Mosquitoes & Zoonoses

Question 1

What is the “extrinsic incubation period” in regards to mosquito zoonoses?

Answer 1

The amount of time it takes for a pathogen to become infectious within a mosquito after the blood meal

Question 2

T/F: Mosquitoes are the most important vectors of human disease worldwide

Answer 2

TRUE

Question 3

What are the 3 equine encephalitis viruses? What family are they from?

Answer 3

Western (WEEV), Eastern (EEEV), and Venezuelan (VEEV)

Togaviridae, genus Alphavirus

Question 4

What pathogenicity is seen in equids with VEEV, EEEV, and WEEV?

Answer 4

VEEV: up to 80% fatality
EEV: 90+% fatal
WEEV: ~ 20-40% case fatality rate

Question 5

Who are the natural reservoirs for WEEV, VEEV, and EEEV?

Answer 5

WEEV: birds
VEEV: rodents - enzootic reservoir and horses - epizootic reservoir
EEV: birds

*epizootics occur periodically

Question 6

What cause epizootics (of EEEV, WEEV), and where do they being?

Answer 6

They begin in nature - increased transmission of virus between mosquitoes and birds and then spills over to incidental hosts

Question 7

T/F: Incidental hosts are usually dead-end hosts (cannot infect mosquitoes)

Answer 7

TRUE

but there are some exceptions

**BOTH horses and humans with VEEV are NOT dead end hosts

Question 8

What is the mosquito vector involved in the enzootic reservoir cycle (wild birds and mosquitoes) of Eastern Equine Encephalitis Virus

Answer 8

Culiseta species

Question 9

What is the “bridge” mosquito spps that is a part of the epizootic cycle between birds and the incidental hosts of EEEV?

Answer 9

Aedes species

Incidental hosts: horses, humans, swine etc
**these are DEAD END hosts

Question 10

What is the most virulent Equine Encephalitis virus?

Answer 10

Easter EEV

Question 11

How soon before human infections of EEEV would you note infections in horses?

Answer 11

Usually about two weeks before human infections

*begin with fever, decreased appetite, and lethargy —-> neuro –> fatal cases have ~5-10day course

Question 12

What are risk factors for humans getting EEEV?

Answer 12

Outdoor activities in an area with EEEV infected mosquitoes

*incubation period if 3-10 days

Question 13

What symptoms are seen in humans with EEEV?

Answer 13

Some people are asymptomatic (90+%)
Symptoms range from flu-like illness to encephalitis, coma, and death
*many survivors will have mild to severe permanent neuro damage

Question 14

What is the species of mosquito involved in the natural cycle of WEEV?

Answer 14

Culex tarsalis

*bridge mosquito is the same as EEEV - Aedes species

Question 15

What clinical signs are seen in horses with WEEV and humans with WEEV?

Answer 15

Horses: infections are rare - being with fever, anorexia, lethargy and can progress to neuro signs and end in coma/fatality in severe cases in about 5-10 days

Humans: symptoms range from flu like illness to encephalitis, coma, and death (much less than EEEV) Mild to severe neuro deficits are seen in survivors

Question 16

Are EEEV and/or WEEV titers in symptomatic horses high or low?

Answer 16

LOW (both in blood and CSF)

Question 17

If you are working on a horse infected with EEEV, and you see him get bit by a mosquito, then that mosquito tries to bite you… Are you scared for your life??

Answer 17

No - that mosquito will not be infectious immediately.

The population of mosquitoes that infected this horse are of more concern

Question 18

What EEV is foreign to the US?

Answer 18

VEEV

Question 19

What species of mosquito and animals are involved in the sylvatic or enzootic cycle of VEEV?

Answer 19

Rodents and Culex species

Question 20

What species of mosquitoes are involved in epizootic transmission of VEEV?

Answer 20

Psorophora and Aedes species

Question 21

For which one of these equine dz can a horse be a reservoir and not just a dead end host?

Eastern EEV
Western EEV
Venezuelan EEV
West Nile Virus
None

Answer 21

Venezuelan EEV

Question 22

What clinical signs will you see in equids with VEEV?

Answer 22

Present either as febrile or encephalitic dz

Peracute death may occur with no previous signs

Question 23

What symptoms will you see in humans infected with VEEV? Are they ever asymptomatic?

Answer 23

Almost 100% of cases are symptomatic

Typically febrile illness with neuro symptoms in less an 1% of adults and fatality in about 10% of those cases (higher in children)

Question 24

How do you prevent VEEV?

Answer 24

It’s a reportable foreign animal dz in the USA
Mosquito/rodent control
Sentinel surveillance using pheasants

Question 25

West Nile Virus is in the genus ________. It is maintained in a mosquito - ________ - mosquito cycle

Answer 25

Flavivirus
Bird

**primarily transmitted via culex species of mosquitoes

Question 26

How long do birds maintain viremia post exposure?

Answer 26

1-4 days

*mosts bird survive

Question 27

What clinical signs will you see in horses with WNV?

Answer 27

Neurological: ataxia, hypermetria, weakness, peri or tetraparesis, recumbency, and death

Question 28

What symptoms will you see in a person infected with WNV?

Answer 28

about 80% of people will be asymptomatic
about 20% develop mild febrile illness
1 in 150 will develop neuroinvasive disease (old people are at highest risk)

Question 29

Who are the dead end hosts of WNV?

Answer 29

Humans and Horses

Question 30

After infection, what kind of immunity to WNV will form?

Answer 30

Life long

Question 31

How does secondary infection of WNV occur?

Answer 31

bloodborne infection
laboratory exposure
breast milk