Orthomyxoviridae and Paramyxoviridae

Orthomyxoviridae

Segmented, (-)ssRNA, mucosal viruses that can reassort including Influenza A

Paramyxoviridae

Non-segmented, (-)ssRNA, mucosal viruses including Measles and Mumps

What do negative-sense RNA viruses have to do?

Convert the negative-sense RNA into positive-sense mRNA before translation

Influenza Infection

• Respiratory

  • May cause pneumonia, bronchitis, Reye’s Syndrome, Inflammation

  • Secondary infection of lungs is dangerous

Influenza Transmission

Aerosols in air (cough/sneeze), saliva, blood, secretion (BUT is not truly airborne because it doesn’t remain in air)

How is Influenza zoonotic?

It is spread from infected bird droppings

Influenza Replication Cycle

1. Attachment with hemagglutinin

2. Fusion and uncoating

3. Replication

4. Assembly

5. Budding and release

Is Influenza enveloped?

Yes, it has an envelope.

Important, unique Influenza Factors

Hemagglutinin (HA) and neuraminidase (NA) - names strains

Hemagglutinin

• Binds to sialic acid receptors for attachment

• Membrane fusion

Neuraminadase

• Glycoside hydrolase that releases particles after maturation

• Breaks down mucins

• CLEAVES SIALIC ACIDS TO ALLOW BUDDING

Antigenic Drift

• Error-prone RNA polymerase results in point mutations

• SLOW change leading to less severe infection

• New vaccines needed every year

Antigenic Shift

• Reassortment of segmented genome resulting in 2 different viruses in 1 cell

• New antigenic properties leading to severe infection without protection

• Epidemics/Pandemics

Sialic Acid

2 different sugar linkages on proteoglycans, which HA binds to

Human Influenza

Easily spread but rarely fatal since binds in upper respiratory

Avian Influenza

Spreads slowly but is often fatal because in lungs

Endemic

Normal, circulating infections (flu in dry/cold seasons)

Epidemic

Outbreak exceeds expectations in a certain region

Pandemic

Epidemic that spreads through a larger region

Spanish Flu (H1N1)

Worldwide spread with high mortality due to cytokine storm

Are measles and mumps enveloped?

Yes, both paramyxoviridae viruses are enveloped.

Capsid Shape of Paramyxoviridae

Helical

Paramyxoviridae Replication

1. Attach to receptors on cell membrane

2. Enter cell via fusion

3. Release RNA and replication

4. Budding and release

Unique Transcription of Paramyxoviridae

Transcriptional polarity

Transcriptional Polarity

• Only 1 promoter

  • Protein-genome interactions

• RNA polymerase may fall off, must reattach at start

• More genes upstream than downstream

What is the most contagious viral disease?

Measles

Mumps Symptoms

Swelling of parotid glands is DIAGNOSTIC

Mumps and Measles Transmission

Respiratory droplets, direct contact; TRULY airborne

Mumps and Measles Replication Site

Respiratory Tract

Mumps and Measles Host

Human is the only host

Complications of Mumps

Testes, ovary, and brain inflammation; meningitis, encephalitis, hearing loss in children

Mumps and Measles Prevention

Vaccine (MMR)

Genome of Mumps, Measles, and Influenza

(-) ssRNA

Measles Symptoms

Koplik’s spots (small and white) inside mouth are DIAGNOSTIC, flat and red rash, cold

Measles Transmission

Respiratory droplets and aerosolization

Measles Incubation

During incubation, it is contagious

Measles Complications

Brain inflammation, corneal ulcers, pneumonia, hearing loss (most profound), acute encephalitis

Diagnosis of Measles

• Fever

• Cough, coryza, or conjunctivitis

• Koplik’s spots

R0

Number of people that a sick person will infect

Which virus has the highest R0?

Measles has the highest.

R>1

Infection will be able to spread.

R<1

Infection will die out.

Why is measles so contagious?

• Hijacks immune cells

• Infection lung epithelium and spreads systemically

• Aerosols remain in air

• Contagious during incubation

• High R0

Why is measles dangerous to children?

• Immune Suppression - erases memory

• Encephalitis and pneumonia (most common cause of death)

• SSPE (rapid brain degeneration)