Transmission of Mycobacterium pinnipedii to humans in a zoo with marine mammals

OBJECTIVES: An outbreak of tuberculosis (TB) in sea lions occurred recently in a zoo in the Netherlands. The disease was detected in a captive colony consisting of 29 animals kept in an open air basin with an indoor night house. Approximately 25 animal keepers were in close contact with the animals.METHODS: The sea lions were investigated using the tuberculin skin test (TST) with avian and bovine purified protein derivative (PPD) and, in case of positivity, necropsied. A survey was conducted among the animal keepers including TSTs with Mycobacterium tuberculosis complex PPD tuberculin, a chest X-ray and an interferon-gamma release assay (IGRA).RESULTS: Necropsy was positive for TB in 13 of the 29 sea lions. Three cases of pulmonary involvement were found. Only one of these was infectious and it was therefore regarded as the source case. The causative mycobacterium was identified as M. pinnipedii. Six of the 25 animal keepers were TST-positive; in five of these, infection was confirmed by a positive IGRA.CONCLUSION: Transmission of M. pinnipedii infection from sea lions to humans was established by TST. IGRA results largely agreed with the TST results. Nebulisation when cleaning the sea lions' enclosure was most likely the main cause of transmission to humans.