• The enteric viruses we’ll learn about are naked capsids that can withstand harsh stomach acids.
• When symptomatic, illness is characterized by diarrhea and vomiting.
• Outcomes are often worse for children and infants, due to malnutrition and dehydration stemming from fluid and electrolyte loss.
• The causative viruses are transmitted via the fecal/oral route.
• Hepatic viruses cause tissue damage and trigger inflammatory responses that produce the symptoms of infection.

Enteric Viruses

• Cause acute gastroenteritis and are typically ingested via contaminated food and water.
  – Vomiting and diarrhea.
  – Other symptoms include possible fever, nausea, abdominal pain or cramping, and myalgia and malaise.
  – Rehydration and electrolyte therapy are common treatments.
• Key viral causes of gastroenteritis:
  –  Norovirus is a leading cause of gastroenteritis in all age groups in the United States; outbreaks have been associated with contaminated shellfish.
  –  Adenovirus accounts for approximately 15% of hospitalized gastroenteritis cases, especially in infants. Recall that adenovirus also causes respiratory and ocular infections.
  – Astrovirus causes mild, watery diarrhea, most commonly in children.
  However, extra-intestinal infections can occur in immune-compromised patients; some viral genotypes, for example, have been associated with central nervous system infections.
  – Rotavirus is the leading cause of severe diarrhea worldwide in children under five years old; in premature neonates, rotavirus can manifest as necrotizing enterocolitis or hemorrhagic gastroenteritis.
  Because of the high morbidity and mortality associated with rotavirus, vaccination is recommended for all infants.
• In immune compromised patients, particularly AIDS patients and transplant recipients, cytomegalovirus (CMV) and Epstein-Barr Virus are associated with gastroenteritis.
• For a list of bacterial pathogens that induce enteric illnesses, see here.

Hepatic Viruses: Hepatitis Viruses A, B, C, D, and E,

• Hepatitis is characterized by inflammation of the liver.
  – Acute hepatitis = Inflammation that lasts less than 6 months
  – Chronic hepatitis = Inflammation that lasts 6 months or longer
  – In some cases, hepatitis can lead to fulminant liver failure; write that this is characterized by rapid, acute livery injury with hepatic encephalopathy.
• Vaccine availability varies for the hepatitis viruses, and there is no vaccine for Hepatitis C virus due to its heterogeneous nature.

Acute hepatitis

• Hepatitis A, B, C, D, and E can cause acute hepatitis.
• Symptoms include: Jaundice, nausea and vomiting, abdominal pain, dark urine, and joint pain, as well as low or no appetite and fatigue.
  – Liver failure is possible with acute hepatitis, but rare.
• General features of acute hepatitis histopathology:
  – Ballooning degeneration: hepatocytes are unusually large, with a “whispy” look
  – Spotty necrosis throughout the liver tissue
  – Mononuclear cell infiltrate
  – Councilman bodies, which are shrunken, acidophilic cells.

• Hepatitis A and E only cause acute hepatitis, not chronic.
  – Both viruses are transmitted via the fecal-oral route, often via contaminated water.
  – No carrier state for these Hepatitis viruses.
  – Both typically cause mild and self-limiting acute hepatitis; fulminant liver failure is possible but rare.
  – An important exception is that Hepatitis E infection has high mortality rates in pregnant women, especially during the third trimester.

Chronic hepatitis

• Caused by Hepatitis B, D, and C.
• Chronic infections can lead to scarring, cirrhosis, and cancer.
  – Smoking, alcohol use, age, sex, and population seem to increase the risk of disease progression.
• Hepatitis viruses B, D, and C are transmitted via body fluids
  – Carrier states exist
  – Hepatitis B can be transmitted from mother to neonate during childbirth.
  – Hepatitis C often produces extra-hepatic effects, including cryoglobulinemia vasculitis and B-cell non-Hodgkin’s lymphoma, and other immune mediated and inflammation mediated diseases.
  – Hepatitis D is often called the “Delta agent”; though infection with Hepatitis D, alone, does not produce illness, when combined with Hepatitis B, it makes infection worseand increases the risk of Fulminant liver failure.
• Hallmarks of Hepatitis B and C histopathology:
  – Hepatitis B often produces “ground glass” hepatocytes; the tiny grains in the cytoplasm are from viral protein accumulation.
  – Hepatitis C infection is characterized by lymphocyte aggregates and follicles, especially around the portal tracts;
  bile ducts are often damaged, and, steatosis (also called fatty change) can also occur.