Unit 2 - Arbovirus Flashcards
(35 cards)
define what an arbovirus is
group of viruses transmitted by arthropod vectors
-ARthropod-BOrne
what are the 4 clinical syndromes that arboviruses can cause?
- systemic febrile illness
- fever with arthritis
- encephalitis
- hemorrhagic fever
what is important about RNA viruses?
- all of the viral hemorrhagic fever (VHF) viruses
- majority of highly pathogenic viruses that produce encephalitis, severe fibrile illnesses
- all arboviruses (transmitted by ticks, mosquitoes)
- many have animal reservoir or animal amplification transmission with humans as an incidental host
- many are endemic with periods of epidemics
what are mosquito-borne viruses that cause systemic febrile illness?
- chikungunya
- O’nyong-nyong
- Ross river
- Dengue
what are mosquito-borne viruses that cause fever with arthritis?
- chikungunya
- Ross river
- O’nyong-nyong
what are mosquito-borne viruses that cause encephalitis?
- Japanese encephalitis
- West Nile virus
- Venezuelan/Eastern/Western equine encephalitis
- Murray Valley encephalitis
what are mosquito-borne viruses that cause hemorrhagic fever?
- yellow fever
- dengue
- Rift valley fever
- chikungunya
explain Eastern Equine Encephalitis virology
Togaviridae family of alphavirus (highest probability of getting EEE)
- focal epidemics of EEE in Eastern USA
- clinical manifestations are inapparent influenza-like illness to encephalitis
- mortality rates are 50%
- causes leukopenia, increased protein, lowered glucose, and inflammation/edema in thalamus area
what are the 4 encephalitic viruses in the alphavirus genus? where are they found? probability of developing? mortaility rates?
Eastern, Western, Venezuelan, and Everglades
- EEE: Eastern USA; highest chance of getting; 50% mortality
- WEE: Western USA; 5% mortality
- VEE: endemic in South and North America; lowest chance of getting; 35% mortality
explain Japanese encephalitis virus description
Flaviviridae, +sense ssRNA
- circulates as single serotype
- 5 genotypes (I - V)
what are the 5 genotypes of Japanese encephalitis and where do each dominate?
I: N. Thailand, Cambodia, Korea
II: S. Thailand, Malaysia, Sarawak, Australia, Indonesia
III: Japan, China, Taiwan, Vietnam, Philippines, Sri Lanka, India, Nepal
-has 4 subgroups
IV: Indonesia
V: Singapore
explain the transmission cycle of JEV
Culex tritaeniorhynchus vector
- night feeders on large domestic animals and birds
- rice fields, marshes, water collections
- rainy season marks highest transmission
- -irrigation allows year-round transmission
- vertical transmission and overwinter is possible
- sexual transmission between mosquitoes
what are the natural hosts and accidental hosts for JEV?
natural: pig
- prolonged and high titer viremia, asymptomatic
- production of numerous uninfected offspring
- viral replication
natural: migrating birds and domestic fowl
accidental: humans and horses
what are the transmission patterns of JEV
- seasonal transmission (large epidemics)
- Japan, China, Taiwan, Korea, N. Vietnam, Thailand, N. India, Nepal - year round transmission (sporadic cases)
- S. Vietnam, Thailand, India, Indonesia, Malaysia, Philippines, Sri Lanka
what is the epidemiology of JEV?
- 50,000 cases each year (underreported)
- 10,000 deaths each year
- in JEV endemic areas:
- -infection common with high seroprevalence rates
- -annual incidence as high as 10-20 per 100,000
- increasing in India and Nepal
- inapparent to apparent infections 200-300 to 1
what are clinical features of JEV?
- incubation period: 6-16 days
- spectrum: febrile headache –> aseptic meningitis –> encephalitis (<1%)
- prodrome (2-3 days): headache, fever, chills, anorexia, N/V, dizziness
- acute (3-4 days): high fever/seizures, dull flat mask-like facies, unblinking eyes, tremor, hypertonia, rigidity, abnormal behavior, acute flaccid paralysis
- subacute (7-10 days) and convalescent (4-7 weeks): tremors, paresis, incoordination, pathologic reflexes, lip smaking, rapidly changing CNS signs
what is the prognosis of JEV?
poor
- respiratory dysfunction, prolonged seizures and fever, albuminuria
- infectious virus in CSF
- low IgM in CSF
is JEV preventable?
yes, 2 vaccines
what is JE-Vax (Biken)?
JEV vaccine
- mouse-brain derived vaccine with JE E-protein of Nakayama strain
- 3 shot series results in long-term immunity
- serious side effect is anaphylactic-like reaction (delayed and rare)
- production has stopped
what is IXIARO?
JEV vaccine from strain SA 14-14-2
- virus suspension treated with protamine sulfate to remove contaminating DNA and proteins
- purified virus inactivated by formaldehyde treatment
- administered in 2 doses 28 days apart
what are adverse reactions to yellow fever vaccine?
serious adverse reactions highest if >60 yo
- immediate hypersensitivity or anaphylactic reactions
- yellow fever vaccine associated neurologic disease (YEL-AND)
- yellow fever vaccine-associated viscerotropic disease (YEL-AVD)
what happens in YEL-AVD?
yellow fever vaccine-associated viscerotropic disease
-febrile illness that starts 3-5 days after vaccination, and clinically resembles naturally acquired yellow fever
yellow fever virology?
Flaviviridiae Flavivirus
- single open reading frame of 10,233 nt, encoding 3 structural and 7 non-structural proteins
- 1 serotype, 5 genotypes
what do phylogenetic analysis of yellow fever tell us?
originated in Africa
- divided into West and East lineages
- West african lineage has progenitor imported into S. America and New world
