PARVOVIRIDAE

• STRUCTURE: Single-stranded DNA. The smallest of the DNA viruses.

• REPLICATION: Occurs in nucleus. First, a complementary DNA (cDNA) is formed, which is then used as a template to form progeny virions.

• Three Subtypes:

  • Densovirus: Infects insects.

  • Parvo Virus: Infects humans and animals, but there is no cross-infection.

  • Dependovirus: Depends on other viruses to replicate.

• HUMAN PARVOVIRUS B19 (HPV B19): A parvovirus.

  • STRUCTURE: There is only one antigenic type, and immunity is lifelong and protective.

  • PATHOGENESIS:

    • It requires dividing cells to divide. It likes erythroid precursor cells.

  • TRANSMISSION: Respiratory, or by blood transfusion.

  • DIAGNOSIS: Immune electron microscopy. ELISA or RIA. PCR.

    • Can assay serum IgM to detect acute infection.

  • MANIFESTATIONS:

    • Erythema Infectiosum: "Fifth Disease" in children.

      • Rash produces a "slapped-cheek" appearance on face, then proceeds to trunk and limb. This progression is like measles -- rash goes from the head down.

      • In adults, it produces mild fever, arthralgia, and limited rash.

    • Aplastic Crisis in people with Sickle Cell Anemia. Virus replicates in erythroid precursor cells and thus can result in fall in hemoglobin and aplastic crisis.

    • Hydrops Fetalis, Spontaneous Abortion: Hydrops fetalis occurs as a result of infection of fetal heart, liver, kidney, and RBC's, with consequent fall in hemoglobin.

    • Mild systemic and respiratory illnesses

• ADENO-ASSOCIATED VIRUS (AAV): A Dependovirus. Defective virus requires Adeno or Herpes virus coinfection.

  • PATHOGENESIS:

    • It produces a latent infection.

    • It integrates into host on specific site of chrom #9 as a provirus, so it is a good candidate for gene therapy.

  • MANIFESTATIONS: We don't know what disease, if any, this virus is associated with.

• RA-1: Virus associated with Rheumatoid Arthritis.

Category: Microbiology Notes