Micro - 4th Asessment - Viral Gastroenteritis - 2007

Viral Gastroenteritis Fourth Medical, 2007 Prof. Widad Al-Nakib, FRCPath.

Viral Gastroenteritis (Intestinal Flu) A

syndrome caused by infection with one of several viruses, usually characterized by vomiting, watery diarrhea, and abdominal cramps.

Etiology and Pathophysiology Viral gastroenteritis is the most common cause of infectious diarrhea in the USA.  Four categories of viruses are known to cause gastroenteritis: rotavirus, calicivirus (including Norwalk virus), enteric adenovirus (serotypes 40 and 41), and astrovirus 

Contd.. The viruses cause illness by infecting the enterocytes within the villous epithelium of the small intestine.  Destruction of cells in this layer causes net transudation of fluid and salts into the intestinal lumen.  Malabsorption of carbohydrates, leading to osmotic diarrhea, may also play a role. 

Characteristics of Viruses Causing Gastroenteritis Virus

Nucleic acid Particle

Serotypes

Rotaviruses

dsRNA, 11 segments

nm of diameter, 3 70 ~ shells, wheel-like structure

G and P /serotypes genotypes

Adenoviruses

dsDNA

nm of diameter, 74 ~ classic icosahedral structure

Serotypes 40 and 41 (Enteric adenoviruses; (EAd

Astroviruses

ssRNA

nm of diameter, 5 28 ~ or 6 points of star-like surface structure

serotypes at 8 least

Caliciviruses Noroviruses Sapoviruses

ssRNA

nm of diameter, 27-32 uncharacteristic surface nm of diameter 33

Many but No. of serotypes unknown

Human Rotavirus

Caliciviruses

Noroviruses

Astroviruses

Adenovirus

Enteroviruses

Epidemiology  

 

Rotavirus is highly contagious, and most infections occur by the fecal-oral route. Adults may be infected after close contact with an infected infant, but the illness in adults is generally mild. In temperate climates, most infections occur in the winter months Rotavirus is the most common cause of severe, dehydrating diarrhea in young children (peak incidence, 3 to 15 mo).

Contd.. Each year in the USA, a wave of rotavirus illness begins in the Southwest in November and ends in the Northeast in March.  Incubation period is 1 to 3 days. 

Contd.. 





Norwalk virus, the prototype calicivirus, most commonly infects older children and adults, and infections occur year-round. Norwalk virus is the principal cause of epidemic viral gastroenteritis; waterborne and foodborne outbreaks are well documented. Person-toperson transmission also occurs because the virus is highly contagious. Incubation is 1 to 3 days.

Contd.. 







Adenovirus serotypes 40 and 41 are the second most common cause of childhood viral gastroenteritis. Infections occur year-round, with a slight increase in summer. Children < 2 yr are primarily affected, and transmission occurs from person to person by the fecaloral route. Incubation period is 8 to 10 days.

Contd.. 

Less is known about the epidemiology of non-Norwalk calicivirus and astrovirus.



Both can infect persons of all ages but usually infect infants and young children.



Calicivirus infections occur year-round, whereas gastroenteritis caused by astrovirus is most common in the winter.



Transmission is via the fecal-oral route. Incubation is 1 to 3 days for both viruses

Signs and Symptoms 

The majority of infections caused by viral enteropathogens are asymptomatic.



In symptomatic infections, watery diarrhea is the most common symptom; stools rarely contain mucus or blood.



Physical findings (eg, dry mucous membranes, tachycardia) are nonspecific and relate to the degree of dehydration.



Infants and young children with rotavirus gastroenteritis may develop severe watery diarrhea lasting 5 to 7 days and leading to isotonic dehydration.

Contd.. 



Vomiting occurs in 90% of patients, and fever > 39° C (102.2° F) occurs in about 30%. Norwalk virus typically causes acute onset of vomiting, abdominal cramps, and diarrhea, with symptoms lasting only 1 to 2 days. In children, vomiting is more prominent than diarrhea, whereas in adults, diarrhea usually predominates.

Contd.. 



Low-grade fever occurs in about 50% of patients. Non-Norwalk calicivirus infections in infants and children are usually indistinguishable from rotaviral illness. However, adults may develop clinical findings more typical of Norwalk virus infection. Astrovirus causes a syndrome similar to mild rotavirus infection.

Viral gastroenteritis is often diagnosed clinically.  Bacterial stool cultures and examinations for ova and parasites will be negative, but these tests are often not necessary in patients presenting with symptoms typical of viral gastroenteritis 

Diagnosis Viral gastroenteritis is often diagnosed clinically.  Bacterial stool cultures and examinations for ova and parasites will be negative, but these tests are often not necessary in patients presenting with symptoms typical of viral gastroenteritis 

Contd.. 

 

Rotavirus, Norovirus and enteric adenovirus infections can be diagnosed rapidly using commercially available assays that detect viral antigen in the stool. Tests to detect the other viral enteropathogens are available in research laboratories only. Electron microscopy,when available,is often used to diagnose these infections. PCR is also now being used more and more

Prevention Prevention of infection is complicated by the frequency of asymptomatic infection and the ease with which these viruses are transmitted from person to person, especially among children in diapers.  Breastfeeding is likely to afford some protection from infection 

Contd..  Caregivers

should wash their hands thoroughly with soap and water after changing diapers, and diaper-changing areas should be disinfected with diluted household bleach or 70% alcohol.

Contd.. 



For rotavirus outbreaks in child care facilities, all children should be tested for excretion of the organism. Infected and uninfected children can then be moved to receive care in different areas and from different caregivers. Several promising rotavirus vaccine candidates are being developed.

New Rotavirus Vaccines Licensed Two new vaccines have recently been licensed  “Rotarix” (GlaxoSmithKline), monovalent, live, oral human 89-12 strain  “RotaTeq” (Merck), pentavalent, live, oral humanbovine reassortants 

Concerns Regarding the Rotavirus Vaccines Concern about the emergence of “new” serotypes and “reassortants” strains require constant monitoring and surveillance.  ‘Updating’ of the new vaccine with the “new” strains could be important to maintain efficacy 

Treatment  

 



The mainstay of therapy is appropriate fluid resuscitation. Even if vomiting, most patients can be effectively rehydrated with oral rehydration solutions. Several of which are available OTC. Sports drinks and carbonated beverages are not appropriate rehydration solutions for children < 5 yr old. IV rehydration is necessary only for patients with severe dehydration.