Packy, the Oregon Zoo's elderly Asian elephant, is suffering from a resurgence of tuberculosis after nearly two years free of the disease, and veterinarians have discontinued treatment as the particular strain that has stricken the pachyderm appears to be resistant to antibiotics.

In September, tests on Packy's trunk showed active tuberculosis in the geriatric elephant. At 54, Packy is the oldest male of his species in North America and one of the oldest on the planet, zoo officials said in a press release.

His most recent diagnosis was troubling to zoo medical staff.

"We had been feeling increasingly optimistic about Packy's treatment regimen, and he had been tolerating it well, so this recent result was disappointing," Tim Storms, the zoo's senior veterinarian, said in a statement.

After some testing, vets ascertained that Packy's strain of the disease was resistant to the two most common classes of antibiotics used to treat the ailment: rifampin and quinolones.

"Without those options, we're very limited in our ability to treat this infection," Storms said. "We've stopped Packy's treatment for the time being, since we now know that it's been ineffective."

But the elderly elephant's prognosis was unclear.

"We're consulting with veterinarians and pharmacologists around the country, considering what to do next," Storms said.

Little is known about how to treat tuberculosis in elephants, curator Bob Lee said, but Packy's keepers are doing everything they can to keep the pachyderm comfortable, giving him daily exercise routines and trying their best to stimulate him mentally.

The zoo has recently treated two pachyderms, Rama and Tusko, for the disease. But very little is known about how tuberculosis acts in elephants, Lee said, so "we don't really know exactly how he's feeling."

"We've been working with this guy since he was born, and he continues to teach us so much," Lee said. "It just happens to be on an unfortunate avenue this time."

Packy's advanced age has made treatment more complicated, officials said.

Vets had made several attempts to treat Packy with isoniazid, the preferred antibiotic. Despite adjusting dosage levels and administration methods, the side effects of the drug -- including appetite loss and elevated liver enzymes -- proved too detrimental to continue.

Storms informed public health officials after the zoo received the latest test results and confirmed the protocols put in place by the facility are adequate to keep the public safe.

"We've continued to work closely with the zoo," said Jennifer Vines, a Multnomah County health officer. "They've been very careful about making sure visitors, volunteers and staff are safe."

Several zoo staffers were infected with the disease after the last outbreak.

Packy's recent diagnosis, however, means he also can't have contact with the rest of the herd of elephants at the zoo. He would have to undergo a year of continuous treatment to be reunited with the other animals or come within 100 feet of the public, zoo officials said, which will make for a lonely elephant who will be hard to see for the general zoo-going public.

"You can catch glimpses of him from time to time in the southernmost yard, which is to the right as you're walking along the pathway into Forest Hall," Lee, who has cared for Packy for 16 years, said in a statement. "And we'll continue to share photos and videos whenever we can."

-- Kale Williams

kwilliams@oregonian.com

503-294-4048