Other RNA viruses Flashcards
To which family do the influenza viruses belong?
Orthomyxoviridae
What is the morphology of the influenza viruses?
- Enveloped negative-sense single-stranded RNA viruses
- Have a segmented genome
- Replicate in the nucleus
- Classified into three types (A, B, and C)
What is the basis of the classification of influenza viruses into three types?
The differences in the nucleocapsid
How is type A influenza classified into subtypes?
Differences in the hemagglutinin protein (H) and neuraminidase protein (N), e.g. H1N1, H5N1, H3N2
What are the common names of H1N1 type A influenza?
Spanish flu, swine influenza
What is the common name of H5N1 type A influenza?
Avian flu
What is the disease caused by type C influenza?
Common cold
What is the difference between antigenic shift and antigenic drift in influenza epidemiology?
- Antigenic drift occurs in types A and B, is caused by mutations in the antigens, and results in outbreaks (epidemics), particularly in the winter
- Antigenic shift occurs in type A only, is caused by exchange of gene segments between human and animal/bird strains, and results in pandemics
How are influenza viruses transmitted?
- Respiratory secretions
- Aerosols
What is the tropism of the influenza viruses?
Epithelial cells of the respiratory tract
What are the clinical features of influenza infection?
- High fever and chills
- Frontal headache
- Generalized weakness
- Myalgia and arthralgia
- Sore throat
- Dry cough
- Pneumonia—either primary (in children, the elderly, or those with chronic disease) or secondary due to bacteria (mainly S. aureus, S. pneumoniae, H. influenzae and Gram-negative bacilli)
How are influenza viruses diagnosed?
- Rapid antigen detection
- PCR
How are influenza viruses treated?
- Mainly supportive treatment
- Antivirals: oseltamivir and zanamivir
Are there vaccines for influenza?
- Live attenuated, inactivated, and recombinant vaccines are available
- Trivalent vaccines contain two strains of type A and one strain of type B
- Quadrivalent vaccines contain two strains of type A and two strains of type B
What is the morphology of the coronaviruses?
- Enveloped positive-sense single-stranded RNA viruses
- Have a large genome
- Replicate in the cytoplasm
Which types of coronavirus cause the common cold?
- 229E
- OC43
- HKU1
- NL63
Which coronaviruses cause severe acute respiratory distress syndrome?
- SARS-CoV-1
- MERS-CoV
What is the mortality rate of SARS?
10%
What is the mortality rate of MERS?
36%
How are coronaviruses diagnosed?
PCR
How are coronaviruses treated?
Supportive treatment
Are there vaccines for coronaviruses?
No (for the coronaviruses required, at least)
What is the morphology of Paramyxoviridae?
- Enveloped negative-sense single-stranded RNA viruses
- Replicate in the cytoplasm
- Measles and mumps have only one antigenic type each and infection results in life-long immunity
Which viruses belong to Paramyxoviridae?
- Parainfluenza viruses (PIV) 1, 2, 3, and 4
- Respiratory syncytial virus (RSV)
- Metapneumovirus
- Measles
- Mumps
Which virus is the major pathogen of the pediatric respiratory tract?
Respiratory syncytial virus
How are Paramyxoviridae transmitted?
- Respiratory secretions
- Aerosols
What is the tropism of Paramyxoviridae?
Epithelial cells of the respiratory tract
What are the clinical features of Paramyxoviridae infection (excluding measles and mumps)?
- Common cold: PIV, RSV, metapneumovirus
- Laryngitis: PIV; with hoarseness of voice and barking cough
- Croup (inflammation of the upper airways, larynx, and trachea): PIV, RSV
- Bronchiolitis: RSV (the major cause of this disease in infants)
- Pneumonia: RSV
- Otitis media: PIV
How are Paramyxoviridae diagnosed?
- Rapid antigen detection
- PCR
- Measles: serology (IgM)
- Mumps: serology (IgM) and PCR
How are Paramyxoviridae treated?
- Supportive treatment
- Antiviral (ribavirin) for lower respiratory infections with RSV
- Vitamin A treatment in developing countries has decreased morbidity and mortality of measles and mumps
Are there vaccines for Paramyxoviridae?
- Live-attenuated vaccine for measles and mumps (as MMR)
- One is in development for RSV
What is the epidemiology of Paramyxoviridae?
- RSV: 80% of infants are infected by age 1 and almost all by age 2 years
- PIV: an important pediatric pathogen
- Reinfections are common
What are the clinical features of measles?
