Outbreak of Mycobacterium orygis in a Shipment …

Investigation and Results

Identification of Mycobacterium orygis

On February 7, 2023, the importer notified CDC of a macaque with a positive TST reaction. The macaque was humanely euthanized, and the carcass underwent postmortem examination, including sample collection for histopathologic and microbiologic testing. Histopathology findings, including acid-fast staining, were consistent with mycobacterial infection, and samples were submitted to U.S. Department of Agriculture’s National Veterinary Services Laboratories (NVSL) for mycobacterial polymerase chain reaction (PCR) testing and culture. PCR testing (1) of lung tissue and tracheobronchial lymph nodes for Mycobacterium tuberculosis complex (MTBC) was positive; however, because this assay has not been validated for NHP, this finding was not considered confirmatory. The case was confirmed when culture and whole-genome sequencing (WGS) conducted at NVSL later identified the presence of Mycobacterium orygis, a species of MTBC that is believed to be most frequently found among humans and animals in South Asia (2). WGS and analysis were performed according to methods published in 2021 (3), using M. tuberculosis H37Rv as the reference. This activity was reviewed by CDC, deemed not research, and was conducted consistent with applicable federal law and CDC policy.^†

Additional Cases Among Macaques

In accordance with CDC regulations, the remaining macaques were required to undergo extended quarantine and have at least five additional negative TST results at a minimum of 2-week intervals. On February 21, the importer notified CDC of eight additional macaques with positive TST reactions. Based on preliminary postmortem diagnostics, seven animals were considered to have suspected tuberculosis (Box); all seven were later confirmed to be infected with M. orygis, based on culture results of affected tissues and WGS.

Macaques with positive TSTs were reported until May 30; a total of 32 macaques received a positive TST result during the outbreak (Table). All animals with a positive TST result were humanely euthanized and had samples submitted for postmortem testing, including histopathology with acid-fast staining, MTBC PCR, culture and, when applicable, WGS. Histopathology was performed by a commercial pathology laboratory, and the remaining tests were performed at NVSL. A total of 26 macaques (4.8% of the shipment) received a positive MTBC culture during the outbreak, including 24 (75%) of 32 with a positive TST result and two of 508 (0.4%) with a negative TST result. All isolates were confirmed to be M. orygis and shared a common ancestor, which had acquired 85 single nucleotide polymorphisms since the most common ancestor in the NVSL database. Starting early in the outbreak, the importer submitted blood samples from TST-positive macaques to a private laboratory for experimental interferon-gamma release assay (IGRA) testing. In early April, all remaining macaques in the cohort were tested with IGRA, which revealed one positive and four indeterminate results. Two macaques (one positive and one indeterminate) were confirmed by postmortem examination to be culture-positive for M. orygis. Overall, macaques receiving positive culture results were identified from 67% of quarantine rooms. The remaining macaques in the cohort were released from quarantine on August 8, 2023, all having received the required five negative TST results after the last TST-positive macaque was removed from the cohort.