Viral Infections

Viruses are small particles of genetic material (either DNA or RNA) that are surrounded by a protein coat. Some viruses also have a fatty "envelope" covering. They are incapable of reproducing on their own. Viruses depend on the organisms they infect (hosts) for their very survival. Viruses get a bad rap, but they also perform many important functions for humans, plants, animals, and the environment. For example, some viruses protect the host against other infections. Viruses also participate in the process of evolution by transferring genes among different species. In biomedical research, scientists use viruses to insert new genes into cells.

When most people hear the word "virus," they think of disease-causing (pathogenic) viruses such as the common cold, influenza, chickenpox, human immunodeficiency virus (HIV), and others. Viruses can affect many areas in the body, including the reproductive, respiratory, and gastrointestinal systems. They can also affect the liver, brain, and skin. Research reveals that that viruses are implicated in many cancers as well.

Respiratory Viral Infections

Respiratory viral infections affect the lungs, nose, and throat. These viruses are most commonly spread by inhaling droplets containing virus particles. Examples include:

• Rhinovirus is the virus that most often causes the common cold, but there are more than 200 different viruses that can cause colds. Cold symptoms like coughing, sneezing, mild headache, and sore throat typically last for up to 2 weeks.
• Seasonal influenza is an illness that affects about 5% to 20% of the population in the US every year. More than 200,000 people per year are hospitalized annually in the US due to complications of the flu. Flu symptoms are more severe than cold symptoms and often include body aches and severe fatigue. The flu also tends to come on more suddenly than a cold.
• Respiratory Syncytial Virus (RSV) is an infection that can cause both upper respiratory infections (like colds) and lower respiratory infections (like pneumonia and bronchiolitis). It can be very severe in infants, small children, and elderly adults.

Frequent hand-washing, covering the nose and mouth when coughing or sneezing, and avoiding contact with infected individuals can all reduce the spread of respiratory infections. Disinfecting hard surfaces and not touching the eyes, nose, and mouth can help reduce transmission as well.

Viral Skin Infections

Viral skin infections can range from mild to severe and often produce a rash. Examples of viral skin infections include:

• Molluscum contagiosum causes small, flesh-colored bumps most often in children ages 1 to 10 years old; however, people of any age can acquire the virus. The bumps usually disappear without treatment, usually in 6 to 12 months.
• Herpes simplex virus-1 (HSV-1) is the common virus that causes cold sores. It's transmitted through saliva by kissing or sharing food or drink with an infected individual. Sometimes, HSV-1 causes genital herpes. An estimated 85% of people in the US have HSV-1 by the time they are in their 60s.
• Varicella-zoster virus (VZV) causes itchy, oozing blisters, fatigue, and high fever characteristic of chickenpox. The chickenpox vaccine is 98% effective at preventing infection. People who have had chickenpox (or in extremely rare instances, people who have received the chickenpox vaccine) are at risk for developing shingles, an illness caused by the same virus. Shingles can occur at any age, but it occurs most often in people age 60 or older.

The best way to avoid viral skin infections is to avoid skin-to-skin contact (especially areas that have a rash or sores) with an infected individual. Some viral skin infections, such as varicella-zoster virus, are also transmitted by an airborne route. Communal showers, swimming pools, and contaminated towels can also potentially harbor certain viruses.

Foodborne Viral Infections

Viruses are one of the most common causes of food poisoning. The symptoms of these infections vary depending on the virus involved.

• Hepatitis A is a virus that affects the liver for a few weeks up to several months. Symptoms may include yellow skin, nausea, diarrhea, and vomiting. Up to 15% of infected individuals experience recurrent illness within 6 months of infection.
• Norovirus has been reported to be responsible for outbreaks of severe gastrointestinal illness that happen on cruise ships, but it causes disease in many situations and locations. About 20 million people in the U.S. become sick from these highly contagious viruses every year.
• Rotavirus causes severe, watery diarrhea that can lead to dehydration. Anyone can get rotavirus, but the illness occurs most often in babies and young children.

Rotaviruses and noroviruses are responsible for many (but not all) cases of viral gastroenteritis, which causes inflammation of the stomach and intestines. People may use the terms “stomach virus” or “stomach flu” to refer to viral gastroenteritis, which causes nausea, vomiting, diarrhea, and abdominal pain.

It's not pleasant to think about it, but foodborne viral illnesses are transmitted via the fecal-oral route. This means that a person gets the virus by ingesting virus particles that were shed through the feces of an infected person. Someone with this type of virus who doesn't wash their hands after using the restroom can transfer the virus to others by shaking hands, preparing food, or touching hard surfaces. Contaminated water is another potential source of infection.