When an antibiotic has lost its ability to effectively control or kill bacteria, the bacteria are considered "resistant.” These bacteria continue to multiply even in the presence of therapeutic levels of an antibiotic. Bacteria become resistant through a genetic mutation or by acquiring the resistance from another bacterium. Every time a person takes antibiotics, sensitive bacteria (bacteria that antibiotics can still attack) are killed, but resistant bacteria survive. The number of drug-resistant bacteria can increase in the environment if an antibiotic is overused.
“Antigenic” drift and shift
Often used when discussing flu virus because it is among the fastest mutating viruses on the planet. As part of its evolutionary process, viruses mutate to try to escape the immune system. As the virus copies itself, its mix of genes can change slightly. This is called “antigenic” drift. Because the new virus is still mostly like the previous version, people usually have some immunity to a virus that has “drifted.” When the numbers of gene “drifts” start to pile up, the virus can become significantly different from its predecessor. This is called antigenic “shift.” When a virus “shifts,” humans have more vulnerability to becoming sick because their immune system doesn’t recognize it.
Single-celled microorganisms that don’t require living hosts. They come in many different shapes and thrive in diverse environments including extreme heat and cold. They live in soil, oceans and the human gut. Bacteria are classified by the makeup of their cell walls and are identified by a Gram stain. Hence the term, a “Gram-positive,” or “Gram-negative” bacteria. Some bacteria share space and resources in our body and are beneficial to human health. Other bacteria cause infections and disease.
A form of terrorism involving the deliberate release of biological agents, such as a virus or bacteria, or toxins to injure or kill people, with the aim of furthering personal or political agendas. This is also called germ warfare. Bioterrorism differs from other methods of terrorism in that all that is needed to turn biological material into a weapon is determination and access to medical supplies or a laboratory. Further, unlike other forms of terrorism, if a bioweapon was unleashed, it could be days or weeks before the attack is known. This means that initial victims could be incubating a disease and then carrying and spreading it to all parts of the U.S. and world before it could be stopped.
The term referring to a disease that is spread by direct physical contact between people or animals. Direct physical contact includes items that the ill individual may have touched, coughed or sneezed on. All diseases are infectious, meaning they are contracted in the environment. But not all of those diseases can be spread to other humans or animals. A person can be infected but non-contagious. Only a disease that can spread via direct contact is considered contagious. Some examples of contagious diseases are smallpox and influenza.
Disease X stands for an “unexpected” disease. The World Health Organization declared in 2018 that Disease “X” was among the diseases it most worries about because it has no medical countermeasures to treat. It stands for an unknown bacteria, or virus that might be lurking in animals or humans, with the potential to suddenly become virulent and contagious, spreading around the world.
A scientist who studies how animals and plants interact with the environment. Disease ecologists study the interactions between pathogens (i.e., bacteria, viruses, and fungi) or parasites (i.e protozoa) and their human and non-human hosts. This work is important because the majority of human infections originate in animals and the environment. Outbreaks are often caused by changes in the interactions between pathogens, humans, animals and the environment.
In biology, an endemic species is one that is native to specific regions, such as the kangaroo being endemic to Australia. The cane toad, on the other hand, was a species introduced to Australia and hence was not endemic (though it is now). In epidemiology, endemic refers to the circulation of a disease within a certain population or geographic area that continues without outside interference or introduction. Once a disease has been eliminated from a geographic region, such as a continent, it is no longer endemic to that region.
The term for a disease of the intestine. It is commonly used in reference to pathogens that have been ingested and produce chemical or allergic reactions. Among bacteria that can cause an enteric infection are Escherichia coli (E. Coli), Vibriocholerae (cholera), Salmonella and Shigella. The pathogen generally causes diarrhea, abdominal discomfort, nausea, vomiting and significant loss of fluid.
A group of cases of a specific disease or illness clearly more than what one would normally expect in a particular geographic area. There is no absolute criterion for using the term epidemic; as standards and expectations change, so might the definition of an epidemic, such as an epidemic of violence.
Scientists who study the causes, patterns, frequency and locations of diseases, and use the information to prevent future outbreaks. Epidemiologists are considered “disease detectives” in the public health world and provide the scientific basis for evidence-based medicine.
The cause of a disease or condition; most often etiology refers specifically to the biological mechanisms underpinning a particular condition.
Bacteria are classified based on a chemical stain that can be seen through the microscope. The Gram stain test was developed by Hans Christian Gram in the late 1800’s. He found that when he stained some bacteria turned purple under the microscope. These were called “gram-positive.” Other bacteria didn’t turn purple and appeared pinkish or red under the microscope. These were called “gram-negative.”
Whether the stain attaches to the bacteria or not, is related to its structure. Gram positive bacteria, like those that cause strep throat or many skin infections, have a thick wall made out of a protein that retains the chemical in the purple dye. Gram negative bacteria, like those that cause cholera or urinary tract infections, has two protective walls, making it harder to penetrate, and doesn’t retain the purple dye.
A means of protecting a whole community from the spread of an infectious disease. The more people (a herd) that are immune from a disease, the better protected the entire community is from an outbreak of that disease. The most common modern way to achieve herd immunity is through vaccination. Each disease, depending upon how they spread, has a threshold, or the minimum number of individuals that need to be immunized to prevent an outbreak. Measles, for example, requires 95 percent of the population to be immunized to prevent an outbreak.
Incidence and prevalence
Incidence is the rate of newly diagnosed cases of a disease. Prevalence is the total number of cases of a disease existing in a population.
The relationship between incidence and prevalence depends on the contagiousness of the disease and the ability to treat it and prevent further spread. There can be a high number of diagnosed cases of a disease, but low prevalence because the disease is treated quickly. With a disease with a low cure rate, but maintenance treatment permits sustained survival, then incidence contributes to a continuous growth of prevalence.
