From Antiviral Agents Bulletin, August 1996, p. 196-7
Pathogenic Molluscum Contagiosum Virus Sequenced
Dr. B. Moss, NIAID, and collaborators reported in the August 9 issue of Science the first full sequencing of the poxvirus that causes molluscum contagiosum, a persistent and sometimes disfiguring opportunistic skin disease often occurring in immune suppressed (e.g., up to 33% of AIDS) patients. The molluscum contagiosum virus (MCV) and variola (smallpox) virus are the only two poxviruses known to specifically infect humans. Unlike variola virus which either invokes a protective immune response or leads to death, molluscum contagiosum is a slow, progressive disease evoking minimal immune response. Dr. Moss reports, “Until now, relatively little has been known about MCV because the virus has never been grown in the laboratory, and there is no animal model to study the infection. With the complete DNA sequence in hand, it will now be possible, for the first time, to test drugs against the various enzymes and other proteins encoded by MCV genes and to study how the virus protects itself from immune responses.”
MCV is transmitted by direct skin contact and the disease occurs most often in small children and sexually active adults, causing papules (small dome-shaped bumps) on the skin about 5 mm in diameter. In healthy individuals, these are usually few in number and generally resolve spontaneously within a few months. Current treatment options include the same physical agents applied to warts, e.g., freezing, caustic agents, surgical removal and electrocauterization. In HIV-infected patients, MCV is often progressive and resistant to treatment. Papules are generally restricted to the groin or face in HIV-infected patients with largely intact immune systems. However, in patients with CD4+ T-cell counts below 200, the lesions proliferate and spread, sometimes coalescing to form lesions as large as 1.5 cm in diameter, while in those with counts below 50, the lesions often extend into the mucosal surfaces of the lips or conjunctiva.
MCV was found to have unique genes, not found in variola virus, that encode proteins that apparently help the virus avoid immune detection. The MCV genome potentially encodes 163 proteins, of which 103 have homologs in the variola virus. MCV lacks counterparts to 83 variola virus genes and 59 MCV genes are predicted to encode previously uncharacterized proteins, including major histocompatibility complex class I, chemokine, and glutathione peroxidase homologs, which may be linked with MCV pathogenesis and provide considerable insights into how viruses can evade antiviral defense mechanisms. Several MCV proteins are very similar to human cellular proteins involved in immune responses, including defective versions of MHC class I receptors; a protein that competes with or blocks chemokine activity; and a protein that protects MCV from inactivation by peroxidases. NIH can be presumed to have filed patent applications related to sequencing MCV. For further information about licensing opportunities, contact Steve Ferguson, Office of Technology Transfer, NIH; Phone: 301-496-7735; Fax: 301-402-0220.