Togaviridae

Question 1

Which genus in Togaviridae contains arthropod borne diseases?

Answer 1

Alphavirus

Question 2

Which genus in Togaviridae contails the rubella virus? (German measles)

Answer 2

Rubivirus

Question 3

Describe Togaviridae’s shape

Answer 3

Spherical, enveloped, T=4 nucleocapsid with icosahedral symmetry, 80 spikes (each a trimer of E1/E2 proteins)

Question 4

Describe the genome of Togaviridae

Answer 4

Linear, single stranded, positive sense RNA

Question 5

What is important about togaviridae’s RNA being positive sense?

Answer 5

It serves as both genome AND viral messenger RNA

Question 6

Where does alphavirus replication occur?

Answer 6

Cytoplasm!

Question 7

What are the mechanisms of transmission of arboviruses? (alphavirus-review!)

Answer 7

Urban/epidemic: human and urban vectors
Sylvatic/enzootic: reservoir vertebrate host and primary vectors
Rural/epizootic cycle: domestic animals (amplifying hosts) and primary or accessory vectors
*Dead end hosts from primary vectors

Question 8

What specific diseases can be caused by alphavirus?

Answer 8

Western equine encephalitis virus (WEEV): mild
Eastern equine encephalitis virus (EEEV): deadliest
Venezuelan equine encephalitis virus: 2 types!

Question 9

T or F: EEEV can cause encephalitis in horses and humans

Answer 9

True!

Therefore, it is zoonotic!

Question 10

Which EEEV lineage is the most virulent to horses and humans?

Answer 10

Type I!

Other types enzootic in Central South America are less virulent

Question 11

When is the most common time of year for EEEV outbreaks to occur?

Answer 11

Late summer and early fall in North America, associated with heavy rainfall!

Question 12

What is the species that is maintains (mostly) the enzootic EEEV cycle?

Answer 12

Passerine birds (reservoirs/amplification hosts)
Mosquitos are main enzootic vector in swamp habitats

Question 13

In which cells does the EEEV replicate?

Answer 13

Myocytes, fibroblasts, reticuloendothelial cells, lymphoid cells, osteoblasts
After cells, replication in organs and then hematogenous route into CNS

Question 14

After entering the CNS, what course does the virus take?

Answer 14

Replication in neurons, endothelial cells, glial cells, then apoptosis of these cells (specifically in gray matter of cerebral cortex, thalamus, hypothalamus)
End result: non-suppurative encephalomyelitis

Question 15

What are the clinical signs of EEEV in horses?

Answer 15

Fever, anorexia, depression, hypersensitivity to sound, colic, walking in circles, tremors/shoulder muscle involuntary movements, paralysis

Question 16

What are the clinical signs of systemic EEEV in humans?

Answer 16

Fever, malaise, arthalgia, myalgia, NO CNS INVOLVEMENT

Question 17

What are the clinical signs of the encephalitic form of EEEV in humans?

Answer 17

Fever, headache, anorexia, vomiting, diarrhea, cyanosis, convulsions, coma

Question 18

T or F: Humans have a very good prognosis if infected with EEEV

Answer 18

False. 1/3 of all people die and if you recover, you may suffer from permanent brain damage

Question 19

Describe EEEV in birds

Answer 19

Asymptomatic mostly, reservoir hosts

Depression, tremors, paralysis, circular movements

Question 20

T or F: WEEV is believed to ave emerged from a genetic recombination of ancestral EEEV

Answer 20

True

Question 21

T or F: Epizootic North American strains of WEEV are more virulent than enzootic strains in South America

Answer 21

True

Question 22

WEEV tends to be ____ virulent than EEEV in horses and has a ____ fatality rate in humans compared to EEEV

Answer 22

Less, lower

Question 23

____ are the primary amplifying hosts and ____ are the secondary amplifying hosts for WEEV

Answer 23

House sparrows, house finches

Jack rabbits and prairie dogs

Question 24

What are the clinical signs of WEEV in horses?

Answer 24

Most cases are mild/asymptomatic but severe cases show clinical signs similar to EEEV

Question 25

What are the clinical signs of WEEV in humans?

Answer 25

Adults, usually mild or asymptomatic

Infants and children can

Question 26

Which types of VEEV are epizootic/epidemic and highly virulent for equines?

Answer 26

1-A, 1-B, 1-C

Question 27

Which types of VEEV are enzootic/endemic and not very virulent for horses?

Answer 27

1-D, 1-E, 1-F, 2, 3, 4, 5, 6

Question 28

What animals are the amplifying hosts for VEEV?

Answer 28

Horses!
And obvi mosquitoes are primary vectors
Rodents can spread disease as well

Question 29

T or F: an endemic strain may mutate to an epidemic strain

Answer 29

True. Epidemic strain 1AB may arise from endemic strains–1D-F and II-vi

Question 30

What are the clinical signs of VEEV in horses?

Answer 30

Same as EEEV! In-utero infection may also occur

Question 31

What are the clinical signs of VEEV in humans?

Answer 31

Normally acute, mild, systemic disease
Headache, chills, coughing, vomiting, diarrhea
Encephalitis in 4% of children, 1% adults, 1% dies
Pregnant women may experience placental damage, fetal encephalitis, abortion/stillbirth, congenital disease

Question 32

What are methods of surveillancing mosquito populations for controlling and preventing equine encephalitis?

Answer 32

Trapping and testing mosquitos, sentinal animals to monitor presence of viruses, dead bird reporting and testing, sentinel chicken serology

Question 33

Are there vaccines available for the prevention of equine encephalitis?

Answer 33

Formalin inactivated EEEV and WEEV vaccines–univalent or bivalent + other antigens (tetanus)
Tissue culture attenuated vaccine with TC-83 for VEEV is available

Question 34

T or F: there are formalin inactivated EEEV and WEEV vaccines available for humans

Answer 34

False. There is only a tissue culture attenuated vaccine for VEEV that is available for laboratory/military personnel

Question 35

Describe the genome of Chikungunya

Answer 35

SS RNA virus

Question 36

What are the clinical signs of Chikungunya?

Answer 36

Fever, polyarthralgia, headache, myalgia, arthritis, nausea, vomiting, lymphopenia, thrombocytopenia