Rotavirus

 

by Sheryl Roxas 

Disease Etiology

Rotavirus comes from the family Reoviridae and there are 7 species or groups (A to G).  It is group A that causes about 90% of infections in humans. Group B is mainly found in China where outbreaks occur annually. Group C is found worldwide, while group D, E, and F has not been found in humans. Rotavirus is known to be a childhood disease since it mainly infects children, though adults can also be susceptible, especially the parents of the infected kids. [1, 5]

 

Transmission

People pass it to each other through ingestion of fecal matter by contact with contaminated objects, surfaces or hands.  It is thought that it could also be transmitted through the respiratory route. [1, 2, 3, 4, 6]

 

Reservoirs

Depending on the species, Rotavirus can infect humans and animals alike. [1]

 

Specific Microbial Characteristics

“Rotavirus is a non-enveloped, icosahedral in symmetry, and is a double capsid virus. It is a 60-80 nm wheel with radiating spokes and it has a double stranded RNA with 11 segments”. VP4 and VP7 are the proteins that make up the outer structure while VP4 is the viral hemagglutinin that forms the spikes on the surface. VP1, VP2, VP3, and VP6 are the proteins that make up the inner core structures while VP6 alone is the antigenic determinant. [1]

 

Specific Test for Identification                                  

There are a couple of ways to diagnose Rotavirus. You can use ELISA (enzyme linked immnuosorbent assay) to detect the antigen in the stool. There are some kits that are ready for purchase at the store but these only detect group A. Another way to is through electron microscopy and this method detects non-group A species. The third way detects only group A by culturing the virus in monkey kidney cells. If there is an outbreak in a specific place, polyacrylamide gel electrophoresis can detect the migration patterns of the viral RNA, which can distinguish different strains of a species. [1, 2, 4] Another test, though uncommonly used, is the reverse transcriptase polymerase chain reaction. [2]

 

Signs/Symptoms

The Rotavirus has an incubation period of less than 4 days and is contagious before the onset of diarrhea (watery stool) until after a few days the diarrhea has disappeared. Usually, a person has nausea and vomiting, then the diarrhea that can last for about a week. [5] The watery stool does not contain blood or leukocytes. Sometimes, a person can also have a low grade fever or abdominal pain [2]. Dehydration is present when there is severe diarrhea and proper hydration is not maintained. A person can also have malabsorption of lactose and fat (lactose intolerance) causing chronic diarrhea. In neonates, necrotizing enterocolitis and hemorrhagic gastroenteritis can occur. [1, 4]

 

Historical Information

1973 was the year Rotavirus was identified by Ruth Bishop through electron microscopy in the specimens from children with diarrhea. Later on, it was proposed to be named Rotavirus (rota is Latin for wheel) since the virus looks like a wheel. [1, 2]

 

Virulence Factor

Rotavirus is stable in the environment up to several months. It is resistant to hand washing but is susceptible to 95% ethanol, formalin, and Lysol but is unstable in a pH below 2. Mature enterocytes lining the intestinal villi are the affected host cells. In animals, hepatocytes are found to also be infected. Rotavirus infects the host cells after protease digestion in the GI tract removes the capsid protein (VP4), so the viral attachment protein is then exposed. Replication occurs in the host cell cytoplasm and the virions enter by endocytosis. Viral mRNA is now transcribed and forms the structural protein units of the capsid using viral RNA polymerase that is already present in the virion. Then, mRNA segments are joined with the immature capsid and replication occurs once more to form the double stranded RNA genome. Rotavirus particles disperse in the watery stool (diarrhea), making it the mode of transmission. The stool becomes watery because the infected cells die and deteriorate causing intestinal fluid secretions due to repopulation of immature secretory cells. When repopulation of the immature secretory cells occurs again, lactose intolerance is the result. [1]

 

Control/Treatment

There are no treatments for Rotavirus, but dehydration that resulted from diarrhea is treatable. Oral or intravenous rehydration is to be maintained if severe diarrhea persists or dehydration can lead to unnecessary death. [1, 2, 3, 4, 5, 6] It is also recommended to eat bland foods and for infants, to drink diluted formula or regular breast milk if breastfeeding. [4]

 

Prevention/Vaccines

Preventative measures include good hand washing technique, disinfecting surfaces, toilets and objects like toys that will find its way to the mouths of children, and chlorinating the water in the community to stop the spread of infection. [1, 4, 6] A person develops partial immunity after the first infection but it is not guaranteed that it will be permanent or you will never be infected again. [2]

Vaccines have been developed to fight Rotavirus. The first vaccine (Rotashield) in the market has been removed (on Oct 1999) when studies have linked it to intussusception. Rota Teq was licensed in the US in 2006 and it has three doses taken at 2, 4, and 6 months of age. The minimum age for the first dose is at 6 weeks old. Rotarix is the other vaccine that was licensed in the US in 2008 and it has a two dose schedule (at 2 and 4 months old). It is said that after the second dose, you get protection through the first two years of life. [1, 2, 4, 6]

 

Local cases/outbreaks

Rotavirus occurs during the winter months of November through May [5], in which it spreads from Mexico and southwest US to north/northeast US and Canada. Annually, 20-40 deaths occur with 50-70,000 hospitalizations [2, 3] and 500,000 doctor visits. Usually, 1-2.5% cases present severe dehydration. Each year, 2.7-3.5 million people in the US are affected with the Rotavirus. [1]

 

Global cases/outbreaks

In contrast with the US, Rotavirus is seen all year round in the tropics. [4]

Rotavirus is found worldwide, “causing major diarrhea-associated hospitalization and 600,000-850,000 deaths per year” [3] and 80% of the deaths that occur are in poorer countries that lack sanitation.[2] It is said that all children by the age of 3 will have been infected by Rotavirus.[1, 4, 5, 6]

 

References

 

  1. Microbiology and Immunology. Virology-Chapter 17-viral agents of Gastroenteritis-Rotavirus. Updated 5/509. http://pathmicro.med.sc.edu/virol/rotaviruses.htm.  2/23/10.
  2. Centers for Disease Control and Prevention. Rotavirus. Updated 9/23/09. http://www.cdc.gov/rotavirus/. 2/23/10.
  3. Merck. Rotavirus Infection. Updated 5/2007. http://www.merck.com/mmhe/sec23/ch 273/ch273k.html. 2/23/10.
  4. Johns Hopkins Medicine. Rotavirus. No information given when created or updated. http://www.hopkinsmedicine.org/heic/ID/rotavirus/. 2/23/10
  5. MedlinePlus. Rotavirus Infection. Updated 1/28/10. http://www.nlm.nih.gov/medlineplus/rotavirusinfections.html. 2/23/10
  6.  Mayo Clinic. Rotavirus. Created 8/8/08. http://www.mayoclinic.com/health/rotavirus/DS00783/METHOD=print. 2/23/10