A 9-year-old boy in New Mexico has come down with the Hantavirus, a disease usually carried by rodents, and now he is fighting for his life. George Hernandez, the boy’s father, reportedly had not even heard of the Hantavirus when his son Fernando starting throwing up in January.

Initially, he went back to school but his symptoms began to worsen, so George took Fernando to a hospital in Farmington, New Mexico. After running some X-rays, doctors noticed some spots on his lungs, and gave him some medicine that they thought would clear it up.

While doctors were initially confident he would make a full recovery, George Hernandez said that things got “really bad,” according to a Fox News report. Fernandez was having trouble breathing on his own and had to go back to the hospital. Eventually, he as airlifted to Children’s Hospital Colorado in Aurora.

Doctors rans some more tests but again were not able to zero in on the cause. They suggested it might be mold, but an inspection of their house came up with nothing. Meanwhile, the boy’s heart stopped and he had to undergo several surgeries and be hooked up to a machine to assist his heart and lungs.

Finally, doctors discovered a cause: Hantavirus, which is carried by infected deer mice and can be transferred by coming into contact with droppings or urine. It’s a rare disease that only afflicts a few hundreds nationwide each year.

However, the disease can be incredibly deadly, killing more than third of victims. Fortunately, it cannot be transferred between humans.