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Glossary - Infectious Diseases

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Acquired immune deficiency syndrome (AIDS) - a disease caused by the human immunodeficiency virus (HIV), which kills or impairs cells of the immune system and progressively destroys the body's ability to fight infections and certain cancers. HIV is most commonly spread in teens and adults by sexual contact with an infected partner. HIV is most commonly spread in infants and children by vertical transmission from an infected mother while in the womb or during delivery.

Antibiotic - a group of drugs that kill bacteria and other organisms that cause disease.

Antibody (also called immunoglobulin) - a protein that is manufactured by lymphocytes to neutralize or destroy an antigen or foreign protein. Many types of antibodies are protective against infection. Rarely, antibodies are produced against tissues in the body resulting in illness (autoimmune disease).

Antigen - a substance that can trigger an immune response causing the production of antibodies as part of the body's defense against infection and disease.

Antihistamine drugs - drugs that block the effects of histamine, a chemical released in the body during an allergic reaction.

Anti-inflammatory drugs - drugs that reduce the signs and symptoms of inflammation.

Asymptomatic - to be without noticeable symptoms of disease.


Base (of lungs) - bottom portion of the lung, located just above the diaphragm.

Bronchiole - a small airway (subdivision of the bronchus) through which air flows into portions of the lung.

Bronchiolitis - inflammation that involves the bronchioles (small airways).

Bronchus - one of two large subdivisions of the trachea through which air passes to and from the lungs.


Chickenpox - a highly infectious viral disease, usually associated with childhood. The disease is caused by the varicella-zoster virus (VZV). Transmission occurs from person-to-person by direct contact or through the air.

Chlamydial infection - very common sexually transmitted disease caused by a bacteria-like organism in the urethra and reproductive system.

Computed tomography scan (also called a CT or CAT scan) - a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce cross-sectional images (often called slices), both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than general X-rays.

Culture - a laboratory test that involves the growing of bacteria or other microorganisms to aid in the diagnosis.


Diphtheria - a serious, infectious disease that produces a toxin (poison) and an inflammatory membrane lining of the throat, nose, trachea, and other tissues.


E. coli - a species of bacteria found in the intestines of humans and healthy cattle; often the cause of urinary tract infections, diarrhea in infants, and wound infections.

E. coli O157:H7 - a specific strain of Escherichia coli that can cause serious disease.

Encephalitis - a viral infection of the brain.

Exanthem - a rash associated with a disease.



Genital herpes - a sexually transmitted disease caused by the herpes simplex virus.

Genital warts - a sexually transmitted disease caused by some types of the human papillomavirus (HPV).

Gonorrhea - a common sexually transmitted disease causing inflammation of the genital mucous membranes. It may involve the upper and lower genital tracts, the bladder and kidneys, and may spread to other structures via the bloodstream.


Haemophilus influenzae (also called H. influenzae) - represents a group of bacteria that may cause different types of infections in infants and children. H influenzae most commonly causes ear, eye, or sinus infections, and pneumonia.

Hepatitis - inflammation of the liver that sometimes causes permanent damage; caused by viruses, drugs, alcohol, or parasites. Hepatitis has the following forms:

Hepatitis A - a form of infectious hepatitis caused by the hepatitis A virus. The virus may be spread by fecal-oral contact, fecal-infected food or water, and may also be spread by a blood-borne infection (which is rare).

Hepatitis B - a form of infectious hepatitis caused by the hepatitis B virus. Transmission of the hepatitis B virus occurs through blood and body fluid exposure such as blood, semen, vaginal secretions, or saliva.

Hepatitis C - a form of infectious hepatitis caused by the hepatitis C virus. Transmission of the hepatitis C virus occurs primarily from contact with infected blood, but can also occur from sexual contact or from an infected mother to her baby.

Hepatitis D - a form of infectious hepatitis caused by the hepatitis (Delta) virus. This form of hepatitis can only occur in the presence of hepatitis B. Transmission of hepatitis D occurs the same way as hepatitis B.

Hepatitis E - a form of infectious hepatitis caused by the hepatitis E virus. This form of hepatitis is similar to hepatitis A. Transmission occurs through fecal-oral contamination. Hepatitis E is most common in poorly developed countries and is rarely seen in the US.

Hepatitis G - the newest form of infectious hepatitis. Transmission is believed to occur through blood and is seen in IV drug users, individuals with clotting disorders, such as hemophilia, and individuals who require hemodialysis for renal failure.

Herpes genitalis - an infection caused by the herpes simplex virus (HSV) and usually spread by sexual contact. Symptoms may include painful blisters or open sores in the genital area, which may be preceded by a tingling or burning sensation in the legs, buttocks, or genital region. The herpes sores usually disappear within a few weeks, but the virus remains in the body and the lesions may recur from time to time.

Herpes zoster (also called shingles) - a common viral infection of the nerves, characterized by a painful skin rash of small blisters anywhere on the body. It is a reactivation of chickenpox virus.

Human papillomaviruses (HPVs) - a group of viruses that can cause warts. Some HPVs are sexually transmitted and cause wart-like growths on the genitals. HPV is associated with some types of cancer, including cervical cancer and cancers of the oral cavity, head, and neck.


