Enveloped RNA Viruses with Icosahedral Symmetry

The enveloped RNA viruses with icosahedral symmetry include:

•Togaviridae

•Flaviviridae

•Retroviridae.

Togaviridae family has two medically significant genera:

Alphavirus (arboviruses)

Rubivirus

Transmitted by mosquito vectors with animal reservoirs.

Alphavirus (arboviruses)

Alphavirus (arboviruses) Examples include:

•Eastern equine encephalitis virus (EEE)

•Western equine encephalitis virus (WEE)

•Venezuelan equine encephalitis virus (VEE)

The only member is the rubella virus, which causes German measles.

Rubivirus

Clinical features:

•Systemic infection with morbilliform rash and posterior auricular lymphadenopathy.

•Congenital rubella syndrome may occur if infection happens during early pregnancy,

Rubivirus

Rubivirus Prevention:

MMR vaccine (live-attenuated).

This family includes both arboviruses and bloodborne pathogens.

Flaviviridae

Flaviviridae Key Viruses

Dengue Virus

Hepatitis C Virus (HCV)

St. Louis Encephalitis Virus

Yellow Fever Virus

West Nile Virus

Dengue Virus is Transmitted by

Aedes mosquitoes.

Transmitted via blood, IV drug use, and transfusions (before screening began in 1992).

Hepatitis C Virus (HCV)

Causes:

•Chronic hepatitis

•Cirrhosis

•Hepatocellular carcinoma (HCC)

Hepatitis C Virus (HCV)

Hepatitis C Virus (HCV) is treated with

direct-acting antivirals (DAAs).

•Mosquito-borne.

•Causes viral encephalitis, especially in older adults.

St. Louis Encephalitis Virus

Transmitted by mosquitoes in Africa and South

Yellow Fever Virus

Yellow Fever Virus Liver histology may show

Councilman bodies.

•Transmitted by Culex mosquitoes.

•Associated with birds as reservoirs.

West Nile Virus

are unique in that they carry a reverse transcriptase enzyme (RNA-dependent DNA polymerase). They are diploid, containing two copies of +ssRNA.

Retroviruses

Retroviridae family is divided into the following genera

•Lentiviruses

•Oncoviruses (Deltaretroviruses)

•Spumaviruses

Includes HIV-1 and HIV-2, the causative agents of AIDS.

Lentivirus

Confirms HIV infection.

HIV-1/2 antibody differentiation immunoassay:

Monitors viral RNA for HIV

HIV viral load (PCR):

Monitors disease progression for HIV

CD4+ T-cell count:

Includes HTLV-I and HTLV-II.

Oncoviruses (Deltaretroviruses)

Causes Adult T-cell Leukemia/Lymphoma (ATLL).

Can also cause HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP).

Transmission: Same routes as HIV.

HTLV-I:

Also called foamy viruses.

Spumaviruses