The study, reported in the journal Tuberculosis
, is the work of researchers at the University of Illinois Zoological Pathology Program (ZPP), a division of the veterinary diagnostic lab at the College of Veterinary Medicine in Urbana-Champaign. ZPP is based in Chicago, serving zoos and wildlife in the region and beyond.
More than 50 elephants in captivity in the U.S. have been diagnosed with tuberculosis since 1994, the research team reports. The evidence suggests that humans can transmit the disease to elephants and that elephants also may serve as a source of exposure for humans.
When infected, elephants may appear healthy or only show general symptoms, such as weight loss, that could be associated with a variety of maladies, said Jennifer Landolfi, a veterinary pathologist who led the new research. Most cases are found as a result of routine tests which involve checking the blood for antibodies against TB, or collecting samples from an elephant's trunk and culturing the bacteria it harbors.
But these approaches are problematic, Landolfi said. Culturing mycobacteria takes time and is imprecise, while antibody responses may take weeks to develop and only indicate exposure, not necessarily infection or disease.
"We are always trying to improve and seek out new diagnostics that will allow for earlier, more accurate detection of this infection," she said. "We also need to find ways to monitor the treatment response."
In humans, exposure to tuberculosis rarely results in full-fledged disease. Most people's immune systems eradicate the bacterium or at least keep the disease at bay, Landolfi said.
"Less than 10 percent of the people who are exposed actually develop the disease," she said. In those cases, an inadequate immune response is almost always to blame. "Our hypothesis is that something similar is happening in the Asian elephants."