- Yaws
- A highly infectious disease caused by the spirochete Treponema pertenue, also called frambesia. Transmitted by direct contact, it is especially prevalent among children of impoverished areas of Africa, South America, and the East and West Indies. The first symptoms appear about a month after exposure, with a single lesion called the “mother yaw.” This will soon ulcerate, creating an open, oozing sore that spreads to all parts of the body. After several years, the disease causes tissue destruction, bone changes, and a shortening of the fingers and toes in a cycle resembling leprosy, and often mistaken for that disease. The organism responsible is closely related to that of syphilis, with both diseases testing positive in the Wassermann test, yet Yaws is classified as a nonvenereal disease.
- Yeast
- A predominantly unicellular rounded fungi that reproduces by budding. Some are fermenters of carbohydrates, and a few are pathogens. Brewer’s yeast (Saccharomyces cerevisiae) is used in making beer and alcoholic liquors and for baking bread. The dried cells of this same strain are used as a natural source of protein, and the B-complex vitamins and are commonly known as “brewer’s yeast” or “nutritional yeast”.
- Yellow Fever
- A viral infection transmitted by certain Aedes mosquitoes (A. aegypti), in which patients develop severe hepatitis.
- Yersinia
- A bacterium causing the diarrheal disease called yersiniosis, generally produced by two species, Yersinia enterocolitica and Y. pseudotuberculosis. The bacterium is also responsible for the plague, or “black death.” The rat flea responsible (xenopsylla cheopis) is usually blamed for causing the plague, but any one of the 1,500 species of flea can be carriers for the organism. All are of the family Enterobacteriaceae, to which Salmonella also belongs.
