infection summary

Learn about infectious agents and how they cause diseases

Written and fact-checked by The Editors of Encyclopaedia Britannica

Below is the article summary. For the full article, see infectious disease.

Gram-negative bacteria such as Neisseria meningitidis are a common cause of septicemia. — Gram-negative bacteria such as *Neisseria meningitidis* are a common cause of septicemia.

infection, Invasion of the body by any of various agents—including bacteria, fungi (see fungus), protozoans, viruses, and worms—and its reaction to them or their toxins. Infections are called subclinical until they perceptibly affect health, when they become infectious diseases. Infection can be local (e.g., an abscess), confined to one body system (e.g., pneumonia in the lungs), or generalized (e.g., septicemia). Infectious agents can enter the body by inhalation, ingestion, sexual transmission, passage to a fetus during pregnancy or birth, wound contamination, animal bites, or insect bites. The body responds with an attack on the invader by leukocytes, production of antibodies or antitoxins, and often a rise in temperature. The antibodies may result in short-term or lifelong immunity. Despite significant progress in preventing and treating infectious diseases, they remain a major cause of illness and death, particularly in regions of poor sanitation, poor nutrition, and crowding.

tetanus Summary

Tetanus, acute infectious disease of humans and other animals, caused by toxins produced by the bacillus Clostridium tetani and characterized by rigidity and spasms of the voluntary muscles. The almost constant involvement of the jaw muscles accounts for the popular name of the disease. Spores of

chickenpox Summary

Chickenpox, contagious viral disease characterized by an eruption of vesicles (small blisters) on the skin. The disease usually occurs in epidemics, and the infected persons are generally between two and six years old, although they can be of any age. Chickenpox is caused by the varicella-zoster

encephalitis Summary

Encephalitis, from Greek enkephalos (“brain”) and itis (“inflammation”), inflammation of the brain. Inflammation affecting the brain may also involve adjoining structures; encephalomyelitis is inflammation of the brain and spinal cord, and meningoencephalitis is inflammation of the brain and

rabies Summary

Rabies, acute, ordinarily fatal, viral disease of the central nervous system that is usually spread among domestic dogs and wild carnivorous animals by a bite. All warm-blooded animals, including humans, are susceptible to rabies infection. The virus, a rhabdovirus, is often present in the salivary