Identifying disease is difficult in elephants as most of them don't show signs of being infected, says expert
Asian elephants, it turns out, can contract tuberculosis (TB). However, diagnosing TB in elephants and treating them is a challenge as very little is known about how they respond to the infection.
A new study is now beginning to address this knowledge gap and offer new tools for detecting and monitoring TB in captive elephants. The study, reported in the journal Tuberculosis, is the work of researchers at US’ University of Illinois Zoological Pathology Program (ZPP), a division of the veterinary diagnostic lab at the College of Veterinary Medicine in Urbana-Champaign.
According to the research team, more than 50 elephants in captivity in the US have been diagnosed with tuberculosis since 1994.
Evidence also suggests that humans can transmit the disease, caused by organism Mycobacterium tuberculosis, to animals and vice versa. “When infected, elephants may appear healthy or only show general symptoms, such as weight loss, that could be associated with a variety of maladies,” says Jennifer Landolfi, a veterinary pathologist and lead author of the research. “We are always trying to improve and seek out new diagnostics that will allow for earlier, more accurate detection of this infection," she adds.
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. Landolfi, however, believes that these approaches are problematic.
"Less than 10 per cent of the people who are exposed actually develop the disease," she says. In those cases, an inadequate immune response is almost always to blame. "Our hypothesis is that something similar is happening in the Asian elephants."
How the research was conducted
To test this, Landolfi and her colleagues looked at protein mediators that are part of an elephant's immune system. These small signalling molecules, called cytokines, spur a cascade of cellular reactions that help the body fight infection. But detecting cytokines in elephants is difficult because antibodies that target elephant cytokines are not available.
"Instead of trying to detect the cytokines using antibodies, we said, why don't we take a step back and detect the nucleotides that code for those proteins?" Landolfi said. She further adds, "We're talking about messenger RNA (mRNA), which is used by the cell to synthesise these proteins."
After developing the tools to detect cytokine mRNA in elephants, the researchers collected blood from eight TB-positive and eight TB-negative Asian elephants, and isolated the white blood cells. They exposed the cells to proteins associated with TB and then analysed the cell culture for expression of certain cytokines.
Their analysis showed that TB-positive and TB-negative elephants differed in their immune responses after exposure to TB bacterial proteins.
"The cytokines were at higher levels in the positive animals," Landolfi says. "That suggested that those animals had more of an immune reaction when they were exposed (to proteins associated with TB) than the animals that were negative."
"That is something that we want to move towards with elephants," she says. "Most of the elephants don't show us a lot of signs of disease, and even when they do appear to be sick, it's very non-specific."
This makes it difficult to diagnose them and to determine if treatment is working, she said. Having a new way to monitor the elephants' immune response would improve both tasks, she says.
If confirmed in future studies, the findings suggest a faster and more reliable way to diagnose TB in captive elephants, Landolfi says. The same kinds of tests are already being used in humans.
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