Unit 2 - Arbovirus Flashcards
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
explain the seasonal incidence of yellow fever
annual cases in S. America 50-300, but in Africa 4000
-large outbreaks can cause 100,000 cases and 30,000 deaths in Africa (due to losing protection provided by mass preventive immunization campaigns)
explain geographic localization of yellow fever?
tropical regions of Africa and S. America in Amazon, Orinoco, Magdalena valleys, Bolivia, Brazil, Colombia, Peru
clinical features of acute period yellow fever
incubation period ranges 3-6 days
- clinical spectrum manifests as mild, nonspecific, febrile illness to fulminating, sometimes fatal hemorrhagic disease
- severe YF begins acutely with fever, chills, severe headache, lumbosacral pain, generalized myalgia, anorexia, N/V, minor gingival hemorrhages, epistaxis
- bradycardia despite rising temperature (Faget’s syn)
- symptoms last 3 days and period of viremia
clinical features of hemorrhagic phase of yellow fever
“coffee-ground” hematemesis (vomito negro), melena, metorrhagia, petechiae, ecchymoses
- volume depletion is secondary to vomiting and plasma leakage
- renal failure manifested by increase in albuminuria and diminishing urine output
- death (in 20-50% severe cases) on 7th to 10th day of illness (preceded by deepining jaundice, hemorrhages, rising pulse, hypotension, oliguria, azotemia)
- hypothermia, agitated delirium, intractable hiccups, hypoglycemia, stupor, coma are terminal signs
- leukpenia, elevation of bilirubin, serum transaminas levels, thrombocytopenia, prolonged PT and PTT, and ST-T wave changes in EKG
what are clinical features of yellow fever convalescent phase?
prolonged convalescence can occur with profound asthenia lasting 1-2 weeks
- late death, occuring at end of convalescence, or even weeks after complete recovery from acute illness, is rare phenomenon attributed to cardiac complications or renal failure
- elevations of serum trasaminase levels can persist for at least 2 months after onset of acute illness
what are Dengue virus virology?
Flavivirus Flaviviridae
- 4 serotypes that are antigenically distinct (DEN-1/2/3/4)
- genetic diversity and phylogenetics between each serotype
- variations in virus virulence due to RNA virus mutations and recombination events
what spreads Dengue virus?
urban Aedes aegypti mosquito
- breeds in standing water
- daytime feeder
- humans are preferred host for blood meal
- multiple probing for single blood meal
what are clinical manifestations of Dengue fever?
after 2-7 day incubation period, high fever, headache, retrobulbar pain, lumbosacral aching pain, conjunctival congestion, facial flushing develops
-fever lasts 6 to 7 days with generalized myalgia, bone pain anorexia, nausea, vomiting, weakness, prostration
-generalized macular rash may appear on the first or second day
-following defervescence (day 3 to 5) a secondary rash,
maculopapular or morbilliform appears on the trunk and then spreads centripetally to the face and limbs but spares the soles and palms
-fever may rise again, creating the second phase of the saddleback course
-peripheral WBC count is depressed with an absolute granulocytopenia, and the platelet count may fall to less than 100,000/mm3
what are clinical manifestations of dengue hemorrhagic fever (secondary dengue)
- petechiae, epistaxis, intestinal bleeding, menorrhagia, positive tourniquet test
- myocarditis may occur, and neurologic disorders
- Reye’s syndrome reported to follow infection
- prolonged convalescence may occur with generalized weakness, depression, bradycardia, and ventricular extrasystoles
what is shock syndrome?
severe form of viral hemorrhagic fever that results from:
- intravascular volume depletion from plasma leakage into third space and/or blood loss
- cardiovascular collapse
what is the most common arbovirus causing human infection in subtropical and tropical regions of the world?
dengue fever
