Rotavirus Case File

Rotavirus Case File

Eugene C.Toy, MD, Cynthia Debord, PHD, Audrey Wanger, PHD, Gilbert Castro, PHD, James D. Kettering, PHD, Donald Briscoe, MD

CASE 35

A 3-year-old male infant is brought to the emergency room in the middle of January with fever, vomiting, and diarrhea for the past day. He has not been able to keep anything down by mouth and has had profuse, very watery stools. He attends day care, and several of his classmates have been out sick recently as well. No adult members of the household have been ill. He has no significant past medical history. On examination, his temperature is 37.9°C (100.2°F), and he has tachycardia. His mucous membranes are dry, and eyes appear somewhat sunken. His abdomen has active bowel sounds and is nontender. His stool is watery and pale. The stool tests negative for blood and fecal leukocytes.

◆ What is the most likely cause of this child’s illness?

◆ How is this virus activated to form an infectious particle?

ANSWERS TO CASE 35: ROTAVIRUS

Summary: A 3-year-old boy who attends day care develops gastroenteritis in the winter.

◆ Most likely cause of this child’s illness: Rotavirus.

◆ How is this virus activated to form an infectious particle: Activation of rotavirus occurs when the outer capsid layer is lysed by gastrointestinal (GI) proteases to create an infectious subviral particle (ISVP).

CLINICAL CORRELATION

Rotaviruses are ubiquitous worldwide and are estimated to cause more than 50 percent of gastroenteritis cases occurring in children less 2–3 years of age, resulting in approximately 4 billion annual cases. Infections typically occur in the cooler months and result in abrupt onset of vomiting followed with frequent watery diarrhea. Illness is typically self-limiting; however, severe infection can result in immunocompromised or malnourished children and may be fatal. Outbreaks are common in day care, preschool, and hospital settings. Adults may also become infected but usually have few if any symptoms.

APPROACH TO SUSPECTED ROTAVIRUS INFECTION

Objectives

1. Be able to describe the characteristics of the virus.
2. Be able to describe the strategies for prevention and treatment of the infection.

Definitions

Tachycardia: An increased heart rate.

Reassortment: The formation of new virions with hybrid genomes assembled in cells with mixed viral infections, which occurs among viruses containing segmented genomes (i.e., influenza viruses and reoviruses), resulting in high genetic variation.

Intussusception: Blockage of the intestines as a result of the bowel telescoping into itself.

DISCUSSION

Characteristics of Rotavirus That Impact Transmission

Rotavirus is one of the four genera of the family Reoviridae and is a common cause of childhood gastroenteritis around the world. The virus consists of a double-layered protein capsid that contains a genome made of 11 segments of double-stranded, negative-sense RNA. The double capsid looks like a wheel with short spokes connecting the outer capsid to the inner capsid and core, thus the name Rotavirus. As a nonenveloped virus, it retains its infectivity in a wide range of pH and temperatures and is resistant to many common detergents as well. Rotavirus is spread through fecal-oral contact, and because of its stability, fomite transmission can also occur. The virus would be inactivated by the pH of a normal, empty stomach but can survive in a buffered stomach or in the gastric environment following a meal. The outer capsid of the virus is partially digested by GI proteolytic enzymes, creating an infectious subviral particle (ISVP). A surface protein of the virus, VP4, is also cleaved by GI proteases, allowing it to bind to the surface of intestinal epithelial cells and allow the ISVP to enter by direct penetration. The RNA genome remains in the viral core and is transcribed into mRNA by a viral polymerase. The mRNA is then transported out of the core to the cell cytoplasm, where it is translated and assembled into new virions. The initial assembly of rotaviral virions is similar to enveloped virions. As the newly formed rotaviral virions bud through the endoplasmic reticulum (ER), they acquire the membrane as an “envelope.” However, this “envelope” is soon lost as the virions continue through the ER, and the infectious rotaviral particles are then released from the host cell by cell lysis.

Rotaviruses have been classified into at least three different major subgroups and nine different serotypes based on antigenic epitopes of the inner capsid protein VP6. There are primarily four serotypes that are important in causing human disease. Because of the segmented nature of the genome, rotaviruses are capable of producing virions with high genetic variation as a result of the reassortment of genome sequences in mixed infections. This high genetic variability results in increased numbers of serotypes for this viral group and allows for reinfection of persons previously exposed to one rotaviral serotype. Reinfections are common, yet successive infections appear to cause less severe symptoms.

