Togaviridae Flashcards
Which genus of togaviridae is significant for veterinarians? what additional genus is important to humans?
Alphavirus big for animal medicine. Arthropod-borne.
for humans, genus Rubivirus, responsible for Rubella.
what kind of genome do alphaviruses have?
linear, positive sense, ssRNA
what are the three forms of equine encephalitis virus?
Western (WEEV)
Eastern (EEEV)
Venezuelan (VEEV)
Eastern equine encephalitis virus is caused by a member of the genus _______, and is transmitted by ________. It causes encephalitis in horses and _______.
Alphavirus
mosquitos
humans
Among the viruses that cause EEEV, which group is the most virulent to humans and horses?
Group I - occurs in US, Canada, and the Caribbean.
Which lineages of EEEV are enzootic in central and south america?
II, III, IV
where in the US does EEEV primarily occur?
Southeast
The EEEV transmission cycle is maintained between _________ as reservoirs/amplification hosts. ________ is the main enzootic vector in swamp habitats.
passerine birds; Culiseta melanura(mosquito)
what are two other reservoirs for EEEV?
rodents and reptiles
Dead end hosts of EEEV? why are they dead end hosts?
humans and horses; don’t develop high enough levels of viremia to infect others
pathogenesis of EEEV?
inoculation of virus from mosquito bite –> virus enters CNS through the hematogenous route –> viral replication occurs in neurons, glial cells, vascular endothelial cells –> apoptosis of glial cells and neurons –> nonsuppurative encephalomyelitis
clinical signs of EEEV?
- fever, anorexia, depression
- hypersensitive to sound
- colic before onset of neurological disease
- walk blindly into objects or in circles
- tremors; facial and shoulder muscles especially
- stage of paralysis follows
- inability to hold up the head/head pressing or leaning back
- incoordination, unnatural postures, complete paralysis
clinical signs of EEEV in humans?
usually no apparent illness
depends on the form; two forms:
systemic: arthralgia, myalgia, no CNS involvement.
encephalitic: anorexia, vomiting, diarrhea, cyanosis, convulsions, coma
prognosis of EEEV in humans?
approximately a third of all infected die from disease
recovered patients may suffer permanent brain damage
t/f - EEEV infections are asymptomatic in most birds.
true; they are reservoir hosts.
what signs might you see in a bird infected with EEEV?
tremors, leg paralysis, involuntary circular movements
WEEV is believed to have emerged from ________ of an ancestral Eastern equine encephalitis virus-like virus and an ancestral ________
genetic recombination; Sindbis-like alphavirus
______ strains of WEEV are more virulent than strains that are enzootic in ________
Epizootic North American; South America
WEEV has a (low/high) fatality rate in humans compared to EEEV
low
In horses, WEEV is (more/less) virulent than EEEV
less
two primary amplifying hosts of WEEV?
House finches, and house sparrows
WEEV main vector?
mosquito Culex tarsalis
also other mosquitoes
what are two additional possible amplifying hosts for WEEV?
lagomorphs and rodents
clinical signs of WEEV in horses?
most cases mild or asymptomatic
severe cases show signs similar to EEEV
clinical signs of WEEV in humans?
usually mild or asymptomatic in adults
infants/children are highly susceptible -> severe encephalitis
overview of the subtypes of Venezuelan Equine Encephalitis virus?
subtype I-A, I-B, and I-C; epizootic/epidemic; highly virulent for horses
subtype I-D, I-E, I-F (II - VI); enzootic/endemic; virulence low or unknown
Describe the enzootic cycle of VEEV
Primary vector: Culex spp
cycle between Culex and rodents, but culex can also bite and transmit to horses/humans (accidental host)
Aedes or Posorophora mosquitos pick up virus from rodent, and bite humans/horses (accidental host)
Describe the epizootic cycle of VEEV
primary vector: mosquitos
cycle between them and horses
other species affected, but not amplifiers
humans infected, dead end host.
in VEEV… Epidemic ____ virus may arise from mutation of Endemic strains (types ______)
1AB;
1D-F and II-vi
Clinical signs of VEEV in horses?
same signs as in EEEV
Clinical signs of VEEV in humans?
- normally acute, mild, systemic disease
- symptoms of encephalitis
- In pregnant women, may cause placental damage, fetal encephalitis, abortion/stillbirth, congenital disease.
what’s key in reducing spread of EEV?
mosquito control:
- source reduction
- surveillance; trapping and testing mosquitos for virus, use of sentinel animals/birds to alert to presence of viruses, dead bird reporting and testing, sentinel chicken serology
describe chemical and biological control of mosquito populations for EEV
biological
-use of natural enemies to manage populations, such as predatory fish that feed on mosquito larvae (Gambusia affinis, carps and minnows)
chemical
-larvicides and adulticides
what can you use for personal protection from mosquitos (and thus EEV?)
clothing, repellents, nets on doors and windows, mosquito nets
