Introduction

Molluscum Contagiosum is a mild, skin disease caused by a viral infection. The disease is commonly found in children however it is possible for anyone to catch the virus. It is not harmful and often shows no other symptoms besides mild irritation. The presentation of disease can be confused with other skin conditions, therefore it is important to know how to recognise it. 

Due to its contagious nature, the skin condition affects approximately 1 per 100 children per year in the UK.¹ It is important to note that this statistic is an estimate, as it can be affected by different regions and year groups and many may go unreported. 

Molluscum contagiosum virus (MCV)

Molluscum contagiosum is a viral infection in the family Poxviridae, to which the variola virus of smallpox also belongs. Molluscum contagiosum virus(MCV) belongs to the largest-sized DNA viruses and is among those with some of the most complicated modes of replication. Apart from other DNA viruses, MCV replicates entirely within the infected cell's cytoplasm and utilises its replication apparatus.²

Replication 

The viral Molluscum resides within the keratinocytes in the topmost layer of the skin - the epidermis. The replication cycle is as follows:⁹ 

1. Virus penetrates the keratinocytes
2. The outer membrane is degraded and the core of the virus exposed 
3. The core becomes uncoated to release the viral DNA within
4. 2 processes occur - early and late transcription
5. Virus proteins are produced to make new viruses
6. New virus released from the cell cytoplasm by exocytosis
7. The infiltrated virus results in Henderson-Patterson bodies, filled with viral material
8. Increased number and size of viral particles and keratinocytes cause the formation of spots, known as Molluscum Contagiosum 

Transmission

Once the replication cycle has taken place, the Molluscum will present as papules on the skin. These spots can rupture and release a discharge that is pus-like. This contains viral material which can spread to others. Therefore, it is transmitted from direct skin-to-skin contact with other infected people. 

Although it can spread through touch, it is not recommended for children to stay home from school or stop regular activity. 

However, unlike some poxviruses that spread throughout the body and affect organs such as the spleen and lymphatic system, MCV is considerably less serious, infecting only the keratinocytes of the epidermis: the cells that form a layer in the upper part of the skin.

Risk factors 

Predisposing factors to the development of Molluscum Contagiosum include:

• Children below the age of 5 due to their greater exposure in schools and playgrounds
• People with weak immunities: Their immune system is weakened, so they are more prone to viral and bacterial infections
• People taking part in contact sports: Most of the sports involve holding onto another person's skin, so the chances of transmission increase
• Children who have skin conditions: In conditions like eczema where the skin is cracked or broken, entry of the virus becomes pretty easy³

Once the virus invades the skin, it infects epidermal keratinocytes. The replicating virus produces characteristic Henderson-Patterson bodies forming papules or spots that rupture to exude a pus-like discharge containing the infectious virus that spreads infection. Due to its contagious nature, children with the infection should not have to be kept home from school or other activities.

Signs and symptoms 

The only symptom of Molluscum Contagiosum is the spots on the skin. These spots have certain aspects making them characteristic of the infection. Some attributes of these spots include 

• Small and round - around 5mm in size
• Pink or skin-coloured 
• Raised with indentations at the top
• ”Wart-like” appearance 
• Present in folds of the skin - stomach, arms, legs and sometimes face 
• Painless but can be itchy 

These symptoms can occur 2-8 weeks after the initial virus has been transferred from an infected individual - known as the incubation period.

Diagnosis 

Most healthcare providers can tell if a patient has Molluscum contagiosum by physical examination of the size and shape of the spots. If not, they may wish to rule out other skin conditions first, to establish if it is a more serious condition, such as basal cell carcinoma which can present similarly.  

If a physical examination is inconclusive, a skin sample can be conducted to be reviewed under a microscope. This is because the spots have histopathologic features helping to identify the virus. Its classic feature is its indentation from the epidermis to the dermis layer of the skin. Additionally, through histological staining, Henderson-Paterson bodies are seen on the spots, which are small pockets within the papules on cells called keratinocytes that are enclosed to contain the Molluscum Contagiosum viral particles.⁴ 

Treatment 

Once diagnosed with Molluscum, healthcare professionals will most often recommend letting the infection run its course instead of prescribing any medications. The skin will start to clear on its own and the viral infection will subside. According to the NHS website, for most healthy children, this may take a few months, sometimes up to a year. 

In the case where treatment is needed, the course of treatment depends on the severity of the infection.

Complications 

The main complications associated with Molluscum Contagiosum involve the risk of secondary bacterial infections. When the spots become itchy, especially in children, it becomes easy to scratch and break the skin. The skin acts as a protective barrier to the body, and when broken, it allows entrance of other infections.⁸

Very rarely, when the contagious spots present themselves near the eye or on the eyelid, it can present ocular complications. This could be due to the viral toxins leaking into the eye, leading to a type of conjunctivitis - follicular conjunctivitis. 

Prevention 

Information about how the virus operates and evades the body’s immune surveillance has been a mystery. This is because there has yet to be an animal or cell model of the disease created. Therefore there is a lack of laboratory research conducted in this area. 

It is known, that to minimise the spread, there are some things to consider:

• Avoid sharing towels, clothes, and bedding with infected individuals 
• Good level of hygiene - encourage children to wash hands 
• Bathe children after nursery/school or other activities involving others
• Regularly wash toys or other shared materials 
• Cover bumps of those infected with bandages - lower the chance of transmission to others⁹

Molluscum contagiosum in adults

Although more common in children, Molluscum is present in adults too. The presence of MCV is more prominent in sexually active adults, as this is a mode of transmission for the virus. Additionally, those who are HIV+ have a higher risk of infection, due to their immunocompromised state.¹⁰

Summary 

Although Molluscum Contagiosum can cause some concern for parents, it is completely benign. With the only symptoms of itching or discomfort, it is perfectly safe for a child to catch the infection. However, education about what the spots look like and the presentation of the disease is important, as it is essential to rule out any other skin lesions such as skin cancer first. 

Despite this childhood illness being so common, there is a limited understanding of the mechanism of disease, due to its complex nature and lack of animal models. However, future research using skin grafts is currently underway to understand more. Fortunately, Molluscum contagiosum is entirely benign, with no record of severe complications, so a diagnosis should not be a cause for worry.