Molluscum contagiosum represents a benign skin infection that predominantly affects children, sexually active adults, and immunocompromised individuals. Worldwide the incidence of this condition (caused by a specific type of poxvirus) ranges from 2 to 8%, and recently it has been linked to the epidemiology of human immunodeficiency virus (HIV).
Even though the virus is transmitted directly and large outbreaks have been noted, the epidemiology of molluscum contagiosum has not been completely elucidated. Available studies on this topic are scarce and are mostly focused on risk factors or rates of the infection in specific population groups (with an emphasis on the age of the subjects and their immunological status).
Disease Distribution and Transmission
Since humans represent the only reservoir of infection, it is globally distributed. Nevertheless, certain regions are characterized by a higher incidence of molluscum contagiosum, most notably the tropics. It is also more commonly observed in crowded areas and closed institutions due to humidity, warmth and inadequate hygiene.
In any case, close contact is pivotal for the transmission of the virus, regardless of whether the disease is spread sexually, by non-sexual skin-to-skin contact, by autoinoculation, or whether the primary vehicles are fomites. The average incubation period after contact is between 2 and 3 months, although it can range from 7 days to 6 months.
As the virus characteristically colonizes the epidermis (i.e. the top layer of the skin), it does not spread throughout the human body and, consequently, cannot spread via sneezing or coughing. Therefore once the lesions disappear, the virus is gone and it is impossible to spread the disease to others. This is in contrast to the herpes virus that can be dormant in the body for long periods of time, eventually reappearing to cause fresh outbreaks of clinical infection.
Historically, molluscum contagiosum has almost exclusively affected young children between 2 and 5 years of age. It has rarely been observed in children younger than 1 year of age, albeit a bimodal age distribution has been described in the medical literature.
However, adults with HIV and acquired immunodeficiency syndrome (AIDS) are increasingly being affected by this viral illness due to specific defects in cellular immunity. Several isolated case reports have come in regarding congenital or vertical transmission, and autoinoculation is also suspected to be a specific mode of transmission.
Disease on the Rise
Recent reports show that prevalence rates of molluscum contagiosum are definitely on the rise. This is especially evident in the UK, where a 50% increase has been observed between 1998 and 2008, and the trend continues even in this decade. Furthermore, in Australia a seroprevalence of 23% has been documented, and as many as 20% of female sex workers from India are affected by this viral disease.
Regional outbreaks are particularly important for the spread of the disease. For example, in one such outbreak that occurred in East Africa, lesions were found in 17% of village population and in 52% of children older than 2 years of age. High prevalence rates are also found in HIV-infected individuals, especially those with CD4 cell counts lower than 100 cells per microliter (µL) of blood.
- Dhar JK. Molluscum Contagiosum. In: Kumar B, Gupta S, editors. Sexually Transmitted Infections, Second Edition. Elsevier Health Sciences, 2012; pp. 374-379.
- Liu D. Molluscum Contagiosum Virus. In: Liu D, editor. Molecular Detection of Human Viral Pathogens. CRC Press, Taylor & Francis Group, 2011; pp. 1001-1008.