The mechanism by which rotaviral infection causes diarrhea is not entirely understood. Rotaviral particles infect the cells of the small intestinal villi and multiply in the cytoplasm of enterocytes. Damaged cells are sloughed off, releasing large numbers of viral particles into the stool. Virus can be excreted for days to weeks after infection. The infection prevents absorption of water, sodium, and glucose, resulting in a loss of water and electrolytes. A virally encoded nonstructural protein also acts as an enterotoxin, similar to those of Escherichia coli and Vibrio cholerae. Typical symptoms of rotaviral infection include fever, vomiting, abdominal pain, and watery diarrhea without blood or mucus. The net result is a profuse watery diarrhea that can cause dehydration without appropriate fluid and electrolyte replacement. Symptoms may last for approximately 1 week, with viral excretion lasting weeks longer. Severe and prolonged illness can occur in immunodeficient and malnourished children and without supportive therapy infection can be fatal. Infection with rotavirus stimulates a humoral response; however, protection against reinfection is temporary and incomplete. The presence of high levels of rotavirus IgA in the lumen of the intestine confers relative protection.

Diagnosis

Because the symptoms of rotaviral infection resemble those of other viral diarrhea producing agents, the definitive diagnoses of rotaviral infection requires the detection of viral antigens in stool samples. Enzyme immunoassay and latex agglutination are two easy, rapid assays used to confirm rotaviral infection. Additionally, PCR can be used for genotyping viral nucleic acid in stool specimens. Viral culture is both difficult and unreliable and therefore is not used for diagnoses.

Treatment and Prevention

Treatment of rotaviral infection is supportive, including the replacement of fluids and electrolytes to restore physiologic balance and prevent dehydration. Both oral and intravenous rehydration therapy are effective, and which one is used depends on the severity of dehydration. Because rotaviruses can retain infectivity over a wide range of pH and temperatures and are resistant to many common detergents, strict hand washing and use of gloves is necessary to limit nosocomial spread.

An attenuated recombinant Rotavirus vaccine was developed and used in children for several years. However, its approval was withdrawn, and its use stopped because of concerns with the development of intussusception among vaccine users. A new rotavirus vaccine was approved by the FDA and released in 2006; to date, it has not been shown to be associated with intussusception. Another difficulty with the production of such a vaccine is that a single vaccine may not protect against all Rotavirus serotypes.

COMPREHENSION QUESTIONS

[35.1] You isolate a virus from the stool of a 1-year-old infant with signs of fever, vomiting, and diarrhea. Laboratory results show that the viral genome is composed of multiple segments of double-stranded RNA, which leads you to suspect that rotavirus is the causative agent of infection. Which of the following statements is true regarding rotavirus replication?

A. The viral genome integrates into the host chromosome.

B. The virus uses the host RNA polymerase for replication of its genome.

C. The segmented genome contributes to the antigenic variation of the virus.

D. The viral agent has a single antigenic type.

E. The newly assembled viral particles are released via budding through the host cell membrane.

[35.2] Similar to rotavirus, which of the following viral agents is also a nonenveloped RNA virus known to cause gastroenteritis diarrhea in young children?

A. Calicivirus

B. Paramyxovirus

C. Parainfluenza virus

D. Coxsackie virus

E. None of the above

Answers

[35.1] C. The segmented genome of rotaviruses, allows for the assembly of new virions with mixed genomes in cells multiply infected as a result of reassortment; answers A, B, D, and E are incorrect: (A) the rotaviral genome consists of double-stranded RNA and replicates in the cytoplasm and thus does not integrate into the host chromosome; (B) as an RNA virus that replicates in the cytoplasm, the rotoviral

genome is replicated by a viral RNA polymerase; (D) the high genetic variability of rotaviruses because of reassortment results in multiple viral serotypes, at least nine different serotypes have currently been

classified in human illness; (E) newly assembled nonenveloped rotaviral particles are released by cell lysis.

[35.2] A. Like rotaviruses, caliciviruses are nonenveloped RNA viruses that cause watery diarrhea, especially in children; answers B, C, D, and E are incorrect: (B) Paramyxoviruses are enveloped RNA viruses that cause childhood respiratory and exanthemous infections; (C) Parainfluenza viruses are enveloped RNA viruses which cause respiratory infections such as croup, bronchiolitis, and pneumonia in children; (D) Coxsackie viruses are nonenveloped RNA viruses that cause nonspecific respiratory tract infections, febrile rashes, and meningitis.

MICROBIOLOGY PEARLS ❖ Rotaviruses are ubiquitous, causing greater than 50 percent of gastroenteritis cases in children under 2–3 years. ❖ Rotaviruses are composed of a double-layered protein capsid and a segmented double-stranded RNA genome, allowing the new virions to have high genetic variation as a result of reassortment. ❖ Clinical manifestations: abrupt onset of fever, vomiting, abdominal pain, and watery diarrhea without blood or mucus. ❖ Only supportive treatment of infection including fluid and electrolyte replacement.

REFERENCES

Brooks GF, Butel JS, Morse SA. Jawetz, Melnick, & Adelberg’s Medical Microbiology, 23rd ed. New York: McGraw-Hill, 2004:505–8. 

Centers for Disease Control and Prevention. Intussusception among recipients of rotavirus vaccine—United States, 1998–1999. Morb Mortal Wkly Rep 1999; 48:577–81. 

Ryan JR, Ray CG. Sherris Medical Microbiology, 4th ed. New York: McGraw-Hill, 2004:577–81.

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