ArboViruses

Question 1

RNA viruses

Answer 1

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

Question 2

when is risk of human infection greatest?

Answer 2

late spring and summer!

Question 3

what diseases show systemic febrile illness?

Answer 3

chikungunya, o’nyong-nyong, ross river, dengue

Question 4

what diseases show fever with arthritis

Answer 4

chikungunya, ross river, o’nyong-nyong

Question 5

what diseases show encephalitis

Answer 5

japanese enceph, west nile, venezuelan equine enceph, eastern equine enceph, western equine enceph, murral valley enceph, powassan

Question 6

what diseases show hemorrhagic fever?

Answer 6

yellow fever, dengue, rift valley fever, chikugunya

Question 7

EEE virology

Answer 7

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.

Question 8

japanese encephalitis virus description

Answer 8

flaviviridiae, positive sense ssRNA. circulates as a single serotype. 5 genotypes, depends on location

Question 9

japanese encephalitis transmission cycle

Answer 9

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

Question 10

japanese enceph enzootic cycle

Answer 10

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

Question 11

japanese enceph epidemiology

Answer 11

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.

Question 12

jap enceph clinical features

Answer 12

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

Question 13

are vaccines available for jap enceph?

Answer 13

yes, 2.

Question 14

adverse reaction to yellow fever vaccine

Answer 14

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

Question 15

yellow fever vaccine associated viscerotropic disease

Answer 15

febrile illness that begins 3-5 days after vaccination. clinically resembles yellow fever.

Question 16

yellow fever epidemiology

Answer 16

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

Question 17

why the increase in YF transmission in africa?

Answer 17

mainly affects countries whose populations have gradually lost the protection provided by the mass preventive immunization campaigns carried out from 1933-1961

Question 18

clinical features of yellow fever: acute period

Answer 18

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

Question 19

YF clinical features: hemorrhagic phase

Answer 19

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

Question 20

YF clinical features: convalescent phase

Answer 20

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

Question 21

dengue viruses

Answer 21

flavivirus. four serotypes. several genotypes within each serotype. variations in virus virulence due to RNA mutations and recombination events

Question 22

characteristics of aedes aegypti

Answer 22

urban mosquito that breeds in standing water. daytime feeder, humans preferred host for blood meal. multiple probing for single blood meal

Question 23

dengue fever clinical manifestations

Answer 23

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

Question 24

dengue hemorrhagic fever clinical manifestations

Answer 24

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

Question 25

shock syndrome

Answer 25

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

Question 26

treatment of dengue hemorrhagic fever

Answer 26

IV fluids and dextrose ringer’s lactate