Molluscum contagiosum virus: Infectious substances pathogen safety data sheet

Section I – Infectious agent

Name

Molluscum contagiosum virus

Agent type

Virus

Taxonomy

Family

Poxviridae

Genus

Molluscipoxvirus

Species

Molluscum contagiosum virus

Synonym or cross-reference

Molluscum contagiosum, water warts, molluscum dermatitis, eczema molluscorum^{Footnote 1}.

Characteristics

Brief description

Molluscum contagiosum virus (MCV) is a double-strand enveloped DNA virus and is separated into four genotypes: MCV 1, MCV 2, MCV 3, and MCV 4^{Footnote 2Footnote 3}. The virus is enveloped, ovoid, or brick-shaped, measuring approximately 325 by 250 µm. The genome is linear with a G+C content of 63%. The MCV 1 genotype has been completely sequenced, having a length of 190 kbp, which code for 180 proteins^{Footnote 4Footnote 5}.

Properties

MCV infects keratinocytes and infections are limited to the epidermis^{Footnote 3Footnote 5}. MCV replicates in the cytoplasm of host cells, producing inclusions and enlarging infected cells. In the host epidermis, infection occurs in the basal layers, where viral cores are found. As the infection moves into the layers above the basal layer, inclusion bodies enlarge as they move towards the granular cell layers. Eventually, the top layer of the epidermis is disintegrated, forming a lesion where infectious virions are released^{Footnote 5}.

MCV is able to evade the host's immune system during its replication due to viral protein-coding genes that have been identified from the MCV genome, such as MC159, MC160, MC132, MC005, and MC163, which alter the activation of nuclear factor kB (NF-kB)^{Footnote 2Footnote 3Footnote 4}. Nf-kB normally facilitates synthesis of pro-inflammatory cytokines and activates immune responses, leading to skin inflammation. Other coding genes that encode for proteins inhibiting the host immune activation include MC53, MC54, MC148, etc.

Section II – Hazard identification

Pathogenicity and toxicity

MCV is the causative agent of molluscum contagiosum, a skin disorder characterized by single, multiple or clustered skin lesions^{Footnote 5}. MCV lesions are self-limiting, lasting approximately 6 to 9 months in immunocompetent individuals^{Footnote 3Footnote 6}; however, cases lasting up to 4 years have been reported. In immunocompetent individuals, the number of lesions is usually less than 20, but 100 or more can occasionally occur^{Footnote 5}. Lesions can appear at any site, but rarely on palms and soles or mucous membranes^{Footnote 7}. The lesions present as firm rounded papules, which typically range between 2 to 5 mm in diameter^{Footnote 5}. Papules are umbilicated pink or skin-colored, and may have an erythematous halo or be pediculated. In children, exposed skin on the trunk, extremities, intertriginous regions, genitals, and face are most commonly affected^{Footnote 8}. Vertical transmission is possible and often results in lesions on the infant's scalp^{Footnote 9}. In adults, lesions are often found on the lower abdomen, thighs, genitals, and perianal area due to sexual transmission^{Footnote 3}. In HIV or otherwise immunosuppressed patients, lesions are typically numerous, widespread and larger (greater than 1 cm in diameter)^{Footnote 10}. In some cases, eczematous plaques may develop around the skin lesions, a condition referred to as molluscum dermatitis or eczema molluscorum^{Footnote 3}. Molluscum dermatitis develops in 9-47% of molluscum contagiosum cases^{Footnote 5}.

Epidemiology

Molluscum contagiosum is found worldwide, with a global prevalence of 2-10%^{Footnote 11}. The prevalence is approximately 8% for children and ranges from 5-18% for AIDS patients^{Footnote 5Footnote 12}. Molluscum contagiosum is more common in warm climates, rural settings, and where individuals live in close proximity^{Footnote 11}. The disease is maintained in the human population, and due to the route of transmission, often occurs in pocketed outbreaks^{Footnote 13Footnote 14}.

MCV 1 is the most common genotype (75–96%), and mainly affects children of 2-5 years of age, followed by MCV 2, which mainly affects adult women and HIV-positive individuals^{Footnote 4Footnote 5}. MCV 3 and 4 are extremely infrequent and are predominantly found in Asia and Australia^{Footnote 4Footnote 5Footnote 15}.

Immunocompromised individuals (e.g., HIV patients, iatrogenic immunosuppression, primary immunodeficiencies) are at greater risk of developing molluscum contagiosum^{Footnote 12Footnote 16}. Atopic dermatitis is also a risk factor for MCV infection^{Footnote 17}. Disease is also more frequent in the pediatric population (2-5 years old) and sexually active adults^{Footnote 5}. 90% of active infections occur in children^{Footnote 4}.

