Viral gastrointeritis

• Viral gastroenteritis is the inflammation of the lining of the stomach, small intestine, and large intestine
• Several different viruses can cause viral gastroenteritis, which is highly contagious and extremely common
• Viral gastroenteritis causes millions of cases of diarrhea each year
• Anyone can get viral gastroenteritis and most people recover without any complications, unless they become dehydrated
• Dehydration


  • The most common complication of viral gastroenteritis
  • Infants, young children, older adults, and people with weak immune systems have the greatest risk of becoming dehydrated
• Symptoms of viral gastroenteritis


  • Nausea
  • Vomiting
  • Headache
  • Stomach cramps
  • Diarrhea
  • Mild fever
  • Fatigue
  • Chills
  • Loss of appetite
  • Muscle aches
• The illness may develop over a period of hours, or it may suddenly start with stomach cramps, vomiting, or diarrhea
• Signs of dehydration in adults


  • Excessive thirst
  • Infrequent urination
  • Dark-colored urine
  • Dry skin
  • Dizziness
• Signs of dehydration in babies and young children


  • Dry mouth and tongue
  • Lack of tears when crying
  • High fever
  • Drowsy behavior
  • Sunken eyes
  • Soft spots in the skull
• Causative agents of viral gastroenteritis


  • Rotavirus
  • Calicivirus
  • Adenovirus
  • Astrovirus
• Rotavirus is the leading cause of gastroenteritis among infants and young children
• Rotavirus


  • Segmented double-stranded RNA genome (11 segments)
  • The RNA is surrounded by a three layered protein capsid without envelope
  • RNA - dependent RNA polymerase
  • Transmitted by the fecal-oral route
• Rotavirus proteins


  • There are six viral proteins (VP), the most important are the outer capsid proteins VP4 and VP7 as they carry epitopes with a significant role in neutralizing activity
  • There are nine species of rotaviruses
  • Group A rotaviruses are the most frequent human pathogen
• Rotavirus pathogenesis


  1. Rotaviruses infect cells in the villi of the small intestine

  2. They multiply in the cytoplasm of enterocytes and damage their transport mechanisms

  3. NSP4 is the viral enterotoxin and induces secretion by triggering a signal transduction pathway

  4. Damaged cells may slough into the lumen of the intestine and release large quantities of virus, which appear in the stool
• Viral excretion usually lasts 2-12 days in most patients but may be prolonged in those with poor nutrition
• Diarrhea caused by rotaviruses may be due to impaired sodium and glucose absorption as damaged cells on villi are replaced by non - absorbing immature crypt cells
• Clinical findings of rotavirus infection


  • Rotaviruses cause the major portion of diarrheal illness in infants and children worldwide
  • The incubation period is 1–3 days
  • Typical symptoms include watery diarrhea, fever, abdominal pain, and vomiting, leading to dehydration
  • In infants and children, severe loss of electrolytes and fluids may be fatal unless treated
• Laboratory diagnosis of rotavirus


  • Virus in stool is demonstrated by enzyme immunoassays
  • Serologic tests can be used to detect an antibody titer rise, particularly ELISA
  • Genotyping of rotavirus nucleic acid from stool specimens by the polymerase chain reaction is the most sensitive detection method
• Immunity to rotavirus


  • Rotaviruses are very common, by age 3 years, 90% of children have serum antibodies to one or more types
  • Rotavirus reinfections are common, young children can suffer up to five reinfections by 2 years of age
  • Local immune factors, such as secretory IgA or interferon, may be important in protection against rotavirus infection
  • Asymptomatic infections are common in infants before age 6 months, the time during which protective maternal antibody acquired passively by newborns should be present
• Treatment of viral gastroenteritis


  Supportive, to correct the loss of water and electrolytes that may lead to dehydration, acidosis, shock, and death. Management consists of replacement of fluids and restoration of electrolyte balance either intravenously or orally
• An oral live attenuated rotavirus vaccine was used in the United States in 1998 for vaccination of infants, but was withdrawn a year later because of reports of bowel blockages as an uncommon but serious side effect associated with the vaccine
• In 2006, an oral pentavalent bovine-based rotavirus vaccine was used in the United States, which is not associated with bowel blockages
• Caliciviruses


