Lecture 5 - Flaviruses and alphaviruses

Question 0

characteritics of arboviruses

Answer 0

transmitted by vectors - mosquito

ZOONOTIC via the mosquito

Question 1

arbovirus transmission cycle

Answer 1

virus must replicate in the mosquito host (ARthropod BOrn)

Question 2

virus biology of flaviruses: nucleic acid, capsid, virion, assembly

Answer 2

ssRNA(+)

capsid: complex
virion: enveloped
assembly: cytoplasm

Question 3

what virus causes west nile?

Answer 3

flavirus

Question 4

vertebrate hosts of flaviruses

Answer 4

viremia is significantly higher in birds compared to humans or horses

• birds are dead 48 hours post-infection and incubation is 2 - 5 days.
• incubation in horses and people is 1 - 2 weeks

Question 5

what is the reservoir for west nile?

Answer 5

birds

Question 6

reservoir capacity =

Answer 6

how well a host maintains the virus in order to be infectious for the next mosquito
poor reservoir = crow
good reservoir = house sparrow, american robin, cardinal, common grackle

Question 7

when do birds become viremic?

Answer 7

1 - 4 days after infection once amplification occurs. after which life-long immunity occurs

high avian losses precedes disease in other hosts

Question 8

what is the seasonality of west nile?

Answer 8

June - October is high season (summer)

Question 9

clinical signs of west nile in the horse

Answer 9

• fasiculation and tremors of the head, neck and trunk
• > 60% change in behavior
• intermittent weakness/paralysis
• flaccid paralysis/recumbency
• change in mentation (lowered head)

Question 10

how is west nile diagnosed?

Answer 10

• IgM capture ELISA (measured at a single cut off, very reliable)
• neutralization testing - highly specific, viruses cause CPE in cell culture, positively exposed animals have antibody confounded by vaccination! ***
• as well as the usual: post-mortem, histopath, IHC, PCR, viral isolation, etc

Question 11

prevention of west nile

Answer 11

4 vaccines available for horses and are highly efficacious

Question 12

virus morphology for arboviruses: nucleic acid, capsid, virion, assembly, release

Answer 12

ssRNA

capsid: complex
virion: envelope
assembly: cytoplasm
release: cell lysis

Question 13

what diseases does arboviruses cause?

Answer 13

eastern equine encephalitis, western equine encephalitis, venezuelan equine encephalitis

Question 14

lifecycle for EEE, WEE

Answer 14

bird is the reservoir

horses and humans are dead end hosts

Question 15

VEE lifecycle

Answer 15

horse is the reservoir!!
endemic cycle: between mosquito and spiney rat
epidemic cycle: between horse and mosquito

virus mutation occurs between the two types of cycles

Question 16

EEE/WEE epidemiology

Answer 16

EEE: causes severe and fatal encephalitis
WEE: milder form
focal outbreaks occur as far north as New York State

Question 17

clinical disease of EEE

Answer 17

exceptional pathogenicity
90 - 100% mortality
dead end host

Question 18

clinical disease of WEE

Answer 18

moderate pathogenicity
40 - 60% mortality
dead end host

Question 19

VEE

Answer 19

moderate pathogenicity

HORSE IS THE RESERVOIR DURING OUTBREAKS!!

Question 20

prevention of EEE/WEE

Answer 20

all diseases have vaccines for horses
VEE used in very southern US
vaccine is highly efficacious