Rotaviruses, Adenoviruses, Caliciviruses, Astroviruses

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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