Molluscum contagiosum pathophysiology
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Molluscum contagiosum Microchapters |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1];Associate Editor(s)-in-Chief: Mahshid Mir, M.D. [2]
Overview
This is a common infection in children and occurs when a child comes into . The virus can spread through contact with contaminated objects, such as towels, clothing, or toys. The virus also spreads by sexual contact. Persons with a weakened immune system (due to conditions such as AIDS) may have a rapidly worse case of molluscum contagiosum.
Pathophysiology
The time from infection to the appearance of lesions ranges from 1 week to 6 months, with an average incubation period of 6 weeks. Diagnosis is made on the clinical appearance.
Transmission
In adults, molluscum infections are often sexually transmitted and usually affect the genitals, lower abdomen, buttocks, and inner thighs. In rare cases, molluscum infections are also found on the lips, mouth, and eyelids. It is spread through direct contact or shared articles of clothing (including towels).
Virology
MC has no animal reservoir, infecting only humans, as did smallpox. However, there are different pox viruses that infect many other mammals. The infecting human MC virus is a DNA poxvirus called the molluscum contagiosum virus (MCV). There are 4 types of MCV, MCV-1 to -4, with MCV-1 being the most prevalent and MCV-2 seen usually in adults and often sexually transmitted. The virus cannot routinely be cultured.
Overview
- Molluscum contagiosum is usually transmitted via direct contact with a lesion route to the human host. Following transmission, the molluscum contagiosum uses the human body cells to replicate.
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- Template Sentence 5: [Disease name] is transmitted in [mode of genetic transmission] pattern.
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- Template Sentence 7: Development of [disease name] is the result from multiple genetic mutations.
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- Template Sentence 9: The progression to [disease name] usually involves the [molecular pathway].
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Pathogenesis
- Molluscum contagiosum is a member of the poxvirus family
- causes a chronic localized infection with small papules on the skin of an infected individual in contrast to the acute, sometimes fatal, disease induced by smallpox.
- the only known host for molluscum is humans
- inability to grow the virus in standard cell culture or in an animal model of infection.
- reports of some success in growth using human foreskin xenograft fragments.[1]
- (MCV) commonly causes asymptomatic cutaneous neoplasms in children and sexually active adults as well as persistent opportunistic acquired immunodeficiency syndrome (AIDS)-associated disease. [1]
- replicates in the cytoplasm of cells, and thus, it is not surprising that more than one-half of the genes are similar to those found in variola and vaccinia viruses.
Genetics
- MCV genome was reported by Senkevich et al.
- 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.[2]
- many genes found in variola and vaccinia are not present in the molluscum contagiosum genome.
- Molluscum contagiosum contains many unique genes that encode proteins responsible for novel host defense mechanisms; these mechanisms inhibit the host inflammatory and immune responses to the infection.
- Sequencing the 190-kilobase pair genome of MCV has now revealed that the virus potentially encodes 163 proteins, of which 103 have homologs in the smallpox virus. MCV lacks counterparts to 83 genes of the smallpox virus, including those important in suppression of host responses to infection, nucleotide biosynthesis, and cell proliferation. MCV possesses 59 genes that are predicted to encode previously uncharacterized proteins, including major histocompatibility complex class I, chemokine, and glutathione peroxidase homologs, which suggests that there are MCV-specific strategies for coexistence with the human host.[1]
- Analysis of the molluscum contagiosum virus (MCV) genome revealed that it encodes approximately 182 proteins, 105 of which have direct counterparts in orthopoxviruses (OPV).
- The corresponding OPV proteins comprise those known to be essential for replication as well as many that are still uncharacterized, including 2 of less than 60 amino acids that had not been previously noted. The OPV proteins most highly conserved in MCV are involved in transcription; the least conserved include membrane glycoproteins. Twenty of the MCV proteins with OPV counterparts also have cellular homologs and additional MCV proteins have conserved functional motifs. Of the 77 predicted MCV proteins without OPV counterparts, 10 have similarity to other MCV proteins and/or distant similarity to proteins of other poxviruses and 16 have cellular homologs including some predicted to antagonize host defenses. Clustering poxvirus proteins by sequence similarity revealed 3 unique MCV gene families and 8 families that are conserved in MCV and OPV. Two unique families contain putative membrane receptors; the third includes 2 proteins, each containing 2 DED apoptosis signal transduction domains. Additional families with conserved patterns of cysteines and putative redox active centers were identified. Promoters, transcription termination signals, and DNA concatemer resolution sequences are highly conserved in MCV and OPV. Phylogenetic analysis suggested that MCV, OPV, and leporipoxviruses radiated from a common poxvirus ancestor after the divergence of avipoxviruses. Despite the acquisition of unique genes for host interactions and changes in GC content, the physical order and regulation of essential ancestral poxvirus genes have been largely conserved in MCV and OPV.[3]
Associated Conditions
Gross Pathology
- In dermoscopic exam of infected tissue, a central umbilication with polylobular, white to yellow amorphous structures is visualized which is typical for diagnosis. Also a peripheral crown of radiating or punctiform vessels may be seen as well.
- This section is a good place to include pictures. Search for copyleft images on The Pathology Wiki [3] and Ask Dr. Wiki [4].
Microscopic Pathology
Electron microscopic evaluation of tissue is not a part of routine diagnosis procedure, but if done it may show:
- Typical brick-shaped poxvirus particles inside the infected tissue which is highly specific for diagnosis.
- Electron microscopy can also identify infected cells that appear normal on light microscopy
References
- ↑ 1.0 1.1 1.2 Fife KH, Whitfeld M, Faust H, Goheen MP, Bryan J, Brown DR (1996). "Growth of molluscum contagiosum virus in a human foreskin xenograft model". Virology. 226 (1): 95–101. doi:10.1006/viro.1996.0631. PMID 8941326.
- ↑ Bugert JJ, Darai G (1997). "Recent advances in molluscum contagiosum virus research". Arch. Virol. Suppl. 13: 35–47. PMID 9413524.
- ↑ Senkevich TG, Koonin EV, Bugert JJ, Darai G, Moss B (1997). "The genome of molluscum contagiosum virus: analysis and comparison with other poxviruses". Virology. 233 (1): 19–42. doi:10.1006/viro.1997.8607. PMID 9201214.