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An organism that has had its genetic material manipulated or altered in a laboratory setting through the use of genetic or genomic engineering techniques. Genetically modified organisms (GMOs) are microorganisms, plants, or animals that have been…

The four main blood types (blood groups) found in humans are A, B, AB, and O. Two particular antigens (A and B) determine the specific blood type—A antigen is present in type A blood; B antigen is present in type B blood; both A and B antigens are…

Any alteration of hearing capacity. Hearing comprises the general perceptual behavior and the specific responses that are made in relation to sound stimuli. Any deterioration or defect concerning the ability to hear (Fig. 1) is termed hearing…

A type of human cancer cell maintained in tissue culture since 1951, originally excised from the cervical carcinoma of a patient named Henrietta Lacks. The first immortal human cells to grow successfully outside the human body were labeled HeLa…

A medical condition that is characterized by the presence of inflammatory cells within the liver and liver cell death. Hepatitis is an inflammatory disease of the liver. In most cases, hepatitis is caused by viruses, including hepatitis A virus…

Microbial flora harbored by normal, healthy persons. The term "human microbiota" pertains to the totality of microorganisms that are present on and in the human body. Although a normal fetus is sterile, the infant is exposed to an increasing number…

Any of the small, nonenveloped, double-stranded DNA viruses of the Papovaviridae family that selectively infect the epithelium of the skin and mucous membranes of humans. More than 200 types of human papillomaviruses (HPVs) [Fig. 1] have been…

A hereditary disorder of the basal ganglia of the brain causing progressive motor incoordination, abnormal involuntary movements (chorea), and intellectual decline. Huntington's disease is a rare disorder that affects approximately five to ten of…

A theory proposing that the absence of exposure to certain microorganisms during the postnatal maturation of a young child's immune system is detrimental to the child. The hygiene hypothesis (sometimes referred to as the "old friends hypothesis")…

A form of disease treatment that seeks to stimulate, modulate, or restore the body's immune system. The immune system is the body's defense system against infection and disease. Immunotherapy is a treatment methodology that uses the innate…

A general term for disorders causing chronic inflammation of the gastrointestinal tract. Two closely related conditions, ulcerative colitis and Crohn's disease (Fig. 1), are the predominant forms of inflammatory bowel disease. In both conditions,…

An acute respiratory viral infection, commonly known as the flu, characterized by fever, chills, sore throat, headache, body aches, and severe cough. Influenza is an infectious disease caused by viruses in the family Orthomyxoviridae. These viruses…

Researchers at Duke University in North Carolina (United States) have developed a test for distinguishing lead isotopes found in coal fly ash from lead isotopes found in other lead-containing sources, such as paint. Fly ash is a fine particulate…

A complex multisystem illness caused by the tick-borne spirochetal bacterium, Borrelia burgdorferi. Lyme disease, also known as Lyme borreliosis, is an infectious disease of growing concern. Without early and proper treatment, individuals who have…

Macular degeneration is the most prevalent cause of vision impairment and loss among people aged 55 years and older. Also termed age-related macular degeneration (AMD), this serious eye condition damages the macula, which is the most sensitive part…

A disease caused by members of the protozoan genus Plasmodium (a widespread group of protists that parasitize the human liver and red blood cells) and transmitted by the bite of the female Anopheles mosquito. Malaria is a serious mosquito-borne…

Marburg hemorrhagic fever (also referred to as Marburg virus disease) is a rare, exotic viral disease that affects both humans and nonhuman primates. The reservoir hosts of Marburg virus are African (or Egyptian) fruit bats (Rousettus aegyptiacus),…

An acute, highly infectious viral disease with cough, fever, and maculopapular rash. Measles, also known as rubeola, is of worldwide endemicity. The infective particle is a ribonucleic acid (RNA) virus, specifically a paramyxovirus belonging to the…

Measles is a highly infectious and communicable disease that is most often contracted in childhood. The infective particle is a ribonucleic acid (RNA) virus—specifically, a paramyxovirus belonging to the genus Morbillivirus. Infected individuals…

