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Rotaviruses

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الكلية كلية طب حمورابي     القسم الكلية ذات القسم الواحد     المرحلة 3
أستاذ المادة نيران كاظم فرهود الربيعي       12/01/2017 18:28:25
RNA Viruses-related to enteric tract infection

1-Rotaviruses
Rotaviruses are the single most important etiologic agents of severe diarrheal infection in neonates and young children.Worldwide, rotavirus is estimated to account for 40% of all cases of severe infant diarrhea.
It is stable in the environment and remains viable for weeks or months if not disinfected. Relatively resistant to hand-washing agents. Susceptible to disinfected (95% ethanol, Lysol, and formalin).
Rotaviruses replicate mainly in the epithelium of small intestine, and infect enterocytes of the villi of the small intestine, leading to structural and functional changes of the epithelium.

Important properties
• It belongs to Reoviridae family .
• dsRNA genome.
• Icosahedral capsid .
• It is Non-enveloped virus ( a naked virus) .
• It has 7 Groups (A- G ) , Group A is important human pathogen.
• It has a characteristic wheel-like appearance when viewed by electron microscopy .

Epidemiology
• Children were almost universally infected before the age of 5 years.
• The peak incidence of infection was between 7 and 15 months.
• Most frequent during the winter.
• Usually endemic, but responsible for occasional outbreaks.

Source and Transmission
• Rotavirus infection is highly contagious, it is founding in other mammals and birds, causing diarrhea.
• Rotavirus transmitted from person to person via (fecal-oral route, fomites).
• poor hygiene.
• contamination of food and water.

Signs and Symptoms
• incubation period is (1- 4) days.
• Three main symptoms of rotavirus infection:
(Fever , Vomiting , Watery diarrhea)
• Abdominal pain may also occur.
• Viremia uncommon.
• Diarrhea usually stops after 3 to 7 days.
• Loss of electrolytes and fluids leading to dehydration.
• May be fatal unless treated.


Laboratory Diagnosis
• Culture: Group A Rotaviruses can be cultured in monkey kidney cells.
• Diagnosed by electron microscopy. The wheel-like appearance of the virus under the microscope.
• Serological test:
- Antigen detection in feces by ELISA or other assays.
- Antibody detection in serum by ELISA.
• polymerase chain reaction (PCR) Technique by (RT-PCR).

Treatment
Fluid replacement
- Management consists of replacement of fluid (ORS) and restoration of electrolyte balance.

- Oral rehydration therapy is highly effective in reducing morbidity and mortality.





Prevention
• A vaccine against rotavirus:
Alive, oral, pentavalent, human-bovine reassortant vaccine.
Currently there are 2 rotavirus vaccines administered at 2,4, and 6 months of age:
– RotaTeqTM
– RotarixTM

The Main characteristics of the two vaccines:
– Both are highly effective and safe.
– Both protect against severe forms of rotavirus disease.
– Both do not protect against diarrhea caused by other agents than rotavirus.









2-Astroviruses

Important properties
• It belongs to Astroviridae family .
• ssRNA genome.
• It has 8 human serotypes: HAstV-1 to HAstV-8
• Non-enveloped
• Icosahedral capsid.
• Virions have a characteristic star-like surface structure (5 or 6 points) when viewed in an electron microscope (hence the name; the Greek word “action” means star).


Source and Transmission
• Astroviruses transmitted from person to person via fecal-oral route (i.e., virus is passed via contaminated food and water)
• Astroviruses are resistant to desiccation and can survive for extended periods of time on inert surfaces.
• Human Astroviruses have been detected in multiple types of water sources, including drinking water, rivers, dams, wastewater and effluents from water treatment plants. Multiple serotypes can be found in a single water sample.
• Human Astrovirus can survive in water after chlorination.

Signs and Symptoms
• incubation period is (3 to 4 ) days.
• Diarrhea: In general, Astrovirus diarrhea is less severe than rotavirus diarrhea and results in fewer hospitalizations
• abdominal pain.
• Vomiting is uncommon
• Fever.
• Dehydration.
• the duration of diarrhea is 2-3 days on average and never bloody.
• Hospitalization rates are about 6%.




Laboratory Diagnosis
• Electron microscopy.
• Serological test:
- Immunofluorescence.
- enzyme-immunoassay (ELISA).
• polymerase chain reaction (PCR) Technique.

Treatment
Disease caused by human Astrovirus is usually not serious enough to require any specific therapy. However, if diarrhea is particularly acute, oral or intravenous rehydration therapy may be necessary. Intravenous immunoglobulin may help in severely immunocompromised patients.

Prevention and Control
There is currently no vaccine for human Astrovirus. Interruption of transmission is crucial in limiting the spread of human Astrovirus. This is especially important in hospitals, daycare centers, and in family settings. Universal hygienic procedures must be enforced in all settings-that is, thorough hand washing after using the bathroom or changing a diaper and before preparing or consuming food.

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3- Noroviruses

Important properties
• It belongs to Caliciviridae family (whose name is derived from calyx, which means cup in Greek)
• ssRNA genome.
• Non-enveloped
• Icosahedral capsid.

Source and Transmission
• The virus is transmitted from person to person via the fecal-oral route.
• contaminated food or water. foods can be contaminated at the source or during preparation by food handlers.
• Contact with contaminated surfaces or fomites.
Pathogenesis
Noroviruses at least 25 genotypes, are the most common causes of outbreaks of gastroenteritis in hospitals, nursing homes and but are increasingly recognized as a common cause of sporadic gastroenteritis in both adults and children.

Epidemiology
Affects all ages, seasonality occurs year round. outbreaks tend to peak in cold weather.

Signs and Symptoms
• incubation period is (12-48) hours.
• Sudden onset of vomiting (more common in children) .
• low-grade fever.
• Nausea.
• Diarrhea (more common in adults). Diarrheal stools usually contain no blood, mucus, or leukocytes.
• Severity of illness Overall, less severe than many other diarrheal infections but can lead to dehydration and hospitalization, especially among children <5 years of age and adults >65 yr of age. Typically this illness is of short incubation and short duration and in children is a less severe disease than rotavirus infection. Viral shedding peaks 1–3 days after onset of illness.

Immunity
Immunity illness results in short-term homologous immunity; infections can occur with other strains or with the same strain later in life; repeated exposure may
generate long-term immunity.


Treatment
Supportive therapy to prevent dehydration; no specific antiviral therapy available.

Prevention and Control
Vaccine development is in early phase. Research has consistently shown that probiotics, such as Lactobacillus and Saccharomyces boulardii, reduce the frequency and/or duration of diarrhea in acute infantile gastroenteritis by 30-70%. Their role in the treatment and prevention of acute infantile gastroenteritis is still undefined.

Table 1. Features of common viruses causing gastroenteritis
Viruses

Family

Genome Type
Genome Organisation Enveloped Morphology
Rotavirus Reoviridae dsRNA Segmented No Spherical with wheel-like surface structure
Astrovirus Astroviridae ssRNA Linear No Small, with star-like surface structure
Norovirus Caliciviridae ssRNA Linear No Small, round structure
Adenovirus Adenoviridae dsDNA Linear No Icosahedral





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