The Oregon Zoo in Portland has witnessed an event, where seven of its workers have been detected with tuberculosis that has been contracted from the three elephants that have been at the zoo since 2013, according to a report issued by U.S. Centers for Disease Control and Prevention (CDC). The employees, who have been found infected with this dormant type of respiratory disease, did not show any symptoms and are not contagious.

The CDC was instructed by a U.S. judge to release documents, associated with the tuberculosis detected in the elephants, to animal-rights group People for the Ethical Treatment of Animals (PETA). The report issued by the CDC comes two days after these instructions were given.

Last year, a lawsuit was filed by PETA against the CDC’s parent organization the U.S. Department of Health and Human Services. PETA has demanded the documents as it believes that the infected elephants pose a serious threat of transferring the disease to other elephants or humans.

The outbreak of disease has been blamed on the lack of research associated with tuberculosis in elephants, according to the CDC’s report. The organization has also demanded enhancement in techniques to detect tuberculosis since the existing technique is likely to be ineffective in certain cases. However, it has not been confirmed that the disease is excessively contagious for elephants or humans, according to Jennifer Vines, Deputy Health Officer for Multnomah County.

The Portland zoo has announced that it will perform regular assessments on the elephants and the workers at least till June 2016. In May 2013, the 20-year-old bull elephant by the name of Rama at the zoo was identified with the tuberculosis during a regular check up. In addition, the 51-year-old Packy, who is Rama’s father, along with the 44-year-old circus performer, Tusko, were detected with the same disease.