Incidence may be a measure of how well surveillance and prevention measures for a disease are working while prevalence may be an indication of the effectiveness of treatment methods.
A disease that can be transmitted to other individuals. An infectious disease is a disease that is caused by the invasion of a host by agents whose activities harm the host's tissues and cause disease. Diseases are spread by direct person-to-person contact, such as through coughing, sneezing, sweating or sexual interaction. Fleas, mosquitos and other carriers (known as vectors) can spread disease when they bite animals with a disease and then bite humans.
This policy involves separating people known or suspected to be infected with a contagious disease from those who are not sick to prevent them from transmitting disease to others. The definition of “suspected” is based on whether the person is showing symptoms of a contagious disease or whether they met certain laboratory criteria demonstrating they have likely been infected.
The microbiome refers to the army of microbes - bacteria, viruses, yeasts and fungi - that live on and in the body. There are more than 10,000 of these microbial species in the body and they are vital to human health. Scientists are still trying to figure out why it is so important to health, and why sometimes these microbes can turn deadly to their human hosts. Read more.
Non-communicable diseases are illnesses that aren’t physically transmissible from person to person. No bacteria, virus or parasite has caused the illness. Non-communicable diseases are usually chronic health conditions, meaning they last three months or longer and can’t be prevented by vaccines or cured with medicine. Heart disease and diabetes are examples. Non-communicable diseases now cause more than 75 percent of the world’s deaths, according to the World Health Organization.
This term is usually used in reference to an infection acquired while under medical care, usually at a hospital. Many times the infection is caused by microbes that are resistant to antibiotics. A nosocomial infection is specifically one that wasn’t present or incubating prior to the patient’s being admitted to the hospital. Two common nosocomial infections are clostridium difficile (c. Diff) and methicillin-resistant staphylococcus aureus (MRSA). C. Diff is a bacteria that can cause diarrhea and dangerous inflammation of the colon. MRSA is a microbe that can cause dangerous skin and blood infections.
A disease outbreak is the occurrence of cases of a disease in excess of what would normally be expected in a defined community, geographical area or season. An outbreak may occur in a restricted geographical area or may extend over several countries.
The definition is subject to debate among public health officials and scientists, but generally it is an epidemic extending over a large geographic area involving a disease with a potentially high mortality rate that is spreading quickly from person-to-person.
Any organism that causes disease. Pathogens include bacteria, virus, and fungi. The body comes in contact constantly with pathogens, but the immune system usually destroys them before they cause harm. A person is considered exposed when they have been in contact with a pathogen and infected when the pathogen has entered the body and caused disease.
Prion diseases, also called transmissible spongiform encephalopathies (TSEs) are a family of rare brain disorders. The disease agent is believed to be a prion, which is a type of protein that can cause other normal brain proteins to fold abnormally and clump, thus creating holes in brain tissue. The disease usually evolves rapidly and is always fatal. There is no known cure to prion disease. Prions can be spread to humans through infected meat products or exposure to infected tissue. They can also be inherited. The most common form of prion disease that affects humans is Creutzfeldt-Jakob disease. In animals, it is Bovine Spongiform Encephalopathy, or mad cow disease. Prion diseases are rare. About 300 cases are reported a year in the U.S., according to Johns Hopkins Medicine Health Library.
Involves health authority separating and restricting the movement of people who have potentially been exposed to a contagious disease, until it can be determined whether they have become sick or no longer pose a risk to others. For example, those suspected of exposure to Ebola were quarantined up to 21 days. Quarantines may take place in the home, or other locations determined by health authorities. If a person shows no symptoms of the disease within the time when a person is considered contagious, they are considered disease-free and released from quarantine.
R0, which is pronounced “R-naught” is the mathematical term for explaining how contagious an infectious disease may be to a population. The number defines how many people a sick person may infect on average, if no one else in the population has immunity to the disease. If the R number is less than 1, it means the outbreak is either on the decline or isn’t likely to cause an epidemic. If the number is higher than 1, it means the disease may be highly contagious or an outbreak may be spreading. For example, measles is one of the most contagious diseases on the planet. It’s R ranges between 12 and 18. It means one person with measles can infect 12 to 18 people, if none of them are vaccinated against the disease. If everyone is vaccinated, then the R drops essentially to zero. Ebola has an average R1.5 to R2.5.
Sepsis is an extreme bodily response to an infection. The body sends a flood of chemicals to the blood stream to fight the infection, which in turn causes widespread inflammation and slows blood flow. If blood flow becomes too slow, it can cause damage to organs and the circulatory system, eventually leading to septic shock and death.
It is most common among the elderly, those with a chronic illness that has severely weakened the immune system and babies under 3 months. More than 1.7 million people get sepsis each year and 270,000 die from it, according to the Centers for Disease Control and Prevention. One in three patients that die in the hospital, die from sepsis.
It is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins or one of its surface proteins. The agent stimulates the body's immune system to recognize the agent as foreign, destroys it, and "remembers" it, so that the immune system can more easily recognize and destroy any of these microorganisms that it later encounters.
The degree of damage a pathogen can cause to the body.
Virology is the study of viruses and virus-like agents, including their types, disease-producing properties, how they multiply and their genetics.
A biological entity with a protein covering that is neither alive nor dead. Viruses circulate in the environment until they find living cells to latch onto and enter. Once inside a cell, a virus hijacks the cell’s genetic material and tells it to make more viruses instead. The hijacked cell then creates so many viruses that it explodes and moves on to enter other healthy cells. Viruses, which are smaller than bacteria, need hosts, like people, animals or plants to multiple.