Transmission of monkeypox among persons exposed to infected prairie dogs in Indiana in 2003.

OBJECTIVE: To describe a cluster of human monkeypox cases associated with exposure to ill prairie dogs in a home child care.

DESIGN, SETTING, PARTICIPANTS: We identified all persons exposed to 2 pet prairie dogs in County A, Indiana; performed active surveillance for symptomatic monkeypox infection; and evaluated the types of exposure that may have resulted in infection. For children who attended the child care where the animals were housed, we also measured the rate of seroconversion to monkeypox virus.

MAIN OUTCOME MEASURES: Nine (13%) of 70 persons exposed to the prairie dogs reported signs and symptoms of monkeypox. Two (40%) of 5 symptomatic child care attendees reported direct contact with the prairie dogs. Two (13%) of 15 child care attendees evaluated tested positive for IgM antibodies against orthopoxvirus; both reported symptoms consistent with monkeypox.

RESULTS: The risk of symptomatic infection correlated with the time and intensity of animal exposure, which was 100% (4/4) among family members with extensive direct contact, 19% (5/26) among the veterinarian and nonfamily child care attendees with moderate exposure, and 0% (0/40) among school children with limited exposure (P<.01).

CONCLUSIONS: Monkeypox virus was transmitted from ill prairie dogs in a child care and veterinary facilities. The risk of symptomatic infection correlated with the amount of exposure to the prairie dogs. Although most cases of human monkeypox were associated with direct animal contact, other routes of transmission cannot be excluded.