There are numerous amounts of serious viral infections, but with the advent of vaccines, many of them, for example smallpox, have been eradicated. However, a few deadly viruses still exist. HIV is a serious viral infection that can be controlled but, as yet, has no cure. Hepatitis C can damage your liver. Viral infections that attack the nervous system, such as rabies and West Nile virus, can be fatal if not treated immediately--West Nile can be life-threatening if it enters the brain, but without treatment, rabies is always fatal. SARS, and the H1N1 virus are the newer problematic viruses. In other parts of the world, dengue fever and yellow fever are common, and both can be dangerous. Ebola is probably the most well known and the most dangerous of the hemorrhagic fevers. What's more, polio has begun to resurface of late.