help prevent this disease from becoming established outside Africa in potential animal reservoirs, such as prairie dogs or released exotic pets. Etiology Monkeypox results from infection by monkeypox virus, a member of the genus Orthopoxvirus in the family Poxviridae (subfamily Chordopoxvirinae). Two viral clades, the West African and Congo Basin clades, have been identified. The Congo Basin viruses are more virulent. Monkeypox virus is closely related to some other orthopoxviruses including variola (smallpox) virus, and it cannot be distinguished from these viruses in some laboratory tests. Monkeypox should not be confused with benign epidermal monkeypox (BEMP), a poxviral disease of primates caused by tanapox virus, an antigenically unrelated virus in the genus Yatapoxvirus of the family Poxviridae. Species Affected The monkeypox virus’s full host range is uncertain. Animals known to be susceptible to infection include diverse Old and New World monkeys and apes, and various rodents, shrews and other small mammals. Among nonhuman primates, clinical cases have been described in chimpanzees (Pan troglodytes) and an infant sooty mangabey (Cercocebus atys) in the wild, as well as captive gorillas (Gorilla gorilla), chimpanzees, Asian orangutans (Pongo pygmaeus), gibbons (Hylobates lar), marmosets (Hapale jacchus), and various monkeys in the genera Cercopithecus, Macaca and Siamiri. Antibodies have been found in other wild or captive nonhuman primates. During an outbreak in the U.S. associated with exotic pets, infected animals included Gambian giant pouched rats (Cricetomys spp.), North American black-tailed prairie dogs (Cynomys ludovicianus) rope squirrels (Funisciurus spp.), dormice (Graphiurus sp.), a groundhog/ woodchuck (Marmota monax), an African hedgehog (Atelerix sp.), a jerboa (Jaculus sp.) and two opossums (Didelphis marsupialis and Monodelphis domestica). Chinchillas (Chinchilla lanigera) and coatimundis (Nasua nasua) developed antibodies after exposure, but viral DNA or infectious virus was not found. Giant anteaters (Myrmecophaga tridactyla) were thought to have been involved in an outbreak among primates at the Rotterdam Zoo in the Netherlands in 1964. Limited early surveillance in sheep, goats and cats in Africa found no evidence of exposure, but antibodies were detected in one pig. A subsequent attempt to infect pigs by rubbing virus into the skin did not result in virus recovery except from the inoculation site. Experimental infections with clinical signs have also been reported in 13-lined ground squirrels (Spermophilus tridecemlineatus), the cotton rat (Sigmodon hispidus), forest giant squirrel (Protexerus strangeri), bobak marmot (Marmota bobak), and red squirrels (Sciurus vulgaris). Adult white rabbits (with the apparent exception of albino rabbits), guinea pigs, white rats (Rattus spp.) and wild type laboratory mice (Mus musculus) are refractory to experimental infection, though newborn rats and rabbits can be infected. Monkeypox © 2004-2022 www.cfsph.iastate.edu page 2 of 9 The reservoir host(s) for monkeypox viruses are uncertain, but are thought to be one or more African rodents or small mammals. It is possible that the Congo Basin and West African clades are maintained in different species. Two genera of African squirrels, Funisciurus spp. (rope squirrels) and Heliosciurus spp. (sun squirrels), are among the top candidates for reservoir hosts, but antibodies have also been found in many other species of African rodents, shrews and other small mammals including Gambian pouched rats. Attempts to detect the virus directly in wild small mammals or other free-living species have generally been unsuccessful, though it was recovered once from a wild rope squirrel with lesions. Zoonotic potential The Congo Basin and West African clades of monkeypox virus can both affect humans. Geographic Distribution Monkeypox is endemic in central Africa (the Congo Basin) and West Africa. An outbreak of monkeypox affecting humans and exotic pets occurred in the U.S. in 2003, but there is no evidence that the virus became established in North America. Isolated human cases were recently imported to other locations, including the U.K., Israel and Singapore, again without the virus becoming established in these locations. Transmission Monkeypox viruses has been found in skin lesions and most or all secretions and excretions (e.g., urine, feces, and oral, nasal and conjunctival exudates) in animals. Likely routes of transmission include inhalation, direct inoculation into breaks in the skin, and the ingestion of infected tissues. The importance of aerosol transmission might differ between species or situations. Experimentally infected prairie dogs can shed monkeypox viruses until 21 days after inoculation, and limited evidence suggests that some small animals, such as dormice and Gambian giant pouched rats, might carry this virus for a few weeks or months. Viral DNA was detected in the tissues, urine and feces of one dormouse for at least 6 months, but no viral antigens were found when this animal was euthanized. Whether such animals can shed infectious virus is not known. Humans can become infected via bites from animals, in aerosols during close contact, or by direct contact with lesions, blood or body fluids. Sexual transmission was suspected in a few cases, when there were lesions on the