Viral Diseases of the Digestive System

Mumps

Mumps was a common childhood viral disease, but widespread vaccination has now made it rare in developed countries.

Learning Objectives

Analyze the cause, symptoms, and prevention of mumps

Key Takeaways

Key Points

  • Mumps is a contagious disease that is spread from person to person through contact with respiratory secretions, such as saliva from an infected person. The common symptoms of mumps include inflammation of the salivary glands, pancreas, and testicles; fever; and headache.
  • A physical examination confirms the presence of the swollen glands. Usually, the disease is diagnosed on clinical grounds and no confirmatory laboratory testing is needed.
  • The most common preventative measure against mumps is a vaccination with a mumps vaccine. The vaccine may be given separately or as part of the routine MMR immunization vaccine which also protects against measles and rubella.
  • Like many other viral illnesses, there is no specific treatment for mumps, other than supportive treatment. Death from mumps is very unusual. The disease is self-limiting, and general outcome is good. Known rare complications of mumps include infertility in men and profound hearing loss.

Key Terms

  • orchitis: A painful inflammation of one or both testes.
  • salivary gland: Any of several exocrine glands that produce saliva to break down carbohydrates in food enzymatically.
  • prodromal symptoms: A prodrome is an early symptom (or set of symptoms) that might indicate the start of a disease before specific symptoms occur.
  • parotid gland: Either of a pair of salivary glands located in front of, and below each ear in humans.

Mumps, also known as epidemic parotitis, was a common childhood viral disease caused by the mumps virus. Before the development of vaccination and the introduction of a vaccine in 1949, it was common worldwide, but now, outbreaks are largely confined to developed countries.

Symptoms

The common symptoms of mumps include inflammation of the salivary glands, pancreas, and testicles; fever, and headache. Swelling of the salivary glands, specifically the parotid gland, is known as parotitis, and it occurs in 60–70% of infections and 95% of patients with symptoms. Parotitis causes swelling and local pain, particularly when chewing. It can occur on one side but is more common on both sides in about 90% of cases. Painful inflammation of the testicles in mumps in known as orchitis. Other symptoms of mumps can include dry mouth, sore face and/or ears and occasionally, in more serious cases, loss of voice. In addition, up to 20% of persons infected with the mumps virus do not show symptoms, so it is possible to be infected and spread the virus without knowing it. Fever and headache are prodromal symptoms of mumps, together with malaise and loss of appetite.

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Child with mumps: This child with mumps displays the typical swelling of the salivary glands caused by the mumps virus.

Causes

Mumps is a contagious disease that is spread from person to person through contact with respiratory secretions, such as saliva from an infected person. When an infected person coughs or sneezes, the droplets aerosolize and can enter the eyes, nose, or mouth of another person. Mumps can also be spread by sharing food and drinks. The virus can survive on surfaces and then be spread after contact in a similar manner. A person infected with mumps is contagious from approximately six days before the onset of symptoms until about nine days after symptoms start. The incubation period can be anywhere from 14–25 days, but is more typically 16–18 days.

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Mumps virus: This transmission electron micrograph (TEM) shows the ultrastructure of the mumps virus. It is a roughly spherical particle made up of layers of fatty lipids, large protein molecules, and nucleic acids. The virus is dotted with large protein “spikes” that enable it to gain entry to host cells. Inside lies a core of a single, long molecule of RNA wrapped up in protein that is released into the host cell.

Diagnostics

A physical examination confirms the presence of the swollen glands. Usually, the disease is diagnosed on clinical grounds, and no confirmatory laboratory testing is needed. If there is uncertainty about the diagnosis, a test of saliva or blood may be carried out. An estimated 20–30% of cases are asymptomatic. As with any inflammation of the salivary glands, the level of amylase in the blood is often elevated.

Prevention

The most common preventative measure against mumps is a vaccination with a mumps vaccine. The vaccine may be given separately or as part of the routine MMR immunization vaccine which also protects against measles and rubella. The MMR vaccine is given at ages 12–15 months and then again at four to six years.

