Viruses are among the most common microbes affecting humans. These microscopic organisms spread easily, usually via person-to-person contact or through exposure to body fluids, such as blood, mucous or saliva. Once inside the body, viruses reproduce quickly, sometimes overwhelming the body’s natural defenses. When this happens, viruses can cause different diseases, some mild and others potentially fatal. Unfortunately only a handful of effective antiviral medications exist. Most of the time, treatment for a viral infection involves dealing with the symptoms until the end of the infection.
Viruses cause many respiratory infections. Rhinovirus, coronavirus and adenovirus cause the common cold. The influenza, or flu, virus can cause upper respiratory infection and pneumonia. Another respiratory virus, called 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 noise sick children make when trying to exhale.
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 2012 article in the journal "American Family Physician," viruses cause between 75 and 90 percent of acute gastrointestinal disease in children. Rotavirus is the most common viral cause of gastroenteritis among children. Norovirus is the leading cause of viral gastroenteritis outbreaks. Other viruses that cause 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 affect the central nervous system, which is composed of the brain and the spinal cord. More commonly, enteroviruses and herpes viruses can cause meningitis and encephalitis. According to a 2009 article published in the journal "Archives of Neurology," other viral causes of central nervous system infections are emerging, including West Nile virus and Japanese encephalitis 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, lethargy and possibly coma. Seizures occur in some people with meningitis or encephalitis.
Viruses cause a wide array of skin infections. Herpes simplex viruses, or HSV, cause some of the most common skin infections. HSV type 1 tends to cause fever blisters or vesicles in the mouth and on the lips. 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. This infection results in itchy vesicles on the skin that eventually scab over. The varicella virus also causes shingles, which is a reactivation of the virus years after the initial chickenpox infection. Another group of viruses, the human papillomaviruses or HPV, cause warts. Warts are a 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. Genital warts in women can predispose to cervical cancer.