- Fever, respiratory symptoms, and a maculopapular rash with complications happening frequently
- Viremia transfers the virus from the airways to the skin and eye
- CNS invovlement is common, resulting in encephalitis, postinfectious encephalomyelitis, and subacute sclerosing panencephalitis
- Otitis media is the most common complication
- Pneumonia from secondary bacterial infection is the most common fatal complication
- Koplik spots (blue/white raised spots on a red base on the buccal mucosa opposite the first molar) are indicative of infection. These spots appear one day before the maculopapular rash
- Measles causes transient immunodeficiency
What are the clinical features of mumps?
- Mild disease in children but complications occur in adults
- Enlargement of one or both salivary glands
- CNS involvement is common, resulting in aseptic meningitis
- Testicular inflammation (orchitis) is extremely painful and can lead to sterility
- Ovarian inflammation (oophoritis) can occur
- Pancreatitis has been reported
Which virus belongs to Togaviridae?
Rubella (German measles)
What is the morphology of Togaviridae?
- Enveloped positive-sense single-stranded RNA virus
- Replicates in the cytoplasm
What are the clinical features of rubella?
- The mildest of the viral infections that cause skin rashes
- Causes a three-day rash (morbilliform rash) with a low-grade fever
- Congenital rubella presents as cataracts, cardiac abnormalities, and deafness
How is rubella transmitted?
- Respiratory secretions
- Vertical transmission
How is rubella diagnosed?
- Serology (IgM)
- PCR
How is rubella treated?
Supportive therapy
Is there a vaccine for rubella?
Live-attenuated vaccine (as MMR)
Which viruses cause gastroenteritis?
- Rotavirus: non-enveloped dsRNA with a segmented virus. Most common cause of gastroenteritis in infants. Live-attenuated vaccine is available
- Norovirus: non-enveloped +ssRNA. Most common cause of gastroenteritis in adults
- Astrovirus: non-enveloped +ssRNA
- Sapovirus: non-enveloped +ssRNA
How are the viruses that cause gastroenteritis transmitted?
Fecal–oral route
How are the viruses that cause gastroenteritis diagnosed?
- Antigen detection
- PCR
- Electron microscopy
What is the most common cause of gastroenteritis in children?
Rotavirus
What is the most common cause of gastroenteritis in adults?
Norovirus
What is the morphology of Filoviridae
- Enveloped negative-sense single-stranded RNA viruses
- Replicate in the cytoplasm
- Filamentous in shape
To which family does the ebola virus belong?
Filoviridae
What are the clinical features of ebola?
- Severe hemorrhagic fever
- High mortality rate
How is ebola transmitted?
- Respiratory droplets
- Direct contact
Is there a vaccine for ebola?
Yes
How is ebola diagnosed?
PCR
What is the morphology of Rhabdoviridae?
- Enveloped negative-sense single-stranded RNA viruses
- Replicate in the cytoplasm
- Bullet-shaped
To which family does the rabies virus belong?
Rhabdoviridae
What are the clinical features of rabies?
- Progressive encephalitis
- Once in the CNS, rabies is fatal, with a case-fatality rate approaching 100%
What is the pathogenesis of rabies?
- Rabies virus multiplies in the muscle or connective tissue of the site of inoculation
- It then enters peripheral nerves at neuromuscular junctions and spreads up to the nerves to the CNS
How is rabies transmitted?
Bites by rabid animals (e.g. dogs, bats, foxes, wolves, racoons, rats)
Is there a vaccine for rabies?
Passive immunization vaccine containing monoclonal antibodies to neutralize the virus
What is an example of a family of arboviruses (arthropod-borne viruses)
Flaviviridae
What is the morphology of Flaviviridae?
- Enveloped positive-sense single-stranded RNA viruses
- Replicate in the cytoplasm
What are the diseases caused by Flaviviridae members?
- Dengue
- Yellow fever
- West Nile fever
- Zika fever
What are the features of dengue?
- Transmitted by mosquitoes
- Symptoms include fever, severe headache, myalgia, arthralgia, nausea and vomiting, eye pain, rash
- The most common arbovirus infection worldwide
What are the features of yellow fever?
- Transmitted by mosquitoes
- Causes hepatitis
What are the features of West Nile fever?
- Transmitted by mosquitoes
- Most infections are asymptomatic
- Causes meningitis
What are the features of Zika?
- Transmitted by mosquitoes
- Can cause microcephaly if transmitted vertically
