An emaciated killer whale, which has been the focus of joint Canada-U.S. rescue efforts, might have a common parasite that can be treated with antibiotics and a de-worming medication, officials say.

The three-year-old whale, known as J50 or Scarlet, has been under scrutiny since June when researchers noticed that she appeared malnourished.

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Last week, the team obtained a fecal sample from the water where she was swimming with her mother and a sibling.

The National Oceanic and Atmospheric Administration revealed on its website late Friday that lab tests of the fecal sample showed high levels of contracaecum -— a parasite commonly found in killer whales and other marine mammals.

“The worm is not usually a problem in healthy animals,” the NOAA said.

“However, in animals that are emaciated or are otherwise compromised, the parasite can penetrate the stomach lining, introducing bacterial infection to the bloodstream, or it can bore into internal organs.”

The NOAA said researchers cannot be sure the sample came from J50, but the veterinary team has made it a priority to administer antibiotics and a dewormer — both of which have been successful in other whales.

“The treatment should help J50/Scarlet by reducing bacterial and parasitic burdens on her system so she can start regaining the weight she has lost,” the NOAA said.

J50 is with the rest of her pod in waters off the west side of Vancouver Island. They’re beyond the reach of the response team, which has been operating out of Friday Harbour, Washington.

But Canada’s Department of Fisheries and Oceans and other partners are watching for the whales’ return, the NOAA said.

The loss of J50, born in December 2014, would be a serious blow to cross-border efforts to save the endangered southern resident killer whales, whose numbers have declined to 75.

The pods — J, K, and L — have had no successful births in three years and J50’s potential reproductive ability offered hope for the recovery efforts.

A week ago, researchers attempted to feed the ailing whale by releasing live hatchery salmon in front of her. It was unclear, however, whether she actually ate the fish. If perfected, the technique could be used to administer medication to J50 in the future.

lkines@timescolonist.com