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Tusko has been diagnosed with tuberculosis. He is the third elephant at the Oregon Zoo to test positive for the respiratory disease.

(Benjamin Brink/The Oregonian)

Oregon Zoo veterinarians have diagnosed a 44-year-old male Asian elephant named Tusko with tuberculosis.

Tusko is the third elephant at the zoo diagnosed with the respiratory disease since spring of last year. The zoo announced last week the elephant might be infected, but that testing had been inconclusive.

"This is not unexpected following the preliminary results," zoo veterinarian Tim Storms said in a release from the Oregon Zoo. "We've been moving forward under the assumption that Tusko does have TB, and we plan to start treatment immediately to help ensure he doesn't get sick. He is showing no signs of illness, which is not unusual when an infection is caught early."

Two other bull elephants – Packy, the 52-year-old elephant who serves as the zoo's unofficial animal face, and his son Rama – were diagnosed with TB last year. Packy is difficult to treat because of his advanced age, the release said. As zoo staff attempted to treat Packy this spring, he lost 1,400 pounds in two weeks, zoo officials said. He's regained most of that weight.

Rama is halfway through his 18-month treatment regimen and is no longer actively shedding. Neither Rama nor Packy have shown signs of illness.

Elephant care staff began offering Tusko placebo capsules -- pills that don't contain medication -- over the weekend so the elephant would be more likely to accept the real medication when the time comes. The veterinary staff is preparing to start an 18-month treatment regimen.

Tuberculosis has been reported in elephants since 1875, and zoo staff regularly test elephants for tuberculosis by culturing fluid from the animals' trunks.

The chronic disease attacks the respiratory system and can be fatal if not caught and treated. The zoo's four female elephants and the 5-year-old male Samudra have all tested negative for TB.

The diagnosis comes at a difficult time for the zoo. Last month, the zoo director and chief veterinarian were both fired in connection with their handling of the January death of a 20-year-old orangutan. The dismissals prompted outrage from other zoo employees, who've defended veterinarian Mitch Finnegan. Two weeks ago, six tamarin monkeys died from unknown causes two days after arriving at the zoo.

-- Melissa Binder