Viruses. We've all heard of them, and we all have them in us right now. Your immune system is capable of fighting off most of the viruses you come in contact with in the United States, such as the common cold, the flu or gastroenteritis, the stomach flu. You can come into contact with a virus at anytime, especially in social settings. They can be spread through food and drink or contact with infected bodily fluids. A virus typically consists of a nucleic acid molecule and a protein coat. It overtakes a living host's cell and forces that cell to replicate viral DNA instead of the host DNA. Before you know it, you're sitting in the doctor's office trying not to lose your lunch. Not every virus is as treatable as the stomach bug though. There are some really dangerous viruses that can cause you to feel a lot worse than the flu does. And without treatment, they will kill you.

1. Marburg virus.

Thought to have originated in African monkeys, Marburg virus is a type of hemorrhagic fever that is caused by the filovirus. The first person to become infected by this virus was a German scientist who was studying monkeys that were brought in from Uganda in 1967. In places with top-of-the-line healthcare available, the fatality rate is about 25 percent, but can be as high as 80 percent to those who do not have access to treatment, such as places in the Congo. Onset of the disease is characterized by a severe headache and extreme lethargy. Within five to seven days, patients begin to experience hemorrhaging and die soon after.

2. Ebola virus.

Named after the Ebola River where it was first discovered, the Ebola virus is another type of hemorrhagic fever that causes headache, fever, muscle pain, internal bleeding and organ failure. The fatality rate of people infected with the virus is around 50 percent, with medical treatment, but has been as high as 90 percent before advances in medicine. It became infamous worldwide after its outbreak in West Africa. People from all over the world went to West Africa to try and treat the sick and stop it from spreading. So many people were dying, locals thought medical professionals were purposefully killing people and were convinced that Ebola was made up to scare them. People were fleeing from treatment and dying on the streets. Makeshift hospitals were torn down and the nurses and doctors chased out of town. African funeral rituals also helped spread the virus. People would touch the body before burial, getting the virus on their hands, infecting themselves and others.

3. Hantavirus.

This virus normally infects rodents and does not cause disease in the animals. But if a human comes into contact with infected rat feces, it can make them very sick, The virus is characterized by fatigue, muscle aches, vomiting and abdominal pain. As the disease state progresses, the person starts to experience shortness of breath and coughing as the lungs fill with fluid. The mortality rate is 3 percent with treatment from a medical professional.

4. Zika virus.

Named after the Zika forest in Uganda, this virus is primarily spread by a bite from an infected mosquito. The most common symptoms of this virus is a rash, fever, joint pain and conjuctivitis. Many people do not realize they are sick. They never go to the hospital and people rarely die from Zika virus. However, the Zika virus is most dangerous to a pregnant woman and her unborn child. The virus can cause a birth defect called microcephaly, which effects the child's brain. Most of the cases that have occurred in the US have been due to traveling outside of the US territories.

5. Dengue virus.

Also spread by mosquito bites, this virus commonly infects people in tropical areas such as Hawaii, Puerto Rico and Latin America. One may experience rash, fever, joint pain and serious bleeding. Dengue is not deadly, but can cause death if complications arise. Complications and death is more likely if you are infected with the virus more than once. Four hundred million people are infected each year.