Recombination events and variability among full-length genomes of co-circulating molluscum contagiosum virus subtypes 1 and 2.

Molluscum contagiosum virus (MCV) is the sole member of the Molluscipoxvirus genus and causes a highly prevalent human disease of the skin characterized by the formation of a variable number of lesions that can persist for prolonged periods of time. Two major genotypes, subtype 1 and subtype 2, are recognized, although currently only a single complete genomic sequence corresponding to MCV subtype 1 is available. Using next-generation sequencing techniques, we report the complete genomic sequence of four new MCV isolates, including the first one derived from a subtype 2. Comparisons suggest a relatively distant evolutionary split between both MCV subtypes. Further, our data illustrate concurrent circulation of distinct viruses within a population and reveal the existence of recombination events among them. These results help identify a set of MCV genes with potentially relevant roles in molluscum contagiosum epidemiology and pathogenesis.

Antibodies to molluscum contagiosum virus in the general population and susceptible patients.

BACKGROUND: Since many attempts to cultivate molluscum contagiosum virus (MCV) in vitro have been unsuccessful, it is difficult to prepare a large quantity of antigens. To assess the seroprevalence of antibodies against MCV in 508 subjects with or without clinical MCV infection, a truncated recombinant protein from open-reading frame MC133L was synthesized using Sendai virus expression system and applied to enzyme-linked immunosorbent assay as an antigen. OBSERVATIONS: Antibodies to MCV were present in 7 (58%) of 12 patients with molluscum contagiosum, 7 (6%) of 108 healthy controls, 7 (9%) of 76 with atopic dermatitis, and 7 (18%) of 39 patients with systemic lupus erythematosus, although no clinical MCV infection was observed in the latter 3 groups. Of 7 human immunodeficiency virus (HIV)-positive patients with molluscum contagiosum, 1 (14%) was antibody positive, compared with 5 (2%) of 266 HIV-positive patients without molluscum contagiosum. Serum samples from patients with atopic dermatitis and systemic lupus erythematosus showed a higher reactivity (P<.001) than those from healthy controls, while serum samples from HIV-positive subjects showed a lower reactivity (P<. 001). CONCLUSION: The humoral immune response to MCV is usually confined to patients with molluscum contagiosum and may be affected by the immunological condition of the host.

Recent advances in molluscum contagiosum virus research.

Molluscum contagiosum virus (MCV) and variola virus (VAR) are the only two poxviruses that are specific for man. MCV causes skin tumors in humans and primarily in children and immunocompromised individuals. MCV is unable to replicate in tissue culture cells or animals. Recently, the DNA sequence of the 190 kbp MCV genome was reported by Senkevich et al. MCV was predicted to encode 163 proteins of which 103 were clearly related to those of smallpox virus. In contrast, it was found that MCV lacks 83 genes of VAR, including those involved in the suppression of the host response to infection, nucleotide biosynthesis, and cell proliferation. However, MCV possesses 59 genes predicted to code for novel proteins including MHC-class I, chemokine and glutathione peroxidase homologs not found in other poxviruses. The MCV genomic data allow the investigation of novel host defense mechanisms and provide new possibilities for the development of therapeutics for treatment and prevention of the MCV infection.

Growth of molluscum contagiosum virus in a human foreskin xenograft model.

Molluscum contagiosum virus (MCV) is a common pathogen causing a troublesome skin condition in many immunocompetent individuals and a widespread, disfiguring affliction in many patients with AIDS. We have successfully infected human foreskin fragments with a patient-derived isolate of MCV. This was demonstrated by exposing the foreskin pieces to a patient lesion extract and implanting the tissue under the renal capsule of athymic mice. Light and electron microscopic examination of infected implants showed the presence of cytoplasmic inclusions containing typical poxvirus particles within 2-3 weeks of implantation. Replication of MCV was established by demonstrating that viable virus was required to produce the cytopathologic effects, and viral DNA replication was demonstrated by incorporation of bromodeoxyuridine into cytoplasmic inclusions. Four additional patient extracts (representing both described MCV types) were also used to successfully infect foreskin implants. A limited number of attempts to pass virus from one infected implant to another were not successful. This system is the most rapid and reproducible for growing MCV that has been reported to date.

Growth and regression of molluscum contagiosum.

The spontaneous evolution of molluscum contagiosum was studied on autoradiograms after incorporation of tritiated thymidine. Three patterns of distribution and intensity of labeling were distinguished and interpreted as three successive stages in the evolution of the lesions, corresponding to growth, steady-state, and regression. The association of an inflammatory cell infiltrate with the traumatic disruption of the infected epithelium may occur during any of the three stages. It is concluded that spontaneous regression of molluscum contagiosum may depend upon two distinct mechanisms that belong to spontaneous noninflammatory and traumatic-inflammatory processes.

Molluscum contagiosum -- a defective poxvirus?

Purified preparations of molluscum contagiosum virus contain a DNA-dependent RNA polymerase (EC 2.7.7.6) with similar but not identical properties to those of the enzyme found in vaccinia virions. The ultraviolet inactivation kinetics of the RNA polymerase from both viruses were similar, displaying fast and slow components. Ultraviolet irradiation destroyed the interfering capacities of molluscum and inactivated vaccinia virions, and the interferon-inducing capacity of molluscum virus slowly and with first-order kinetics. Inactivation studies of the interferon-inducing capacity of vaccinia virus were complicated by cytotoxic effects. Electron microscopical studies showed all stages of virus growth in vaccinia-infected mouse embryo cells; molluscum virus appeared to be degraded in lysosome-like bodies. In preliminary studies, marked changes in cytoplasmic RNA synthesis and in patterns of polypeptide synthesis were found in vaccinia-infected but not in molluscum-infected mouse embryo cells.

Some biological and physical properties of molluscum contagiosum virus propagated in cell culture.

Molluscum contagiosum virus propagated in FL cells of human amnion origin has a one-step growth cycle time of 12 to 14 h. The appearance and exponential increase of intracellular virus preceded the release of extracellular virus by approximately 2 h. Demonstration of comparable titers of extracellular and intracellular virus at the end of the replication cycle indicated that a substantial amount of virus remained associated with cells exhibiting cytopathogenic changes. Mean buoyant density values of virus in sucrose ranged from 1.275 to 1.278 g/cm3, but in CsCl the virus banded at densities at 1.325 to 1.340 and 1.261 to 1.281 g/cm3. Although virus infectivity was not affected by high concentrations of CsCl, it was found by polyacrylamide gel electrophoresis that the salt removed several nonglycosylated polypeptides with estimated molecular weights of 15,000 to 60,000. This suggested that the high-density band (1.325 to 1.340) may reflect the loss of these structural components. The half-life of virus infectivity was approximately 26.5 h at 26 degrees C and 11.2 h at 37 degrees C. Although the virus was rapidly inactivated at 50 degrees C, it could be stabilized at this temperature by the presence of 1.0 M MgCl2. Virus did not agglutinate newborn chick, adult chicken, or type "0" human erythrocytes. Virus infectivity was found to be sensitive to acid pH but resistant to treatment with diethyl ether or chloroform. The replication of molluscum virus in FL cells was not inhibited by 5-iodo-2'-deoxyuridine, 5-bromo-2'-deoxyuridine, or cytosine arabinonucleoside in noncytotoxic concentrations of 200 to 400 mug/ml, but greater than 99% reduction in the yield of herpes simplex virus or vaccinia virus in FL cells was obtained with 200 mug of these compounds per ml. Guanidinium chloride in concentrations of 100 to 200 mug/ml reduced molluscum virus yields by more than 99.9%.