Mosquitoes & Zoonoses

Question 1

Extrinsic incubation period is

Answer 1

Number of days for pathogen to develop in mosquito. Can vary based on pathogen, mosquito, & temp

Question 2

What is the most important vector of human disease worldwide

Answer 2

mosquitoes

Question 3

Mosquito borne diseases found in North America

Answer 3

EEE
WEE
VEE (?)
WNV
St. Louis encephalitis
LaCrosse encephalitis
Powassan encephalitis

Question 4

Pathogenicity of EEV in equids

Answer 4

VEE: up to 80% fatality
EEE: 90+% fatality
Wee: 20-40% fatality

Question 5

EEV transmission

Answer 5

• naturally circulate between mosquitoes and wild animals

- reservoirs develop high viral titers allowing transmission to mosquitoes

Question 6

Epizootic cycles

Answer 6

• begin in nature and increased transmission spills over to incidental hosts
• many environmental factors
• In VEE both horses and humans (both dead-end hosts) can infect mosquitoes. This is an exception to the normal cycle.

Question 7

EEE reservoirs

Answer 7

Culiseta & birds

• Epizootic cycle requires “bridge” vector, Aedes.
• Epi cycle tends to be self limiting

Question 8

EEE in animals

Answer 8

• appears 2 weeks before human cases

- fever, lethergy, etc. Progresses to excitability, drowsiness, paresis, sezures & coma (5-10 days)

Question 9

EEE in humans

Answer 9

• incubation 3-10 days
• 90+% of people are asymptomatic
• flu-like illness to enceph. coma, & death
• 50-90% have lasting damage

Question 10

WEE transmission

Answer 10

Culex & birds

• “bridge” vector, is the same
• common in farming areas, low level of occurance in rural west w/ sporadic infection
• Epi cycle tends to be 5-10 years
• No significant US outbreaks in 20 years

Question 11

WEE clinical signs

Answer 11

• Cases are rare

- fever, lethergy, etc. Progresses to excitability, drowsiness, paresis, sezures & coma (5-10 days)

Question 12

WEE in humans

Answer 12

~1:1000 infections are symptomatic

-flu-like to enceph, coma, & death, but much less than EEE

Question 13

WEE vet risk

Answer 13

• minimal risk from infected horses (low blood & CSF levels)
• Be careful during necropsy
• Being in same pasture means exposure to same mosquitoes

Question 14

VEE transmission

Answer 14

Rodents & Cules

• Foreign to North America
• Horses are key reservoir species
• levels in human blood can get high enough to transmit to mosquitoes

Question 15

VEE in humans

Answer 15

• almost 100% symptomatic

- febrile, neuro symptoms in 1% (10% fatality in those)

Question 16

VEE prevention

Answer 16

• Reportable

- Sentinel surveillance

Question 17

WNV

Answer 17

Mosquito-bird-mosquito cycle

-most birds survive

Question 18

WNV in horses & humans

Answer 18

• horses: neurologic

- humans: 80% asymptomatic. 1/150 develop neuroinvasive disease. Age >50 have highest risk

Question 19

WNV transmission

Answer 19

• bite of mosquito

- Secondarily, thru bloodborn infection, lab exposure, & breast milk