Human viruses cause a variety of maladies, depending on the virus type and the tissues infected. All humans contract multiple viruses throughout the course of life. The severity of viral illnesses ranges from mild to lethal. Cold, flu, stomach and hepatitis viruses are among the most common types of human viruses encountered worldwide.
Cold Viruses
The common cold remains a vexing and ubiquitous human affliction. In the United States alone, approximately 1 billion head colds occur each year. Viral infection of the lining of the nasal passages leads to runny nose, watery eyes, scratchy throat and sneezing. The typical course of the common cold is seven to 14 days. The National Institute of Allergy and Infectious Diseases asserts that more than 200 known virus strains can cause a head cold, with rhinoviruses proving the most frequent culprits. Other virus types that may cause a cold include adenovirus, coronavirus, coxsackievirus, echovirus, enterovirus, orthomyxovirus, paramyxovirus and respiratory syncytial virus.
Flu Viruses
Three types of viruses cause influenza, more commonly known as the flu. The Centers for Disease Control and Prevention reports that influenza virus types A and B cause seasonal flu infections, which typically occur from late fall through early spring. Influenza type C infections occur far less frequently and typically cause a mild form of the illness. Common symptoms of the flu include body aches, fever, fatigue, headache, scratchy throat, dry cough and a stuffy nose. Influenza immunizations provide protection against infection due to influenza types A and B.
Stomach Viruses
Stomach viruses invade the tissues of the stomach and upper intestine, causing viral gastroenteritis. Common symptoms include abdominal pain or cramps, diarrhea, nausea and vomiting. Rotavirus frequently causes gastroenteritis in infants and young children; symptoms include fever, vomiting and watery diarrhea. Norovirus is another common stomach virus that affects both children and adults. According to the Centers for Disease Control and Prevention, diarrheal symptoms predominate in children with norovirus; adults often experience persistent vomiting. Other common stomach viruses include strains of adenovirus, sapovirus and astrovirus.
Hepatitis Viruses
The hepatitis viruses infect the liver, causing inflammation. Five different virus cause hepatitis, denoted by the letters A through E. Hepatitis viruses A, B and C predominate in the United States. The Centers for Disease Control and Prevention explains that the hepatitis A virus is a contracted through ingestion of stool-contaminated food or water. The virus causes a short-lived episode of hepatitis. Hepatitis B virus can cause acute or chronic liver infection. The virus is present in blood and semen. Sexual intercourse, sharing injection drug equipment and mother-to-child transmission during pregnancy and childbirth are the primary mechanisms of contracting hepatitis B. Hepatitis C virus infection occurs through contact with infected blood. Sharing injection drug equipment is the most frequent route of transmission. Mother-to-child infections also occur. Infection with the hepatitis C virus is usually chronic, frequently leading to cirrhosis.
References
- Centers for Disease Control and Prevention: Common Cold and Runny Nose
- National Institute of Allergy and Infectious Diseases: Common Cold, Overview
- National Institute of Allergy and Infectious Diseases: Common Cold, Cause
- Centers for Disease Control and Prevention: Types of Influenza Viruses
- World Health Organization: Influenza (Seasonal)
