Poxvirus and Rabies Branch, US Centers for Disease Control and Prevention 1600 Clifton Rd. NE; Mailstop G-43, Atlanta, GA 30333, USA.
on behalf of Inger Damon
The eradication of smallpox during the latter half of the 20th Century was a crowning achievement of public health and international cooperation. It was possible to eradicate Variola (the causative agent of smallpox) by interrupting human-to-human transmission, because there was no animal reservoir or other persistent environmental source for the virus. Other orthopoxviruses that cause human illness –such as Monkeypox and Vaccinia – are, however, transmissible from animals to humans, and it is conceivable that one or both of these viruses may be able to exploit the ecologic (immunologic) niche left vacant by eradication of Variola. Human infections with Monkeypox virus were first observed in 1970, during the intensification of the smallpox eradication campaigns. Since the mid-1990s, sizable outbreaks (> 500 cases reported in total) of monkeypox have been recorded in DRC, and in the past 6 years, human infections have been newly reported in three countries that had never before reported cases: the Republic of the Congo, Sudan and the United States. Though it is naturally a virus of sylvan animals, Monkeypox virus can be transmitted from person-to-person, and up to 6 generations of serial transmission have been observed in the Republic of the Congo. Epidemiologic investigations conducted during the US outbreak revealed that certain types of both direct and indirect human contact with infected animals (including being scratched by an infected animal, handling one, or cleaning a soiled cage) were associated with increased risk for monkeypox disease acquisition. Additionally, although it was not possible to empirically define a role for childhood smallpox vaccination in providing protection from disease acquisition, it was observed that the route of human infection (percutaneous inoculation versus or respiratory/mucuocutaneous infection) had a measurable influence on the manifestations and severity of monkeypox illness. Monkeypox severity has also been shown to be influenced by virus genotype. Two genetic clades of monkeypoxvirus have been defined and distinctive virologic and epidemiologic characteristics have been attributed to each, although both share similar ecologic niches. Preventing the introduction of Monkeypox into human communities and controlling person-to-person spread (including nosocomial) are important immediate public health goals for diminishing the potential for this zoonotic orthopoxvirus to emerge as a significant human pathogen.
