Togaviridae Flashcards
Which 3 viruses belong to the family alphavirus that are of veterinary importance?
- eastern equine encephalitis virus
- western equine encephalitis virus
- venezuelan dquine encephalitis virus
- are all part of group A**
Most alphaviruses are _______
Neurotropic
- distributed worldwide
- maintained in enzootic infection cycle
- specific mosquito and vertebrate host
- host range defined by feeding preference of insect host
Animals and humans are ______ hosts
Dead end
- may serve as amplifying hosts
What are the 3 categories of alphaviruses?
- neurological disease (encephalitis)
- febrile illness with polyarthritis
- no apparent disease
Western equine encephalitis virus includes:
- western equine encephalitis virus
- highlands J virus
Getah virus is located in _____
Southeast Asia
- febrile disease
Semiliki forest virus is located in ______
Africa
- febrile disease
Togaviridae morphology
Spherical virions
- lipid envelope with fine spikes
Togaviridae genome
Single stranded, positive sense RNA (same as mRNA)
What 4 viruses encompass equine alphaviruses?
- eastern equine encephalitis virus
- western equine encephalitis virus
- venezuelan equine encephalitis virus
- highlands j virus
Equine alphaviruses cause sever disease in _______
Horses and humans
- birds or mammals serves as reservoirs
- progressive systemic disease and death (fever, drowsiness, incoordination, depression, neurologic manifiestations
Neurological manifestations of equine alphaviruses
- abnormally wide stance
- hanging head, drooping ears, flaccid lips
- irregular gait
- signs of encephalitis (impaired vision, photophobia, inability to swallow)
- head pressing
- inability to rise, paralysis, convulsions
Case mortality rate
- EEEV (lineage 1): 50-90%
- WEEV: 40%
- VEEV: 80%
EEEV is enzootic in _______
Eastern US, Caribbean basin, Central America
- maintained in North America in resident birds in freshwater marshes
- viremic in wading birds, passerine and starlings
Vector of EEEV
- ornithophilic mosquito: Culiseta melanura
- bride mosquitoes: Aedes and Coquillettidia
EEEV is amplified in ______
Spring and summer
- oubreaks occur in late summer, fall
EEEV susceptible species
Virutally all birds are susceptible
- passerine develop high titer viremia, minimal mortalitiy
- clinical disease occurs in pheasants, partridges, and turkeys
WEEV
North American strains are more prevalent
- passerine birds and Culex tarsalis
Feeding pattern of Culex tarsalis
- spring: birds
- late summer: mammals
WEEV susceptible species
Rodents, rabbits, bats, squirrels, ungulates, tortoises, emus
What are the 2 subgroups of venezuelan equine encephalitis virus?
- enzootic VEE: groups 1-6
- epizootic VEE: group 1, subtype 1AB, and 1C
Enzootic VEEV
Groups 1-6 in Central/South America, group 3 in Florida
- Culex spp (melanoconion) and small animals (cotton, spiny rats)
- horses do not develop enough viremia to infect mosquitoes
- rarely clinical in humans and domestic animals
Epizootic VEEV
Venezuela, Colombia, Peru, and Ecuador
- virulent to horses with high viremia
- horses serve as amplification host
- severe disease in horses, neurological sequelae
Highland J virus
Sporadic cause of encephalitis in horses
- pathogenic for turkeys and partridges
Prevention and control
Reduce mosquito exposure and vaccinate
Vaccination for equine alphaviruses
Immunity is lifelong!
- inactivated vaccines for EEE, WEE, and VEE
- annual after 2-3 primary immunizations
- used in emus and endangered avian species
Is the genome of togaviridae infectious?
Yes!
- positive sense RNA molecule that can directly translate viral proteins for replication or by transfection of susceptible cells
- naked viral RNA molecule that can produce infectious viral particles
What are the amplifying hosts for VEEV?
Wild birds, equine, and other mammals!!
Geographic distributions of alphaviruses
- EEEV: fresh water swamp
- WEEV: irrigation areas and rural areas
Neurological disease is most severe in _______
EEE
Transmission cycle
Virus enters blood via saliva of infected female mosquito –> targets monocytes and endothelial cells near the entry site or in regional lymph node –> replication results in primary viremia which allows virus to invade extraneural tissues –> further replication leads to secondary viremia
What is necessary for the virus to invade the CNS?
Higher titers of virus in the blood
- infect the capillary endothelial cells to enter the CNS = neuronal necrosis
What are the most severely infected areas of brain in terminal cases of alphavirus infection?
- cerebral cortex
- thalamus
- hypothalamus
Diagnosis of active infection
IgM captured ELISA
- last several weeks after infection
