DENVER (KDVR) – Colorado is monitoring two people who had potential exposure to monkeypox after encountering an infected traveler on a flight. The Colorado Department of Public Health and Environment confirmed the possible exposures on Monday evening.

CDPHE said at the time that both people appeared healthy with no symptoms of infection. Travelers are being monitored daily by public health through July 30, which is the end of the monkeypox incubation period, CDPHE said.

The news comes after a Texas man was first diagnosed with the disease in mid-July after he returned to the U.S. from travel in Lagos, Nigeria. Monkeypox is a rare disease caused by infection with the monkeypox virus, and it’s only been documented six times outside of Africa, according to the U.S. Centers for Disease Control and Prevention.

In humans, the symptoms of monkeypox are similar to those of smallpox, but milder. The main difference between symptoms of smallpox and monkeypox is that monkeypox causes lymph nodes to swell (lymphadenopathy) while smallpox does not. The incubation period (time from infection to symptoms) for monkeypox is usually 7−14 days but can range from 5−21 days, the CDC says.

The CDC says the illness begins with fever, headache, muscle aches, backache, swollen lymph nodes, chills and exhaustion. Within one to three days (sometimes longer) after the appearance of fever, the patient develops a rash, often beginning on the face then spreading to other parts of the body. The illness typically lasts for 2−4 weeks, according to the CDC.