This document discusses four common viruses that cause gastroenteritis - rotaviruses, adenoviruses, caliciviruses, and astroviruses. It provides details on their morphology, genome, and epidemiological aspects. Rotaviruses are the leading cause of severe diarrhea in young children worldwide. Noroviruses account for about 10% of all cases of viral gastroenteritis. While most were initially identified using electron microscopy, reverse transcription polymerase chain reaction (RT-PCR) is now commonly used for molecular diagnosis.

2. Gastroenteritis
viruses
ROTAVIRUSES, ADENOVIRUSES, CALICIVIRUSES, ASTROVIRUSES
DR.KAVEH HARATIAN, ALBORZ UNIVERSITY OF MEDICAL SCIENCES

3. Viruses causing gastroenteritis
Virus Approximate diameter
of virion(nm)
Important
morphological
features
Genome
Rotavirus 70 A number of spokes
radiate from a central
hub (=wheel)
Linear dsRNA, 18kbp,
11 segments
Adenovirus type 40, 41 80 – 110 Icosahedral, fibers
extending from the
apices
Linear dsdna, 36kbp,
ITR and protein primer
at each 5`
Calicivirus 35 32 cup-like
indentation on
surface(=cup)
Linear ssRNA+, 7.5kb,
a 5` VPg, poly A tail at
3` end.
Astrovirus 30 Arrangement of
capsomers gives the
appearance of 5-6
pointed star
Linear ssRNA+, 7kb,
poly A tail at 3` end.
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4. Start points…
 Over 300 million episodes of diarrhea yearly in adults .
 500,000 hospitalization and 3000 deaths.
 Noroviruses accounts for 10% of mentioned above.
 Rotavirus is the leading cause of severe diarrhea.
 Most of them were first recognized by EM(still used for diagnosis)
 Some of them do not grow in the laboratory.
 RT-PCR is used for molecular diagnosis .
 Spread rapidly by fecal-oral route. (washing hands after defection)
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5. Rotaviruses properties
 Members of Reoviridae
 REO : Respiratory Enteric Orphan
 Identified in respiratory tract and gut.
 A genus plus Orbivirus and Coltivirus.
 The capsid has a double shell, #100 nm.
 Single shelled particles also may be seen (some smaller)
 Virus particles comprises 3 layers : inner, intermediate and outer.
 Main proteins of each layer :
 Inner core : VP2 and RNA dependent RNA polymerase(replicase,VP1)
 Inner icosahedral capsid is essentially group specific antigen VP6
 Outer icosahedral capsid is essentially VP7.
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6. Rotavirus (EM) 6

7. Rotavirus genome 7

8. Rotavirus clinical features
 Primarily infects the young of many species : humans.
 Babies U2 are the main victims.
 Outbreaks in elderly esp. in institutions.
 IP=2-4 d., vomiting diarrhea & fever (silent infections may occur).
 Diarrhea mainly is caused by viral NSP4 (enterotoxin).
 Dehydration is prominent ,must be dealt promptly.
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9. Rotavirus pathogenesis
 Virus attack the columnar epithelium at the apices of the villi of the
duodenum and upper ileum.
 Results in malabsorption.
 Regeneration of the villi is normally rapid after the acute attack.
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10. Rotavirus epidemiology
 Outbreaks typically occur in the winter !
 Spread is mainly from the fecal – oral route + seasonal incidence :
respiratory infection can not be ruled out.
 Virus is relatively resistant to chemical disinfectants.
 Spreads rapidly when hygiene is inadequate.
 Chronic rotavirus infection can be troublesome in patients with primary
immunodeficiency.
 Six serotypes(A-F) identified basis on VP6 , most human rotaviruses are
members of group A.
 Due to segmentation of genome there may be reassortant strains.
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11. Calicivirus properties
 Such as Norovirus.
 Family Caliciviridae
 Infect a very wide host range : mammals, birds, reptiles and even
fish.
 Four genera (2 infects humans):
 Norovirus(formerly Norwalk-like viruses)
 Sapovirus
 Noroviruses undoubtedly is the major pathogen in this family.
 Hepatitis E virus(HEV) is a Calicivirus.
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12. Calicivirus(EM) 12

13. Hepatitis E Virus distribution 13

14. Calicivirus epidemiological aspects
 Norwalk, Hawaii, Taunton, Snow mountain virus, …
 Etiological role of some of these was proved by volunteers.
 Modes of transmission :
 Fecal – oral
 Inhalation of aerosols from vomit
 Contamination from food/water
 shellfish
 Norovirus causes:
 Outbreaks of vomiting, projectile + diarrhea
 Ip= 12-48 h., onset is often sudden.
 Abdominal pain, nausea, low-grade fever
 Stool do not contain blood or mucus.
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15. Astrovirus properties
 Only 1 genus : Astrovirus : 8 serotypes affects humans.
 Outbreaks of diarrhea secondly after rotavirus worldwide.
 IP=3-4 d., Vomiting is not a predominant feature.
 Well-marked peak of incidence in temperature climate in winter.
 Adults show symptoms if exposed to high doses of virus.
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16. Astrovirus(EM) 16

17. Laboratory diagnosis
 There are 2 approaches to diagnosis :
 Electron Microscopy of fecal extracts :
 A specific antiserum added before specimen is mounted and stained will
clump any Virion of same specificity.
 Used for Rota, Adeno, Astro and some enteroviruses.
 Specific tests : for Calici, Astro, Adeno and Rotaviruses
 ELISA tests
 RT-PCR
 Antibody detecting(for that replicate but don’t make CPEs)
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