ArboViruses Flashcards
RNA viruses
All of the VHF viruses. majority of the highly pathogenic viruses that produce encephalitis, severe febrile illnesses. all arboviruses. many have animal reservoir or human amplification transmission with humans as an incidental host. many are endemic with periods of epidemics
when is risk of human infection greatest?
late spring and summer!
what diseases show systemic febrile illness?
chikungunya, o’nyong-nyong, ross river, dengue
what diseases show fever with arthritis
chikungunya, ross river, o’nyong-nyong
what diseases show encephalitis
japanese enceph, west nile, venezuelan equine enceph, eastern equine enceph, western equine enceph, murral valley enceph, powassan
what diseases show hemorrhagic fever?
yellow fever, dengue, rift valley fever, chikugunya
EEE virology
togaviridae family. positive ssRNA enveloped virus, 60-65 nm in diameter. clinical manifestations vary from inapparent to influenza like illness to the syndrome of encephalitis.
japanese encephalitis virus description
flaviviridiae, positive sense ssRNA. circulates as a single serotype. 5 genotypes, depends on location
japanese encephalitis transmission cycle
vector: culex tritaeniorhynchus. night feeders on large domestic animals and birds, around small collections of water. rainy season is highest transmission. natural host is the pig. prolonged and high titer viremia, asymptomatic. produce uninfected offspring. migrating birds and domestic fowl are also host. accidental are humans and horses
japanese enceph enzootic cycle
culex mosquitoes are primary vectors. transmission patterns: seasonal transmission (epidemics) in japan, china, taiwan, korea, northern vietnam and thailand, northern india, nepal. year round transmission (sporadic) in south vietnam, thailand, india, indonesia, malaysia, philippines, sri lanka
japanese enceph epidemiology
50,000 cases each year, 10,000 deaths each year. underreported. annual incidence as high as 10-20 per 100,000. increasing in india and nepal.
jap enceph clinical features
6-16 day incubation. febrile headache -> aseptic meningitis -> encephalitis
prodrome (2-3 days): headache, fever, chills, anorexia, dizzy
acute (3-4 days): high fever, seizures, dull facies, unblinking eyes, tremor, rigidity, abnormal behavior, flaccid paralysis
subacute (7-10 days) and convalescent (4-7 weeks): tremors, paresis, incoordination, pathologic reflexes, lip smacking. respiratory dysfunction, seizures, infectious virus in CSF, low IgM in CSF
are vaccines available for jap enceph?
yes, 2.
adverse reaction to yellow fever vaccine
highest among people aged 60 and up. three events: immediate hypersensitivity or anaphylactic reaction, YF vaccine-associated neurologic disease, and YF vaccine-associated viscerotropic disease
yellow fever vaccine associated viscerotropic disease
febrile illness that begins 3-5 days after vaccination. clinically resembles yellow fever.
yellow fever epidemiology
seasonal incidence: number of cases in south america 50-300, 4000 in africa. some large outbreaks in africa can reach 100000 cases.
geographic localization: tropical regions of africa and south america in the amazon region, orinoco and magdalena valleys, bolivia, brazil, colombia, and peru
why the increase in YF transmission in africa?
mainly affects countries whose populations have gradually lost the protection provided by the mass preventive immunization campaigns carried out from 1933-1961
clinical features of yellow fever: acute period
3-6 day incubation. clinical spectrum can be as a mild nonspecific febrile illness to fulminating sometimes fatal hemorrhagic disease. severe YF begins with fever, chills, headache, back pain, myalgia, N/V, gingival hemorrhages or epistaxes. symptoms may last for 3 days and period of viremia
YF clinical features: hemorrhagic phase
coffee-ground hematemesis, melena, metorrhagia, petechiae, and ecchymoses. volume depletion secondary to vomiting and plasma leakage. renal failure due -> increase albuminuria and low urine output. death on 7-10th day preceded by jaundice, rising pulse, hypotension, oliguria, azotemia. terminal signs: hypothermia, delirium, hiccups, hypoglycemia, stupor, coma. lab shows leukopenia, increased bilirubin, transaminase lvls, thrombocytopenia, PT and PTT long, ST-T wave changes
YF clinical features: convalescent phase
prolonged convalescence can occur with profound asthenia 1-2 weeks. late death is rare phenomenon due to cardiac complications or renal failure. increased serum transaminase can persist for 2 months
dengue viruses
flavivirus. four serotypes. several genotypes within each serotype. variations in virus virulence due to RNA mutations and recombination events
characteristics of aedes aegypti
urban mosquito that breeds in standing water. daytime feeder, humans preferred host for blood meal. multiple probing for single blood meal
dengue fever clinical manifestations
2-7 day incubation. high fever, headache, retrobulbar pain, back ache, conjunctival conjestion, facial flusing. fever 6-7 says with N/V, myalgia, bone pain. macular rash may appear on first or second day. secondary rash following fever appears on trunks and spreads to face and limbs but spares soles and palms. peripheral WBC count is depressed
dengue hemorrhagic fever clinical manifestations
petechiae, epistaxis, intestinal bleeding, menorrhagia, positive tourniquet test. myocarditis may occur and neuro disorders. reye’s syndrome has also been reported to follow dengue infection (swelling in liver and brain). prolonged convalescence can occur, with weakness, depression, bradycardia, and ventricular extrasystoles
PLASMA LEAKAGE IS THE HALLMARK FEATURE
shock syndrome
severe form of viral hemorrhagic fever and results from intravascular volume depletion from plasma leakage into third splace and/or blood loss, as well as cardiovascular collapse
treatment of dengue hemorrhagic fever
IV fluids and dextrose ringer’s lactate
