Viral Spread Flashcards
What are the 4 fates of polio and what are the approximate proportions?
- inapparent infection (90-95% of infected individuals)
- abortive polio (4-8%) - fever, sore throat, headache
- aseptic meningitis (non-paralytic polio) 1% - higher fever, headache, stiff neck, CSF pleocytosis
- paralytic polio (0.1%) - all of the abortive polio plus vomiting for 1-2 days is the prodromal stage. Then major illness follows in 5 days - this is meningitis followed by paralysis
Bulbar form - medulla oblongata infection and respiratory paralysis
What is the incubation of polio
7-14 days
What is the classifcation of the polio virus
small. no envelope, icosahedral, single straded +strand RNA. family: picornaviridae (like rhinovirus)
How many serotypes are there?
- They are all on the capsid surface proteins
What cells does it infect
poliovirus infects the motor neurons
What is endemic country mean?
countries that have never stopped transmission. For polio: afghanistan, nigeria, pakistan. must have no cases for 3 years to be polio free
What is a re-established country mean?
Countries that it was polio-free, but an imported case started an epidemic that has lasted greater than 12 months. angola, chad, DRC for polio
What is an imported country
poliofree countries that have an ongoing outbreak
What are long-term sequelae of polio
30-40 years after recovery, there can be fatigue, muscle weakness, and pain.
Describe the pathogenesis of poliovirus systemically
virus is ingested. replication in the mucosa of pharynx and gut (esp. tonsils and peyers patches of the ileum). virus spreads through the lymphatics to deep lymph nodes. now minor viremia to extraneural tissues. then major viremia correlating with prodrome and spread to the CNS.
What does polio do to the CNS
it specifically targets motor neurons in the anterior horn cells of the spinal cord. This leads to neuron necrosis and paralysis.
what is the most severe form of polio
infection involving the medulla oblangata and respiraotry paralysis
How is virus shed?
feces. fecal-oral
Difference between parenteral and oral polio vaccine?
oral feeding of live vaccine leads to circulating ab and to local gut immunity mediated by IgA. the jab of killed vaccine leaves the gut susceptible, but protects against viremia. Neutralizing IgG persists for life.
transmission patterns in the US used to be…
summer and early autumn. endemic from ancients to late 1800s. epidemic from late 1800s to 1950s (changed by hygiene). 3. vaccine era.
IPV?
Inactivated virus made by jonas salk. grown in monkey kidney cells. multiple boosters are needed
OPV?
developed by Sabin. vaccine is live . it is trivalent requiring multiple doses
When were americas free of polio?
- the last 10 cases in the US were vaccine-related. in 1997 ACIP decided on 2 doses of killed vaccine followed by 2 doses of live vaccine.
Measles description
acute febrile disease with eruption of red maculopapular rashes. start on forehead and spread down the body trunk
How long is the incubation period of measles?
10-14 days
how long is the prodrome and what characterizes it?
cough, coryza, conjunctivitis
classification?
paramyxoviridae family. envelope present. negative-strand single-stranded RNA. Surface glycoproteins are H (hemagglutinin) and F (fusion)
What are the neurological complications of measles
- post-infectious encephalyomyelitis
- inclusion encephalitis (only immunosuppresed host)
- subacate sclerosing panencephalitis (SSPE)
Describe the pathogenesis of measles
virus enters by the respiratory route. replicates in the respiratory epithelium. spread to lymphatics where it replicates. Then spreads to blood to spleen and more lymph tissue. After an additional round of viremia, it infects the DERMAL ENDOTHELIAL CELLS. this spreads to the epidemeral layers leading to edema and mononuclear infiltration leading to the maculopapular lesions.
