yellow fever An acute, systemic viral illness transmitted to humans through the bite of infected mosquitos that may cause a flu-like illness or a more severe illness with high fever, bleeding into the skin, and death of cells (necrosis) in the kidney and liver. The liver damage (hepatitis) causes yellowing of the skin from severe…
yellow fever vaccination A live attenuated (weakened) viral vaccine for yellow fever. Yellow fever vaccination is recommended for people traveling to or living in the tropical areas in the Americas and Africa where yellow fever occurs. Because yellow fever vaccination is a live vaccine, it should not be given to infants or people with immune-system…
yellow jacket stings Stings from yellow jackets that can trigger allergic reactions of varying severity. Avoidance and prompt treatment of allergic reactions (including diphenhydramine, brand name: Benadryl; and epinephrine, brand name: Epi-Pen) are essential. In selected cases, allergy injection therapy is highly effective for prevention.
Yersinia A family of bacteria that includes Yersinia pestis, which causes the bubonic, pneumonic, and septicemic plagues; Y. entercolitica, which causes intestinal infections, including mesenteric lymphadenitis, a condition that mimics appendicitis; and Y. pseudotuberculosis, which usually adversely affects only animals but can cause illness in immunocompromised patients. Both Y. entercolitica and Y. pseudotuberculosis have also…
Y-linked A gene on the Y chromosome that is passed from father to son. See also holandric inheritance.
Y-linked inheritance See holandric inheritance.
yoga A relaxing form of exercise that was developed in India and involves assuming and holding postures that stretch the limbs and muscles, doing breathing exercises, and using meditation techniques to calm the mind. Yoga appears to have benefits for increasing physical flexibility and reducing internal feelings of stress. Yoga may be recommended as an…
yogurt Milk that is fermented with a culture of Lactobacillus (the milk bacillus) and often with acidophilus and other helpful bacteria. See also probiotic.
xeroderma pigmentosum A genetic disease that is characterized by such extraordinary sensitivity to sunlight that it results in the development of skin cancer at a very early age. Abbreviated XP. Children with XP can only play outdoors safely after nightfall. XP is due to defective repair of damage done to DNA by ultraviolet (UV) light….
xerophagia Having a tendency to eat a dry diet.
xerophthalmia Dry eyes. Xerophthalmia can be associated with systemic diseases, such as Sjogren’s syndrome, systemic lupus erythematosus, and rheumatoid arthritis; deficiency of vitamin A; and use of some medications. It results from inadequate function of the lacrimal glands, which produce tears. When xerophthalmia is due to vitamin A deficiency, the condition begins with night blindness…
xerosis Abnormal dryness of the skin, mucous membranes, or conjunctiva (xerophthalmia). There are many causes of xerosis, and treatment depends on the particular cause.