these diseases are similar to noninfectious
diseases in humans. Cancer affects
many older dogs, cats, and other animals.
Pets and many wild animals can
suffer from arteriosclerosis. This is a
disease in which the blood vessels
become blocked. Many animals can also
develop cloudy growths, called cataracts,
over their eyes.
#More to explore
Animal • Disease, Human • Vaccine
Disease, Human
Diseases, also called illnesses or sicknesses,
are conditions that make people
unhealthy. Human diseases fall into two
major groups: infectious diseases and
noninfectious diseases.
Infectious Diseases
Infectious diseases are contagious, or
catching. People may catch these diseases
in a number of ways. Direct contact
between humans spreads some
infectious diseases. Animals, such as
mosquitoes, spread others. Still others
spread through air, water, or food.
Tiny living things called pathogens, or
germs, cause infectious diseases. Once a
pathogen has entered the body, the person
is said to be infected. Pathogens
include viruses, bacteria, fungi, and protozoans.
Some diseases caused by viruses are the
common cold, influenza (the flu),
chicken pox, measles, and AIDS. Diseases
caused by bacteria include strep
throat, tuberculosis, and Lyme disease.
Fungi cause some skin diseases—for
example, athlete’s foot and ringworm.
Different protozoans cause malaria and
sleeping sickness.
Doctors can often cure diseases caused
by bacteria with drugs called antibiotics.
Various medicines can treat diseases
To learn more about human diseases and disorders, turn to these articles:
AIDS
Alzheimer’s Disease
Arthritis
Asthma
Cancer
Cerebral Palsy
Chicken Pox
Cholera
Cold, Common
Diabetes
Down Syndrome
Epilepsy
Food Poisoning
Hepatitis
Influenza
Lyme Disease
Malaria
Measles
Meningitis
Mental Illness
Mononucleosis
Mumps
Parkinson’s Disease
Plague
Pneumonia
Polio
Reye’s Syndrome
Rubella
Scarlet Fever
Smallpox
Strep Throat
Tonsillitis
Tuberculosis
West Nile Virus
Yellow Fever
56 Disease, Human BRITANNICA STUDENT ENCYCLOPEDIA
caused by viruses, fungi, and protozoans.
Doctors also use vaccines to prevent
people from catching many infectious
diseases, especially those caused by bacteria
and viruses.
Noninfectious Diseases
Many human diseases do not result from
pathogens. These diseases are called
noninfectious. They are not contagious.
Some noninfectious diseases are inherited,
or passed down through families.
They happen when there is a problem
with one or more genes. (Genes are tiny
units of information inside a person’s
cells.) Sickle cell anemia is a common
inherited disease. It affects the shape of
blood cells.
A person’s lifestyle can lead to certain
noninfectious diseases. People who eat
poorly and do not exercise are in danger
of getting heart disease or diabetes.
People who smoke cigarettes are more
likely to get lung cancer than nonsmokers.
Environmental dangers or pollution can
also cause noninfectious diseases. People
who live close to polluting factories or
toxic waste dumps may get cancer or
other diseases.
Doctors do not know the exact causes of
many noninfectious diseases. Alzheimer’s
disease and multiple sclerosis are
two diseases whose causes are unknown.
Drugs, surgery, and other treatments can
help to control some noninfectious diseases.
But many of these diseases cannot
be cured. Scientists today are researching
ways to cure inherited and other noninfectious
diseases.
#More to explore
Bacteria • Genetics • Medicine • Virus
Disney,Walt
Walt Disney was a pioneer in the field of
animated, or cartoon, films. He is best
known for creating such characters as
Mickey Mouse and Donald Duck.
Walter Elias Disney was born on
December 5, 1901, in Chicago, Illinois.
At an early ageWalt had a gift for
drawing and painting. While attending
high school he took art classes to develop
these skills. Disney left school to serve as
an ambulance driver duringWorldWar I.
Walt Disney stands by a picture of Mickey
Mouse. Mickey Mouse starred in more than
100 short cartoons.
BRITANNICA STUDENT ENCYCLOPEDIA Disney, Walt 57
In 1923 Disney moved to Hollywood,
California. There he began creating the
characters that would make him famous.
In 1928 he released the short cartoon
film SteamboatWillie. It starred a cheerful
mouse named Mickey. The next year
Disney formedWalt Disney Productions
to create more animated films.
Other popular cartoon characters followed.
In the 1930s audiences were
introduced to Minnie Mouse, Donald
Duck, and Goofy. Disney’s first fulllength
animated film, Snow White and
the Seven Dwarfs, was released in 1937.
In the 1940s Disney’s company began
making movies with live actors. Mary
Poppins, from 1964, was the most
successful of these. Disney also
continued making animated features,
including such classics as Pinocchio
(1940), Cinderella (1950), and Peter
Pan (1953).
In 1955 Disney’s company opened Disneyland,
a large theme park in Anaheim,
California. Walt DisneyWorld, a second
and larger amusement park, opened in
Orlando, Florida, in 1971. Disney died
on December 15, 1966.
#More to explore
Animation • Cartoon • Movie
Diwali
The Hindu religious holiday called
Diwali (or Divali) celebrates the new
