The red bloody patches on the skin and ulcers are usually caused by bacteria. (Ill. 59-62, 65-67, 68-71) In some cases this bacterial infection occurs after a parasitic infection. (Ill. 72-78) Another possible cause is viral infections. (Ill. 63+64+68) An accurate diagnosis is necessary to determine the appropriate treatment. Tip: We must not automatically assume that the red bloody patch or ulcer has been caused by a bacterial infection as the primary cause may have been a parasitic infection.