bubble_chart Overview

This disease is a skin pestilence caused by the pestilence molluscum virus. It is generally transmitted through direct contact with pestilence and can also spread through autoinoculation.

bubble_chart Epidemiology

Molluscum contagiosum is a globally prevalent disease, with the highest incidence among children in Papua New Guinea, Fiji, and other regions. In Western countries, the incidence of this disease has been rising and parallels the increase in cases of genital herpes, syphilis, and gonorrhea. According to Willcox's report, from 1971 to 1973, male cases of molluscum contagiosum increased by 29.6%, while female cases rose by 25.0%. The dermatology department of Huashan Hospital in Shanghai, China, reported that this disease is primarily common among children.

The disease can be transmitted in public baths, swimming pools, or through sexual contact. Sexual transmission is mainly observed among sexually active young adults and is often associated with intercourse, leading to its classification as a sexually transmitted disease (STD). The evidence includes: ① Molluscum lesions frequently occur on the genitals or adjacent areas, with anal lesions common among homosexual individuals; ② Higher transmission rates are observed between sexual partners; ③ Other STDs often co-occur in these sexually active populations. The disease is rarely seen in the elderly, though recent reports have documented cases in AIDS patients. In individuals with predisposing factors or heightened sensitivity to the virus, lesions may become widespread. Reports indicate extensive skin lesions in patients with sarcoidosis, leukemia, or those using corticosteroids and immunosuppressants. Natural infections have also been reported in chimpanzees, kangaroos, and horses.

bubble_chart Pathogen

There are many poxviruses that infect humans (see table). The virus causing this disease is a DNA virus belonging to the Poxviridae family and is one of the largest sexually transmitted disease pathogens in humans, measuring approximately 300×200×100 μm. Electron microscopy studies reveal that the formation of the virus is closely related to the cytoplasm. The cytoplasmic matrix condenses, and eosinophilic granules appear, aggregating into large granules, known as granular assembly-type viruses (initial stage [first stage] viruses). Subsequently, fine granular-type viruses (intermediate stage [second stage] viruses) form, and finally, a brick-like outer shell and a dumbbell-shaped DNA core develop. The entire cytoplasmic matrix transforms into viral inclusion bodies, also called molluscum bodies. Morphologically, they resemble smallpox, cowpox, sheep pox, and other animal viruses. So far, cultivation and animal experiments have not been successful. It has been reported that pestilence molluscum can produce cytopathic effects (CPE) in primary human amniotic membrane cells, human foreskin fibroblasts, monkey kidney cells, and FL cells. However, because it cannot pass through the membrane-shedding stage, the virus struggles to grow in any cell line, making cell culture isolation of the virus impractical as a routine method.

The inability of pestilence molluscum virus to replicate in tissue culture cells hinders analysis of its DNA. Limited reports indicate that this virus has a higher G+C content than vaccinia virus and at least two subtypes. Viruses isolated from the genital area are classified as type II, while those isolated from other parts of the body are classified as type I. However, lesions caused by the two types are not necessarily confined to specific regions. In clinical specimens, pestilence molluscum virus particles resemble orthopoxviruses in morphology, but their "M" particles have protruding tubular structures similar to those of Yatapoxvirus, distinguishing them from smallpox, monkeypox, and vaccinia viruses. Additionally, molluscum virus lacks an envelope, unlike Tanapox virus. The characteristic skin lesions produced by pestilence molluscum virus are easily diagnosed clinically, but when they appear as dermatitis or ulcers in the genital area, they are often confused with genital herpes virus. In such cases, diagnosis can only be confirmed by electron microscopy.

Table: Poxviruses and Human Diseases

bubble_chart Pathological Changes

Characteristically, numerous intracytoplasmic inclusion bodies appear in the epidermal cells, known as molluscum bodies. These bodies compress the nucleus of each affected cell, causing the nucleus to become crescent-shaped and located at the cell's periphery. The molluscum bodies change from eosinophilic to basophilic, and numerous basophilic molluscum bodies with a diameter of 35μm can be observed in the stratum corneum. If the central stratum corneum ruptures, the molluscum bodies are discharged, forming a crater-like center. In follicular pestilential molluscum, the dermis contains numerous enlarged hair follicles filled with molluscum bodies.

Electron microscopy reveals viral particles within the cytoplasm.

bubble_chart Clinical Manifestations

The incubation period ranges from 1 week to 6 months.

The typical lesion is a papule formed by the proliferation of infected local epidermal cells, measuring 2–8 mm in diameter, solitary or multiple, round or hemispherical, with a waxy sheen, a central umbilication, and containing a caseous plug. The papule appears flesh-colored or pink. In the initial stage [first stage], it is firm in texture, softens upon maturation, and can be extruded to release caseous material. Clinically, it can be divided into two types:

① Childhood type: Infection occurs through direct skin contact or via pestilence vectors, with molluscum contagiosum appearing on the face, trunk, and limbs.

② Adult type: This can be sexually transmitted, with molluscum contagiosum commonly found on the external genitalia, buttocks, lower abdomen, pubic area, and inner thighs, or around the anus in those who engage in anal intercourse. Lynch reported 55 such cases among U.S. soldiers returning from Vietnam and Korea, who had a history of prostitution in those countries.

Lesions can occur on any contact site except the metatarsus of the palm and may also appear on the lips, tongue, buccal mucosa, and conjunctiva. Conjunctival lesions may be accompanied by reactive conjunctivitis or keratitis. A few lesions may be unusually large, termed giant molluscum contagiosum, while others may keratinize and resemble small cutaneous horns, known as keratotic molluscum contagiosum. Generally, there are no subjective symptoms.

In HIV-infected cases, the incidence of pestilence-related molluscum contagiosum increases, with widespread dissemination and large lesions. There have been reports of AIDS patients presenting with giant molluscum contagiosum on the face, which can easily be confused with basal cell epithelioma. Additionally, two cases of extensive, acute molluscum contagiosum with hundreds of lesions have been reported in patients with a history of immunosuppressive therapy involving prednisolone and methotrexate, suggesting a link between the condition and immunosuppression.

The disease is self-limiting and typically lasts from several months to several years.

bubble_chart Treatment Measures

Use small forceps to grasp and extract the molluscum bodies from the lesion by squeezing or picking them out, then apply concentrated carbolic acid or trichloroacetic acid and apply pressure to stop bleeding. Alternatively, a curette can be used to scrape them off, followed by applying 2% iodine tincture externally, or 0.1% retinoic acid alcohol for local application. Other methods include electrodessication, cryotherapy with liquid nitrogen or dry ice, and surgical excision for large lesions. Sexual partners should be treated simultaneously.

bubble_chart Differentiation

The diagnosis of this disease is straightforward based on the clinical presentation of waxy, round or hemispherical papules with central umbilication, from which caseous material can be expressed, along with characteristic histopathological features. Genital lesions in sexually active young individuals should prompt screening for sexually transmitted diseases. Larger skin lesions should be differentiated from basal cell carcinoma and keratoacanthoma.

Laboratory testing methods for molluscum contagiosum virus are summarized in the table.

Table: Detection of molluscum contagiosum virus particles and antigens in sexually transmitted diseases

Objective	Method	Result
1. Direct detection of virus particles	Smear staining: Express caseous material, Wright staining	Molluscum bodies (+)
	Electron microscopy: Biopsy specimen	Molluscum virus (+)
	Histopathology:	Diagnostic features present
2. Direct detection of viral antigens	Agar gel precipitation test (AGP)	(+)
	Complement fixation test (CF)	(+)
	Indirect immunofluorescence test (IIF)	(+)
	Neutralization test (Nt)	(+)