Viral Infections and Reoviridae Family

Study Notes

Viral infections are a common cause of gastrointestinal (GIT) illnesses, affecting millions yearly.
Viral gastroenteritis is particularly dangerous in children, resulting in thousands of deaths annually, especially in developing countries.
Viral hepatitis is a significant health concern worldwide, including in Egypt.

Reoviridae is a family of double-stranded RNA (dsRNA) viruses.
The name comes from "respiratory," "entero," and "orphan" as they were initially isolated from respiratory secretions and stool without a known associated human disease.
The most medically important member of this family is Rotavirus.
Reoviruses have icosahedral capsids and are non-enveloped.
Their genomes are segmented into 10-12 segments grouped by size: L (large), M (medium), and S (small).

Rotavirus is the main member of the Reoviridae family.
It is a dsRNA virus with three shells: an outer, an inner, and a core encapsulating 11 segments of dsRNA.
Rotavirus infections cause endemic and epidemic gastroenteritis, particularly infantile diarrhea, a leading cause of death in developing countries.
Infections are generally self-limiting but can be fatal in infants without proper treatment.
The virus is prevalent in children, especially in daycare settings.
Infection occurs through the fecal-oral route.
Diagnosis involves detecting the virus in stool using electron microscopy (EM) or isolating it through culture.
Treatment focuses on oral rehydration therapy with isotonic glucose/mineral salt solutions.
No specific antiviral drugs are available.

Rotarix is a monovalent, human, live attenuated rotavirus vaccine containing one rotavirus strain.
It is administered orally in two doses at 2 and 4 months of age.
RotaTeq is a live attenuated, oral pentavalent vaccine containing five rotavirus strains produced through reassortment.
RotaTeq (RV5) is given in three doses at 2, 4, and 6 months of age.

Noroviruses, also known as Norwalk viruses, are caliciviruses.
Many strains cause gastroenteritis.
Millions of cases occur annually, primarily in infants, young children, and the elderly.

Noroviruses (NoV) are genetically diverse, single-stranded, positive-sense RNA viruses belonging to the Caliciviridae family.
They are non-enveloped.
Noroviruses are classified into seven genogroups (GI, GII, GIII, GIV, GV, GVI, and GVII), which can be further subdivided into genotypes.
Genogroups GI and GII are the most common in human infections.

Norovirus infections present with similar symptoms to rotavirus: watery diarrhea, mild cramps, and fever.
Sometimes, projectile vomiting occurs.
Illness is usually mild, developing 12 to 48 hours after exposure and resolving within two days without treatment.
Dehydration can be a concern.

Astroviruses are a family of single-stranded, positive-sense RNA viruses.
They cause vomiting, diarrhea, and fever, primarily in children under 5 years old.
Astroviruses are a common cause of acute gastroenteritis in children, with a varying prevalence depending on the geographical region.

Enteroviruses are small, non-enveloped viruses belonging to the Picornaviridae family.
They are single-stranded, positive-sense RNA viruses.
Enteroviruses can cause a range of illnesses, including polio, hand-foot-and-mouth disease, and viral meningitis.

Poliovirus is a highly contagious enterovirus responsible for poliomyelitis (polio).
Polio is a paralytic disease that can cause permanent disability and death.
Poliovirus spreads through the fecal-oral route.
Infection occurs through the ingestion of contaminated food or water.
Polio can lead to paralysis by affecting the central nervous system.

There are two main types of poliovirus vaccines:
- Salk vaccine (inactivated poliovirus vaccine, IPV)
- Sabin vaccine (oral poliovirus vaccine, OPV)
The Salk vaccine is an inactivated vaccine that contains killed poliovirus.
The Sabin vaccine is a live attenuated vaccine that contains a weakened form of poliovirus.
Both vaccines are effective in preventing polio.
OPV is administered orally and provides herd immunity, while IPV is injected and does not provide herd immunity.
IPV has replaced OPV in most countries due to its effectiveness and safety.

Presents with fever, vomiting, and diarrhea, diagnosed with viral gastroenteritis.
The doctor inquires about recent poliomyelitis vaccine booster and Rotavirus vaccination status.
Ali is treated with fluids due to dehydration.
After recovering, Ali receives a Rotavirus vaccine.