Nonenveloped (+) strand RNA viruses - Aucoin

Question 1

Name the viral genus’ that are part of the family picornaviradae.

Answer 1

1. enterovirus
2. rhinovirus
3. heparnavirus

Question 2

Name the viruses that are part of the genus enterovirus.

Answer 2

1. poliovirus
2. cocksackie virus A and B
3. Echovirus
4. enterovirus

Question 3

Name the viruses that are part of the genus rhinovirus.

Answer 3

rhinovirus

Question 4

Name the viruses that are part of the genus heparnavirus.

Answer 4

Hepatitis A

Question 5

Describe the unique properties of Picornaviruses.

Answer 5

1. Virion is naked, small, icosahedral capsid enclosing positive strand SSRNA genome - N:ICO:(+)ss
2. enteroviruses are resistant to pH 3-9, detergents, sewage treatment and heat, spread thru fecal-oral route
3. rhinoviruses are labile at acidic pH with an optimum growth at 33 degrees celsius.
4. genome is mRNA so is infectious without capsid
5. replicates in cytoplasm
6. polyprotein produced from viral RNA genome

Question 6

Poliovirus is an example of the picornaviradae family. Describe its infection and replication.

Answer 6

1. binds to tropic tissue and gets into cel via receptor-mediated endocytosis.
2. loses capsid in endosome.
3. has Vpg, a protein primer that takes the place of the 5 prime cap so that the pos. sense RNA can bind to ribosome.
4. RNA dependent RNA polymerase is made so that virus can replicate.
5. virions self assemble and leave via lysis.

Question 7

What is essential for the replication of pos. strand RNA viruses?

Answer 7

They must encode for RNA-dependent RNA polymerase, since the genome is basically mRNA , this enzyme does not have to be itself included in the virion.

Question 8

Describe some important characteristics of Poliovirus.

Answer 8

1. transmitted via the fecal-oral route
2. is an enterovirus in the family of picornaviradae
3. paralytic polio remains high in developing countries
4. only 1% of infections are clinically apparent

Question 9

Describe the clinical course of Poliovirus.

Answer 9

1. initial replication in oropharynx and small intestines - causes nausea and vomiting.
2. disease ranges from asymptomatic to paralytic poliomyelitis.
3. polio is an acute viral infection of the meninges and the motor neurons of the spinal cord and brainstem.
4. eradicated in West but still endemic to Nigeria, Pakistan and Afghanistan.
5. diagnosis - poliomyelitis may be suspected in pt’s with acute onset of flaccid paralysis. recovery of poliovirus from a stool sample or swab of pharynx.

Question 10

Describe drop leg syndrome.

Answer 10

This is a cardinal sign of polio and presents as the gastrocnemius constantly flexing while the anterior tibialis is constantly relaxing so the the toe looks like it is pointing.

Question 11

What is one cause of viral meningitis?

Answer 11

Enterovirus - from the family picronaviradae and the genus enterovirus.

Question 12

Describe viral meningitis.

Answer 12

1. usually less severe than bacterial meningitis.
2. most cases in the summer, caused by enteroviruses.
3. occurs mostly in children younger than age 5.
4. spread via fecal-oral route.
5. characterized by a sudden onset of fever, headache, and stiff neck.
6. other symptoms - nausea, vomiting, photophobia, altered mental status.
7. symptoms last from 7-10 days and immune intact patients usually recover completely.
8. diagnosis - blood sample, CSF sample tested for virus.

Question 13

Describe some important characteristics of Coxsackie virus.

Answer 13

1. family picornaviridae, genus enterovirus.
2. Group A or B types.
3. usually causes symptoms in young children with naieve immune systems.
4. spread via fecal-oral route and respiratory aerosols.

Question 14

Describe the clinical course of coxsackie virus.

Answer 14

1. Group A - causes ‘hand,foot, and mouth’ disease or herpangina. Presents with ulcers in oropharynx, fever and sore throat.
2. Group B - causes pleurodynia - fever and severe pleuritic-type chest pain. Can also cause myocarditis - fever, chest pain, and signs of congestive heart failure.
3. Both A and B can cause aspetic meningitis and mild paralysis.
4. diagnosis via PCR of virus in spinal fluid , no treatment for virus itself.

Question 15

Describe Echovirus.

Answer 15

1. family picornaviridae, genus enterovirus.
2. ECHO stands for enteric, cytopathic human orphan
3. has over 30 serotypes
4. spread via fecal-oral route, often transmitted via pool water.

Question 16

Describe the clinical course of Echovirus.

Answer 16

1. one of leading causes of aseptic meningitis - fever, headache, stiff neck, photophobia.
2. also may cause upper respiratory tract infection - fever, infantile diarrhea, hemhorragic conjunctivitis.
3. may also cause hand, foot and mouth disease.
4. diagnosis - PCR, no antiviral therapy or vaccine available.

Question 17

Describe Rhinovirus.

Answer 17

1. family picornaviridae, genus rhinovirus.
2. main cause of common cold.
3. over 100 serotypes.
4. transmitted by aerosolized droplets or fomites.
5. portal of entry is upper respiratory tract.

Question 18

Describe the clinical course of rhinovirus.

Answer 18

1. infection limited to upper respiratory tract since virus is sensitive to pH and temp.
2. replicates better at 33 degrees celsius so infects nose rather than lower respiratory tract.
3. incubation period of 2-4 days.
4. symptoms - sneezing, nasal discharge, sore throat, cough and headache - USUALLY NO FEVER.
5. lasts about a week.

Question 19

Describe the Hepatitis A virus.

Answer 19

1. family picornaviridae, genus heparnavirus.
2. only one serotype - also known as enterovirus 72.
3. spread via fecal-oral route.
4. infection from fecally contaminated water and food.

Question 20

Describe the clinical course of Hepatitis A virus.

Answer 20

1. symptoms - fatigue, fever, nausea, vomiting, jaundice, dark urine, pale feces, and elevated AST and ALT.
2. can be asymptomatic, mild or severe.
3. IgG detected 1-3 weeks later and provides lifelong protection.
4. resolves in 2-4 weeks, no chronic infection so no chance of cancer.
5. diagnosis - IgM or 4-fold rise in IgM titers.
6. vaccine available and recommended for travel.
7. long incubation period - 15-50 days.

Question 21

What is one clinically important virus of the family Caliciviradae?

Answer 21

Norwalk virus.

Question 22

Describe Norwalk virus.

Answer 22

1. family caliciviradae, genus norovirus.
2. spread via fecal-oral route.
3. spreads easily in close quarters.

Question 23

Describe the clinical course of norwalk virus.

Answer 23

1. one of the most common causes of viral gastroenteritis in older children and adults in the US.
2. caused by ingestion of contaminated seafood or water - pools, cruise ships are common sources.
3. infects mucosal cells of GI tract.
4. characterized by sudden onset of vomiting, non-bloody diarrhea, low-grade fever and abdominal cramping.
5. short incubation period - about 24 hours.
6. no vaccine or therapeutic available.
7. diagnosis - clinical, PCR can be done on stool sample