Togavirida - Alphaviruses Flashcards
Describe the three Equine Encephalitis viruses and their differences.
All three viruses—Eastern, Western, and Venezuelan equine encephalitis viruses—belong to the Alphavirus genus within the Togaviridae family and are transmitted by mosquitoes. However, they differ in geographic distribution, severity of disease, natural reservoirs, and outbreak patterns:
Eastern Equine Encephalitis (EEE)
Severity: EEE is considered the most severe. In humans, it can cause a rapidly progressing encephalitis with a high mortality rate (up to 30% or more) and significant long-term neurological damage in survivors.
Transmission & Reservoirs: Its natural cycle mainly involves birds and mosquito species (particularly in freshwater swampy areas), though humans and horses are incidental hosts.
Geographic Distribution: Predominantly found in the eastern parts of North America, though cases also occur in parts of South America.
Western Equine Encephalitis (WEE)
Severity: WEE generally causes milder disease compared to EEE. The fatality rate in humans is lower, and many infections may even be subclinical or result in less severe symptoms.
Transmission & Reservoirs: WEE has a natural cycle involving birds and mosquitoes, similar to EEE, but the virus tends to be less virulent.
Geographic Distribution: Historically, WEE has been more common in the western parts of North America. Its incidence has declined significantly in recent decades.
Venezuelan Equine Encephalitis (VEE)
Severity and Outbreak Potential: VEE is unique in its ability to cause large-scale epidemics. It often leads to widespread outbreaks affecting both humans and equines. While many human cases are mild, some outbreaks result in significant neurological disease.
Transmission & Reservoirs: The virus circulates in an enzootic cycle often involving rodents and other small mammals. However, some strains can amplify rapidly in equines, which then serve as important hosts for mosquito transmission, sparking epizootics.
Geographic Distribution: VEE is most commonly seen in Central and South America. Its ability to jump into epizootic cycles distinguishes it from the more endemic patterns seen with EEE and WEE.
Key Differences
Disease Severity: EEE tends to be the most severe, with a high fatality rate, whereas WEE usually causes milder disease. VEE, meanwhile, is notable for its epidemic potential, sometimes causing large outbreaks.
Reservoir Hosts: EEE and WEE are primarily maintained in bird populations, while VEE has a cycle that includes small mammals and can involve equines as amplifiers during outbreaks.
Geographical Patterns: EEE is mostly found in the eastern regions of North America (with some South American cases), WEE was historically more common in the western regions of North America (but is now less common), and VEE is primarily a concern in Central and South America.
Epizootic vs enzooitc?
Enzootic diseases are those that maintain a constant presence within a specific animal population or area, indicating a stable, expected level of prevalence. Conversely, epizootic diseases are marked by their sudden, widespread occurrence, often spreading rapidly and affecting a large number of animals within a population or geographic area.
Two subtypes of EEEV?
North American EEEV
- High mortality and responsible for cases in North America
Madriaga - 3 of the 4 remaining strains of EEEV with milder phenotype and transmission in South America
Vectors and hosts for EEEV, WEEV, VEEV?
EEEV
- Culiseta mosquitos as vector but all other mostquito types can transmit during epizootic transmission times.
- Passerine birds are hosts
WEEV
- Spread by Culex mosquitoes with wild bird reservoirs
VEEV
- Enzooting types are transmitted between rodents and culex mosqitos
- Epizooting forms are amplified in horses and transmitted via aedes mosquitos.
List the Alphaviruses?
Arithrogenic
- Chikungunya
- Ross River
- Barmah Forrest Virus
- Mayaro
- Sindbis
- O’Nyong nyong
Encephalitic
- WEEV
- EEEV - most pathogenic
- VEEV
Vector for chik?
Aedes albopictus/aegypti
Complications of Chik?
Long lasting arthritis similar to inflammatory arthritis.
Chik vaccine?
Single dose live vaccine approved by EMC (doesn’t seem to be in UK)
IXCHIQ
Given to high risk travellers and occupational risk
