Video: Father shares 'heartbeat' with sick baby daughter

SHAWNEE, Okla. (FOX 35 ORLANDO) - At only 6 months old, Opal Rose Trimble is in the fight of her life.

On March 2, the precious baby girl from Shawnee, Oklahoma was diagnosed with acute flaccid myelitis (AFM), a rare, neurological disease that affects an area of the spinal cord called gray matter. This can cause a person's muscles and reflexes to become weak. Opal has been in the hospital ever since.

Her mother and father, Gretchen and Josh Trimble, spend every moment they can by her hospital bedside.

Josh also has a 5-year-old son and 3-year-old daughter to take care of, so he sometimes has to leave, but the loving father has found a special way to let Opal know he is always with her.

Last week, Gretchen Trimble recorded a video of Josh saying good-bye to Opal at the Center Rehabilitation Hospital in Bethany, Oklahoma. As he stood over her crib, Josh pounded on his chest. Just seconds later, Opal mimicked her father, pounding on her chest, too.

Josh said that their new ritual is his way of showing Opal he's always with her and there for her, and that they "share a heartbeat."

After spending weeks being nearly immobile, the 'heartbeat' gesture is a hopeful sign that Opal is getting stronger every day.

"We were just so encouraged because the fact that she was mimicking him told us she knew what she wanted to do, and she did it."

"Compared to when this all started, she has made strides," Gretchen tells Fox 35. "She continues to make small improvements everyday. Her mobility is getting better and better."

According to the Centers for Disease Control, AFM is so rare that less than two out of a million children in the U.S. get it each year. The disease had only been on the CDC's radar since 2014, when they saw a large number of cases being reported.

"We still have a long road ahead of us, but we are so encouraged by how much she has improved in the past few weeks," said Gretchen.

If you'd like to help donate to Opal's medical bills, click HERE.