Septicemic omphalophlebitis by Streptococcus equi subsp. zooepidemicus in a southern right whale calf (Eubalaena australis).

Southern right whales (Eubalaena australis) are mysticete cetaceans commonly observed in the coastal waters of Brazil, particularly in Santa Catarina State. There is limited understanding of the causes of calf mortality in this species, particularly concerning infectious diseases. We report a case of omphalophlebitis caused by Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) that led to septicemia in a Southern right whale calf. Gross examination revealed an incompletely healed umbilicus with fibrin deposition and amorphous yellow material present in the lumen of the umbilical vein on the cut surface. The main histopathological findings showed fibrinosuppurative omphalophlebitis with numerous coccoid basophilic bacterial aggregates. These aggregates were also observed in the lamina propria, submucosa, and muscular layers of the small intestine and uterus, as well as in the interstitium of the kidneys and within blood vessels of the skin, skeletal muscle, heart, and ovaries. Tissue samples taken from the umbilicus and uterus were inoculated on 5% sheep blood agar and MacConkey agar. Small, transparent colonies that exhibited complete hemolysis were identified on blood agar. Gram staining revealed the presence of Gram-positive cocci arranged in chains. The bacterial isolate was analyzed using the MALDI-TOF technique, which confirmed its identity as S. zooepidemicus. The presence of S. equi antigen in the extra-umbilical aggregates was confirmed through immunohistochemistry. These findings underscore the significance of streptococcal infections in cetaceans and contribute valuable data regarding calf mortality in baleen whales. Furthermore, we provide new insights into the understanding of marine ecosystem health markers.