Inflammation - redness, swelling, heat, and pain in a tissue due to chemical or physical injury, infection, or allergic reaction.

Immune system - a collection of cells and proteins that works to protect the body from potentially harmful, infectious microorganisms, such as bacteria, viruses, and fungi.

Immunocompromised - an abnormal condition where one's ability to fight infection is decreased. This can be due to a disease process, certain medications, or a condition present at birth.

Inflammation - redness, swelling, heat, and pain in a tissue due to chemical or physical injury, infection, or allergic reaction.

Influenza (also called the flu) - a viral respiratory tract infection. The influenza viruses are divided into three types: A, B, and C.




Lymph - part of the lymphatic system; a thin, clear fluid that circulates through the lymphatic vessels and carries blood cells that fight infection and disease.

Lymph nodes - part of the lymphatic system; bean-shaped organs, found in the underarm, groin, neck, and abdomen, that act as filters for the lymph fluid as it passes through them.

Lymph vessels - part of the lymphatic system; thin tubes that carry lymph fluid throughout the body.

Lymphangiogram (LAG) - an imaging study that can detect cancer or abnormalities in the lymphatic system and structures. It involves a dye being injected to the lymph system.

Lymphatic system - part of the immune system; includes lymph, ducts, organs, lymph vessels, lymphocytes, and lymph nodes, whose function is to produce and carry white blood cells to fight disease and infection.

Lymphocytes - part of the lymphatic system; white blood cells that fight infection and disease.

Lyme disease (LD) - a bacterial infection caused by infected ticks, usually by a deer tick bite.


Measles - a very contagious viral illness characterized by a distinct rash and a fever; spread through airborne droplets of nasal secretions.

Meningitis - an inflammation of the covering of the brain and spinal cord.

Meningococcal infections - caused by a group of bacteria called Neisseria meningitidis. The most common forms of meningococcal infections include meningitis (infection of the membranes that surround the brain and spinal cord) and blood stream infections.

Mumps - an acute and highly contagious viral illness that usually occurs in childhood. Spread by airborne droplets from the upper respiratory tract, the disease usually takes two to three weeks to appear.


Nodule - a solid, raised bump.


Oophoritis - inflammation of the ovary.

Orchitis - inflammation of the testicle.


Pancreatitis - inflammation of the pancreas.

Pertussis (also called whooping cough) - mainly affects infants and young children; caused by a bacterium, it is characterized by paroxysms of coughing that end with the characteristic whoop as air is inhaled. Pertussis caused thousands of deaths in the 1930s and 1940s, but with the advent of a vaccine, the rate of death has declined dramatically.

Pleural effusion - a collection of fluid between the lung and chest wall.

Pneumothorax - air becomes trapped in the pleural space (the area between the lung and the chest wall); causes the lung to collapse.

Poliomyelitis - a highly contagious infectious disease caused by various types of poliovirus. Spread though feces and airborne particles, the poliovirus usually causes no more than a mild illness. However, some of the more serious manifestations of the disease include meningitis, which can lead to extensive paralysis.



Rabies - a widespread, viral infection spread through the bite of certain warm-blooded animals. It attacks the nervous system and, if left untreated, is 100 percent fatal in animals.

Respiratory diphtheria - when a person is infected with diphtheria, the bacterium usually multiplies in the throat, leading to the respiratory version of diphtheria. A membrane may form over the throat and tonsils, causing a sore throat. Other common symptoms of respiratory diphtheria may include: breathing difficulty, a husky voice, enlarged lymph glands, and an increased heart rate.

Respiratory syncytial virus (RSV) - an infection that causes inflammation of the lower airways and pneumonia.

Rocky Mountain Spotted Fever (RMSF) - an infection caused by the bite of an infected tick, usually a wood tick or dog tick.

Rubella (also called German measles) - an acute viral infection that causes a mild illness in children and slightly more severe illness in adults. The disease is spread person-to-person through airborne particles and takes two to three weeks to incubate. It can cause birth defects or fetal death.


Skin (cutaneous) diphtheria - one type of diphtheria; the symptoms are usually milder and may include yellow spots or sores (similar to impetigo) on the skin.

Syphilis - a sexually transmitted disease; the initial symptom of syphilis is a painless open sore that usually appears on the penis or around or in the vagina. If untreated, syphilis may go on to more advanced stages, including a transient rash and, eventually, serious involvement of the heart and central nervous system.


Tetanus - a disease caused by the bacteria Clostridium tetani that produces painful, rigid muscle contractions, especially in the neck and jaw. Immunization against tetanus can prevent the disease.

Toxic shock syndrome (TSS) - describes a cluster of symptoms that involve many systems of the body. TSS is usually caused by Staphylococcus aureus and Streptococcus pyogenes.

Tuberculosis (TB) - an infectious disease that was once a major killer worldwide. The predominant TB organism is Mycobacterium tuberculosis (M. tuberculosis). Spread person-to-person in airborne droplets caused by sneezing or coughing, the bacteria usually infects the lungs. However, due to improved nutrition, housing, sanitation, medical care, and the introduction of antibiotics, reported TB cases in the US have declined dramatically.





X-ray - a diagnostic test which uses invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs onto film.



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