Togaviridae

Question 1

Which genus of togaviridae is significant for veterinarians? what additional genus is important to humans?

Answer 1

Alphavirus big for animal medicine. Arthropod-borne.

for humans, genus Rubivirus, responsible for Rubella.

Question 2

what kind of genome do alphaviruses have?

Answer 2

linear, positive sense, ssRNA

Question 3

what are the three forms of equine encephalitis virus?

Answer 3

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

Question 4

Eastern equine encephalitis virus is caused by a member of the genus _______, and is transmitted by ________. It causes encephalitis in horses and _______.

Answer 4

Alphavirus
mosquitos
humans

Question 5

Among the viruses that cause EEEV, which group is the most virulent to humans and horses?

Answer 5

Group I - occurs in US, Canada, and the Caribbean.

Question 6

Which lineages of EEEV are enzootic in central and south america?

Answer 6

II, III, IV

Question 7

where in the US does EEEV primarily occur?

Answer 7

Southeast

Question 8

The EEEV transmission cycle is maintained between _________ as reservoirs/amplification hosts. ________ is the main enzootic vector in swamp habitats.

Answer 8

passerine birds; Culiseta melanura(mosquito)

Question 9

what are two other reservoirs for EEEV?

Answer 9

rodents and reptiles

Question 10

Dead end hosts of EEEV? why are they dead end hosts?

Answer 10

humans and horses; don’t develop high enough levels of viremia to infect others

Question 11

pathogenesis of EEEV?

Answer 11

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

Question 12

clinical signs of EEEV?

Answer 12

• 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

Question 13

clinical signs of EEEV in humans?

Answer 13

usually no apparent illness
depends on the form; two forms:

systemic: arthralgia, myalgia, no CNS involvement.
encephalitic: anorexia, vomiting, diarrhea, cyanosis, convulsions, coma

Question 14

prognosis of EEEV in humans?

Answer 14

approximately a third of all infected die from disease

recovered patients may suffer permanent brain damage

Question 15

t/f - EEEV infections are asymptomatic in most birds.

Answer 15

true; they are reservoir hosts.

Question 16

what signs might you see in a bird infected with EEEV?

Answer 16

tremors, leg paralysis, involuntary circular movements

Question 17

WEEV is believed to have emerged from ________ of an ancestral Eastern equine encephalitis virus-like virus and an ancestral ________

Answer 17

genetic recombination; Sindbis-like alphavirus

Question 18

______ strains of WEEV are more virulent than strains that are enzootic in ________

Answer 18

Epizootic North American; South America

Question 19

WEEV has a (low/high) fatality rate in humans compared to EEEV

Answer 19

low

Question 20

In horses, WEEV is (more/less) virulent than EEEV

Answer 20

less

Question 21

two primary amplifying hosts of WEEV?

Answer 21

House finches, and house sparrows

Question 22

WEEV main vector?

Answer 22

mosquito Culex tarsalis

also other mosquitoes

Question 23

what are two additional possible amplifying hosts for WEEV?

Answer 23

lagomorphs and rodents

Question 24

clinical signs of WEEV in horses?

Answer 24

most cases mild or asymptomatic

severe cases show signs similar to EEEV

Question 25

clinical signs of WEEV in humans?

Answer 25

usually mild or asymptomatic in adults

infants/children are highly susceptible -> severe encephalitis

Question 26

overview of the subtypes of Venezuelan Equine Encephalitis virus?

Answer 26

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

Question 27

Describe the enzootic cycle of VEEV

Answer 27

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)

Question 28

Describe the epizootic cycle of VEEV

Answer 28

primary vector: mosquitos
cycle between them and horses

other species affected, but not amplifiers
humans infected, dead end host.

Question 29

in VEEV… Epidemic ____ virus may arise from mutation of Endemic strains (types ______)

Answer 29

1AB;

1D-F and II-vi

Question 30

Clinical signs of VEEV in horses?

Answer 30

same signs as in EEEV

Question 31

Clinical signs of VEEV in humans?

Answer 31

• normally acute, mild, systemic disease
• symptoms of encephalitis
• In pregnant women, may cause placental damage, fetal encephalitis, abortion/stillbirth, congenital disease.

Question 32

what’s key in reducing spread of EEV?

Answer 32

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

Question 33

describe chemical and biological control of mosquito populations for EEV

Answer 33

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

Question 34

what can you use for personal protection from mosquitos (and thus EEV?)

Answer 34

clothing, repellents, nets on doors and windows, mosquito nets