Treatment and Complications

Like many other viral illnesses, there is no specific treatment for mumps. Symptoms may be relieved by the application of intermittent ice or heat to the affected neck/testicular area and by the acetaminophen or ibuprofen for pain relief. Warm salt water gargles, soft foods, and extra fluids may also help relieve symptoms. Patients are advised to avoid acidic foods and beverages, since these stimulate the salivary glands, which can be painful.

Death from mumps is very unusual. The disease is self-limiting, and general outcome is good, even if other organs are involved. Known complications of mumps include:

  • In teenage males and men, complications from orchitis such as infertility or sub-fertility are rare, but present.
  • Spontaneous abortion in about 27% of cases during the first trimester of pregnancy.
  • Mild forms of meningitis in up to 10% of cases.
  • Profound hearing loss is very rare, but mumps was the leading cause of acquired deafness before the advent of the mumps vaccine.

After the illness, life-long immunity to mumps generally occurs; re-infection is possible but tends to be mild and atypical.

Hepatitis

Hepatitis is the inflammation of the liver. Causes include viruses, bacterial infections, alcohol, autoimmune disorders, drugs, and toxins.

Learning Objectives

Differentiate between acute and chronic hepatitis

Key Takeaways

Key Points

  • Hepatitis is acute when it lasts less than six months and chronic when it persists longer.
  • The initial symptoms of hepatitis are nonspecific flu-like symptoms, common to almost all acute viral infections and may include malaise, muscle and joint aches, fever, nausea or vomiting, diarrhea, and headache.
  • A diagnosis of hepatitis is usually made by a combination of blood work and physical examination. When the liver is inflamed, levels of certain liver enzymes that are found in the blood will be elevated. If a patient has viral hepatitis, the presence of the virus can be detected in the blood.
  • There are many causes of liver inflammation or hepatitis. The most common cause of acute hepatitis is infection with the Hepatitis B, C, or D viruses. Bacterial diseases can also cause liver inflammation, such as tuberculosis and tick-borne diseases.
  • Non-infectious causes of hepatitis include alcohol, autoimmune conditions, drugs, circulatory insufficiency, metabolic diseases, pregnancy, and toxins.
  • For those with alcohol-induced hepatitis, cessation of drinking is recommended, as alcoholic hepatitis is often the beginning of more serious drinking-related liver disorders.

Key Terms

  • ascites: An accumulation of fluid in the peritoneal cavity, frequently symptomatic of liver disease.
  • jaundice: A yellowish pigmentation of the skin, the whites of the eyes (sclera), and other mucous membranes caused by increased levels of bilirubin in the blood that build up in extracellular fluid, usually due to liver disease.
  • cirrhosis: A chronic disease of the liver caused by damage from toxins (including alcohol), metabolic problems, hepatitis, or nutritional deprivation. It is characterized by an increase of fibrous tissue and the destruction of liver cells.
  • hepatitis: inflammation of the liver, sometimes caused by a viral infection

Hepatitis is the inflammation of the liver. The condition can be self-limiting (healing on its own) or can progress to fibrosis (scarring) and cirrhosis.

Hepatitis may occur with limited or no symptoms, but often leads to jaundice, poor appetite, and malaise. Hepatitis is acute when it lasts less than six months and chronic when it persists longer. A group of viruses, known as the hepatitis viruses, cause most cases of hepatitis worldwide, but it can also be due to toxins, notably alcohol, certain medications, some industrial organic solvents, and plants.

Symptoms

The initial symptoms of hepatitis are nonspecific flu-like symptoms, common to almost all acute viral infections and may include malaise, muscle and joint aches, fever, nausea or vomiting, diarrhea, and headache. More specific symptoms, which can be present in acute hepatitis from any cause, are profound loss of appetite, aversion to smoking among smokers, dark urine, yellowing of the eyes and skin and abdominal discomfort. Physical findings are usually minimal, apart from jaundice and liver swelling. Some patients exhibit enlarged lymph nodes or enlargement of the spleen.

