Detection of Brucella ceti and Brucella-Associated Disease in Stranded Cetaceans in Hawaii, USA, 2000-24

Numerous marine mammal populations worldwide are declining because of increased anthropogenic and natural threats, including infectious disease. Brucella ceti, morbillivirus, and herpesvirus have been detected from stranded cetaceans and been recognized as pathogens that may result in considerable cetacean morbidity and mortality. Beaked whale circovirus has been reported in multiple cetacean species in Hawaii, USA, and the western Pacific Ocean, but the pathologic relevance in these species remains uncertain. We screened for the presence of Brucella in 66 cetaceans of 17 species that stranded in Hawaii 2000-24 by targeting the insertion sequence 711 partial sequence using PCR. All Brucella-positive individuals were PCR tested for herpesvirus, morbillivirus, and circovirus coinfections. Of 66 individuals across eight species, 21 (31.8%) were positive for Brucella; 10/10 (100%) striped dolphins (Stenella coeruleoalba) and 5/6 (83.3%) pygmy killer whales (Feresa attenuata) tested were positive. Tissue positivity was highest in brain and lung tissue, with corresponding meningitis, hydrocephalus, and bronchopneumonia. We detected Brucella positivity across seven species; 7/10 (70%) of the positive subadults were striped dolphins. A single humpback whale (Megaptera novaeangliae) fetus was positive; the mother had died during dystocia. Viral coinfections were detected in 6/21 (33.3%) positive cases; circovirus was the most common coinfection, followed by morbillivirus and herpesvirus. Brucella ceti infection caused fatal disease in cetaceans in Hawaii, with a high percentage of strandings due to neurobrucellosis in striped dolphins.