Mosquitoes & Zoonoses Flashcards
What is the “extrinsic incubation period” in regards to mosquito zoonoses?
The amount of time it takes for a pathogen to become infectious within a mosquito after the blood meal
T/F: Mosquitoes are the most important vectors of human disease worldwide
TRUE
What are the 3 equine encephalitis viruses? What family are they from?
Western (WEEV), Eastern (EEEV), and Venezuelan (VEEV)
Togaviridae, genus Alphavirus
What pathogenicity is seen in equids with VEEV, EEEV, and WEEV?
VEEV: up to 80% fatality
EEV: 90+% fatal
WEEV: ~ 20-40% case fatality rate
Who are the natural reservoirs for WEEV, VEEV, and EEEV?
WEEV: birds
VEEV: rodents - enzootic reservoir and horses - epizootic reservoir
EEV: birds
*epizootics occur periodically
What cause epizootics (of EEEV, WEEV), and where do they being?
They begin in nature - increased transmission of virus between mosquitoes and birds and then spills over to incidental hosts
T/F: Incidental hosts are usually dead-end hosts (cannot infect mosquitoes)
TRUE
but there are some exceptions
**BOTH horses and humans with VEEV are NOT dead end hosts
What is the mosquito vector involved in the enzootic reservoir cycle (wild birds and mosquitoes) of Eastern Equine Encephalitis Virus
Culiseta species
What is the “bridge” mosquito spps that is a part of the epizootic cycle between birds and the incidental hosts of EEEV?
Aedes species
Incidental hosts: horses, humans, swine etc
**these are DEAD END hosts
What is the most virulent Equine Encephalitis virus?
Easter EEV
How soon before human infections of EEEV would you note infections in horses?
Usually about two weeks before human infections
*begin with fever, decreased appetite, and lethargy —-> neuro –> fatal cases have ~5-10day course
What are risk factors for humans getting EEEV?
Outdoor activities in an area with EEEV infected mosquitoes
*incubation period if 3-10 days
What symptoms are seen in humans with EEEV?
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
What is the species of mosquito involved in the natural cycle of WEEV?
Culex tarsalis
*bridge mosquito is the same as EEEV - Aedes species
What clinical signs are seen in horses with WEEV and humans with WEEV?
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
Are EEEV and/or WEEV titers in symptomatic horses high or low?
LOW (both in blood and CSF)
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??
No - that mosquito will not be infectious immediately.
The population of mosquitoes that infected this horse are of more concern
What EEV is foreign to the US?
VEEV
What species of mosquito and animals are involved in the sylvatic or enzootic cycle of VEEV?
Rodents and Culex species
What species of mosquitoes are involved in epizootic transmission of VEEV?
Psorophora and Aedes species
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
Venezuelan EEV
What clinical signs will you see in equids with VEEV?
Present either as febrile or encephalitic dz
Peracute death may occur with no previous signs
What symptoms will you see in humans infected with VEEV? Are they ever asymptomatic?
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)
How do you prevent VEEV?
It’s a reportable foreign animal dz in the USA
Mosquito/rodent control
Sentinel surveillance using pheasants
West Nile Virus is in the genus ________. It is maintained in a mosquito - ________ - mosquito cycle
Flavivirus
Bird
**primarily transmitted via culex species of mosquitoes
How long do birds maintain viremia post exposure?
1-4 days
*mosts bird survive
What clinical signs will you see in horses with WNV?
Neurological: ataxia, hypermetria, weakness, peri or tetraparesis, recumbency, and death
What symptoms will you see in a person infected with WNV?
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)
Who are the dead end hosts of WNV?
Humans and Horses
After infection, what kind of immunity to WNV will form?
Life long
How does secondary infection of WNV occur?
bloodborne infection
laboratory exposure
breast milk