Practices that are implemented to ensure the quality of meat foods and their products to avoid contamination and foodborne illnesses. Food safety involves the proper handling, preparation, and storage of all foods and must be adhered to throughout…

Any agent administered for the treatment of disease; also, the science and art of treating and healing disease. The term medicine has two general meanings. The first indicates any material, notably in the drug category, which is given to prevent,…

A type of skin cancer caused by the uncontrolled proliferation of epidermal melanocytes (cells containing dark pigments). Melanoma (see illustration) is well known for its rapid progression, metastasis, and poor prognosis. Statistics from the United…

Inflammation of the meninges. The meninges are protective membranes that cover the brain and spinal cord. Meningitis is the condition that arises when the meninges are infected by certain pathogenic organisms, leading to inflammation (swelling)…

Pathologies of metabolism principally involving an imbalance in nucleic acids, proteins, lipids, or carbohydrates. Metabolic disorders occur when abnormal biochemical reactions disrupt the normal processes of metabolism. In general, metabolic…

The multidisciplinary science of microorganisms that began with the study of bacteria. Microbiology is the scientific study of microorganisms (that is, microbes, or organisms too small to be seen without a microscope), including bacteria (Fig. 1),…

The collective term for the microorganisms or microbes that inhabit an environment, creating an ecological community or ecosystem; also the collective genetic material of these microorganisms or microbes. The term microbiome has a dual meaning.…

A microsurgical procedure to provide an oocyte (an immature egg cell or ovum) possessing dysfunctional mitochondria with healthy mitochondria. Mitochondrial replacement therapy (MRT) strategies could allow women who are carriers of mitochondrial…

A two-winged fly belonging to the family Culicidae in the insect order Diptera. Mosquitoes are slender, fragile insects (Fig. 1) and are recognized by their long legs, a long and slim abdomen, and narrow wings with characteristic scaled-wing…

Pathologies of form and function that affect the oral cavity and its related structures. The mouth, or oral (buccal) cavity, which comprises the lips, tongue, teeth, gums, and related structures, is subject to a large number of disease processes.…

A chronic, degenerative, inflammatory disease of the central nervous system that affects neuromuscular function and characteristically involves the destruction of myelin, the insulating material around nerve fibers. The best early description of…

Pathological conditions affecting skeletal (voluntary) muscles. The muscular system comprises the set of anatomical structures (muscle cells, contractile elements, and associated connective tissues) that are responsible for body movements in…

An autoimmune disease resulting from an abnormality in neuromuscular transmission, characterized by a fluctuating degree of muscle weakness. Myasthenia gravis is a chronic autoimmune neuromuscular disorder (see illustration) characterized by varying…

A drug that diminishes the awareness of sensory impulses, especially pain, by the brain. Narcotics are useful therapeutically as analgesics and are the most powerful pain-relieving agents available. However, their use is complicated by a number of…

A general classification of the pathologies or diseases that impact upon the nervous system. An understanding of the disorders and diseases of the nervous system should include not only the type of lesion and reaction to injury, but also the site of…

Caused by the rod-shaped bacterium Mycobacterium tuberculosis and transmitted by airborne droplets from a diseased individual, tuberculosis (TB) is a chronic infectious disease of humans (and other animals) that destroys body tissue. When M.…

A disease or infection acquired in a hospital or other health-care facility. Nosocomial diseases are pathological disorders that occur in patients during the course of a hospital stay. They also can occur in other health-care facilities, such as a…

The application of principles from the basic sciences, social sciences, and humanities for the physical and mental care of people. Nursing is concerned with the provision of care for sick and infirm individuals (see illustration). In the practice of…

The science of nourishment, including the study of the nutrients that each organism must obtain from its environment to maintain life and health and to reproduce. Nutrition is essential for survival. Organisms nourish themselves by assimilating the…

