September 01, 2020

A novel coronavirus sickened four U.S. Navy dolphins in spring 2019, according to a research letter.

Sea lions in the same program developed similar illnesses at the same time, although tests on samples from those animals were negative for the virus, according to one of the letter authors.

Atlantic bottlenose dolphins in the U.S. Navy Marine Mammal Program in San Diego developed acute-onset illness with lack of appetite, diarrhea, and lethargy in April and May 2019, according to a letter published in the July 2020 issue of Emerging Infectious Diseases. Researchers identified a gammacoronavirus in fecal samples from the dolphins.

Navy animals are trained for tasks such as identifying underwater objects and marking their locations.

Dr. Leyi Wang, who is one of the authors and a veterinary virologist and clinical assistant professor at the University of Illinois College of Veterinary Medicine, said four dolphins and three sea lions in the Navy program developed similar clinical signs, although only samples from the dolphins were positive for the virus. The National Marine Mammal Foundation and U.S. Army Veterinary Corps, which care for the Navy dolphins, collected diagnostic samples and shipped them to veterinary diagnostic laboratories for the University of Illinois and University of Georgia, he said.

Initial checks for Escherichia coli, Clostridium perfringens, herpesviruses, Salmonella, and other known pathogens turned up no results, Dr. Wang said. Whole-genome sequencing on fecal samples helped identify a coronavirus.

All the animals recovered with supportive care, including fluid therapy, Dr. Wang said. He wants to search for antibodies against the virus if funding becomes available.

In response to questions about monitoring since the illnesses, Navy officials provided a statement that a team monitors the health of all Navy marine mammals each day.

“The animals that displayed these relatively mild clinical signs suspected to be caused by the gammacoronavirus described in the paper all made a full recovery,” according to the statement.

The new virus is a cetacean coronavirus, a member of a recently proposed species of gammacoronavirus, the authors wrote. It’s related to two other coronaviruses: beluga whale coronavirus SW1, identified in 2008, and bottlenose dolphin coronavirus HKU22, identified in 2014.

An article published in January 2014 by the Journal of Virology describes the discovery of one of the prior coronaviruses in the feces of three Indo-Pacific bottlenose dolphins in a Hong Kong oceanarium. But that virus likely is associated with subclinical to mild infection, as none of those dolphins developed notable clinical signs or persistent shedding, the article states.

The researchers who found the virus collected respiratory, fecal, and blood samples from 45 marine mammals—dolphins, sea lions, and harbor seals at the oceanarium—from August 2008 through July 2010 on a hypothesis that marine mammals could be hosts for groups or species of gammacoronaviruses.

The article notes that the prior discovery of a coronavirus in a 13-year-old beluga whale occurred after that whale died of heart disease and liver failure. Dr. Wang noted the beluga whale had lived in captivity in the U.S.