Urethritis, Nonspecific

Nonspecific urethritis (yoo-re-THRY-tis) is a common urinary tract infection. It is also called nongonococcal (non-gon-o-KOK-al) urethritis.

Urinary Tract Infection

When an infection causes inflammation* in the urethra, it is called ure-thritis (yoo-re-THRY-tis). Infections that inflame the bladder are called cystitis (sis-TY-tis).

Uterine and Cervical Cancer

The uterus* is the hollow, pear-shaped organ in which a baby develops when a woman is pregnant. The cervix* is the lower part of the uterus, which extends into the vagina (va-JY-na), the canal that connects to the outside of the body.

Varicose Veins

The body has two systems for carrying blood to and from all its cells, tissues, and organs. Arteries carry blood from the heart to the organs, and veins return blood back to the heart.


Vertigo is different from other forms of dizziness because it is caused by disturbances in the structures that control the sense of balance. These structures include the vestibule and semicircular canals in the ear, the vestibular (ves-TIB-u-lar) nuclei in the brain stem, and the eyes.

Viral Infections

Viruses are far smaller than bacteria. They are so small that they could not be seen until the electron microscope was invented in the 1940s.


Melanocytes (MEL-a-no-sites) are special skin cells that make the pigment* that colors the skin, hair, eyes, and body linings. If these cells die or cannot make pigment, the affected skin gets lighter or completely white, causing vitiligo (vit-i-LY-go).


Despite all the stories, warts are not caused by touching a frog. Warts are small, hard bumps on the skin or inner linings of the body that are caused by a virus—too small to be seen with the naked eye—called human papillomavirus (pap-i-LO-ma-VY-rus), or HPV.

Whooping Cough (Pertussis)

Whooping cough is an infection of the respiratory system that occurs most frequently in young children. It is caused by two related bacteria: Bordetella pertussis (bor-de-TEL-a per-TUS-is) and Bordetella parapertussis (bor-de-TEL-a para-per-TUS-is).


Diseases and conditions caused by worms are as varied as the types of worms that cause them. Worms that act as parasites* come in thousands of different species, including roundworms, tapeworms, flatworms, flukes, and leeches.

Yeast Infection, Vaginal

*fungus (FUN-gus) is any organism belonging to the kingdom Fungi (FUN-ji), which includes mushrooms, yeasts, and molds.

Yellow Fever

Once causing epidemics* in many parts of the world, including the United States, yellow fever now is confined almost entirely to tropical parts of Africa and South America. There it occurs in two forms, urban and sylvan.


Many organisms cause disease only in people. Others affect only certain animals.