Viral Diseases of the Digestive System
Mumps. The virus that causes mumps contains RNA. Transmitted in saliva and respiratory secretions, it replicates in the host's respiratory tract and causes swelling of one or both of the parotid glands below the ear and near the angle of the jaw. Fever is sometimes present, and in adult males, complications may occur if the virus infects the testis. Inflammation of the testis is called orchitis. Immunity to mumps is rendered by an injection of the MMR vaccine, using attenuated mumps virus.
Hepatitis A. Hepatitis A is caused by an RNA virus usually placed in the Picornaviridae family. The virus passes among individuals by the fecal‐oral route, and the disease is sometimes called infectious hepatitis. Individuals are contagious before they display symptoms and after symptoms have lessened. Contaminated food and water are often involved.
The hepatitis A virus affects the liver. Tissue damage is accompanied by vomiting, nausea, dark urine, and jaundice (a yellow discoloration of the skin and the whites of the eyes). Immunization may be rendered with an injection of the hepatitis A vaccine containing inactivated viruses. Prevention of symptoms is possible with hepatitis gamma globulin, a preparation of serum rich in hepatitis A antibodies. The hepatitis A virus is extremely resistant and remains active outside the body in the environment.
Hepatitis B. Hepatitis B, also called serum hepatitis, is caused by a DNA virus that is classified in the Hepadnaviridae. The virus is extremely fragile and passes directly from person to person, primarily in blood and semen. Hepatitis B is accompanied by liver infection, and in some cases, liver failure. Symptoms are similar to those in hepatitis A but tend to be more severe. Liver cancer (hepatocarcinoma) is a possible long‐range complication of hepatitis B. Immunization may be rendered with an injection of genetically engineered hepatitis B vaccine prepared in yeasts. Injections of gamma globulin containing hepatitis B antibodies are used for passive immunization in those infected by the virus.
Other forms of hepatitis. In addition to hepatitis A and hepatitis B, other forms of hepatitis are now known to exist. Hepatitis C is caused by an RNA virus transmitted by blood and semen. Most cases are associated with transfusions.
Delta hepatitis is related to an antigen called the delta antigen, which is a part of an RNA virus called the delta virus. Infection with this type of hepatitis accompanies infection with hepatitis B virus because the delta antigen relies on hepatitis B virus for its replication. This hepatitis is sometimes called hepatitis D.
Hepatitis E is also known to exist. The responsible virus is an RNA virus. Cases appear to be restricted to Asia, Africa, and India. Types of hepatitis such as these are often considered non‐A non‐B hepatitis.
Viral gastroenteritis. Viral gastroenteritis is a general expression for viral infection of the intestine. A major cause is the rotavirus, a virus transmitted by the fecal‐oral route and capable of causing severe diarrhea. Dehydration may be a problem in patients, and antiviral therapies are generally inadequate.
Another possible cause of viral gastroenteritis is the Norwalk agent, probably a virus but not yet identified with certainty. The Coxsackie virus is an RNA virus also capable of causing intestinal infection. Contaminated food and water transmit this virus. Another possible cause of gastroenteritis is the echovirus, also an RNA virus.