progressive vaccinia: a severe or even fatal form of vaccinia that occurs mainly in persons with an immunological deficiency; characterized by progressive enlargement of the initial lesion
vaccinia: a local infection induced in humans by inoculation with the virus causing cowpox in order to confer resistance to smallpox; normally lasts three weeks and leaves a pitted scar
genus ichthyostega: second earliest fossil amphibian ever found; of the Devonian; found in Greenland