Host range

Natural host(s)

Humans^{Footnote 3}, horses, donkeys, and kangaroos^{Footnote 18Footnote 19Footnote 20}.

Other host(s)

None.

Infectious dose

Unknown.

Incubation period

The incubation period varies from 14 to 50 days, possibly up until 6 months, with an average of two to seven weeks^{Footnote 3Footnote 11Footnote 21Footnote 22}.

Communicability

MCV is usually transmitted through direct contact (sexual or non-sexual) with infected skin or contact with contaminated fomites, often in communal bathing or swimming facilities^{Footnote 3}. Autoinoculation occurs through the transfer from affected areas to non-infected areas of the body^{Footnote 3Footnote 11}. Cases of vertical transmission from mother to child during delivery have been reported^{Footnote 3Footnote 23}. Injection is also a possible route of transmission; a blood donor presented with MCV infection at the site of a venipuncture^{Footnote 24}. Infection could have occurred during the injection process or through exposure of damaged skin to the virus. Tattooing has also been linked to MCV transmission, which supports injection as a possible route of transmission^{Footnote 25Footnote 26}. Infection could have occurred due to contamination of either the ink or equipment with the virus.

Section III – Dissemination

Reservoir

MCV is maintained in human hosts^{Footnote 3}.

Zoonosis

None.

Vectors

None.

Section IV – Stability and viability

Drug susceptibility/resistance

Cidofovir, an antiviral drug, is effective at inactivating MCV, topically (1-3%) or intravenously (2-5 mg/kg)^{Footnote 7Footnote 27}. Topical treatments such as cantharidin, an inhibitor of phosphodiesterase, and potassium hydroxide will not destroy the virus but can help treat skin lesions^{Footnote 7Footnote 28}. Drug resistance has not been reported.

Susceptibility to disinfectants

Poxviruses are susceptible to 0.02% sodium hypochlorite, 30% isopropanol, 40% ethanol, 0.02% glutaraldehyde, 2% formaldehyde, 0.12% ortho phenylphenol, and 1% hydrogen peroxide^{Footnote 29}.

Physical inactivation

MCV is sensitive to temperatures above 50℃, acidic pH levels (pH ≤ 3), and UV irradiation of 15W^{Footnote 30Footnote 31}.

Survival outside host

MCV is able to survive outside the host^{Footnote 3Footnote 11Footnote 14}; however, the exact survival time has not been determined^{Footnote 32}. Poxviruses are extremely resistant to drying and remain stable over a period of several months at ambient temperatures^{Footnote 29}.

Section V – First aid/medical

Surveillance

Diagnosis of molluscum contagiosum is based on a visual inspection of the lesions to identify distinguishing features^{Footnote 3}. If insufficient for accurate diagnosis, a dermoscope may be used to identify characteristic structures that may not be visible to the naked eye^{Footnote 33}. A potassium hydroxide prep, where the core of a lesion is scraped between two glass slides, treated with potassium hydroxide, and viewed under a microscope, can be used to confirm diagnosis^{Footnote 7}. In cases where the lesions are obscured, or the diagnosis is still uncertain, histopathology tests may be used to confirm disease^{Footnote 34}. Enzyme-linked immunosorbent assay (ELISA) methods can be used to determine global seroprevalence^{Footnote 5Footnote 35}.

Note: The specific recommendations for surveillance in the laboratory should come from the medical surveillance program, which is based on a local risk assessment of the pathogens and activities being undertaken, as well as an overarching risk assessment of the biosafety program as a whole. More information on medical surveillance is available in the Canadian Biosafety Handbook.

First aid/treatment

Active treatment is not required in most cases, as the disease is self-limiting. Cryotherapy may be recommended in cases with extensive lesions or secondary complications^{Footnote 28}. Curettage, physically removing the lesions, is also commonly used^{Footnote 28}. Similar to curettage, manual extrusion using fingers or forceps is an alternative to remove lesions^{Footnote 7}. Pulsed Dye Laser which targets the vasculature to the lesion is typically used for recalcitrant infections^{Footnote 7}. Topical agents containing cantharidin (0.7-0.9%), cidofovir (1-3%), or potassium hydroxide (5-20%) have also proven effective^{Footnote 7Footnote 27Footnote 28}. Topical agents that stimulate the patient's immune system such as imiquimod, oral cimetidine, or candidin have also been effective in resolving lesions^{Footnote 7}.

Note: The specific recommendations for first aid/treatment in the laboratory should come from the post-exposure response plan, which is developed as part of the medical surveillance program. More information on the post-exposure response plan can be found in the Canadian Biosafety Handbook.

Immunization

No vaccine is currently available.

Note: More information on the medical surveillance program can be found in the Canadian Biosafety Handbook, and by consulting the Canadian Immunization Guide.

Prophylaxis

No post-exposure prophylaxis is currently available.