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Jaundice: Jaundice, seen here as yellowing of the eyes, is often a symptom of hepatitis.

Acute Hepatitis

Acute viral hepatitis is more likely to be asymptomatic in younger people. Symptomatic individuals may present after convalescent stage of 7 to 10 days, with the total illness lasting 2 to 6 weeks.

A small proportion of people with acute hepatitis progress to acute liver failure, in which the liver is unable to clear harmful substances from the circulation, leading to confusion and coma due liver insufficiency, and unable to produce blood proteins, leading to peripheral edema and bleeding. This may become life-threatening and, occasionally, requires a liver transplant.

Chronic Hepatitis

Chronic hepatitis often leads to nonspecific symptoms, such as malaise, tiredness and weakness, and often causes no symptoms at all. It is commonly identified on blood tests performed either for screening or to evaluate nonspecific symptoms. The occurrence of jaundice indicates advanced liver damage. On physical examination, there may be enlargement of the liver.

Extensive damage and scarring of liver, known as cirrhosis, leads to weight loss, easy bruising and bleeding tendencies, peripheral edema and accumulation of ascites, or fluid in the abdominal cavity. Eventually, cirrhosis may lead to various complications, including esophageal varices, which are enlarged veins in the wall of the esophagus that can cause life-threatening bleeding; hepatic encephalopathy, which causes confusion and coma; and kidney dysfunction.

Diagnoses

A diagnosis of hepatitis is usually made by a combination of blood work and physical examination. When the liver is inflamed, levels of certain liver enzymes that are found in the blood will be elevated. If a patient has viral hepatitis, the presence of the virus can be detected in the blood. Patients with progressing liver damage will often display jaundice, or yellowing of the whites of the eyes and skin, and their livers will be visibly enlarged.

Causes

There are many causes of liver inflammation, or, hepatitis. The most common cause of acute hepatitis is infection with the Hepatitis B, C, or D viruses. Bacterial diseases can also cause liver inflammation, such as tuberculosis and tick-borne diseases.

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Hepatitis B Virus: The hepatitis B virus is a common cause of liver inflammtion.

Non-infectious causes of hepatitis include alcohol, autoimmune conditions, drugs, circulatory insufficiency, metabolic diseases, pregnancy, and toxins.

Alcohol is a significant cause of hepatitis worldwide. Usually alcoholic hepatitis comes after a period of increased alcohol consumption. Alcoholic hepatitis is characterized by a variable constellation of symptoms, which may include feeling unwell, enlargement of the liver, development of fluid in the abdomen ascites, and a modest elevation of liver blood tests. Alcoholic hepatitis can vary from mild with only liver test elevation to severe liver inflammation with development of jaundice and liver failure.

Alcoholic hepatitis is distinct from cirrhosis caused by long-term alcohol consumption. Alcoholic hepatitis can occur in patients with chronic alcoholic liver disease and alcoholic cirrhosis. Alcoholic hepatitis by itself does not lead to cirrhosis, but cirrhosis is more common in patients with long-term alcohol consumption.

Treatment

Treatment of hepatitis typically involves treating the underlying condition that caused the inflammation.

In acute hepatitis caused by the hepatitis viruses, often, the liver inflammation will subside when the viral illness has subsided. Antiviral medications, such as interferon, can be used to treat the hepatitis viruses. There is currently a vaccination for Hepatitis B, but not for C or D. Similarly, hepatitis caused by a bacterial disease will typically resolve once the bacterial illness is treated with antibiotics.

For non-infectious causes of hepatitis, treatment of the underlying cause is necessary. For those with alcohol-induced hepatitis, cessation of drinking is recommended, as alcoholic hepatitis is often the beginning of more serious drinking-related liver disorders.

