.

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

Chronic Disease: Any disease that is long lasting or recurrent, as opposed to an acute disease.

Contagion: A general term for any disease-causing infectious agent.

Disease: Any abnormal condition in which cells in the body are damaged and symptoms of illness begin to appear.

DNA: 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.

Epidemic: An event that occurs when the incidence of new cases of a certain disease, over a given period of time, substantially exceeds what is expected in a specific population.

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

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

Gene: A specific sequence of nucleotides in either DNA or RNA that serves a functional unit of inheritance in a living organism, controlling the transmission and expression of one or more traits.

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

Host: An organism that harbors a parasite or another organism where there is a commensal or mutually beneficial relationship.

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

Immunization: The process of strengthening the body’s defense against a particular infectious agent.

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

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

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

Latent Infection: A type of persistent viral infection in which the virus is not currently producing additional viral offspring, but could later be reactivated and begin producing copies of the virus without the host being re-infected.

Metabolism: The sum total of chemical reactions that occur within a living cell both to build new molecules within the cell and break down and assimilate sources of energy for the cell.

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

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

Mortality: The number of deaths in a given time or place.

Mucous Membrane: A special membrane full of mucous glands which lines body passages and internal cavities involved with absorption and secretion of substances.

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

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

Organism: A living being.

Outbreak: 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.

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.

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

Pathogen: A biological agent that causes disease.

Plasmid: A ring of DNA usually found in bacteria that is separate from and can replicate independently from DNA in a chromosome.

Public health: An organized activity of society to promote, protect, improve, and when necessary, restore the health of individuals, specified groups, or the entire population. It is a combination of sciences, skills, and values that function through collective societal activities and involve programs, services, and institutions aimed at protecting and improving the health of all people. The term “public health” can describe a concept, a social institution, a set of scientific and professional disciplines and technologies, and a form of practice. It is a way of thinking, a set of disciplines, an institution of society, and a manner of practice. It has an increasing number and variety of specialized domains and demands of its practitioners an increasing array of skills and expertise.

Prion: A causative agent of infectious disease that is composed primarily of protein.

Protein: A type of complex organic compound made up of amino acids linked together by peptide bonds that performs a variety of essential functions in living organisms.

Protozoa: 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. 

Reproduction: The process by which parent organisms create new offspring by either sexual or asexual means.

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

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

RNA: Short for ribonucleic acid, RNA is a type of single-stranded molecule of nucleic acids that contains ribose and is responsible for controlling a number of chemical activities within cells.

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

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

Sterilization: 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.

Strain: A genetic variant or specific subtype of microorganism or virus.

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

Universal Flu Vaccine: A vaccine that is effective against all forms of the influenza virus.

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

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

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

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

World Health Organization (WHO): 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.

Yeast: 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.

Zoonoses: Any disease that can be transmitted from non-human animals to humans.