Enveloped RNA Viruses with Helical Symmetry

The plus (+) strand, also called the

sense strand

The plus (+) strand, defined by its equivalence to

mRNA:

The minus (–) strand, also called the

antisense strand

This strand serves as the template during transcription.

minus (–) strand

Segmented, negative-sense ssRNA genome

Helical nucleocapsid, enveloped with surface glycoproteins

Orthomyxoviridae

binds to sialic acid receptors on host cells.

Hemagglutinin (HA):

facilitates viral release.

Neuraminidase (NA):

beneath the envelope, helps virion structure.

Matrix protein (M1):

causes most pandemics/epidemics; infects humans and animals.

Orthomyxoviridae Type A:

epidemics, limited antigenic variation.

Orthomyxoviridae Type B:

mild illness, rare, not epidemiologically significant.

Orthomyxoviridae Type C:

is linked to aspirin use in children with influenza B or varicella.

Reye’s syndrome

Minor point mutations in HA/NA → yearly epidemics.

Drift:

Reassortment of gene segments (only in Type A) → pandemics (e.g., 2009 H1N1).

Shift:

•Non-segmented, negative-sense ssRNA.

•Large enveloped viruses with fusion (F) protein and hemagglutinin-neuraminidase (HN) or hemagglutinin (H) for attachment.

Paramyxoviridae

Genera Paramyxovirus

Parainfluenza viruses

Morbillivirus: Measles virus (Rubeola)

Pneumovirus: Respiratory Syncytial Virus (RSV)

cause croup (laryngotracheobronchitis) in children.

Parainfluenza viruses:

fever, cough, coryza, conjunctivitis, Koplik’s spots, maculopapular rash.

Measles virus (Rubeola):

Can cause subacute sclerosing panencephalitis (SSPE) years after infection.

Morbillivirus:

Leading cause of bronchiolitis and pneumonia in infants.

Respiratory Syncytial Virus (RSV):

Treatment: supportive; palivizumab for prophylaxis in high-risk infants.

Respiratory Syncytial Virus (RSV):

Ambisense ssRNA (contains both positive and negative sense regions).

Arenaviridae

Grainy ("sandy") appearance due to ribosomes in virions.

Arenaviridae

Transmission via rodents (inhalation of excreta).

Arenaviridae

Key Viruses for Arenaviridae

Lassa virus

Junin & Machupo

Lymphocytic choriomeningitis virus (LCMV)

hemorrhagic fever (West Africa).

Lassa virus:

South American hemorrhagic fevers.

Junin & Machupo:

•Flu-like symptoms, aseptic meningitis.

•Transmitted by infected rodent urine, especially pet hamsters/mice.

Lymphocytic choriomeningitis virus (LCMV):

•Bullet-shaped, negative-sense ssRNA

Rhabdoviridae-Rabies virus

Retrograde axonal transport to CNS → encephalitis.

Rabies virus

Histopathology: Negri bodies in neurons (especially hippocampus, Purkinje cells).

Rabies virus

Positive-sense ssRNA, enveloped, club-shaped spike (S) proteins giving corona appearance.

Coronaviridae

Largest RNA genome among RNA viruses.

Coronaviridae

Coronaviridae Key Viruses:

Common cold strains: OC43, 229E.

SARS-CoV (2002)

MERS-CoV (2012)

SARS-CoV-2 (2019)

Common cold strains of coronaviridae

OC43, 229E.

Severe acute respiratory syndrome.

SARS-CoV (2002):

Middle East respiratory syndrome.

MERS-CoV (2012):

COVID-19 pandemic.

SARS-CoV-2 (2019):

Negative-sense ssRNA, segmented, enveloped.

Bunyaviridae

Many are arboviruses (arthropod-borne) in Bunyaviridae, except

Hantavirus.

causes Hantavirus Pulmonary Syndrome (HPS).

Sin Nombre virus (U.S.):

Transmission: inhalation of aerosolized rodent excreta (e.g., deer mice).

Hantavirus (now Hantaviridae family):

•Cause viral encephalitis in children.

•Transmission: Aedes mosquitoes.

•Geography: Mississippi & Ohio River Valleys (U.S.).

California Encephalitis Virus & La Crosse Virus: