Poxvirus infections
Poxvirus infections are caused by viruses from the Poxviridae family, which includes notable members like variola (smallpox), vaccinia, mpox, cowpox, mousepox, and molluscum contagiosum. While smallpox was a significant historical illness, it was eradicated in 1980 due to a global vaccination campaign. Molluscum contagiosum is the only other poxvirus disease that primarily affects humans, while the rest usually involve animal hosts and can occasionally infect humans. Transmission of smallpox typically occurred through respiratory droplets, whereas molluscum contagiosum spreads primarily through direct skin contact or contaminated objects. Symptoms of poxvirus infections often feature high fever and distinctive skin lesions that can lead to scarring. Currently, there is no specific treatment for smallpox or mpox, though vaccination against smallpox can help prevent and lessen mpox severity. Prevention strategies for molluscum contagiosum include avoiding contact with infected individuals and contaminated items. Understanding these viruses' transmission and prevention methods is key to managing potential outbreaks and protecting public health.
Poxvirus infections
ANATOMY OR SYSTEM AFFECTED: Skin
Definition
Poxvirus infections are infections with any organism from the family of viruses known as Poxviridae. These infections include variola (smallpox), vaccinia, mpox, cowpox, mousepox, and molluscum contagiosum. Smallpox and molluscum contagiosum are diseases of humans; the others are diseases of animals that occasionally occur in humans. Smallpox, which was one of the scourges of history, was eradicated through a worldwide vaccination campaign in the 1970s. Chickenpox, despite the similarity of name, is caused by a virus from another family.
The Poxviridae viruses are large, enveloped, brick-shaped viruses containing linear, double-stranded DNA (deoxyribonucleic acid). There are eight genus categories (subgroups) of Poxviridae, the most significant being orthopoxvirus, to which the smallpox virus belongs.
Causes
Smallpox was typically spread through the respiratory tract. Sneeze or cough droplets from infected persons were inhaled by others who had not had the disease and who had not been vaccinated. Though less common, smallpox could also be spread through contact with pustules.
In the vaccination process, healthy persons are cutaneously exposed to vaccinia virus. Molluscum contagiosum virus is spread through direct skin-to-skin contact or through contact with contaminated objects (fomites). Most often, however, the disease is spread through sexual contact.
There are many Poxviridae organisms, including cowpox and mpox viruses, whose principal reservoir is animals, making cowpox and mpox zoonotic diseases. These diseases occasionally are spread to humans through animal-human contact. Mpox is the most significant of these diseases; a mpox outbreak involving about fifty people occurred in the United States in 2003. Mpox later returned to headlines in 2022 when the World Health Organization (WHO) declared a global mpox outbreak to be a public health emergency of international concern.
Risk Factors
The principal risk factors for smallpox were one’s location (Africa and the Indian subcontinent) and one’s vaccination status. (Smallpox vaccination programs were discontinued after the World Health Organization declared the disease eradicated in 1980.) Smallpox is now considered a possible biological weapon, and because few people have been vaccinated, most people would be vulnerable to attack. As a result, contact with a recently vaccinated member of the military became a risk factor.
The risk factor for molluscum contagiosum is skin contact with an infected person. Persons with human immunodeficiency virus infection or with compromised immune systems are susceptible to more serious infections. The risk factor for zoonotic poxvirus infection is exposure to animals.
Symptoms
Poxvirus infection typically begins with high fever and respiratory symptoms, but the hallmark symptom is the characteristic vesicular skin lesions that eventually form pustules. The resolution of the skin lesions typically involves significant scarring. The other poxviruses typically cause localized lesions only. Mpox is the exception, and its symptoms can be both generalized and severe.
Screening and Diagnosis
Smallpox can be differentiated from chickenpox by the simultaneous presentation of skin lesions (all lesions will be at the same stage, contrary to the lesions of chickenpox) and by the severity of general malaise.
Treatment and Therapy
No direct treatment for variola major, which has a mortality rate as high as 30 percent, was ever developed. Treatment involved supportive therapy for symptoms such as high fever and dehydration. Left untreated, molluscum contagiosum usually resolves within six months. Treatment options include surgical removal of the lesions; cryotherapy, which uses cold to freeze the lesions off of the skin (liquid nitrogen may be used for this treatment); and retinoid or imiquimod cream, separately or in combination. No treatment exists for mpox, but the smallpox vaccine has been shown to help prevent and reduce the severity of the disease.
Prevention and Outcomes
Two laboratory reservoirs of smallpox virus were retained after WHO declared smallpox to be eliminated worldwide. The challenge now is to balance the risks of vaccination complications (serious complications occur in about 1 in 1,000 persons) with the risks of a potential smallpox outbreak caused by bioterrorism.
To reduce the risk of exposure to the molluscum contagiosum virus, one should avoid contact with infected persons; avoid sharing towels, clothing, baths, and pools; and avoid sexual contact with infected persons. The smallpox vaccine is the best prevention against mpox. In high-risk areas, people should limit exposure to wild animals.
Bibliography
Damon, Inger K. “Smallpox, Monkeypox, and Other Poxvirus Infections.” In Cecil Medicine, edited by Lee Goldman and Dennis Arthur Ausiello. 23d ed. Philadelphia: Saunders/Elsevier, 2008.
Henderson, D. A. Smallpox: The Death of a Disease—The Inside Story of Eradicating a Worldwide Killer. Amherst, N.Y.: Prometheus Books, 2009.
Reed, Kurt D. “Monkeypox and Other Emerging Orthopoxvirus Infections.” In Emerging Infectious Diseases: Trends and Issues, edited by Felissa R. Lashley and Jerry D. Durham. 2d ed. New York: Springer, 2007.
"Training to Build Community Capacity to Meaningfully Engage in Mpox Response." World Health Organization, 13 June 2023, www.who.int/news/item/13-06-2023-training-to-build-community-capacity-to-meaningfully-engage-in-mpox-response. Accessed 23 May 2024.