In the human body, bacteria help keep the digestive tract working properly. Like viruses, however, bacteria can cause hundreds of illnesses. Some bacterial infections are common in childhood, such as strep throat and ear infections. Others cause major diseases, such as tuberculosis, plague, syphilis, and cholera.n the human body, bacteria help keep the digestive tract working properly. Like viruses, however, bacteria can cause hundreds of illnesses. Some bacterial infections are common in childhood, such as strep throat and ear infections. Others cause major diseases, such as tuberculosis, plague, syphilis, and cholera.