Questions and Answers About TB at the Zoo
On Saturday, April 24, 2004, the National Zoo closed the Great Ape House and outdoor gorilla yard to the public. The area may remain closed for several weeks as a precautionary measure, due to an inconclusive tuberculosis (TB) test result in a four-year-old male Zoo gorilla.
Below are some questions and answers about the Zoo’s decision to close the exhibit.
My family and I were at the Zoo last week, and we visited the Great Ape House and yard. Were we exposed to TB?
It’s highly unlikely that the general public was ever at risk from the Zoo’s gorillas, says Dr. Thomas Lawford, the Smithsonian’s occupational health physician. According to Dr. Lawford, people who have visited the Great Ape House in recent weeks were at little to no risk of contracting TB, even if further tests on the gorilla confirm the bacteria’s presence. Here’s why:
1. The risk in the Great Ape house was no greater than it is walking around downtown Washington, D.C. That’s because TB is a known public health disease problem among people. According to the Centers for Disease Control and Prevention, during 2003, Washington, D.C. and 12 states reported rates above the national average, which is 5.1 cases per 100,000 population.
2. To be spreading TB, an animal (or person) has to be sick—coughing and sneezing. TB bacteria are spread through the air in droplets after an infected person or animal coughs or sneezes. Those people or animals nearby may breathe in the bacteria and become infected. Most (90 percent) of those exposed to TB do not get the disease.
The Zoo’s gorilla with the inconclusive test results is showing no signs of illness—he isn’t coughing or sneezing. Also, an x-ray recently taken on the gorilla showed no signs of infection.
“The bottom line is that TB is transmissible from primate to primate, and this gorilla’s mother hasn’t caught it from him, even with months of intimate contact,” said Dr. Lawford.
3. The Great Ape House is designed to keep visitors at a distance from the animals with a see-through wall and separate ventilation/air systems.
When will you know if the gorilla has TB?
The conclusive test results won’t be available for perhaps 12 weeks—in mid July—which is standard for all TB tests. The only definitive test for TB is done on cells and organisms from the gorilla’s lungs. On Friday, April 23, Zoo veterinarians performed this test and sent the material to a California lab, which will determine if the TB bacterium is present. The test results won’t be known for up to 12 weeks, because it can take many weeks for the TB bacteria to grow.
This week, the gorilla is undergoing another round of tests. The results of these tests will provide Zoo vets with more data to help guide treatment options, while they are waiting for definitive test results, which will be completed in about 12 weeks.
What are you doing for the Zoo staff who work around the gorillas?
The staff and volunteers at the Great Ape House are tested annually for TB. This week, they are being re-tested, as a precautionary measure.
If it is not TB, then what does this gorilla have?
There are more than 20 types of mycobacteria in the environment, including many that do not cause disease, as well as the ones that cause human TB, bovine TB, and avian TB. Many times, a TB skin test will have a positive result when the animal does not have the disease. This is called a false-positive result, and is why a culture test—which can take up to 12 weeks—is the only definitive answer.
Why did you wait after the suspicious TB test in the gorilla to close the Great Ape House?
We closed the gorilla exhibit within 24 hours after receiving the inconclusive test results. The Zoo’s animal programs and veterinary staff consulted with a number of experts, including the Smithsonian’s occupational health physician. The health and other zoo experts did not believe this precaution was necessary because all of the gorillas and staff are healthy, and had recent negative TB tests. The decision was made to close the house to the public simply as an extra precaution.
Has the Zoo had human TB in its primate collection in the last ten years?
No. According to our database, which dates to 1975, there have been no documented cases of the human TB in primates.
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