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Pox Diseases of Nonhuman Primates

(Monkey Pox, Benign Epidermal Monkeypox, & Cowpox)

Monkeypox is an orthopoxvirus closely related to smallpox and produces a clinical disease similar to smallpox. Sporadic cases of the human disease are noted in Africa. Recently, squirrels of the genera Funisciurus and Heliosciurus have been identified as hosts and important reservoirs of the virus. Natural outbreaks of monkeypox also have been recorded in nonhuman primates in the wild and in laboratory settings.

Benign epidermal monkeypox, or tanapox, is a poxvirus that affects monkeys of the genus Presbytis in Africa and captive macaques in the United States.

Cowpox virus is antigenically and genetically related to variola virus, vacinnia virus, and monkeypox virus. With the eradication of smallpox, routine vaccination with vaccinia ceased, which created a niche for animal poxviruses to infect humans. Cowpox is a rare zoonosis (PDF), but has recently been reported in nonhuman primates.

The transmission of monkeypox from laboratory nonhuman primate populations to humans has not been recorded. Human-to-human transmission of the agent has occurred, presumably through close contact with active lesions, recently contaminated fomites, or respiratory secretions. The possibility of zoonotic spread should be considered.

Benign epidermal monkeypox has been transmitted from monkeys to humans in the laboratory-animal environment. Direct contact with infected animals or contaminated fomites is necessary for disease transmission.

Monkeypox is of interest and importance primarily because it produces a disease similar to smallpox characterized by fever, malaise, headache, severe backache, prostration, and occasional abdominal pain. Lymphadenopathy and maculopustular rash develop later. Some patients develop severe fulminating disease and die.

Benign epidermal monkeypox is characterized by the development of circumscribed, oval to circular raised red lesions usually on the eyelids, face, body, or genitalia. The lesions regress spontaneously in 4-6 weeks.

The diagnosis of poxvirus infections can be established on the basis of the characteristic structure of viral particles as seen with the electron microscope. Virus isolation and characterization with specific biological tests are needed to differentiate among the various orthopoxviruses. Vaccinia vaccination is protective against monkeypox in humans and in nonhuman primates.

Personnel should rely on the use of protective clothing, personal hygiene, and sanitation measures to prevent the transmission of the disease.