Topic 29 - Herpes + Measles + Polio

Which polyomavirus causes encephalitis in humans?

JC virus

What disease does JC virus cause?

Progressive Multifocal Leukoencephalopathy (PML)

What is PML?

Demyelinating disease of the brain

Who is most at risk for PML?

Immunocompromised individuals (AIDS, elderly)

What happens in PML?

Destruction of myelin-producing cells leading to no repair

What are the symptoms of PML?

Headache, aphasia, seizures, cognitive decline

What is the outcome of PML?

Death in 1-9 months

What are common symptoms of encephalitis?

Headache, fever, seizures, altered mental status, neurologic deficits

Which viruses are alphaherpesviruses?

HSV-1, HSV-2, VZV

Why do alphaherpesviruses infect neurons?

Immune evasion, safe transport, easy access from skin

Where do HSV-1 and HSV-2 stay latent?

HSV-1 → trigeminal ganglion; HSV-2 → spinal cord

What type of genome do herpesviruses have?

dsDNA

What are the 4 main parts of a herpesvirus?

DNA genome, capsid, tegument, envelope

What is the tegument?

Layer between capsid and envelope

What is the function of the tegument?

Provides ~20 proteins immediately after entry

Why is the tegument important?

Rapid infection, immune evasion, helps virus exit cell

What is rolling circle replication?

Continuous DNA replication producing long concatemers

What starts rolling circle replication?

Nick in one DNA strand

What happens after the initial nick in rolling circle replication?

Continuous DNA synthesis from 3' end

What happens to the displaced strand in rolling circle replication?

Copied using RNA primers (Okazaki fragments)

What is produced during rolling circle replication?

Long DNA concatemers (linked genomes)

What happens after long DNA concatemers are produced?

Cut into unit-length genomes

Why don't herpesviruses need telomeres?

Rolling circle produces long repeats, avoiding shortening

What is latency in viral infections?

Virus remains dormant in neurons

How does the virus travel in neurons?

Retrograde to CNS, anterograde back to skin

What triggers reactivation of the virus?

Stress, illness, immune suppression

How is mumps transmitted?

Respiratory droplets

Where does mumps replicate first?

Upper respiratory tract

What is primary viremia in mumps?

Virus enters bloodstream and spreads

What is the main target organ of mumps?

Parotid (salivary) glands

What is the classic symptom of mumps?

Swollen salivary glands

What are other symptoms of mumps?

Fever, malaise, muscle aches

What are serious complications of mumps?

Orchitis, sterility, meningitis, encephalitis

How is mumps prevented?

MMR vaccine (live attenuated)

How is measles transmitted?

Aerosol (very contagious)

What is the R₀ of measles?

12-18 (extremely high)

What are the prodromal symptoms of measles?

Fever, cough, runny nose, conjunctivitis

What are Koplik spots?

White spots in mouth (diagnostic for measles)

What is the rash pattern of measles?

Starts on face and spreads downward

Why is measles dangerous?

Causes immunosuppression, wiping immune memory

What are major causes of death in measles?

Pneumonia and bronchitis

What is SSPE?

Chronic measles infection of CNS

When does SSPE occur?

7-10 years after infection

What are the symptoms of SSPE?

Behavioral changes, seizures, cognitive decline

Why does SSPE happen?

Mutation in matrix protein leading to virus persistence

What is the outcome of SSPE?

Death within ~3 years

How is measles prevented?

MMR vaccine

Why are infants initially protected from measles?

Maternal IgG antibodies

What is the transmission route of polio?

Fecal-oral

Where does polio replicate first?

GI tract

How does polio reach the CNS?

Through the blood to neurons

What is encephalitic polio?

Brain inflammation leading to death

What is bulbar polio?

Affects brainstem, causing breathing failure

Why is polio dangerous?

Destroys motor neurons, leading to paralysis

What does echovirus stand for?

Enteric Cytopathic Human Orphan virus

What are common symptoms of echovirus?

Diarrhea, fever

What severe disease can echovirus cause in newborns?

Liver failure, myocarditis

What is aseptic meningitis?

Meningitis without detectable bacteria

What is the common cause of aseptic meningitis?

Echovirus

What are the symptoms of aseptic meningitis?

Fever, stiff neck, headache

What is the transmission route of Coxsackievirus?

Fecal-oral

What types of diseases does Coxsackievirus cause?

Polio-like illness, meningitis

What causes most viral meningitis cases?

Enteroviruses (Coxsackie + Echo)

What is the most contagious virus?

Measles

Which virus is most likely to cause latent infection?

Herpesviruses

Which virus destroys immune memory?

Measles

Which virus causes delayed CNS disease years later?

Measles (SSPE)

What is the most common cause of viral meningitis?

Enteroviruses