Note: More information on prophylaxis as part of the medical surveillance program can be found in the Canadian Biosafety Handbook.

Section VI – Laboratory hazard

Laboratory-acquired infections

There are no reported cases of MCV laboratory-acquired infections.

Note: Please consult the Canadian Biosafety Standard and Canadian Biosafety Handbook for additional details on requirements for reporting exposure incidents. A Canadian biosafety guideline describing notification and reporting procedures is also available.

Sources/specimens

Tissues samples, affected skin, or removed lesions^{Footnote 5}.

Primary hazards

Exposure of mucous membranes or skin to infectious material, autoinoculation with infectious material, and exposure to contaminated fomites are primary hazards associated with exposure to MCV^{Footnote 5}.

Special hazards

None.

Section VII – Exposure controls/personal protection

Risk group classification

MCV is a Risk Group 2 Human Pathogen and Risk Group 1 Animal Pathogen^{Footnote 36Footnote 37}.

Containment requirements

Containment Level 2 facilities, equipment, and operational practices outlined in the Canadian Biosafety Standard for work involving infectious or potentially infectious materials, animals, or cultures.

Protective clothing

The applicable Containment Level 2 requirements for personal protective equipment and clothing outlined in the Canadian Biosafety Standard are to be followed. The personal protective equipment could include the use of a labcoat and dedicated footwear (e.g., boots, shoes) or additional protective footwear (e.g., boot or shoe covers) where floors may be contaminated (e.g., animal cubicles, PM rooms), gloves when direct skin contact with infected materials or animals is unavoidable, and eye protection where there is a known or potential risk of exposure to splashes.

Note: A local risk assessment will identify the appropriate hand, foot, head, body, eye/face, and respiratory protection, and the personal protective equipment requirements for the containment zone and work activities must be documented.

Other precautions

A biological safety cabinet (BSC) or other primary containment devices to be used for activities with open vessels, based on the risks associated with the inherent characteristics of the regulated material, the potential to produce infectious aerosols or aerosolized toxins, the handling of high concentrations of regulated materials, or the handling of large volumes of regulated materials.

Use of needles and syringes are to be strictly limited. Bending, shearing, re-capping, or removing needles from syringes to be avoided, and if necessary, performed only as specified in standard operating procedures (SOPs). Additional precautions are required with work involving animals or large-scale activities.

For diagnostic laboratories handling primary specimens that may contain molluscum contagiosum virus, the following resources may be consulted:

• Human Diagnostic Activities Biosafety Guideline
• Local Risk Assessment Biosafety Guideline

Section VIII – Handling and storage

Spills

Allow aerosols to settle. Wearing personal protective equipment, gently cover the spill with absorbent paper towel and apply suitable disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up (Canadian Biosafety Handbook).

Disposal

All materials/substances that have come in contact with the regulated materials should be completely decontaminated before they are removed from the containment zone or standard operating procedures (SOPs) to be in place to safely and securely move or transport waste out of the containment zone to a designated decontamination area / third party. This can be achieved by using decontamination technologies and processes that have been demonstrated to be effective against the regulated material, such as chemical disinfectants, autoclaving, irradiation, incineration, an effluent treatment system, or gaseous decontamination (Canadian Biosafety Handbook).

Storage

The applicable Containment Level 2 requirements for storage outlined in the Canadian Biosafety Standard are to be followed. Primary containers of regulated materials removed from the containment zone to be labelled, leakproof, impact resistant, and kept either in locked storage equipment or within an area with limited access.

Section IX – Regulatory and other information

Canadian regulatory information

Controlled activities with molluscum contagiosum virus require a Human Pathogens and Toxins licence issued by the Public Health Agency of Canada.

The following is a non-exhaustive list of applicable designations, regulations, or legislations:

• Human Pathogen and Toxins Act and Human Pathogens and Toxins Regulations
• Health of Animals Act and Health of Animals Regulations
• Transportation of Dangerous Goods Regulations

Last file update

October 2023

Prepared by

Centre for Biosecurity, Public Health Agency of Canada.

Disclaimer

The scientific information, opinions, and recommendations contained in this Pathogen Safety Data Sheet have been developed based on or compiled from trusted sources available at the time of publication. Newly discovered hazards are frequent and this information may not be completely up to date. The Government of Canada accepts no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information.

Persons in Canada are responsible for complying with the relevant laws, including regulations, directives and standards applicable to the import, transport, and use of pathogens and toxins in Canada set by relevant regulatory authorities, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment and Climate Change Canada, and Transport Canada. The risk classification and related regulatory requirements referenced in this Pathogen Safety Data Sheet, such as those found in the Canadian Biosafety Standard, may be incomplete and are specific to the Canadian context. Other jurisdictions will have their own requirements.

Copyright ^© Public Health Agency of Canada, 2023, Canada