Viral Respiratory Infections - RNA Viruses Flashcards
What family are the influenzaviruses in, and what are its physical characteristics?
Orthomyxovirus
Enveloped, negative-sense RNA geneome with 8 segments
What influenza protein is primarily involved in attachment and what does it bind?
Hemagglutinin (HA) - binds sialic acid (blocked via mucins)
How is influenza virus uptaken and envelope fused?
Uptaken by receptor-mediated endocytosis, endosome fuses with viral membrane due to pH drop triggering conformational change in HA
What is the function of the M2 protein?
Ion channel which allows protons to enter the virion interior, facilitating pH drop. This frees the ribonuclear complex (RNP) which is RNA + protein
This was targeted by some anti-influenza drugs, but now resistant
Where does influenza-virus replicate?
In the nucleus -> a rarity for RNA viruses
Similar to how poxviruses are DNA and replicate in cytoplasm
What is the function of transcribing RNPs?
Yields + sense RNA, which can be used to transcribe more RNA or viral genomes
What is the function of M1 protein?
Interacts with nascent RNP’s to acquire envelopes by budding thru plasma membrane
What is the function of viral neuraminidase (NA)?
Removes sialic acid from cell surface as well as surrounding mucous decoy receptors. Guarantees the virus will not re-infect a previously infected cell, and thins mucuous
What are the two protein components of HA?
Formed from HA0,
HA1 - Binds sialic acid
HA2 - Contains transmembrane domain and fusion peptide for endosome
How do Oseltamivir and Zamanivir work?
Neuraminidase inhibitors
What are the three most common influenza forms and what is the best protective antibody?
H1N1, H2N2, H3N2
Best protective antibody is anti-hemagglutinin
What is antigenic shift vs antigenic drift?
Shift - large change via genetic reassortment and coinfection of two influenza A viruses - cause pandemics
Drift - minor antigenic changes via point mutations - seasonal flu - cause epidemics
What does a typical season flu vaccine formulation contain in it?
Trivalent
Most likely H1N1 strain (Influenza A)
Most likely H3N2 strain (Influenza A)
Most likely Influenza B
What makes an influenza strain especially virulent?
When it has a broad cell tropism (not trypsin dependent, which is only in lungs), which can cause disease in young adults.
Also causes cytokine storm causing inflammation, and predisposes to nasty bacterial superinfections.
Why is trypsin required for influenza?
It is a part of human cells -> required for cleavage of HA0 into HA1 and HA2
How do influenza viruses suppression antiviral interferon responses?
Via NS1 protein, which blocks interferon-induced RNaseL pathway
What type of viruses are Paramyxoviruses?
negative (-) sense RNA genomes, unsegmented
What are the major viruses of the paramyxovirus subfamily?
Human parainfluenza viruses (HPIV 1-4), Mumps Virus, Measles Virus
(Rubella is a Togavirus)
What are the major viruses of the pneumovirus subfamily? This is a part of the paramyxoviridae family
Respiratory syncytial virus (RSV) Human Metapneumovirus (MPV)
How common are paramyxovirus infections and how are they spread?
Extremely common, especially in childhood. Spread via direct contact with respiratory secretions, aerosols, and fomites.
Most people will have had HPIV and RSV by age 2.
Are repeated infections of paramyxovirus common?
Yes, they are RNA viruses
What is croup? What clinical finding is associated with it?
Laryngotracheobronchitis - An infection and inflammation of the larynx, trachea, and bronchi, narrowing the airway leading to difficulty breathing (upper airway inflammation)
Associated with “stridor” - characteristic sound on inhalation
What viruses tend to cause croup? Do patients need treatment?
HPIV-1 is the most common cause
Other HPIV’s and RSV / MPV can cause it too.
Patient needs rapid medical attention due to respiratory distress
What do the paramyxoviruses typically cause in adults?
Laryngitis and pneumonia
What are all the viral causes of pneumonia?
HPIV’s, RSV, hMPV, Influenzavirus, Adenovirus, Coronavirus
What is bronchiolitis, does it happen in adults, and what causes it?
Infection and inflammation of the bronchioles
-> small airways between bronchi and alveolae
Symptoms are dyspnea or cough
Rare in adults, mostly in children under 2, primarily caused by RSV
What is Measles Virus also called, and what are its prodomal symptoms?
Rubeola virus
Remember the 4 C's of the prodrome: Cough Coryza Conjunctivitis Coplik's spots
okay so its spelled Koplik but whatever
What are Koplik’s spots?
Tiny blue-white spots on red buccal mucosa in measles prodrome = pathonomonic
What is the pattern of rash in measles? What type of rash it it?
Begins on face, then spreads to trunk and limbs like Rubella
Can form a confluent rash -> spots will start to blend together into a sheet of red
How are mumps transmitted?
Salivary or respiratory secretions -> less infectious than measles
What are the most common manifestations of mumps? Atypical?
Painful swelling of parotid glands (unilateral or bilateral), ear pain
Atypical:
Orchitis -> more severe, can cause infertility if bilateral
Also meningitis
What is german measles and its genome structure?
Rubella
Togavirus with enveloped icosahedral virus, single stranded +sense RNA
What are the symptoms of Rubella?
- Lymph node swelling, especially postauricular and occipital nodes
- Maculopapular rash starting in head and going down (same as measles)
Arthritis in adult women
How long is the incubation period of M,M, and R?
All about 2-3 weeks
What are the features of congenital rubella syndrome?
Sensorineural deafness, intellectual impairment, jaundice / hepatosplenomegaly, cataracts, blueberry muffin rash, patent ductus arteriosus, CNS infection
How many doses of MMR Vaccine should be given?
1st dose at 12-18 months, 2nd dose at 4-6 years
What is the structure of a coronavirus?
Large ss+RNA genome, with envelope and HELICAL nucleocapsid
What type of infection are coronaviruses generally associated with?
Mild to moderately severe URI
What are two coronaviruses of consequence?
SARS - Severe Acute RS - zoonosis from China, caused pneumonia and acute respiratory distress
MERS - Middle East RS - zoonosis from camels, high case fatality
What is the main distinguishing feature of a cold? What is the most common viral cause?
Usually no or mild fever
Rhinovirus
What is the structure of picornaviruses?
naked ss+RNA
How are picornaviruses spread and what are two main viral subfamilies?
They infect skin and mucous membranes, and thus spread by saliva, mucous, or feces
- Coxsackievirus
- Echovirus
What two major diseases does Coxsackie A virus cause?
- Hand, Foot, and Mouth Disease
2. Herpangina (mouth blisters and ulcers, especially on soft palate)
What are rare complications of measles?
SSPE - Subacute Sclerosing Pan Encephalitis - from measles reactivation in brain
Pneumonia
