Clinical Manifestations of Human Monkeypox Influenced by Route of Infection

Background: In April 2003, an outbreak of monkeypox occurred in the United States following the importation of monkeypox virus (MPXV)-infected animals in a consignment of exotic pets from West Africa. Transmission of the virus to non-African captive species, including prairie dogs, preceded human disease.

Methods: We evaluated the influence of the route of infection on clinical illness for persons with confirmed and probable cases of human monkeypox. Exposures were categorized as being "noninvasive" (e.g., the person touched an infected animal, cleaned an infected animal's cage, and/or stood within 6 feet of an infected animal) or "complex" (e.g., invasive bite or scratch from an ill prairie dog plus potential noninvasive exposure), and associations between exposure, illness manifestation, and illness progression (i.e., elapsed time from first exposure to an ill prairie dog through various benchmarks of illness) were assessed.

Results: Patients with complex exposures were more likely than patients with noninvasive exposures to have experienced pronounced signs of systemic illness (49.1% vs. 16.7%; P=.041) and to have been hospitalized during illness (68.8% vs. 10.3%; P<.001). Complex exposures were also associated with shorter incubation periods (9 days for complex exposures vs. 13 days for noninvasive exposures) and the absence of a distinct febrile prodrome.

Conclusions: The findings of this study indicate that route of infection can influence monkeypox illness manifestations.