Molluscum Contagiosum Case File

Molluscum Contagiosum Case File

Eugene C.Toy, MD, Cynthia Debord, PHD, Audrey Wanger, PHD, Gilbert Castro, PHD, James D. Kettering, PHD, Donald Briscoe, MD

CASE 31

A 4-year-old girl is brought in by her mother for the evaluation of multiple skin growths on her neck and upper chest. They have been present for a month or two. They are not pruritic or painful. The mother thinks that they are “pimples” because she squeezed a couple of them and some white material was expressed. She has been treating the lesions with an over-the-counter acne preparation, but it hasn’t helped. The child has no significant medical history, takes no medications, and has no allergies. On examination you see multiple discrete, isolated 1–2-mm papules on her upper chest and lower neck. They are flesh colored, have a central umbilication, and feel firm on palpation. The remainder of her examination is normal. You suspect Molluscum contagiosum.

◆ How did the girl most likely acquire this infection?

◆ What would you see microscopically on a stained slide of material expressed from the core of one of these lesions that would confirm your diagnosis?

ANSWERS TO CASE 31: MOLLUSCUM CONTAGIOSUM

Summary: A 4-year-old girl with multiple discrete 1–2-mm papules on her upper chest and lower neck that are flesh colored, have a central umbilication, consistent with Molluscum contagiosum.

◆ Most likely mechanism of acquisition of infection: Direct contact with the virus or via contact with contaminated fomites.

◆ Microscopic findings of expressed material confirming diagnosis: Microscopic observation of the core material would show eosinophilic cytoplasmic inclusions, also known as molluscum bodies.

CLINICAL CORRELATION

Molluscum contagiosum is a poxvirus that causes benign cutaneous disease worldwide. It is transmitted via direct contact with infected cells or with objects contaminated with virus particles. It causes small wart-like growth on infected skin, and occurs more frequently in children than adults.

APPROACH TO SUSPECTED MOLLUSCUM CONTAGIOSUM INFECTION

Objectives

1. Be aware of the characteristics of the poxvirus.
2. Be able to describe the mechanism of infection and strategies for prevention and treatment.

Definitions

Molluscum bodies: Eosinophilic cytoplasmic inclusions seen in epidermal cells infected with Molluscum contagiosum.

Umbilicated lesions: Lesions with cup-shaped crater and a white core.

Papules: Lesions that are raised and well circumscribed.

DISCUSSION

Characteristics of Molluscum Contagiosum That Impact Transmission

Poxviruses are among the largest, most complex viruses known. They have a linear, double-stranded DNA genome that is fused at both ends. The virion binds to a cell surface receptor and enters the target cell by fusion of the outer envelope with the cell membrane. Replication of poxviruses occurs entirely in the host cytoplasm, making them unique among DNA viruses and requiring them to provide all enzymes necessary for viral replication. For example, poxviruses encode proteins for mRNA synthesis, DNA synthesis, nucleotide scavenging, and immune escape mechanisms. Viral DNA replication and virion assembly occurs in cytoplasmic inclusions called Guarnieri inclusions. The newly assembled virions are released on cell lysis.

Because the worldwide eradication of smallpox has been documented, Molluscum contagiosum is the only poxvirus specific for humans. Viral inoculation occurs through small skin abrasions, either from direct contact with infectious particles or via contaminated fomites. The incubation period for Molluscum contagiosum infection is approximately 2 weeks to 6 months. Some documented forms of viral spread include direct contact with lesions during wrestling matches, in swimming pools, sharing of towels, and sexual contact. Molluscum contagiosum infection is more common in children than in adults, and in adults it is most often transmitted by sexual contact. Immunocompromised persons who are infected with Molluscum contagiosum may develop hundreds of lesions. Patients who are at greatest risk for this presentation are those with late-stage AIDS, with a CD4 count <200 cells/μL.

Diagnosis

Molluscum contagiosum clinically causes discrete, flesh-colored papules with a central umbilication. These nodular lesions most commonly form in groups of 5–25 occurring on the trunk, genitalia, and extremities. They are also known to cause “kissing lesions” via direct contact of a lesion with an uninfected area of skin on the same host; such as a lesion on the lateral chest may cause a “kissing lesion” on the inner arm. The semisolid core of these lesions can be expressed and examined microscopically for the presence of large, eosinophilic inclusions, known as molluscum bodies.

