Pygmy sperm whale (Kogia breviceps) are some of the least understood mammals in the ocean. They spend most of their lives far from the coast, usually traveling in small groups and diving deep to hunt squid and fish. Scientists have had little opportunity to observe them in the wild, as they are quiet and secretive, rarely appearing on land.
Much of what researchers know about pygmy sperm whales comes from animals that wash ashore. Strandings are especially common along the southeastern United States, where this species occurs more frequently than almost any other large marine mammal.
Whale stranding reveals hidden health issues
Examination of the stranded whale revealed several recurring medical problems, including stomach ulcers. These ulcers may be associated with Helicobacter, a group of bacteria that can live in the stomachs and intestines of many animals, including humans and whales.
After reviewing more than 20 years of stranding records and archived tissue samples, researchers from the Florida Atlantic University Harbor Branch Marine Research Institute and collaborating institutions identified three Helicobacter genotypes never before documented.
This study Wildlife Disease Journalmarks the first confirmed discovery of the genotypes of these bacteria in pygmy sperm whales. The researchers named them Kogia Helicobacter 1, 2, and 3. The discovery not only provides new insights into the elusive whale species, but also raises broader questions about how bacterial infections affect marine wildlife and ocean health.
“Helicobacter bacteria have long been associated with gastrointestinal disorders in humans and other animals, including chronic gastritis, ulcers, and even gastric cancer,” said senior author Annie Page, DVM, associate research professor and clinical veterinarian at FAU Harbor Branch. “It’s exciting to discover new species of these bacteria in deep-diving whale species.”
Three bacterial genotypes known for the first time to science
From 1999 to 2020, the FAU Port Branch responded to strandings of 59 pygmy sperm whales. Post-mortem examinations have been completed on 80% of these animals.
In four cases, scientists found spiral-shaped “spiral” bacteria within the stomach tissue. The research team then reexamined the archived samples using histopathology, molecular testing, and DNA sequencing. The analysis revealed several previously unknown Helicobacter genotypes.
“Two of the genotypes, Kogia Helicobacter 1 and 2, are genetically similar to known Helicobacter species previously discovered in other cetaceans, such as dolphins and porpoises, and in humans,” said corresponding author Wendy Marks, research coordinator in the FAU Harbor Branch’s Marine Wildlife Veterinary Medicine and Laboratory. “However, Kogia Helicobacter 3 belongs to a more diverse lineage, highlighting that there may be many more undiscovered bacteria in the ocean than we realize.”
The researchers found both Kogia Helicobacter 1 and 3 in forestomach tissue from one whale.
Infected whales showed gastric damage
Each of the four whales that tested positive also showed clear signs of gastrointestinal disease.
“All four whales that tested positive for Helicobacter had visible gastric lesions,” Page said. “We saw signs of gastritis, gastric ulcers, fibrosis, and nematode infestation. In one case, we also saw colitis, suggesting that the infection may not be limited to the stomach. Although Helicobacter was not cited as the cause of death in any of the whales, these lesions raise questions about the role of Helicobacter in gastrointestinal disease.”
The researchers did not conclude that Helicobacter directly caused the whale’s death. However, the recurring presence of inflammation, ulcers, tissue scarring, and other digestive problems suggests that bacteria may be contributing to chronic disease.
Helicobacter was first described in marine mammals in 2000. Since then, related bacteria have been detected in several cetaceans around the world. In some animals, infections are associated with low energy, loss of appetite, reflux, stomach ulcers, and inflammation. Many of these symptoms are similar to those seen in infected humans.
Possible risks to vulnerable whale populations
“Like humans, whales appear to be susceptible to certain microbial infections, but we’re only just beginning to understand them,” Marks said. “If chronic infection with Helicobacter causes health problems in these animals, it can affect not only the health of individual whales, but entire populations, especially species that are already vulnerable.”
Pygmy sperm whales are extremely difficult to study at sea, so researchers do not yet know how widespread the newly identified bacteria are or how much they will affect the animals over time. Additional testing will be needed to determine whether these infections are contributing to disease, strandings, or population-level health problems.
The project brought together researchers from the FAU Harbor Branch, the University of Florida College of Veterinary Medicine, Colorado State University, and the Marine Mammal Pathology Service.
Decades of stranding research yields results
“This study highlights the value of long-term marine mammal stranding programs,” Page said. “Without the ability to study these stranded animals for decades, we would never have discovered these bacteria. Every whale has a story, and sometimes those stories lead us into entirely new areas of science.”
Co-author of the study is Dr. Jessy Castellanos-Gell. Dr. Stephen Tillis; James FX Wellehan, DVM, Ph.D., DACZM. April Childress is a professor at the University of Florida College of Veterinary Medicine. Nicole Pegg, FAU Port Branch; David Rotstein, DVM, Marine Mammal Pathology Service. Sushan Han, DVM, Ph.D., Colorado State University Diagnostic Medicine Center; Steve Burton, Stranding and Population Assessment Director, FAU Port Branch;
This research was supported by the Florida Specialty License Plate Program through a “Florida Whale Conservation” grant administered by the Harbor Branch Marine Laboratory Foundation.
