A hantavirus is suspected of causing an outbreak aboard a cruise ship that has killed three people and sickened others.
Studies indicate hantaviruses have been around for centuries, with outbreaks documented in Asia and Europe.
The disease gained attention last year after late actor Gene Hackman's wife, Betsy Arakawa, died from a hantavirus infection in New Mexico.
The virus is spread by rodents and more rarely, people, mainly through contact with rodents or their urine, saliva or droppings.
While rare, hantaviruses may spread between people, and most U.S. cases are in Western states, with New Mexico and Arizona being hotspots.
Symptoms of hantavirus pulmonary syndrome usually show between one to eight weeks after contact with an infected rodent, and can rapidly progress and become life-threatening.
There is no specific treatment or cure, but early medical attention can increase the chance of survival.
The best way to avoid the germ is to minimize contact with rodents and their droppings, and use protective gloves and a bleach solution for cleaning up rodent droppings.