Viral Gastroenteritis

Gastroenteritis is caused by two different virus types in adults and children.

Learning Objectives

Recognize the viruses that cause gastroenteritis and their mode of transmission

Key Takeaways

Key Points

  • Rotaviruses typically causes gastroenteritis in children. These are double-stranded viruses, which have two coats or capsids.
  • Noroviruses, which cause most adult cases of gastroenteritis, are fast mutating viruses.
  • The key to the treatment of gastroenteritis is rehydration, either orally or, in severe cases, intravenously.

Key Terms

  • replication: Process by which an object, person, place or idea may be copied mimicked or reproduced.
  • kbp: kilobase pair
  • substitutions per site per year: A DNA mutation where one DNA base pair is replaced with another; often used synonymous with the term mutation rate.

Gastroenteritis is a medical condition characterized by inflammation (“-itis”) of the gastrointestinal tract that involves both the stomach (“gastro”-) and the small intestine (“entero”-), resulting in some combination of diarrhea, vomiting, abdominal pain and cramping. Gastroenteritis has also been referred to as gastro, stomach bug, and stomach virus. Although unrelated to influenza, it has also been called stomach flu and gastric flu.

Viruses that are known to cause gastroenteritis include rotavirus, norovirus, adenovirus, and astrovirus. Globally, Rotavirus is the most common cause of gastroenteritis in children, and produces similar incidence rates in both the developed and developing world. In adults, norovirus and Campylobacter are more common causes.

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Gastroenteritis Viruses: Electron Micrographs of viruses that cause gastroenteritis in humans. A = rotavirus, B = adenovirus, C = norovirus and D = astrovirus. They are shown at the same magnification of approximately x 200,000

Viruses cause about 70% of episodes of infectious diarrhea in the pediatric age group. Rotavirus is a genus of double-stranded RNA virus in the family Reoviridae. Reoviruses are non-enveloped and have an icosahedral capsid composed of an outer and inner protein shell. The genomes of viruses in Reoviridae contains 10-12 segments which are grouped into three categories corresponding to their size: L (large), M (medium) and S (small). Segments range from ~ 3.9 kbp – 1kbp and each segment encodes 1-3 proteins. Since these viruses have dsRNA genomes, replication occurs exclusively in the cytoplasm and the virus encodes several proteins which are needed for replication.

The virus can enter the host cell via a receptor on the cell surface. The receptor is not known. After binding to the receptor the outer shell is partially digested to allow cell entry. The inner shell particle then enters the cytoplasm by a yet unknown process to start replication. Viral particles begin to assemble in the cytoplasm 6–7 hours after infection.

Rotavirus is a less common cause in adults due to their acquired immunity. Norovirus is the leading cause of gastroenteritis among adults in America, causing greater than 90% of outbreaks. Noroviruses contain an RNA genome of approximately 7.5 kbp, encoding a major structural protein (VP1) and a minor capsid protein (VP2). The virus particles demonstrate an amorphous surface structure when visualized using electron microscopy and are between 27-38 nm in size.

The most variable region between different viruses of the same type is a portion of the viral capsid. Specifically a region which contains antigen-presenting sites and carbohydrate-receptor binding regions, which is probably the region of the virus that binds to target cells. The estimated mutation rate (1.21 x 10-2 to 1.41 x 10-2 substitutions per site per year) in this virus is high, even compared with other RNA viruses. Norovirus epidemics typically occur when groups of people spend time in close physical proximity to each other, such as on cruise ships, in hospitals, or in restaurants. People may remain infectious even after their diarrhea has ended. Norovirus is the cause of about 10% of cases in children.

The foundation of management of gastroenteritis, viral-caused or otherwise, is adequate hydration. For mild or moderate cases, this can be typically achieved via oral rehydration solution. For more severe cases, intravenous fluids may be needed. Gastroenteritis primarily affects children and those in the developing world.