Treatment and Prevention

The lesions of Molluscum contagiosum generally develop within 2–3 months of contact and usually resolve within 1–2 years. Cell-mediated and humoral immunity both appear to be important for disease resolution. When indicated, the lesions can be removed by curettage, electrocautery, or liquid nitrogen applications.

COMPREHENSION QUESTIONS

[31.1] The incidence of Molluscum contagiosum as a sexually transmitted disease is increasing in young adults and results in the formation of small wart-like lesions in the genital region. Which of the following viruses might also be suspected in such a case of sexually acquired lesions?

A. Cytomegalovirus

B. Varicella-zoster virus

C. Human papillomavirus

D. Human immunodeficiency virus

[31.2] Which of the following statements best describes the viral characteristics of Molluscum contagiosum?

A. A large and complex virus containing single-stranded linear RNA

B. A double-stranded DNA virus encoding a DNA-dependent RNA polymerase

C. A double-stranded linear DNA virus that integrates into the chromosome

D. A single-stranded DNA virus that replicates in the host cytoplasm

E. A double-stranded circular DNA virus

[31.3] A sexually active 17-year-old man presents to the local free clinic to check some small papules that appeared on his penis. The papules are small and white and contain a central depression in their center. There is no penile discharge, nor is there pain on urination. To what group is the organism most likely associated with?

A. Poxviridae

B. Papovaviridae

C. Adenoviridae

D. Parvoviridae

E. Arenaviridae

Answers

[31.1] C. Human papillomavirus; answers A, B, and D are incorrect; cytomegalovirus is known as a sexually transmitted disease but does not characteristically form lesions in or around the genitalia; varicella-zoster virus does form vesicular lesions but appears clinically as a vesicular rash of the head, trunk, or extremities in a dermatomal pattern, not as a genital infection; human immunodeficiency virus is also known to be transmitted via sexual contact, yet it manifests clinically primarily through suppression of the host immune response, not through the formation of genital lesions.

[31.2] B. Molluscum contagiosum is a poxvirus and therefore is a doublestranded DNA virus encoding a DNA-dependent RNA polymerase; answers A, C, D, and E are incorrect: (A) describes the characteristics of rabies virus; (C) more appropriately describes herpes simplex viruses; (D) poxviruses do replicate in the host cytoplasm, and Molluscum contagiosum is a double-stranded DNA virus; (E) more appropriately describes human papillomaviruses.

[31.3] A. The disease in question is Molluscum contagiosum, which belongs to the Poxviridae and is characterized by small white papules with a central umbilication usually found in the genital region; answers B, C, D, and E are incorrect: (B) Papovaviridae include human papillomavirus and BK, JC polyomavirus, and although HPV causes genital warts, they do not have the central umbilication present in Molluscum contagiosum; (C) Adenoviridae include a variety of viral serotypes which cause respiratory, ocular, and gastrointestinal diseases; (D) Parvoviridae include erythema infectiosum characterized by the slapped cheek appearance; (E) Arenaviridae include lymphocytic choriomeningitis and Lassa virus, which are not described in the question stem.

MICROBIOLOGY PEARLS ❖ Molluscum contagiosum is a poxvirus transmitted via direct contact with infected cells, sharing of towels, or via sexual contact. ❖ Clinical manifestations are small flesh colored umbilicated lesions occurring on the trunk, extremities, or genitalia. ❖ Lesions will resolve spontaneously over time, or can be removed via scraping or treatment with liquid nitrogen.

REFERENCES

Brooks GF, Butel JS, Morse SA. Jawetz, Melnick, & Adelberg’s Medical Microbiology, 23rd ed. New York: McGraw-Hill, 2004:463–4. 

Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology, 5th ed. St. Louis, MO: Mosby, 2005:523–4. 

Ryan JR, Ray CG. Sherris Medical Microbiology, 4th ed. New York: McGraw-Hill, 2004:528–9.

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