Togaviridae/Alphaviruses

Question 1

WEE/EEE/VEE structure & classification

Answer 1

Family: Togaviridae
Genus: Alphavirus

(+) ssRNA

Baltimore: IV

Vectors/reservoir:
WEE - Culex/Birds
EEE- Culiseta/Birds
VEE - Culex/Rodents

Question 2

Chikungunya structure & classification

Answer 2

Genus: Alphavirus (sole genus in family)
Family: Togaviridae

(+) ss RNA

Baltimore: IV

Vector: Aedes, Transmission of chikungunya via blood products has been described in France, where a nurse was infected by exposure to blood while caring for a patient infected in Réunion. Maternal-fetal transmission of chikungunya virus has been described, and maternal chikungunya virus infection has been associated with miscarriage.

Question 3

Togaviridae structure & groups

Answer 3

family of small, Enveloped viruses with (+) ss RNA genomes

Baltimore: IV

Alphavirus is the sole genus

Chikungunya
Onyong-nyong
Ross River
Barmah Forest
Semliki Forest
Sindbis
Mayaro
EEE
VEE
WEE

Question 4

Chik pathogenesis

Answer 4

typically develop viremia within a few days of infection, and the virus directly invades and replicates within the joints.

Chronic arthritis due to chikungunya virus develops in up to approximately 60 percent of infected individuals.

Question 5

Chik incubation

Answer 5

1-14 days

Question 6

Chik diagnostics

Answer 6

RT-PCR
EIA IgM - D5
EIA IgG - 2 weeks

Question 7

Chik vaccine

Answer 7

A live-attenuated chikungunya virus vaccine (VLA1553, or Ixchiq) was approved by the US FDA & EMA in 2023. NOT LICENCED IN THE UK.

Approval was based on a double-blind, randomized trial based in the United States in which 4128 healthy adults (age ≥18 years) were randomly assigned to a single dose of vaccine or placebo [27]. Among the 266 patients who were assessed for immunogenicity, a seroprotective neutralizing antibody response occurred in 99 percent by 28 days after vaccination and persisted in 96 percent at 180 days.

Question 8

Chik mortality

Answer 8

0.1%

Question 9

WEE/VEE/EEE mortality

Answer 9

WEE - 3 to 7%

VEE - 1%

EEE - 50 to 75%

Question 10

WEE/EEE/VEE incubation & clinical syndromes

Answer 10

VEE - 1 to 6 days, least severe. Usually flu like symptoms only. Encephalitis rarely.

WEE - 2 to 7 days. small proportion encephalitis. Some asymptomatic.

EEE - 4 to 10 days. Most severe. Encephalitis.

Question 11

WEE/EEE/VEE diagnostics & vaccines

Answer 11

IgM ELISA
IgG 4-fold increase
RT-PCR

CSF IgM

Vaccines exist in horses for all 3 - none licensed in humans