90-Second Read: Hantavirus takes a long time to show symptoms. Experts say more cases could appear

Because symptoms can take weeks to show up, additional cases could still emerge, complicating public health efforts to contact trace possible exposures and transmission chains. Of the 18 passengers who returned this week to the U.S., at least one person has tested positive for the Andes Hantavirus, which has killed three passengers who had been on the 147-person cruise that was diverted to the Canary Islands. On Tuesday the World Health Organization director announced that a total of 11 cases have been reported in the outbreak. The remaining two-a symptomatic person and their spouse who had no symptoms-were transferred to Atlanta for treatment and monitoring. Centers for Disease Control and Prevention ( data ) Hantaviruses are a broad family of viruses, and different types can have varying incubation periods, says.

Based on the timeline of cases in the current outbreak reported to date, Pastula estimates that the incubation period has been two to three weeks, which is within the expected range. Although Hantaviruses are primarily spread through exposure to infected rodents or their feces or urine, the Andes virus is the only Hantavirus type known to spread human-to-human. It is not yet clear whether Andes Hantavirus can be transmitted before people show symptoms, however, Pastula says. But the situation is rapidly evolving and things could change. There's a possibility that the incubation period could be as long as seven weeks, but that's uncommon," he says.

They will quarantine for 42 days-many of them at a special facility-while they are monitored for signs of infection. HHS officials also said that risk of Andes virus to the general public is still low. Studies have shown that the virus can be present in the blood and other bodily fluids weeks before symptoms start. Longer incubation periods can reduce pathogens' ability to spread quickly from person to person, which typically gives public health officials the upper hand in identifying contacts and monitoring them to control outbreaks. The length of sequestration is to cover the incubation period of the virus, or the time from exposure to signs of infection.

The Andes virus's comparatively long incubation time could also reflect how it attacks the body and initially evades immune detection. She has appeared as a guest on radio shows, podcasts and stage events. Whether they get it through a mouse bite, inhaling aerosolized mouse excrement [or from close contact with] an infected human, I think that all probably plays a role in what the incubation periods are," Pastula says. In a 2007 study in Chile, researchers took blood samples of 76 people infected with Andes virus and 476 household contacts. Her work has appeared in Scholastic MATH, School Library Journal, IEEE Spectrum, Atlas Obscura and Smithsonian Magazine.