Monkeypox virus is an Orthopoxvirus, a genus that includes camelpox, cowpox, vaccinia, and variola viruses. The virus is the foremost Orthopoxvirus affecting human populations since smallpox eradication, confirmed by the World Health Organization in 1980. Clinical recognition, diagnosis, and prevention still remain challenges in the resource-poor endemic areas where monkeypox is found. Monkeypox epidemiology is informed by studies conducted at the end of smallpox eradication, but new assessments are needed now that routine smallpox vaccination has ended and there is associated waning herd immunity. Additionally, foundational ecological studies are necessary to better understand the animal species involved in transmission and maintenance of the virus, and to further inform prevention measures
Human monkeypox was not recognized as a distinct infection in humans until 1970 during efforts to eradicate smallpox, when the virus was isolated from a patient with suspected smallpox infection in The Democratic Republic of the Congo (DRC) [1]. The majority of the clinical characteristics of human monkeypox infection mirror those of smallpox (discrete ordinary type or modified type, Table 1) [2–4]. An initial febrile prodrome is accompanied by generalized headache and fatigue. Prior to, and concomitant with, rash development is the presence of maxillary, cervical, or inguinal lymphadenopathy (1–4 cm in diameter) in many patients (Figure 1). Enlarged lymph nodes are firm, tender, and sometimes painful. Lymphadenopathy was not characteristic of smallpox. The presence of lymphadenopathy may be an indication that there is a more effective immune recognition and response to infection by monkeypox virus vs variola virus, but this hypothesis requires further study [5].
Historically, there have been reports of human monkeypox infections in West Africa, but since 1981 most reported infections have occurred in the Congo Basin of Central Africa [17]. DRC continues to report the majority of human monkeypox cases each year. Recently, infections also were noted in the Central African Republic, ROC, and Sudan [8, 18, 19], but it is unclear if these infections were the result of movement across the DRC border or the occurrence of indigenous disease. Improved phylogeography and georeferencing of human cases will aid in a better understanding of the distribution of cases, and these data can be used to develop more accurate ecological models of monkeypox distribution [20, 21]. Domestically, the United States experienced a monkeypox outbreak among humans and captive prairie dogs in 2003, and traceback studies identified a shipment of wild rodents from Ghana as the probable source [22, 23].