  • Caliciviruses cause infection in people of all ages
  • Norovirus is the most common caliciviruses and the most common cause of viral gastroenteritis in adults
  • People infected with norovirus typically experience nausea, vomiting, diarrhea, abdominal cramps, fatigue, headache, and muscle aches
  • The symptoms usually appear 1 to 2 days after exposure to the virus
• Norovirus


  • Virion: Non - enveloped, non - segmented, linear, positive - sense, single - stranded RNA
  • Proteins: Icosahedral capsid composed of a single protein
  • Replication: Cytoplasm
  • Human viruses are noncultivable

  
• Pathogenesis and immunity of Norovirus

  • Infection by Norovirus was observed to produce an expansion of the villi of the proximal small intestine. The mechanism by which diarrhea is produced is unknown, although it has been suggested that the delay in gastric emptying observed in norovirus gastroenteritis may play a role
  • Infection by Norovirus induces serum antibody response. Two weeks after infection with the virus, an increase in jejunal synthesis has been demonstrated for IgA, and most patients are resistant to reinfection for 4-6 months
• Laboratory diagnosis of Norovirus


  • Stool electron microscopy
  • Polymerase chain reaction to determine the viral genome
  • ELISA to detect viral antigens in stool
  • Latex agglutination for viral antigens

  
• Adenovirus


  • Adenovirus mainly infects children younger than 2 years old
  • Over 50 types of adenoviruses, one strain affects the gastrointestinal tract, causing vomiting and diarrhea
  • Symptoms typically appear 8 to 10 days after exposure to the virus
• Adenovirus properties


  • The virion is non - enveloped, medium in size
  • Genome linear dsDNA
  • They are the only viruses with a fiber protruding from each of the 12 vertices of the capsid. The fiber is the organ of attachment and is a hemagglutinin
  • Human adenoviruses are divided into 7 types (A to G) on the basis of physical, chemical and biological properties

  
• Adenovirus pathogenesis


  1. Adenoviruses infect and replicate in the epithelial cells of the respiratory tract, eyes, GIT, urinary bladder and liver

  2. They do not spread beyond regional lymph nodes, Group C viruses persist as latent in the adenoids and tonsils

  3. The viruses are transmitted either by aerosols or by fecal-oral routs
• Laboratory diagnosis of adenovirus


  • Isolation of the virus in cell culture
  • Shell vial technique (detection of viral specific Ag in tissue culture from patients using monoclonal antibodies directed against group-reactive Ag)
  • Complement fixation
  • Heamagglutination inhibition
  • PCR can be used to detect nucleic acid of the viruses in tissue samples
• There is no specific treatment for adenovirus infection and vaccine is no more used nowadays
• Astrovirus


  • Astrovirus primarily infects infants and young children, but adults may also be infected
  • This virus causes vomiting and watery diarrhea
  • Symptoms usually appear 3 to 4 days after exposure to the virus
  • The symptoms are milder than the symptoms of norovirus or rotavirus infections
  • Infections occur year-round, but the virus is most active during the winter months
• Astrovirus properties


  • Astroviruses are about 28–30 nm in diameter and exhibit a distinctive star-like morphology in the electron microscope
  • The precursor of the capsid proteins (87-kDa), gives rise to the structural capsid proteins VP26, VP29, and VP32
  • These proteins, especially VP26, seem to be responsible for the antigenic variation observed among the different serotypes
  • They contain single-stranded, positive-sense RNA
  • The viruses are transmitted by the fecal - oral route

  
• Pathogenesis and immunity of astrovirus


  • The pathogenesis of the disease induced by astrovirus has not yet been established, although it has been suggested that viral replication occurs in intestinal tissue
  • Symptomatic astrovirus infection occurs mainly in small children and the elderly, which suggests a reduction in antibodies in recent years, but the determinants of immunity are not well known
• Laboratory diagnosis of astrovirus


  • Stool culture to see if the virus is present
  • Blood tests to look for antibodies to the virus
  • Reverse transcription polymerase chain reaction to determine which astrovirus is causing the illness