The presence of excess body fat that confers numerous risks to health. Obesity is an excessive accumulation of adipose tissue (body fat) that typically leads to a variety of health risks, including diabetes, cardiovascular disorders, arthritis, and…

Any of the genes that contribute to the conversion of a normal cell into a cancerous cell. Oncogenes are defective genes that can cause a cell to divide in an unregulated manner, leading to cancer. Oncogenes can derive from cellular genes that…

The study of cancer, including its causes, development, characteristics, and treatment. There are five major areas of oncology: etiology, prevention, biology, diagnosis, and treatment. As a clinical discipline, oncology draws upon a wide variety of…

An emerging cancer therapy in which oncolytic viruses are used to target and destroy cancer cells without harming healthy cells. Oncolytic viruses (that is, viruses that destroy cancer cells, but not normal cells) are able to infect, replicate…

Any drug naturally derived from opium, the dried juice of opium poppy (Papaver somniferum) seed pods. In its raw state, opium is an opaque, milky sap that concentrates its active ingredients in the pod (capsule). The pharmacologically active…

A metabolic bone disease in which the amount of bone tissue is reduced sufficiently to increase the likelihood of fracture. Osteoporosis involves deossification (the loss or removal of the mineral constituents of bone) with an absolute decrease in…

Osteoprotegerin (OPG) is a protein that plays a central role in the regulation of bone mass. Also known as osteoclastogenesis inhibitory factor (OCIF), this naturally occurring protein [a soluble decoy receptor protein that belongs to the tumor…

A variety of neoplastic and nonneoplastic disorders that occur in the ovary. Ovarian disorders are diseases or conditions that primarily affect the ovaries, which make up part of the reproductive system of all female vertebrates. In particular,…

Pathologies of the pancreas. The pancreas (Fig. 1) is affected by a variety of congenital and acquired diseases. These diseases can have grave consequences because the pancreas is a gland with three types of cells that serve three different…

A member of the genus Paramyxovirus of the family Paramyxoviridae which is associated with a variety of respiratory illnesses. The virus particles range in size from 90 to 200 nanometers, agglutinate red blood cells, and (like the influenza viruses)…

A group of viruses that belong to the genus Paramyxovirus of the family Paramyxoviridae. The family includes two other genera, Morbillivirus and Pneumovirus. The genus Parainfluenza includes viruses such as mumps and Newcastle disease (in fowl and…

Disorders involving excessive or deficient blood levels of parathyroid hormone caused by abnormal functioning of the parathyroid gland. Parathyroid hormone is responsible for keeping the concentration of calcium in blood within a narrow normal…

A progressive degenerative disorder of the nervous system belonging to a group of conditions called motor system disorders. Parkinson's disease results in the loss of brain cells that produce dopamine. The cause of this progressive degenerative…

A technique of selective chemical etching to reveal tracks of heavy nuclear particles in a wide variety of solid substances. Developed in order to see fossil particle tracks in extraterrestrial materials, the technique finds application in many…

A genus of gram-negative, nonmotile, nonsporulating, facultatively anaerobic coccobacillary to rod-shaped bacteria which are parasitic and often pathogens in many species of mammals, birds, and reptiles. It was named to honor Louis Pasteur in 1887.…

A variety of infectious diseases caused by the coccobacilli Pasteurella multocida and P. haemolytica. However, the term pasteurellosis also applies to diseases caused by any Pasteurella species. For example, P. caballi is considered to have a causal…

Any agent capable of causing disease. The term pathogen is usually restricted to living agents, which include viruses, rickettsia, bacteria, fungi, yeasts, protozoa, helminths, and certain insect larval stages.Pathogenicity is the ability of an…

The study of the etiologies, mechanisms, and manifestations of disease. Techniques and knowledge gained from other disciplines, including anatomy, physiology, microbiology, biochemistry, and histology, are utilized. The information obtained from the…

Human infestation with lice. There are two biological varieties of the human louse, Pediculus humanus, var. capitis and var. corporis, each showing a strong preference for a specific location on the human body. Pediculus humanus capitis colonizes…