Viruses cause a broad array of human diseases. These microscopic particles spread easily, typically via person-to-person contact or touching contaminated surfaces. Once inside the body, viruses enter cells and reproduce quickly. Viral infections cause a host of different diseases, some mild and others potentially fatal. Unfortunately, effective antiviral medications exist for only a few of the many human viral diseases. In many cases, treatment for a viral illness involves relieving symptoms until the body's immune system clears the infection.
A variety of viruses cause different types of respiratory infections. Rhinovirus, coronavirus and adenovirus are the leading causes of the common cold. Influenza viruses infect the upper respiratory system and sometimes spreads to the lungs causing pneumonia. Another virus called the respiratory syncytial virus (RSV) causes a respiratory infection called bronchiolitis in infants and toddlers. The symptoms of bronchiolitis include dry cough, rapid breathing and wheezing, a high-pitched sound sick children make when exhaling.
Digestive System Infections
Several types of viruses cause viral gastroenteritis, commonly called the stomach flu. This common illness, characterized by diarrhea, nausea and vomiting, is caused by many different viruses, but not the influenza virus. According to a June 2012 "American Family Physician" article, viruses cause 75 to 90 percent of acute gastrointestinal disease in children.
Rotavirus is the most common cause of viral gastroenteritis among children. Norovirus is the leading cause of viral gastroenteritis outbreaks. Other viruses that cause the stomach flu include adenovirus, calicivirus and astrovirus. Most cases of viral gastroenteritis clear on their own within 2 to 4 days, but dehydration may require medical treatment.
Central Nervous System Infections
Several viruses can infect the central nervous system, which consists of the brain and spinal cord. For example, enteroviruses and herpes viruses can cause meningitis and encephalitis. According to an October 2014 article published in the "The Neurohospitalist," other viral causes of central nervous system infections are emerging, including West Nile virus, Japanese encephalitis virus, human parechoviruses and Chikungunya virus.
Meningitis is an inflammation of the tissue surrounding the brain and spinal cord. Encephalitis is an inflammation of the brain tissue itself. The symptoms of these central nervous system infections overlap and can include fever, headache, neck stiffness and light sensitivity. Mental status changes are common, including confusion, mood instability, extreme lack of energy and possibly coma. Seizures occur in some people with meningitis or encephalitis.
Viruses cause a wide array of skin infections. Herpes simplex viruses (HSV) cause some of the most common skin infections. HSV type 1 tends to cause vesicles in the mouth and on the lips, commonly known as cold sores or fever blisters. HSV type-2 tends to cause genital herpes. According to the Cleveland Clinic, 85 percent of the population has blood test evidence of exposure to HSV-1, even if they never had symptoms. The varicella virus causes chickenpox, an illness characterized by itchy fluid-filled bumps on the skin that eventually rupture and scab over. The varicella virus also causes shingles, which is a reactivation of the virus years after the initial bout of chickenpox.
Another group of viruses, the human papillomaviruses (HPV), cause warts. Warts are a very common skin infection and can affect any skin surface. The feet, hands and face are frequently affected by common warts or plantar wart. Genital warts are the most common sexually transmitted infection. Among women, genital warts caused by certain types of HPV can predispose to cervical cancer. The HPV vaccine protects against these cancer-causing types of HPV.
Many Other Diseases
There are obviously many other human diseases caused by viruses. Indeed, many professional medical books are devoted exclusively to this topic. A few notable examples that have garnered the attention of the public health community and the population at large include:
-- Zika: a virus spread primarily by mosquitoes that can cause birth defects
-- MERS-CoV: the virus responsible for Middle East respiratory syndrome, a potentially deadly respiratory infection
-- Ebola: virus spread through contact with infected body fluids that can causes an often fatal illness called Ebola hemorrhagic fever
-- HIV: virus responsible for acquired immunodeficiency syndrome (AIDS)
-- Hepatitis C: virus that typically establishes long-term infection of the liver, and is the leading cause of liver transplants and liver cancer in the U.S.
Reviewed and revised by: Tina M. St. John, M.D.