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RNA Viruses Infecting Humans - Microbiology

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  • What distinguishes + sense RNA viruses from - sense RNA viruses?
    + sense RNA viruses have genomes that act directly as mRNA, while - sense RNA viruses must bring their own RNA polymerase to transcribe their genome.
  • Name some naked + sense RNA virus families.
    Picornaviridae, Hepeviridae, Caliciviridae, and Astroviridae are naked + sense RNA viruses.
  • Describe the pathogenesis of poliovirus infection.
    Poliovirus enters via fecal-oral route, replicates in mucosal cells, causes mild viremia, and rarely invades spinal cord causing flaccid paralysis (poliomyelitis).
  • What is the main clinical feature of hand-foot-and-mouth disease caused by Coxsackieviruses?
    Ulcers in the mouth and/or rash on palms and soles.
  • How is Hepatitis A virus transmitted and what are its symptoms?
    Transmitted fecal-orally; symptoms include fatigue, nausea, clay-colored feces, jaundice, and last 2-6 months.
  • Why are vaccines unlikely for human rhinoviruses?
    Because of the high number of serotypes (150-170) and variable accessible antigens acting as decoys.
  • What is the main cause of viral gastroenteritis in the US related to Caliciviruses?
    Norovirus causes about one-third of viral gastroenteritis and 60% of food-borne illness.
  • What is unique about Reoviridae viruses?
    They have double-stranded segmented RNA genomes and are naked icosahedral viruses.
  • What are the three types of influenza viruses and their hosts?
    Type A infects warm-blooded animals and birds; Type B infects humans and some animals; Type C infects humans, pigs, dogs, and cattle.
  • What are hemagglutinin (H) and neuraminidase (N) in influenza viruses?
    H is the glycoprotein for binding and entry; N helps release new virions by cleaving sialic acid.
  • Explain antigenic drift and antigenic shift in influenza viruses.
    Antigenic drift is gradual mutation; antigenic shift is reassortment of RNA segments between strains causing major changes.
  • What is the incubation period and main symptoms of influenza infection?
    Incubation 1-5 days; symptoms include sudden high fever, body aches, dry cough, and respiratory tract infection.
  • Name some antiviral drugs used to treat influenza and their targets.
    Amantadine blocks M2 ion channel; oseltamivir inhibits neuraminidase; baloxavir inhibits cap stealing.
  • What are Bunyaviruses and Arenaviruses, and how are they transmitted?
    Enveloped segmented -RNA viruses; Bunyaviruses mostly insect/tick-borne; Arenaviruses rodent-borne with some person-to-person transmission.
  • Describe the pathogenesis and transmission of rabies virus.
    Enters via bite, replicates at trauma site, travels via nerves to brain, causes fatal encephalitis; transmitted by saliva.
  • What are the clinical phases of rabies infection?
    Prodromal (pain at wound), furious (agitation, hydrophobia), dumb (paralysis), then coma and death.
  • What are the main diseases caused by Paramyxoviruses?
    Measles (Morbillivirus), mumps (Rubulavirus), respiratory syncytial virus, and parainfluenza infections.
  • What is the hallmark oral lesion of measles infection?
    Koplik spots—small white spots on the buccal mucosa.
  • What is the main cause of severe respiratory infection in infants under 6 months?
    Respiratory Syncytial Virus (RSV).
  • What are the main arbovirus families and their vectors?
    Flaviviruses and Togaviruses transmitted by mosquitoes; Bunyaviruses and Reoviruses also include arboviruses.
  • What is the clinical significance of Zika virus infection?
    Usually mild but can cause congenital Zika syndrome with microcephaly and other birth defects.
  • What is the main transmission route and clinical feature of Dengue fever?
    Transmitted by Aedes mosquitoes; causes 'breakbone fever' with severe muscle and joint pain.
  • What is the role of reverse transcriptase in Retroviruses?
    It copies viral RNA into DNA for integration into the host genome.
  • What are the main clinical syndromes caused by HTLV-1 infection?
    Adult T-cell leukemia/lymphoma and HTLV-1 associated myelopathy/tropical spastic paraparesis.
  • How is HIV transmitted and what cells does it infect?
    Transmitted via sex, blood, birth, breast milk; infects CD4+ T cells and some macrophages.
  • What defines AIDS diagnosis in an HIV-positive person?
    CD4+ count <200 cells/ml, or <14% lymphocytes, or presence of AIDS-defining illnesses.
  • What are the main strategies for preventing HIV infection?
    Monogamy, condoms, male circumcision, universal precautions; no vaccine available.
  • What is the principle of antiretroviral therapy (ART) for HIV?
    Combination of drugs targeting multiple viral enzymes to slow disease progression.